The PANDA Barrel DIRC detector

Abstract The PANDA experiment at the new Facility for Antiproton and Ion Research in Europe (FAIR) at GSI, Darmstadt, will study fundamental questions of hadron physics and QCD using high-intensity cooled antiproton beams with momenta between 1.5 and 15 GeV/c. Efficient Particle Identification for a wide momentum range and the full solid angle is required for reconstructing the various physics channels of the PANDA program. Hadronic Particle Identification in the barrel region of the detector will be provided by a DIRC counter. The design is based on the successful BABAR DIRC with important improvements, such as focusing optics and fast photon timing. Several of these improvements, includin…

Quasi-elastic polarization-transfer measurements on the deuteron in anti-parallel kinematics

We present measurements of the polarization-transfer components in the H2(e→,e′p→) reaction, covering a previously unexplored kinematic region with large positive (anti-parallel) missing momentum, pmiss, up to 220MeV/c, and Q2=0.65 (GeV/c)2. These measurements, performed at the Mainz Microtron (MAMI), were motivated by theoretical calculations which predict small final-state interaction (FSI) effects in these kinematics, making them favorable for searching for medium modifications of bound nucleons in nuclei. We find in this kinematic region that the measured polarization-transfer components Px and Pz and their ratio agree with the theoretical calculations, which use free-proton form factor…

Observation ofHΛ4Hyperhydrogen by Decay-Pion Spectroscopy in Electron Scattering

At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from decays of strange systems was performed by electron scattering off a ^9B

Recent developments with microchannel-plate PMTs

Abstract Microchannel-plate (MCP) PMTs are the favored photon sensors for the DIRC detectors of the PANDA experiment at FAIR. Until recently the main drawback of MCP-PMTs were serious aging effects which led to a limited lifetime due to a rapidly decreasing quantum efficiency (QE) of the photo cathode (PC) as the integrated anode charge (IAC) increased. In the latest models of PHOTONIS and Hamamatsu an innovative atomic layer deposition (ALD) technique is applied to overcome these limitations. During the last five years comprehensive aging tests with ALD coated MCP-PMTs were performed and the results were compared to tubes treated with other techniques. The QE in dependence of the IAC was m…

An infrared light-guide based target positioning system for operation in a harsh environment

In the PANDA experiment's hypernuclear and hyperatom setup, a positioning system for the primary production target is required, which will be located in the center of the solenoid magnet, in ultra-high vacuum, and exposed to high radiation levels. In this work, a prototype for a positioning sensor was built using a bisected light guide for infrared light and a low-priced readout system based on microcontrollers. In contrast to many modern positioning systems that require electronics in direct proximity, this setup has no active electronic components close to the moving parts. The prototype system was operated with a resolution of better than 5$\micro$m, and with a repeatability of better th…

Lowest- Q2 measurement of the γp → Δ reaction: Probing the pionic contribution

To determine nonspherical angular momentum amplitudes in hadrons at long ranges (low Q^2), data were taken for the p(\vec{e},e'p)\pi^0 reaction in the Delta region at Q^2=0.060 (GeV/c)^2 utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios at W=1232 MeV are: M_{1+}^{3/2} = (40.33 +/- 0.63_{stat+syst} +/- 0.61_{model}) (10^{-3}/m_{\pi^+}),Re(E_{1+}^{3/2}/M_{1+}^{3/2}) = (-2.28 +/- 0.29_{stat+syst} +/- 0.20_{model})%, and Re(S_{1+}^{3/2}/M_{1+}^{3/2}) = (-4.81 +/- 0.27_{stat+syst} +/- 0.26_{model})%. These disagree with predictions of constituent quark models but are in reaso…

Hypernuclear physics at $\overline{\mbox{P}}$ ANDA

Hypernuclear research will be one of the main topics addressed by the \(\overline{\mbox{P}}\) anda experiment at the planned Facility for Anti-proton and Ion Research FAIR at Darmstadt, Germany. A copious production of Ξ-hyperons at a dedicated internal target in the stored anti-proton beam is expected, which will enable the high-precision γ-spectroscopy of double strange systems for the first time. In addition to the general purpose \(\overline{\mbox{P}}\) anda setup, the hypernuclear experiments require an active secondary target of silicon layers and absorber material as well as high purity germanium (HPGe) crystals as γ-detectors. The design of the setup and the development of these det…

Measurement of the Generalized Polarizabilities of the Proton at Intermediate $Q^2$

Background: Generalized polarizabilities (GPs) are important observables to describe the nucleon structure, and measurements of these observables are still scarce. Purpose: This paper presents details of a virtual Compton scattering (VCS) experiment, performed at the A1 setup at the Mainz Microtron by studying the $e p \to e p \gamma$ reaction. The article focuses on selected aspects of the analysis. Method: The experiment extracted the $P_{LL} -P_{TT} / \epsilon$ and $P_{LT}$ structure functions, as well as the electric and magnetic GPs of the proton, at three new values of the four-momentum transfer squared $Q^2$: 0.10, 0.20 and 0.45 GeV$^2$. Results: We emphasize the importance of the ca…

Noise and radiation damage in silicon photomultipliers exposed to electromagnetic and hadronic radiation

For the electron arm tracking system in the KAOS spectrometer at the Mainz Microtron MAMI a detector based on 2 m long scintillating fibres read out by silicon photomultipliers (SiPM) is planned. Because of the detector's close proximity to the intense electron beam a study of noise and radiation damage in SiPM has been performed. A sample of devices was exposed directly to a 14 MeV electron beam and to a mixed radiation field in the experimental area. First noticeable effects are a large increase in the dark count rate and a severe loss of the gain uniformity.

On the operation of silicon photomultipliers at temperatures of 1–4 kelvin

Abstract SiPM operation at cryogenic temperatures fails for many common devices. A particular type from Zecotek with deep channels in the silicon substrate instead of quenching resistors was tested at liquid helium temperature. Two similar types were thoroughly characterized from room temperature down to liquid nitrogen temperature by illuminating them with low light levels. At cryogenic temperatures the SiPMs show an unchanged rise-time and a fast recovery time, practically no after-pulses, and exhibit no increased cross-talk probability. Charge collection spectra were measured to extract the pixel gain and its variation, both comparable to room temperature at the same over-voltage. The qu…

Efficiency studies for a tracking detector based on square 1.5m long scintillating fibers read out by SiPM

Abstract A tracking detector based on 1.5 m long scintillating fibers is being developed for the electron arm of the KAOS spectrometer at the Mainz Microtron MAMI. Measurements on light attenuation, particle detection efficiencies and accidental coincidence rates with a prototype set-up using 2 × 2 mm 2 fibers read out by silicon photomultipliers (SiPM) are presented. The highest efficiency at the lowest accidental coincidence rate was reached for high trigger thresholds at the largest SiPM bias voltages. The influence of signal attenuation and dispersion on detection efficiencies is discussed. The results are in good agreement with a Monte Carlo model that was used to predict detector char…

Characterization of SiPM properties at liquid nitrogen temperature

SiPM operation at cryogenic temperatures fails for many common devices. A particular type with deep channels in the silicon substrate instead of quenching resistors was thoroughly characterized from room temperature down to liquid nitrogen temperature by illuminating it with low light levels. The devices were mounted in vacuum with the temperature stabilized to allow long-term operation. SiPM signals from a LED pulser were acquired with single-pixel resolution. Generalized fits to the charge collection spectra were used to extract properties like single-pixel gain, inter-pixel variation, breakdown voltage, and photon detection efficiency. With these measurements a deeper investigation of th…

Prototyping the PANDA Barrel DIRC

The design of the Barrel DIRC detector for the future PANDA experiment at FAIR contains several important improvements compared to the successful BABAR DIRC, such as focusing and fast timing. To test those improvements as well as other design options a prototype was build and successfully tested in 2012 with particle beams at CERN. The prototype comprises a radiator bar, focusing lens, mirror, and a prism shaped expansion volume made of synthetic fused silica. An array of micro-channel plate photomultiplier tubes measures the location and arrival time of the Cherenkov photons with sub-nanosecond resolution. The development of a fast reconstruction algorithm allowed to tune construction deta…

Particle tracking in kaon electroproduction with cathode-charge sampling in multi-wire proportional chambers

Abstract Wire chambers are routinely operated as tracking detectors in magnetic spectrometers at high-intensity continuous electron beams. Especially in experiments studying reactions with small cross-sections the reaction yield is limited by the background rate in the chambers. One way to determine the track of a charged particle through a multi-wire proportional chamber (MWPC) is the measurement of the charge distribution induced on its cathodes. In practical applications of this read-out method, the algorithm to relate the measured charge distribution to the avalanche position is an important factor for the achievable position resolution and for the track reconstruction efficiency. An al…

Beam-normal single spin asymmetry in elastic electron scattering off 28Si and 90Zr

We report on a new measurement of the beam-normal single spin asymmetry $A_{\mathrm{n}}$ in the elastic scattering of 570 MeV transversely polarized electrons off $^{28}$Si and $^{90}$Zr at $Q^{2}=0.04\, \mathrm{GeV}^2/c^2$. The studied kinematics allow for a comprehensive comparison with former results on $^{12}$C. No significant mass dependence of the beam-normal single spin asymmetry is observed in the mass regime from $^{12}$C to $^{90}$Zr.

Radiation resistance and optical properties of lead fluoride Cherenkov crystals

Abstract Optical properties of large size lead fluoride (PbF 2 ) crystals of three different manufacturers and their degradation caused by 60 Co γ-radiation have been investigated. Transmission losses have been systematically studied at absorbed energy doses between 0.1 and 7 kGy. Several radiation induced absorption bands have been observed. Optical bleaching with light of wavelengths ≳365 nm has been found very effective to restore the original characteristics even after repeated irradiations. This observation together with the high density and the ultraviolet extended transmission make PbF 2 an excellent choice for high rate and high resolution e.m. calorimetry.

Components of polarization-transfer to a bound proton in a deuteron measured by quasi-elastic electron scattering

We report the first measurements of the transverse (Px and Py) and longitudinal (Pz) components of the polarization transfer to a bound proton in the deuteron via the H2(e→,e′p→) reaction, over a wide range of missing momentum. A precise determination of the electron beam polarization reduces the systematic uncertainties on the individual components to a level that enables a detailed comparison to a state-of-the-art calculation of the deuteron using free-proton electromagnetic form factors. We observe very good agreement between the measured and the calculated Px/Pz ratios, but deviations of the individual components. Our results cannot be explained by medium modified electromagnetic form f…

The influence of Fermi motion on the comparison of the polarization transfer to a proton in elastic e→p and quasi-elastic e→A scattering

Abstract A comparison between polarization-transfer to a bound proton in quasi-free kinematics by the A ( e → , e ′ p → ) knockout reaction and that in elastic scattering off a free proton can provide information on the characteristics of the bound proton. In the past the reported measurements have been compared to those of a free proton with zero initial momentum. We introduce, for the first time, expressions for the polarization-transfer components when the proton is initially in motion and compare them to the 2H data measured at the Mainz Microtron (MAMI). We show the ratios of the transverse ( P x ) and longitudinal ( P z ) components of the polarization transfer in H 2 ( e → , e ′ p → …

The HypHI project at GSI and FAIR

Even though both experimental and theoretical activities on hypernuclear physics have been extended by a number of international projects, direct measurements on hypernuclear magnetic moments and studies of hypernuclei at extreme isospins have never been performed. The international HypHI collaboration proposes to perform hypernuclear spectroscopy with stable heavy ion beams and rare isotope beams at GSI and FAIR in order to study neutron and proton rich hypernuclei and to measure directly hypernuclear magnetic moments. The project is divided into four phases. In the first Phase 0 experiment, the feasibility of precise hypernuclear spectroscopy with heavy ion beams will be demonstrated by o…

Tremendously increased lifetime of MCP-PMTs

Abstract Microchannel plate (MCP) PMTs are very attractive photon sensors for low light level applications in strong magnetic fields. However, until recently the main drawback of MCP-PMTs was their aging behavior which manifests itself in a limited lifetime due to a rapidly decreasing quantum efficiency (QE) of the photo cathode (PC) as the integrated anode charge (IAC) increases. In the latest models of PHOTONIS, Hamamatsu, and BINP novel techniques are applied to avoid these aging effects which are supposed to be mainly caused by feedback ion impinging on the PC and damaging it. For more than four years we are running a long-term aging test with new lifetime-enhanced MCP-PMT models by sim…

The frontiers of the virtual photons program at MAMI

The most recent results and the future physics program of the high precision electron-scattering experiment at MAMI are briefly outlined. The A1 high-resolution spectrometers facility allows for a unique quality of virtual photon experiments. High precision form factor measurements, few-baryon systems highresolution structure studies and the innovative way in the search of dark photons illustrate the interplay between such diverse fields as precision atomic physics, nuclear astrophysics and astroparticle physics, where hadron physics plays a central and connecting role.

Modeling and Characterization of SiPM Parameters at Temperatures between 95 K and 300 K

The modeling and characterization of silicon photomultipliers (SiPMs) in a wide temperature range from 95 K to 300 K is presented. The devices under study had the distinctive feature of forward-biased p-n junctions situated under each pixel as active quenching resistors making them particularly appropriate to be operated at cryogenic temperatures. The voltage drop across the diode in a forward direction was measured for a series of injected currents in this temperature range. It was observed that the characteristics of different SiPM types influence the temperature dependence of the reverse saturation current. The devices were further characterized by low-level light-pulse measurements. The…

Decay pion spectroscopy: a new approach

We propose a new experiment for decay pion spectroscopy of light hypernuclei at electron- and proton-beam facilities, using the recoil distance technique for separation of produced hypernuclei and a magnetic spectrometer for precise measurement of the decay pion momentum. Low-pressure MWPCs are advocated for low-energy recoil detection as they provide position and time information and are highly insensitive to gamma-ray and electron background. The position and timing characteristics of such a recoil detector were studied using ~5 MeV {\alpha}-particles. By using the present proposed approach the rate of the detected hypernuclei can be increased by one-to-two orders of magnitude compared to…

Measurements of the induced polarization in the quasi-elastic A(e,e′p→) process in non-coplanar kinematics

Abstract We report measurements of the induced polarization P → of protons knocked out from 2H and 12C via the A ( e , e ′ p → ) reaction. We have studied the dependence of P → on two kinematic variables: the missing momentum p miss and the “off-coplanarity” angle ϕ p q between the scattering and reaction planes. For the full 360° range in ϕ p q , both the normal ( P y ) and, for the first time, the transverse ( P x ) components of the induced polarization were measured with respect to the coordinate system associated with the scattering plane. P x vanishes in coplanar kinematics, however in non-coplanar kinematics, it is on the same scale as P y . We find that the dependence on ϕ p q is si…

Deuteron photodisintegration by polarized photons in the region of the $d^*(2380)$

We report the first large-acceptance measurement of the beam–spin asymmetry for deuteron photodisintegration (γ→d→pn) in the photon energy range 420<Eγ<620MeV. The measurement provides important new constraints on the mechanisms of photodisintegration above the Δ resonance and on the photocoupling of the recently discovered d⁎(2380) hexaquark.

Observation of scattering and absorption centers in lead fluoride crystals

For the first time, lead fluoride is used as a fast and compact material in electromagnetic calorimetry. Excellent optical and mechanical properties of the pure Cherenkov crystals are necessary for the A4 collaboration to perform a measurement of the nucleon's strange form factors. Visible scattering and absorption centers as well as surface damages have been investigated to characterize the quality of more than one thousand crystals. Besides, transmittance measurements have been performed on all crystals to reveal absorption bands produced by intrinsic or impurity related point-structure defects. As a consequence, 89 crystals had to be replaced by the Chinese manufacturer SICCAS.

Determination of quadrupole strengths in the γ∗p→Δ(1232) transition at Q2=0.20(GeV/c)2

Abstract We report new precise p ( e → , e ′ p ) π 0 measurements at the peak of the Δ + ( 1232 ) resonance at Q 2 = 0.20 ( GeV / c ) 2 performed at the Mainz Microtron (MAMI). The new data are sensitive to both the electric (E2) and the Coulomb (C2) quadrupole amplitudes of the γ ∗ N → Δ transition. They yield precise quadrupole to dipole amplitude ratios: CMR = ( − 5.09 ± 0.28 stat + sys ± 0.30 model ) % and EMR = ( − 1.96 ± 0.68 stat + sys ± 0.41 model ) % for M 1 + 3 / 2 = ( 39.57 ± 0.75 stat + sys ± 0.40 model ) ( 10 −3 / m π + ) . The new results are in disagreement with Constituent Quark Model predictions and in qualitative agreement with models that account for mesonic contributions…

A Disc-DIRC Cherenkov detector with high resolution micro channel plate photomultiplier tubes

The upcoming PANDA Experiment at FAIR in Germany will be equipped with a novel Cherenkov detector type for high-energy particle identification. This very compact Disc-DIRC detector uses a large disc-shaped fused silica plate of 2 cm thickness as its Cherenkov radiator. The internally reflected Cherenkov light is transported to the rim of the disc where it is focused by quartz light guides onto microchannel plate photomultiplier tubes (MCP-PMTs) with high spatial resolution (pitch 0.5 mm) and high time resolution (σ ≈ 100 ps). The device has an active area of about 3 m2 and will be able to identify pions and kaons with a separation power of more than 3σ in the momentum range up to 4 GeV/c. I…

Statistical decay of hyperfragments

Combining the unique features of the hypernuclear electro-production mechanism and the high precision in magnetic spectroscopy, the proposed E-08-012 experiment at Jefferson Lab, Virginia, and the scheduled hypernuclear experiment at MAMI, Germany, focus on the high-resolution spectroscopy of weak two-body decay pions from hypernuclei. These experiments will provide insight on a wide range of light hypernuclei via the production of hyperfragments from 9 Be, 6,7 Li and 12 C targets. In the present work we explore the production of Λ-hypernuclei following the micro-canonical break-up of an initially excited hypernucleus which is created by the electro/photo-production reaction. Finally the mo…

The PANDA DIRC Detectors at FAIR

The PANDA detector at the international accelerator Facility for Antiproton and Ion Research in Europe (FAIR) addresses fundamental questions of hadron physics. An excellent hadronic particle identification (PID) will be accomplished by two DIRC (Detection of Internally Reflected Cherenkov light) counters in the target spectrometer. The design for the barrel region covering polar angles between 22 deg. to 140 deg. is based on the successful BABAR DIRC with several key improvements, such as fast photon timing and a compact imaging region. The novel Endcap Disc DIRC will cover the smaller forward angles between 5 deg. (10 deg.) to 22 deg. in the vertical (horizontal) direction. Both DIRC coun…

Measurements of the electron-helicity asymmetry in the quasi-elastic A(e→,e′p) process

Abstract We present measurements of the electron helicity asymmetry in quasi-elastic proton knockout from 2H and 12C nuclei by polarized electrons. This asymmetry depends on the fifth structure function, is antisymmetric with respect to the scattering plane, and vanishes in the absence of final-state interactions, and thus it provides a sensitive tool for their study. Our kinematics cover the full range in off-coplanarity angle ϕ p q , with a polar angle θ p q coverage up to about 8°. The missing energy resolution enabled us to determine the asymmetries for knock-out resulting in different states of the residual 11B system. We find that the helicity asymmetry for p-shell knockout from 12C d…

The PANDA Barrel DIRC

The PANDA detector at the international accelerator Facility for Antiproton and Ion Research in Europe (FAIR) addresses fundamental questions of hadron physics. Experiments concerning charmonium spectroscopy, the search for hybrids and glueballs and the interaction of hidden and open charm particles with nucleons and nuclei will be performed with antiproton beams impinging on hydrogen or nuclear targets. Cooled beams allow the precision scan of resonances in formation experiments. The momentum range of the antiproton beam between 1.5 GeV/c and 15 GeV/c tests predictions by perturbation theory and will reveal deviations originating from strong QCD . An excellent hadronic particle identificat…

Spectroscopy of A=9 hyperlithium with the (e,e′K+) reaction

High resolution spectroscopic study ofBeΛ10

Spectroscopy of a Be-10(Lambda) hypernucleus was carried out at JLab Hall C using the (e, e' K+) reaction. A new magnetic spectrometer system (SPL+ HES+ HKS), specifically designed for high resolution hypernuclear spectroscopy, was used to obtain an energy spectrum with a resolution of similar to 0.78 MeV (FWHM). The well-calibrated spectrometer system of the present experiment using p(e, e' K+)Lambda, Sigma(0) reactions allowed us to determine the energy levels; and the binding energy of the ground-state peak (mixture of 1(-) and 2(-) states) was found to be B-Lambda = 8.55 +/- 0.07(stat.) +/- 0.11(sys.) MeV. The result indicates that the ground-state energy is shallower than that of an em…

Ground-state binding energy of HΛ4 from high-resolution decay-pion spectroscopy

Abstract A systematic study on the Λ ground state binding energy of hyperhydrogen H Λ 4 measured at the Mainz Microtron MAMI is presented. The energy was deduced from the spectroscopy of mono-energetic pions from the two-body decays of hyperfragments, which were produced and stopped in a 9Be target. First data, taken in the year 2012 with a high resolution magnetic spectrometer, demonstrated an almost one order of magnitude higher precision than emulsion data, while being limited by systematic uncertainties. In 2014 an extended measurement campaign was performed with improved control over systematic effects, increasing the yield of hypernuclei and confirming the observation with two indepen…

Scintillating fiber detectors for the HypHI project at GSI

WOS: 000270326800009

The Endcap Disc DIRC of PANDA

Abstract The Endcap Disc DIRC (EDD) for PANDA has been designed to identify traversing pions, kaons and protons in the future PANDA experiment. Its central part is a 2 cm thick fused silica plate. Focussing optics are attached to the outer rim of the plate, outside of the acceptance of the experiment. Fast, high-resolution MCP-PMTs, designed to register single Cherenkov photons, have been tested in magnetic field. Filters limit the spectral acceptance of the sensors to reduce dispersion effects and to extend their lifetime. A compact and fast readout is realized with ASICs. Analytical reconstruction algorithms allow for fast particle identification. The angular resolution of a DIRC prototyp…

Feasibility study for the measurement of πN transition distribution amplitudes at P¯ANDA in p¯p→J/ψπ0

The exclusive charmonium production process in (P) over barp annihilation with an associated pi 0 meson (p) over barp -> J/psi pi(0) is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J/psi -> e(+) e(-) decay channel with the AntiProton ANnihilation at DArmstadt ((P) over bar ANDA) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the (P) over barp -> pi(+)pi(-)pi(0) and (p) over barp -> J/psi pi(0)pi(0) reactions are performed with PANDAROOT, the simulation and analysis software framework of the (P) over bar ANDA experiment. It is show…

Tests and developments of the PANDA Endcap Disc DIRC

The PANDA experiment at the future Facility for Antiproton and Ion Research (FAIR) requires excellent particle identification. Two different DIRC detectors will utilize internally reflected Cherenkov light of charged particles to enable the separation of pions and kaons up to momenta of 4 GeV/c. The Endcap Disc DIRC will be placed in the forward endcap of PANDA's central spectrometer covering polar angles between 5° and 22°. Its final design is based on MCP-PMTs for the photon detection and an optical system made of fused silica. A new prototype has been investigated during a test beam at CERN in May 2015 and first results will be presented. In addition a new synthetic fused silica material…

Detector response of Cherenkov radiators for calorimetry in the energy range below 14 MeV

Abstract A study of the detector response of PbF 2  crystals and three different types of lead glass blocks to electrons from a 14-MeV beam of the Mainz Microtron MAMI is presented. For the first time, signal height, signal width, and homogeneity of the response of these Cherenkov radiators were determined for energies between 10 and 14 MeV. To complement the beam tests, optical properties of the materials, in particular measured transmittances in the near UV and visible spectrum, were studied. The measured detector responses were also compared to Monte Carlo simulations of energy-loss, light production, transport, and detection. These Cherenkov radiators are considered as active material o…

Hypernuclear Spectroscopy with Electron Beams

A Λ-hyperon bound to a nuclear core, forming a hypernuclei, is a unique probe of the interior of hadronic many-body systems. Only recently, the spectroscopy of Λ-hypernuclei with electron beams was realized. Today, two places worldwide offer the possibility to study hypernuclei with high intensity continuous electron beams: MAMI at Mainz, Germany, and Jefferson Lab (JLab), Virginia. At least two different techniques exist for such studies: reaction spectroscopy, which requires two high-resolution spectrometers, one for kaons and one for the scattered electrons, and decay particle spectroscopy of hyperfragments. In the latter case a strangeness tagger in forward direction is of great advanta…

First measurement of the polarization observable E and helicity-dependent cross sections in single π 0 photoproduction from quasi-free nucleons

The double-polarization observable $E$ and the helicity-dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ have been measured for the first time for single $\pi^{0}$ photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the $\pi^0$ meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the $\pi^{0}N$ final state. A comparison to data mea…

STATUS OF STRANGENESS ELECTRO-PRODUCTION AT MAMI

At the Institut für Kernphysik in Mainz, Germany, the microtron MAMI has been upgraded to 1.5 GeV electron beam energy and can now be used to study strange hadronic systems. The magnetic spectrometer KAOS from GSI was dismantled and re-installed in the spectrometer facility operated by the A1 collaboration. The spectrometer's primary purpose is to study strangeness electro-production. Its compact design and its capability to detect negative and positive charged particles simultaneously under forward scattering angles complements the existing spectrometers. In 2008, an important milestone has been reached by the successful measurement of kaon production off a liquid hydrogen target. The ide…

Performance of sensl C-Series SiPM with high photoelectron resolution at cryogenic temperatures

The C-Series of silicon photomultipliers (SiPM) from SensL provides devices with a fast response and high performance at low cost. The device's ability to detect light at temperatures of liquid nitrogen (77K) and liquid helium (4 K) with high photoelectron resolution was demonstrated. Results include relative photon detection efficiency (PDE), gain, microcell capacitance, and cross-talk probability at different over-voltages, both at room and at cryogenic temperatures. At 77K the SiPM demonstrated significantly improved operating characteristics while at 4K the observed increase in break-down voltage, the reduction of PDE by a factor of 2-3, and the extensively dropped microcell capacitance…

Novel optical interferometry of synchrotron radiation for absolute electron beam energy measurements

Abstract A novel interferometric method is presented for the measurement of the absolute energy of electron beams. In the year 2016, a pioneering experiment was performed using a 195 MeV beam of the Mainz Microtron (MAMI). The experimental setup consisted of two collinear magnetic undulators as sources of coherent optical synchrotron light and a high-resolving grating monochromator. Beam energy measurements required the variation of the relative undulator distance in the decimeter range and the analysis of the intensity oscillation length in the interference spectrum. A statistical precision of 1 keV was achieved in 1 h of data taking, while systematic uncertainties of 700 keV were present …

The PANDA Endcap Disc DIRC

Journal of Instrumentation 13(02), C02002 - C02002 (2018). doi:10.1088/1748-0221/13/02/C02002

Performance of HPGe detectors in high magnetic field

A new generation of high-resolution hypernuclear gamma$-spectroscopy experiments with high-purity germanium detectors (HPGe) are presently designed at the FINUDA spectrometer at DAPhiNE, the Frascati phi-factory, and at PANDA, the antiproton proton hadron spectrometer at the future FAIR facility. Both, the FINUDA and PANDA spectrometers are built around the target region covering a large solid angle. To maximise the detection efficiency the HPGe detectors have to be located near the target, and therefore they have to be operated in strong magnetic fields B ~ 1 T. The performance of HPGe detectors in such an environment has not been well investigated so far. In the present work VEGA and EURO…

The Barrel DIRC detector of PANDA

The PANDA experiment is one of the four large experiments being built at FAIR in Darmstadt. It will use a cooled antiproton beam on a fixed target within the momentum range of 1.5 to 15 GeV/c to address questions of strong QCD, where the coupling constant $\alpha_s \gtrsim 0.3$. The luminosity of up to $2 \cdot 10^{32} cm^{-2}s^{-1}$ and the momentum resolution of the antiproton beam down to \mbox{$\Delta$p/p = 4$\cdot10^{-5}$} allows for high precision spectroscopy, especially for rare reaction processes. Above the production threshold for open charm mesons the production of kaons plays an important role for identifying the reaction. The DIRC principle allows for a compact particle identif…

Comparison of recoil polarization in the C12(e→,e′p→) process for protons extracted from s and p shells

Abstract We present the first measurements of the double ratio of the polarization-transfer components ( P x ′ / P z ′ ) p / ( P x ′ / P z ′ ) s for knock-out protons from the s and p shells in C 12 measured by the C 12 ( e → , e ′ p → ) reaction in quasi-elastic kinematics. The data are compared to theoretical predictions in the relativistic distorted-wave impulse approximation. Our results show that the differences between s- and p-shell protons, observed when compared at the same initial momentum (missing momentum), largely disappear when the comparison is done at the same proton virtuality. We observe no difference in medium modifications between protons from the s and p shells with the…

High precision mass measurements of hypernuclei - achievements and perspectives

A. Essera, S. Nagaoe, F. Schulza, P. Achenbacha, C. Ayerbe Gayosoa, R. Bohma, O. Borodinaa,b, D. Bosnarc, A. Botvinag, V. Bozkurtb, L. Debenjakd , M.O. Distlera, I. Friscicc, Y. Fujiie, T. Gogamie, M. Gomez Rodrigueza, O. Hashimotoe∗, S. Hirosee, H. Kandae, M. Kanetae, E. Kimb, Y. Kohla, J. Kusakae, A. Margaryan f , H. Merkela, M. Mihovilovicd , U. Mullera, S.N. Nakamurae, J. Pochodzalla†a,g, C. Rappoldb, J. Reinholdh, T.R. Saitoa,b,g, A. Sanchez Lorenteg, S. Sanchez Majosa, B.S. Schlimmea, M. Schotha, C. Sfientia, S. Sircad , L. Tangi, M. Thiela, K. Tsukadae, A. Webera, K. Yoshidab

The HypHI Phase 0 experiment

10th International Conference on Hypernuclear and Strange Particle Physics -- SEP 14-18, 2009 -- Tokai, JAPAN

Breakthrough in the lifetime of microchannel plate photomultipliers

Abstract Cherenkov detectors using the DIRC (Detection of Internally Reflected Cherenkov Light) principle are foreseen for particle identification in the P ¯ ANDA experiment at FAIR. Promising sensors for the detection of the Cherenkov light are the so-called micro-channel plate (MCP) photomultipliers (PMT). They have an excellent time resolution, can be operated at high gain for single photon detection and have a high resistivity against magnetic fields. The disadvantage of these devices was their limited lifetime, due to damage by feedback ions on the photocathode. The lifetime of various types of MCP-PMTs from different manufactures has been tested under conditions similar to that in the…

Unpolarized and polarized elementary kaon electroproduction cross sections measured at MAMI

Present and future research into the electroproduction of kaons plays an im- portant role at Mainz Microtron MAMI. With the Kaos spectrometer employed for kaon detection in the multi-spectrometer facility, cross section measurements of the exclusive p(e;e 0 K + ); 0 reactions at low momentum transfers have been performed. Isobar and Regge-plus-resonance models were compared with the data. These measurements have clearly discriminated between e ective Lagrangian models for photo- and electroproduc- tion of strangeness. New experiments with polarized beam at low four-momentum transfer are addressing the imaginary part of the longitudinal-transverse response in this process, that can be separa…

Experiments with the High Resolution Kaon Spectrometer at JLab Hall C and the new spectroscopy ofΛ12Bhypernuclei

Since the pioneering experiment E89-009 studying hypernuclear spectroscopy using the (e, e’K+) reaction was completed, two additional experiments, E01-011 and E05-115, were performed at Jefferson Lab. These later experiments used a modified experimental design, the "tilt method", to dramatically suppress the large electromagnetic background, and allowed for a substantial increase in luminosity. Additionally, a new kaon spectrometer, HKS (E01-011), a new electron spectrometer, HES, and a new splitting magnet (E05-115) were added to produce new data sets of precision, high-resolution hypernuclear spectroscopy. All three experiments obtained a spectrum for 12B-Lambda, which is the most charact…

Development of an Endcap DIRC for PANDA

Abstract The aim of this research is to develop a planar DIRC detector showing advantages and performance similar to a classical, barrel shaped DIRC, but at smaller polar angles which cannot be accessed using a cylindrical geometry. The device will complement the PANDA Barrel DIRC by covering polar angles from 5° to 22°. The envisaged π /K-separation is ≥ 3 σ up to 4 GeV/c. A major challenge is the adaption of the device to the PANDA environment including a magnetic field of ~1–2 T, high rates and radiation, limited space for optics and sensors as well as the lack of a common first-level trigger. This paper discusses a detector design which forms a compromise between these constraints and a…

Electron beam studies of light collection in a scintillating counter with embedded fibers

The light collection of several fiber configurations embedded in a box-shaped plastic scintillating counter was studied by scanning with minimum ionizing electrons. The light was read out by silicon photomultipliers at both ends. The light yield produced by the 855-MeV beam of the Mainz Microtron showed a strong dependence on the transverse distance from the beam position to the fibers. The observations were modeled by attributing the collection of indirect light inside of the counter and of direct light reaching a fiber to the total light yield. The light collection with fibers was compared to that of a scintillating counter without fibers. These studies were carried out within the develop…

Status of hypertriton binding energy measurements at the Mainz Microtron

Measurement of the beam-helicity asymmetry in photoproduction of π0η pairs on carbon, aluminum, and lead

The beam-helicity asymmetry was measured, for the first time, in photoproduction of $\pi^{0}\eta$ pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for $\pi^{0}\eta$ pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the $D_{33}$ partial wave with the $\eta\Delta(1232)$ intermediate state.

Design criteria for multi-layered scintillating fibre arrays with inclined columns

Multi-layered scintillating fibre arrays read-out are commonly used as high resolution charged particle hodoscopes. Fibres of a column along the geometrical trajectory of incident particles are typically grouped to one pixel of a multi-channel read-out device. In some applications the incident particles will cross the detection plane with large angles w.r.t. the normal to the layers. Then, the packing of the fibres needs to be adapted to the incident particles and the columns need to be inclined. In this paper possible fibre array geometries are shown, relevant design criteria for detectors are discussed, and the effect of diverging particles incident on fibre arrays was studied using a Mon…

Measurement of polarization-transfer to bound protons in carbon and its virtuality dependence

We measured the ratio Px/Pz of the transverse to longitudinal components of polarization transferred from electrons to bound protons in C12 by the C12(e→,e′p→) process at the Mainz Microtron (MAMI). We observed consistent deviations from unity of this ratio normalized to the free-proton ratio, (Px/Pz)C12/(Px/Pz)H1, for both s- and p-shell knocked out protons, even though they are embedded in averaged local densities that differ by about a factor of two. The dependence of the double ratio on proton virtuality is similar to the one for knocked out protons from H2 and He4, suggesting a universal behavior. It further implies no dependence on average local nuclear density.

In-beam tests of scintillating fibre detectors at MAMI and at GSI

The performance of scintillating fibre detectors was studied with electrons at the spectrometer facility of the Mainz microtron MAMI, as well as in a C-12 beam of 2 AGeV energy and in a beam of different particle species at GSI. Multi-anode photomultipliers were used to read out one or more bundles of 128 fibres each in different geometries. For electrons a time resolution of FWHM = 1 ns was measured in a single detector plane with a detection efficiency epsilon > 99%. A time resolution of 310 ps (FWHM) between two planes of fibres was achieved for carbon ions, leading to a FWHM = 220 ps for a single detector. The hit position residual was measured with a width of FWHM = 0.27 mm. The var…

Search for narrow dibaryon resonances in neutral pion photoproduction from the deuteron

The reaction γd↦π0 X has been measured with TAPS at MAMI in the energy range E γ = 140-300 MeV. Using the Glasgow tagging spectrometer a photon energy resolution of 0.8 MeV was achieved. The energy excitation functions of integral and differential total cross-sections show no structures of statistical significance > 2σ. Upper limits for the production of narrow isoscalar or isovector dibaryons with masses m? 2100 MeV/c2 were deduced. They are in the range 2-5 μb averaged over the 0.8 MeV energy resolution.

A low-noise and fast pre-amplifier and readout system for SiPMs

Abstract To operate silicon photomultipliers (SiPMs) in a demanding environment with large temperature gradients, different amplifier concepts were characterized by analyzing SiPM pulse-shapes and charge distributions. A fully differential 4-wire SiPM pre-amplifier with separated tracks for the bias voltage and with good common-mode noise suppression was developed and successfully tested. To achieve highest single-pixel resolutions an online after-pulse and pile-up suppression was realized with fast readout electronics based on digital filters.

Characterisation and calibration of a scintillating fibre detector with > 4000 multi-anode photomultiplier channels

In the Kaos spectrometer at the Mainz Microtron a high-resolution coordinate detector for high-energy particles is operated. It consists of scintillating fibres with diameters of 4000 multi-anode photomultiplier channels. It is one of the most modern focal-plane detectors for magnetic spectrometers world-wide. To correct variations in the detection efficiency, caused by the different gains and the different optical transmittances, a fully automated off-line calibration procedure has been developed. The process includes the positioning of a radioisotope source alongside the detector plane and the automated acquisition and analysis of the detector signals. It was possible to characterise and …

Characterisation of radiation damage in silicon photomultipliers with a Monte Carlo model

Measured response functions and low photon yield spectra of silicon photomultipliers (SiPM) were compared to multi-photoelectron pulse-height distributions generated by a Monte Carlo model. Characteristic parameters for SiPM were derived. The devices were irradiated with 14 MeV electrons at the Mainz microtron MAMI. It is shown that the first noticeable damage consists of an increase in the rate of dark pulses and the loss of uniformity in the pixel gains. Higher radiation doses reduced also the photon detection efficiency. The results are especially relevant for applications of SiPM in fibre detectors at high luminosity experiments.

Measurement of the p(e,e′π+)n reaction close to threshold and at low Q2

The cross section of the $p(e,e'\pi^+)n$ reaction has been measured for five kinematic settings at an invariant mass of $W = 1094$ MeV and for a four-momentum transfer of $Q^2 = 0.078$ (GeV/$c$)$^2$. The measurement has been performed at MAMI using a new short-orbit spectrometer (SOS) of the A1 collaboration, intended for detection of low-energy pions. The transverse and longitudinal cross section terms were separated using the Rosenbluth method and the transverse-longitudinal interference term has been determined from the left-right asymmetry. The experimental cross section terms are compared with the calculations of three models: DMT2001, MAID2007 and $\chi$MAID. The results show that we …

Spectroscopy of the neutron-rich hypernucleusHeΛ7from electron scattering

The missing mass spectroscopy of the HeΛ7 hypernucleus was performed using the Li7(e, e ′K+)HeΛ7 reaction at the Thomas Jefferson National Accelerator Facility Hall C. The Λ- binding energy of the ground-state (1/2+) was determined with a smaller error than that of the previous measurement, being BΛ=5.55±0.10stat.±0.11sys.MeV. The experiment also provided new insight into charge symmetry breaking in p-shell hypernuclear systems. Finally, a peak at BΛ=3.65±0.20stat. ±0.11sys.MeV was observed and assigned as a mixture of 3/2+ and 5/2+ states, confirming the "gluelike" behavior of Λ, which makes an unstable state in He6 stable against neutron emission.

Overview of the electromagnetic production of strange mesons at MAMI

Abstract The Mainz Microtron MAMI provides a continuous-wave unpolarized or spin-polarized electron beam with energies up to 1.6 GeV and high degrees of polarization. Electro-production of strange mesons is performed in the multi-spectrometer facility with the Kaos spectrometer for kaon detection and a high-resolution spectrometer for electron detection in plane or out of plane. Differential cross section measurements of exclusive p ( e , e ′ K + ) Λ , Σ 0 reactions at low four-momentum transfers in the nucleonʼs third resonance region have been done, followed by a measurement of the beam helicity asymmetry for p ( e → , e ′ K + ) Λ . These studies are important for the understanding of the…

Recent results with lifetime enhanced microchannel-plate photomultipliers

Abstract The favored photon sensors for the DIRC (detection of internally reflected Cherenkov light) detectors at the PANDA (Anti-proton Annihilation at Darmstadt) experiment at FAIR (Facility for anti-proton and ion research) are micro-channel-plate photomultipliers (MCP-PMTs). The main problem until a few years ago was the limited lifetime of the MCP-PMTs caused by a rapid decrease in quantum efficiency (QE) of the photo cathode (PC) with increasing integrated anode charge (IAC). These limitations are overcome by applying an atomic layer deposition (ALD) coating on the MCPs, as recently done by PHOTONIS and Hamamatsu. During the last years’ tests of lifetime enhanced MCP-PMTs were perform…

New Insight in the $Q^2$-Dependence of Proton Generalized Polarizabilities

Virtual Compton scattering on the proton has been investigated at three yet unexplored values of the four-momentum transfer $Q^2$: 0.10, 0.20 and 0.45 GeV$^2$, at the Mainz Microtron. Fits performed using either the low-energy theorem or dispersion relations allowed the extraction of the structure functions $P_{LL} -P_{TT} / \epsilon$ and $P_{LT}$, as well as the electric and magnetic generalized polarizabilities $\alpha_{E1}(Q^2)$ and $\beta_{M1}(Q^2)$. These new results show a smooth and rapid fall-off of $\alpha_{E1}(Q^2)$, in contrast to previous measurements at $Q^2$ = 0.33 GeV$^2$, and provide for the first time a precise mapping of $\beta_{M1}(Q^2)$ in the low-$Q^2$ region.

Resolution, efficiency and stability of HPGe detector operating in a magnetic field at various gamma-ray energies

Abstract The use of High Purity Germanium detectors (HPGe) has been planned in some future experiments of hadronic physics. The crystals will be located close to large spectrometers where the magnetic fringing field will not be negligible and their performances might change. Moreover high precision is required in these experiments. The contribution of magnetic field presence and long term measurements is unique. In this paper the results of systematic measurements of the resolution, stability and efficiency of a crystal operating inside a magnetic field of 0.8 T, using radioactive sources in the energy range from 0.08 to 1.33 MeV, are reported. The measurements have been repeated during sev…

Operation and characterization of a windowless gas jet target in high-intensity electron beams

Abstract A cryogenic supersonic gas jet target was developed for the MAGIX experiment at the high-intensity electron accelerator MESA. It will be operated as an internal, windowless target in the energy-recovering recirculation arc of the accelerator with different target gases, e.g., hydrogen, deuterium , helium, oxygen, argon, or xenon. Detailed studies have been carried out at the existing A1 multi-spectrometer facility at the electron accelerator MAMI. This paper focuses on the developed handling procedures and diagnostic tools, and on the performance of the gas jet target under beam conditions. Considering the special features of this type of target, it proves to be well suited for a n…

Hypernuclear production cross section in the reaction of 6Li + 12C at 2 A GeV

WOS: 000358624800021

Hypernuclear spectroscopy of products from Li-6 projectiles on a carbon target at 2 A GeV

WOS: 000322848900009

Measurement of propagation time dispersion in a scintillator

One contribution to the time resolution of a scintillation detector is the signal time spread due to path length variations of the detected photons from a point source. In an experimental study a rectangular scintillator was excited by means of a fast pulsed ultraviolet laser at different positions along its longitudinal axis. Timing measurements with a photomultiplier tube in a detection plane displaced from the scintillator end face showed a correlation between signal time and tube position indicating only a small distortion of photon angles during transmission. The data is in good agreement with a Monte Carlo simulation used to compute the average photon angle with respect to the detecti…

Experimental investigations of the hypernucleus $_Λ^4$H

International audience; Negatively charged pions from two-body decays of stopped _Lambda^4H hypernuclei were studied in 2012 at the Mainz Microtron MAMI, Germany. The momenta of the decay-pions were measured with unprecedented precision by using high-resolution magnetic spectrometers. A challenge of the experiment was the tagging of kaons from associated K^+∧ production off a Be target at very forward angles. In the year 2014, this experiment was continued with a better control of the systematic uncertainties, with better suppression of coincident and random background, improved particle identification, and with higher luminosities. Another key point of the progress was the improvemen…

Future use of silicon photomultipliers for Kaos at MAMI and P¯ANDA at FAIR

A characterisation of scintillating fibres with silicon photomultiplier read-out was performed in view of their possible application in fibre tracking detector systems. Such a concept is being considered for the Kaos spectrometer at the Mainz Microtron MAMI and as a time-of-flight start detector for the hypernuclear physics programme at the PANDA experiment of the FAIR project. Results on particle detection effciency and time resolution are discussed. In summary, the silicon devices are very suitable for the detection of the low light yield from scintillating fibres insofar a trigger scheme is found to cope with the noise rate characteristics.

Measurement of coherent and incoherent π0 photoproduction off the deuteron with tagged photons up to the Δ region

Coherent and incoherent pi(0) photoproduction off the deuteron has been measured for incident quasi-monoenergetic photons in the energy range from pi(0) threshold up to 300 MeV using the TAPS setup together with the Glasgow tagger at MAMI. Integral and differential cross sections over the full angular range have been obtained. Coherent and incoherent production are found to exhibit very different angle and energy dependences. The sum of both processes, the total pi(0) production off the deuteron is quantitatively extremely well described by a pure quasifree model, whereas the data for coherent and incoherent channels necessitate strong FSI effects for their description. Finally upper limits…

Low-energy Compton scattering and the polarizabilities of the proton

Differential cross-sections for Compton scattering from the proton have been measured at the MAMI tagged photon facility using the TAPS setup. The data cover an angular range of θlab γ = 59°-155° and photon energies ranging from 55 MeV to 165 MeV. Our results are in good agreement with those from previous experiments, but yield higher precision. Using dispersion relations the proton polarizabilities have been determined to be = [11.9±0.5stat.±1.3syst.±0.3mod.] . 10-4 fm 3 and = [1.2±0.7stat.±0.3syst.±0.4mod.)] . 10-4 fm 3. These results confirm the Baldin sum rule which was re-evaluated to be + = [13.8±0.4] . 10-4 fm 3. We can also conclude that there is no significant additional asymptotic…

Silicon Detector Telescope for proton detection in electron scattering reactions at MAMI

Abstract A new Silicon Detector Telescope has been constructed and installed within the experimental facility of the A1 collaboration at Mainz Microtron, with the goal to detect low-energy protons. It consists of seven silicon layers for energy and angle measurement and a plastic scintillator for triggering purposes. The detector subtends a solid angle up to 88 msr, depending on the distance from the target and covers the proton kinetic energy range of 25–41  MeV with the mean energy resolution σ E = 0.47 MeV , operating at 500 kHz. Digital signal processing methods applied for energy reconstruction have been important for keeping the acceptable energy resolution at high counting rates. The…

Production of hypernuclei in peripheral HI collisions: The HypHI project at GSI

ECT Workshop on Strange Hadronic Matter -- SEP 26-30, 2011 -- Trento, ITALY

Frontend electronics for high-precision single photo-electron timing using FPGA-TDCs

Abstract The next generation of high-luminosity experiments requires excellent particle identification detectors which calls for Imaging Cherenkov counters with fast electronics to cope with the expected hit rates. A Barrel DIRC will be used in the central region of the Target Spectrometer of the planned PANDA experiment at FAIR. A single photo-electron timing resolution of better than 100 ps is required by the Barrel DIRC to disentangle the complicated patterns created on the image plane. R&D studies have been performed to provide a design based on the TRB3 readout using FPGA-TDCs with a precision better than 20 ps RMS and custom frontend electronics with high-bandwidth pre-amplifiers and …

Recoil Polarization and Beam-Recoil Double Polarization Measurement ofηElectroproduction on the Proton in the Region of theS11(1535)Resonance

The beam-recoil double polarization P{sub x{sup '}}{sup h} and P{sub z{sup '}}{sup h} and the recoil polarization P{sub y{sup '}} were measured for the first time for the p(e-vector,e{sup '}p-vector){eta} reaction at a four-momentum transfer of Q{sup 2}=0.1 GeV{sup 2}/c{sup 2} and a center of mass production angle of {theta}=120 deg. at the Mainz Microtron MAMI-C. With a center of mass energy range of 1500 MeV<W<1550 MeV the region of the S{sub 11}(1535) and D{sub 13}(1520) resonance was covered. The results are discussed in the framework of a phenomenological isobar model (Eta-MAID). While P{sub x{sup '}}{sup h} and P{sub z{sup '}}{sup h} are in good agreement with the model, P{sub y{sup '…

Prospects for hypernuclear physics at Mainz: From KAOS@MAMI to PANDA@FAIR

Abstract At the Mainz Microtron hypernuclei are produced by ( e , e ′ K ) reactions. A dedicated kaon spectrometer located at 0° with respect to the electron beam is used to detect kaons emitted in forward direction thus tagging events involving strangeness production. By measuring the momenta of pions from two body weak decays using high resolution magnetic spectrometers one gains direct access to the ground state masses of the produced hyperfragments. At FAIR the PANDA Collaboration intends to produce double-hypernuclei by numbers with an antiproton beam and study their high resolution γ -spectroscopy thus providing for the first time precise information on the level structure of these nu…

Vertical Beam Polarization at MAMI

For the first time a vertically polarized electron beam has been used for physics experiments at MAMI in the energy range between 180 and 855 MeV. The beam-normal single-spin asymmetry $A_{\mathrm{n}}$, which is a direct probe of higher-order photon exchange beyond the first Born approximation, has been measured in the reaction $^{12}\mathrm C(\vec e,e')^{12}\mathrm C$. Vertical polarization orientation was necessary to measure this asymmetry with the existing experimental setup. In this paper we describe the procedure to orient the electron polarization vector vertically, and the concept of determining both its magnitude and orientation with the available setup. A sophisticated method has …

Lifetime of MCP-PMTs and other performance features

The ANDA experiment at FAIR will use DIRC detectors for the separation of hadrons. The compactness of the ANDA detector requires the image planes of these detectors to be placed inside the magnetic field of the solenoid. Due to this and other boundary conditions MCP-PMTs were identified as the only suitable photon sensors. Until recently the major obstacle for an application of MCP-PMTs in high rate experiments like ANDA were serious aging problems which led to damage at the photo-cathode and a fast declining quantum efficiency as the integrated anode charge (IAC) increased. With new countermeasures against the aging, in particular due to the application of an atomic layer deposition (ALD) …

Instrumentation and optimization studies for a beam dump experiment (BDX) at MESA — DarkMESA

Abstract At the Institute for Nuclear Physics in Mainz the new electron accelerator MESA will go into operation within the next years. The high-power beam dump of the P2 experiment is ideally suited for a parasitic dark sector experiment — DarkMESA. In the first stage 1,000 high density Cherenkov radiators from a previous experiment will be used. The experiment is studied with a simulation based on MadGraph and Geant4 . The simulation includes an optical photon study, where the response of possible calorimeter materials – PbF 2, BGO, the Pb glasses SF5, SF6 and SF57HTultra from Schott – was investigated. The simulation outcomes are compared with the results of prototypes tested at the Mainz…

Delayed Pion Spectroscopy of Hypernuclei

New possibilities of hypernuclear studies at modern electron accelerators based on recently developed radio frequency photomultiplier tubes are discussed.

Gain stabilization and noise minimization for SiPMs at cryogenic temperatures

Abstract The performance of solid-state photon detectors such as avalanche photodiodes or silicon photomultipliers (SiPMs) is strongly affected by temperature. Important device characteristics for the detection of low light levels or single photons are photon detection efficiency, dark noise, and gain. In the present work the C-series SiPMs from SensL was characterized in cryogenic environments. At 77  K the SiPMs proved to be an excellent choice for single photon detection and an operation point with minimum noise contributions was found. At 4  K the performance was degraded, exhibiting a smaller gain and a larger noise.

Charge symmetry breaking inA= 4 hypernuclei

Charge symmetry breaking in the A = 4 hypernuclear system is reviewed. The data on binding energies of the mirror nuclei and hypernuclei are examined. At the Mainz Microtron MAMI the high-resolution spectroscopy of decay-pions in strangeness electro-production is used to extract the Λ hyperon ground state binding energy in 4 Λ H. This binding energy is used together with the 4 Λ He ground state binding energy from nuclear emulsion experiments and with energy levels of the 1 + excited state for both hypernuclei from γ-ray spectroscopy to address the charge symmetry breaking in the strong interaction. The binding energy difference of the ground states in the mirror pair is reduced from its lo…

Strangeness nuclear physics at P¯ANDA

First measurement of helicity-dependent cross sections in π0η photoproduction from quasi-free nucleons

The helicity-dependent cross sections for the photoproduction of $\pi^0\eta$ pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the $\sigma_{1/2}$ (photon and target spin antiparallel) and $\sigma_{3/2}$ (parallel spins) components to be measured for quasi-free production of $\pi^0\eta$ pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant pr…

Kaon Tagging at 0° Scattering Angle for High-Resolution Decay-Pion Spectroscopy

At the Mainz Microtron hypernuclei can be studied by (e,e'K) reactions. By detecting the kaon which is emitted in forward direction, with the KAOS spectrometer placed at 0 scattering angle, reactions involving open strangeness production are tagged. High-resolution magnetic spectrometers are then used to coincidentally detect the mono- energetic decay-pions from mesonic two-body weak decays of light hypernuclei at rest. As a pioneering experiment has confirmed, the KAOS spectrometer is exposed to a large flux of background particles, mostly positrons from bremsstrahlung pair production. In order to increase the e ciency of kaon identification the KAOS spectrometer was modi- fied to suppress…

Improved lifetime of microchannel-plate PMTs

Abstract The charged particle identification at the PANDA experiment will be mainly performed with DIRC detectors. Because of their advantageous properties the preferred photon sensors are MCP-PMTs. However, until recently these devices showed serious aging problems which resulted in a diminishing quantum efficiency (QE) of the photo cathode. By applying innovative countermeasures against the aging causes, the manufacturers recently succeeded in drastically improving the lifetime of MCP-PMTs. Especially the application of an ALD coating technique to seal the material of the micro-channels proves very powerful and results in a lifetime of ≈ 6 C / cm 2 integrated anode charge without a substa…

Simulation and reconstruction of the PANDA Barrel DIRC

Hadronic particle identification (PID) in the barrel region of the PANDA experiment at the new Facility for Antiproton and Ion Research in Europe (FAIR) at GSI, Darmstadt will be provided by a DIRC (Detection of Internally Reflected Cherenkov light) counter. To optimize the performance and reduce the detector cost, detailed simulations of different design elements, such as the width of the radiators, the shape of the expansion volume, and the type of focusing system, were performed using Geant. Custom reconstruction algorithms were developed to match the detector geometry. We will discuss the single photon resolution and photon yield as well as the PID performance for the Barrel DIRC baseli…

Experiments and Facilities for Accelerator-Based Dark Sector Searches

This paper provides an overview of experiments and facilities for accelerator-based dark matter searches as part of the US Community Study on the Future of Particle Physics (Snowmass 2021). Companion white papers to this paper present the physics drivers: thermal dark matter, visible dark portals, and new flavors and rich dark sectors.

Double- π0 photoproduction from the deuteron

The photoproduction of two neutral pions from the deuteron has been studied for incident photon energies from 200 MeV to 820 MeV with the TAPS spectrometer at MAMI (Mainz Microtron). The total cross-section was determined and used to deduce the cross-section from the neutron. Due to the good statistical quality of the data Dalitz plots for the three particles in the exit channel (pi (0)pi N-0) could be constructed. The invariant mass distributions derived from them are presented in this paper. They indicate that the important reaction mechanism in the second resonance region is a sequential decay pattern involving the population of the Delta (1232)-resonance as an intermediate state.

High Resolution Λ Hypernuclear Spectroscopy with Electron Beams

T. Gogami1 ∗, P. Achenbach2, A. Ahmidouch3, I. Albayrak4, D. Androic5, A. Asaturyan6, R. Asaturyan6, O. Ates4, P. Baturin7, R. Badui7, W. Boeglin7, J. Bono7, E. Brash8, P. Carter8, C. Chen4, A. Chiba1, E. Christy4, S. Danagoulian3, R. De Leo10, D. Doi1, M. Elaasar11, R. Ent9, Y. Fujii1, M. Fujita1, M. Furic5, M. Gabrielyan7, L. Gan12, F. Garibaldi13, D. Gaskell9, A. Gasparian3, O. Hashimoto1, T. Horn9, B. Hu14, Ed. V. Hungerford21, M. Jones9, H. Kanda1, M. Kaneta1, S. Kato19, M. Kawai1, D. Kawama1, H. Khanal7, M. Kohl4, A. Liyanage4, W. Luo14, K. Maeda1, A. Margaryan6, P. Markowitz7, T. Maruta1, A. Matsumura1, V. Maxwell7, A. Mkrtchyan6, H. Mkrtchyan6, S. Nagao1, S. N. Nakamura1, A. Narayan…

The Endcap Disc DIRC detector of PANDA

Abstract At the international FAIR laboratory, an upcoming significant enlargement of the GSI installations near Darmstadt, Germany, the PANDA antiproton experiment will investigate fundamental questions of hadron physics in the charm quark energy range. Antiprotons in the 1.5 to15 GeV/c momentum range will interact with gas jet or pellet fixed targets. The Endcap Disc DIRC (Detection of Internally Reflected Cherenkov light) covers the forward endcap solid angle of the PANDA target spectrometer to positively identify charged kaons. Monte-Carlo simulations indicate that from 1 up to 4 GeV/c one can achieve kaon–pion separation with a separation power of at least 3 standard deviations. For th…

First Measurement of the $Q^2$ Dependence of the Beam-Normal Single Spin Asymmetry for Elastic Scattering off Carbon

We report on the first Q^{2}-dependent measurement of the beam-normal single spin asymmetry A_{n} in the elastic scattering of 570 MeV vertically polarized electrons off ^{12}C. We cover the Q^{2} range between 0.02 and 0.05  GeV^{2}/c^{2} and determine A_{n} at four different Q^{2} values. The experimental results are compared to a theoretical calculation that relates A_{n} to the imaginary part of the two-photon exchange amplitude. The result emphasizes that the Q^{2} behavior of A_{n} given by the ratio of the Compton to charge form factors cannot be treated independently of the target nucleus.

A tracking fiber detector based on silicon photomultipliers for the KAOS spectrometer

A tracking detector based on two meters long scintillating fibers read out by silicon photomultipliers (SiPM) is being developed for the Kaos spectrometer at the Mainz Microtron MAMI. Results from a prototype setup using 2 mm square fibers and large area SiPM readout are presented. The detection efficiency of such a combination was measured to be between 83 and 100% depending on the threshold on the SiPM amplitude. A Monte Carlo simulation based on a physical model was employed in order to extract the photon detection efficiency of the SiPM devices.

Signatures of the d*(2380) Hexaquark in d(γ,pn→)

We report a measurement of the spin polarization of the recoiling neutron in deuterium photodisintegration, utilizing a new large acceptance polarimeter within the Crystal Ball at MAMI. The measured photon energy range of 300-700 MeV provides the first measurement of recoil neutron polarization at photon energies where the quark substructure of the deuteron plays a role, thereby providing important new constraints on photodisintegration mechanisms. A very high neutron polarization in a narrow structure centered around E_{γ}∼570 MeV is observed, which is inconsistent with current theoretical predictions employing nucleon resonance degrees of freedom. A Legendre polynomial decomposition sugge…

Silicon photomultiplier properties at cryogenic temperatures

Abstract The properties of different types of silicon photomultipliers (SiPMs) were studied at cryogenic temperatures. In liquid nitrogen at 77 K, problems with quenching in Hamamatsu SiPMs and with the protective epoxy layer, covering Zecotek SiPMs, were observed. Tests with one Zecotek SiPM were successful after removal of the epoxy layer. In liquid helium at 4 K, fast signals with pulse lengths shorter than 50 ns were observed, the dark count rate was below 10 Hz and no after-pulses were detected. The gain, as a function of over-voltage, was comparable to room temperature. The SiPM׳s response to photons was found to be linear with intensity for low light levels and single-photon detectio…

Near threshold photoproduction of η mesons from 4 He

Photoproduction of η mesons from 4He has been measured for the first time. The experiment was performed at the Mainz Microtron (MAMI) using the TAPS photon spectrometer and the Glasgow/Mainz tagged photon facility. η mesons were identified in coincidence with recoil nucleons. Total and differential cross sections are presented in the photon energy range between threshold and 818 MeV. The exclusive data are used to determine the ratio of the elementary production cross sections on bound neutrons and protons, σn/σp= 0.68 ± 0.02 ± 0.09. In addition, upper limits for the total coherent cross section have been derived.

Deuteron form factor measurements at low momentum transfers

A precise measurement of the elastic electron-deuteron scattering cross section at four-momentum transfers of 0.24 fm−1 ≤ Q ≤ 2.7 fm−1 has been performed at the Mainz Microtron. In this paper we describe the utilized experimental setup and the necessary analysis procedure to precisely determine the deuteron charge form factor from these data. Finally, the deuteron charge radius rd can be extracted from an extrapolation of that form factor to Q 2 = 0.

Beam-Recoil Polarization Measurement of π0 Electroproduction on the Proton in the Region of the Roper Resonance

The helicity-dependent recoil proton polarizations P_{x}^{'} and P_{z}^{'} as well as the helicity-independent component P_{y} have been measured in the p(e[over →],e^{'}p[over →])π^{0} reaction at four-momentum transfer Q^{2}≃0.1  GeV^{2}, center-of-mass proton emission angle θ_{p}^{*}≃90°, and invariant mass W≃1440  MeV. This first precise measurement of double-polarization observables in the energy domain of the Roper resonance P_{11}(1440) by exploiting recoil polarimetry has allowed for the extraction of its scalar electroexcitation amplitude at an unprecedentedly low value of Q^{2}, establishing a powerful instrument for probing the interplay of quark and meson degrees of freedom in t…

High Precision Momentum Calibration of the Magnetic Spectrometers at MAMI for Hypernuclear Binding Energy Determination

We propose a new method for absolute momentum calibration of magnetic spectrometers used in nuclear physics, using the time-of-flight (TOF), differences of pairs of particles with different masses. In cases where the flight path is not known, a calibration can be determined by using the TOF differences of two pair combinations of three particles. A Cherenkov detector, read out by a radio frequency photomultiplier tube, is considered as the high-resolution and highly stable TOF detector. By means of Monte Carlo simulations it is demonstrated that the magnetic spectrometers at the MAMI electron-scattering facility can be calibrated absolutely with an accuracy $\delta p/p\leq 10^{-4}$, which w…

Initial state radiation experiment at MAMI

In an attempt to contribute further insight into the discrepancy between the Lamb shift and elastic scattering determinations of the proton charge radius, a new experiment at MAMI is underway, aimed at measuring proton form-factors at very low momentum transfers by using a new technique based on initial state radiation. This paper reports on the conclusions of the pilot measurement performed in 2010, whose main goal was to check the feasibility of the proposed experiment and to recognize and overcome any obstacles before running the full experiment. The modifications to the experimental apparatus are then explained which significantly improved the quality of data collected in the full scale…

A luminosity monitor for the A4 parity violation experiment at MAMI

A water Cherenkov luminosity monitor system with associated electronics has been developed for the A4 parity violation experiment at MAMI. The detector system measures the luminosity of the hydrogen target hit by the MAMI electron beam and monitors the stability of the liquid hydrogen target. Both is required for the precise study of the count rate asymmetries in the scattering of longitudinally polarized electrons on unpolarized protons. Any helicity correlated fluctuation of the target density leads to false asymmetries. The performance of the luminosity monitor, investigated in about 2000 hours with electron beam, and the results of its application in the A4 experiment are presented.

First measurements of Λ and hyperons in elementary electroproduction at MAMI

Abstract Since 2008 the magnetic spectrometer Kaos , dedicated to the detection of charged kaons, is operating at the 1.5 GeV electron beam of MAMI at the Institut fur Kernphysik in Mainz, Germany. The strangeness programme performed in 2008–9 is addressing some important issues in the field of elementary kaon photoelectro-production reactions. The identification of Λ and Σ 0 hyperons in the missing mass spectra from kaon production off a liquid hydrogen target demonstrates the capability of the extended facility to perform strangeness electro-production spectroscopy at low momentum transfers Q 2 0.5 ( GeV / c ) 2 . Systematic uncertainties in the cross-section extraction from the data are …

Threshold enhancement in η photoproduction from 2H and 4He

The photoproduction of η-mesons from 2H and 4He has been studied for energies close to the production thresholds. The experiments were carried out with the tagged photon beam of the Mainz MAMI accelerator. The η-mesons were detected via their two photon decays with the electromagnetic calorimeter TAPS. Total cross-sections, angular and momentum distributions of the η-mesons have been determined for both reactions. The total cross-sections in the threshold region show a large enhancement over the predictions of a participant-spectator model, indicating significant final-state interaction effects. The results are compared to recent model calculations taking into account nucleon-nucleon and nu…