0000000000916711
AUTHOR
C. Sfienti
showing 32 related works from this author
Measurement of the decay η′→π0π0η at MAMI
2018
An experimental study of the eta' -> pi(0)pi(0)eta -> 6 gamma decay has been conducted with the best up-to-date statistical accuracy, by measuring. 0 mesons produced in the gamma p -> eta'p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the eta' -> pi(0)pi(0)eta matrix element are consistent with the most recent results for eta' -> pi pi eta decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the pi(+)pi(-) thorn p-mass threshold, the magnitude and sign of which, checked within the framewo…
Helicity-dependent cross sections for the photoproduction of π0 pairs from nucleons
2020
The double-polarization observable $E$ and helicity-dependent cross sections $\sigma_{1/2}$, $\sigma_{3/2}$ have been measured for the photoproduction of $\pi^0$ pairs off quasi-free protons and neutrons at the Mainz MAMI accelerator with the Crystal Ball/TAPS setup. A circularly polarized photon beam was produced by bremsstrahlung from longitudinally polarized electrons and impinged on a longitudinally polarized deuterated butanol target. The reaction products were detected with an almost $4\pi$ covering calorimeter. The results reveal for the first time the helicity- and isospin-dependent structure of the $\gamma N\rightarrow N\pi^0\pi^0$ reaction. They are compared to predictions from re…
Insight into the narrow structure in η-photoproduction on the neutron from helicity\ud dependent cross sections
2016
The double polarization observable E and the helicity dependent cross sections σ1/2 and σ3/2 were measured for η photoproduction from quasifree protons and neutrons. The circularly polarized tagged photon beam of the A2 experiment at the Mainz MAMI accelerator was used in combination with a longitudinally polarized deuterated butanol target. The almost 4π detector setup of the Crystal Ball and TAPS is ideally suited to detect the recoil nucleons and the decay photons from η→2γ and η→3π0. The results show that the narrow structure previously observed in η photoproduction from the neutron is only apparent in σ1/2 and hence, most likely related to a spin-1/2 amplitude. Nucleon resonances that …
Fast Frontend Electronics for high luminosity particle detectors
2015
Future experiments of nuclear and particle physics are moving towards the high luminosity regime, in order to access suppressed processes like rare B decays or exotic charmonium resonances. In this scenario, high rate capability is a key requirement for electronics instrumentation, together with excellent timing resolution for precise event reconstruction. The development of dedicated FrontEnd Electronics (FEE) for detectors has become increasingly challenging. A current trend in R&D is towards multipurpose FEE which can be easily adapted to a great variety of detectors, without impairing the required high performance. We report on high-precision timing solutions which utilise high-band…
Feasibility study for the measurement of πN transition distribution amplitudes at P¯ANDA in p¯p→J/ψπ0
2017
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…
Performance of HPGe detectors in high magnetic field
2006
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…
Carbon fragmentation measurements and validation of the GEANT4 nuclear reaction models for hadrontherapy
2012
Nuclear fragmentation measurements are necessary when using heavy-ion beams in hadrontherapy to predict the effects of the ion nuclear interactions within the human body. Moreover, they are also fundamental to validate and improve the Monte Carlo codes for their use in planning tumor treatments. Nowadays, a very limited set of carbon fragmentation cross sections are being measured, and in particular, to our knowledge, no double-differential fragmentation cross sections at intermediate energies are available in the literature. In this work, we have measured the double-differential cross sections and the angular distributions of the secondary fragments produced in the (12)C fragmentation at 6…
Photoproduction of π 0 mesons off protons and neutrons in the second and third nucleon resonance regions
2018
Photoproduction of mesons off quasi-free nucleons bound in the deuteron allows to study the electromagnetic excitation spectrum of the neutron and the isospin structure of the excitation of nucleon resonances. The database for such reactions is much more sparse than for free proton targets. Single $\pi^0$ photoproduction off quasi-free nucleons from the deuteron was experimentally studied. Nuclear effects were investigated by a comparison of the results for free protons and quasi-free protons and used as a correction for the quasi-free neutron data. The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator for photon energies between 0.45~GeV and 1.4~GeV, using an…
Timing in a FLASH
2017
Abstract A prototype detector, called FLASH (Fast Light Acquiring Start Hodoscope), was built to provide precise Time-of-Flight (TOF) measurements and reference timestamps for detector setups at external beam lines. Radiator bars, made of synthetic fused silica, were coupled to a fast MCP-PMT with 64 channels and read out with custom electronics using Time-over-Threshold (TOT) for signal characterization. The TRB3 system, a high-precision TDC implemented in an FPGA, was used as data acquisition system. The performance of a system consisting of two FLASH units was investigated at a dedicated test experiment at the Mainz Microtron (MAMI) accelerator using its 855 MeV electron beam. The TOT me…
Study of doubly strange systems using stored antiprotons
2016
Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the PANDA experiment at FAIR. For the first time, high resolution gamma-spectroscopy of doubly strange Lambda Lambda-hypernuclei will be performed, thus complementing measurements of ground state decays of Lambda Lambda-hypernuclei at J-PARC or possible …
The PANDA Barrel DIRC
2018
The PANDA experiment at the international accelerator Facility for Antiproton and Ion Research in Europe (FAIR) near GSI, Darmstadt, Germany will address fundamental questions of hadron physics. Excellent Particle Identification (PID) over a large range of solid angles and particle momenta will be essential to meet the objectives of the rich physics program. Charged PID for the barrel region of the PANDA target spectrometer will be provided by a DIRC (Detection of Internally Reflected Cherenkov light) detector. The Barrel DIRC will cover the polar angle range of 22$^\circ$-140$^\circ$ and cleanly separate charged pions from kaons for momenta between 0.5 GeV/c and 3.5 GeV/c with a separation…
Status and prospects of Rn measurements at Mainz
2013
Parity-violating electron scattering is particularly sensitive to the neutron density. The recent PREX experiment at the Jefferson Laboratory (JLab) has demonstrated the feasibility of this method meanwhile outlining its major experimental challenges. On the other side intermediate energy photons are an ideal probe for studying the properties of strongly interacting matter from the nuclear scale down to the sub-nuclear components of the nucleus. Among others, coherent pion photoproduction on nuclei is an attractive approach to obtain information on the existence and nature of neutron skins in nuclei. The simultaneous combination of different techniques allows a systematic determination of t…
Measurement of the π0→e+e−γ Dalitz decay at the Mainz Microtron
2017
The Dalitz decay π0→e+e−γ has been measured in the γp→π0p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the π0 electromagnetic transition form factor, aπ=0.030±0.010tot, is in agreement with existing measurements of this decay and with recent theoretical calculations. The uncertainty obtained in the value of aπ is lower than in previous results based on the π0→e+e−γ decay.
First measurement of helicity-dependent cross sections in π0η photoproduction from quasi-free nucleons
2018
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…
The FIRST experiment at GSI
2012
The FIRST (Fragmentation of Ions Relevant for Space and Therapy) experiment at the SIS accelerator of GSI laboratory in Darmstadt has been designed for the measurement of ion fragmentation cross-sections at different angles and energies between 100 and 1000 MeV/nucleon. Nuclear fragmentation processes are relevant in several fields of basic research and applied physics and are of particular interest for tumor therapy and for space radiation protection applications. The start of the scientific program of the FIRST experiment was on summer 2011 and was focused on the measurement of 400 MeV/nucleon 12C beam fragmentation on thin (8 mm) graphite target. The detector is partly based on an alread…
Resolution changes of MCP-PMTs in magnetic fields
2016
Micro-channel plate photomultiplier tubes (MCP-PMTs) are chosen in many applications that have to cope with strong magnetic fields. The DIRC detectors of the PANDA experiment plan to employ them as they show excellent timing characteristics, radiation hardness, relatively low dark count rates and sufficient lifetime. This article mainly focuses on the performance of the position reconstruction of detected photons. Two different MCP-PMTs with segmented anode geometries have been tested in magnetic fields of different strengths. The variation of their performance has been studied. The measurements show improved position resolution and image shifts with increasing magnetic field strength.
Endcap Disc DIRC for PANDA at FAIR
2018
The Endcap Disc DIRC (EDD) has been developed to provide an excellent particle identification in the future PANDA experiment by separating pions and kaons up to a momentum of 4 GeV/c with a separation power of 3 s.d.. The detector is placed in the forward endcap of the PANDA target spectrometer. It consists of a fused silica plate and focusing elements placed at the outer rim, which focus the Cherenkov light on the photo cathodes of the attached MCP-PMTs. A compact and fast readout of the signals is realized with special ASICs. The performance has been studied and validated with different prototype setups in various testbeam facilities.
Single π0 production off neutrons bound in deuteron with linearly polarized photons
2021
The quasifree γ→d→π0n(p) photon beam asymmetry, Σ, has been measured at photon energies, Eγ, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49∘ to 148∘. In this kinematic region, polarization observables are sensitive to contributions from the Δ(1232) and N(1440) resonances. The extracted values of Σ have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID and Bonn–Gatchina anal…
Study of $\eta$ and $\eta'$ photoproduction at MAMI
2017
The reactions $\gamma p\to \eta p$ and $\gamma p\to \eta' p$ have been measured from their thresholds up to the center-of-mass energy $W=1.96$GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections were obtained with unprecedented accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section and excitation functions for $\eta$ photoproduction at the energies in vicinity of the $\eta'$ threshold, $W=1896$MeV ($E_\gamma=1447$MeV). This behavior is explained in a revised $\eta$MAID isobar model by a significant branching of the $N(1895)1/2^-$ nucleon resonance to both, $\eta p$ and $\eta'…
Insight into the narrow structure in {\boldmath{$\eta$}}-photoproduction on the neutron from helicity dependent cross sections
2017
The double polarization observable $E$ and the helicity dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ were measured for $\eta$ photoproduction from quasi-free protons and neutrons. The circularly polarized tagged photon beam of the A2 experiment at the Mainz MAMI accelerator was used in combination with a longitudinally polarized deuterated butanol target. The almost $4\pi$ detector setup of the Crystal Ball and TAPS is ideally suited to detect the recoil nucleons and the decay photons from $\eta\rightarrow 2\gamma$ and $\eta\rightarrow 3\pi^0$. The results show that the narrow structure previously observed in $\eta$ photoproduction from the neutron is only apparent in $\sigma_…
First measurement of helicity-dependent cross sections in Photoproduction From Quasi-free Nucleons
2018
The helicity-dependent cross sections for the photoproduction of π0η 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 σ1/2 (photon and target spin antiparallel) and σ3/2 (parallel spins) components to be measured for quasi-free production of π0η pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant protons and neutrons. The absolute cou…
Study of eta and eta' Photoproduction at MAMI
2017
The reactions γp→ηp and γp→η′p are measured from their thresholds up to the center-of-mass energy W=1.96 GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections are obtained with unprecedented statistical accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section for η photoproduction at the energies in the vicinity of the η′ threshold, W=1896 MeV (Eγ=1447 MeV). Within the framework of a revised ηMAID isobar model, the cusp, in connection with a steep rise of the η′ total cross section from its threshold, can only be explained by a strong coupling of the poorly known N(1895)1/2− sta…
Study of η and η' Photoproduction at MAMI
2017
The reactions γp → ηp and γp → η0\ud p are measured from their thresholds up to the center-of-mass\ud energy W ¼ 1.96 GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross\ud sections are obtained with unprecedented statistical accuracy, providing fine energy binning and full\ud production-angle coverage. A strong cusp is observed in the total cross section for η photoproduction at the\ud energies in the vicinity of the η0 threshold, W ¼ 1896 MeV (Eγ ¼ 1447 MeV). Within the framework of a\ud revised ηMAID isobar model, the cusp, in connection with a steep rise of the η0 total cross section from its\ud threshold, can only be explained by a strong coupling of …
The DIRC detectors at the PANDA experiment
2015
PANDA is an experiment at the new FAIR facility at GSI and will, among other physics goals,\ud perform charmonium spectroscopy and search for gluonic excitations using high luminosity antiproton beams up to 15 GeV/c. A high performance particle identification system applying DIRC\ud detectors will allow pion/kaon separation up to 4 GeV/c. A Barrel DIRC with fused silica radiator bars or plates will surround the target at a radial distance of 48 cm and will cover a polar\ud angle range of 22 to 140 degrees; a novel Endcap Disk DIRC built of a segmented fused silica\ud disk of 210 cm diameter will be installed in the forward region to cover the polar angles from\ud 5 to 22 degrees. The design…
The Innovative Design of the Endcap Disc DIRC Detector for PANDA at FAIR
2019
The key component of the future PANDA experiment at FAIR is a fixed-target detector for collisions of antiprotons with a proton target up to a beam momentum of 15 GeV/c and is designed to address a large number of open questions in the hadron physics sector. In order to guarantee an excellent PID for charged hadrons in the polar angle range between $5^\circ$ and $22^\circ$, a new type of Cherenkov detector called Endcap Disc DIRC (EDD) has been developed for the forward endcap of the PANDA target spectrometer. The desired separation power of at least 3 s.d. for the separation of $\pi^\pm$ and $K^\pm$ up to particle momenta of 4 GeV/c was determined with simulation studies and validated duri…
Helicity-dependent cross sections and double-polarization observable E in eta photoproduction from quasi-free protons and neutrons
2017
Precise helicity-dependent cross sections and the double-polarization observable $E$ were measured for $\eta$ photoproduction from quasi-free protons and neutrons bound in the deuteron. The $\eta\rightarrow 2\gamma$ and $\eta\rightarrow 3\pi^0\rightarrow 6\gamma$ decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz. A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were de…
Feasibility study for the measurement of pi N transition distribution amplitudes at (P)over-barANDA in (P)over-barp -> J/psi pi(0)
2017
The exclusive charmonium production process in pp¯ annihilation with an associated π0 meson pp¯ → J=ψπ0 is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J=ψ → eþe− decay channel with the AntiProton ANnihilation at DArmstadt (PANDA ¯ ) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the pp¯ → πþπ−π0 and pp¯ → J=ψπ0π0 reactions are performed with PANDAROOT, the simulation and analysis software framework of the PANDA ¯ experiment. It is shown that the measurement can be done at PANDA ¯ with significant constraining power under the assu…
Insight into the Narrow Structure in eta Photoproduction on the Neutron from Helicity-Dependent Cross Sections
2016
The double polarization observable E and the helicity dependent cross sections σ1/2 and σ3/2 were measured for η photoproduction from quasifree protons and neutrons. The circularly polarized tagged photon beam of the A2 experiment at the Mainz MAMI accelerator was used in combination with a longitudinally polarized deuterated butanol target. The almost 4π detector setup of the Crystal Ball and TAPS is ideally suited to detect the recoil nucleons and the decay photons from η→2γ and η→3π0. The results show that the narrow structure previously observed in η photoproduction from the neutron is only apparent in σ1/2 and hence, most likely related to a spin-1/2 amplitude. Nucleon resonances that …
New developments of the PANDA Disc DIRC detector
2015
The DIRC principle (Detection of Internally Reflected Cherenkov light) allows a very compact\ud approach for particle identification detectors. The PANDA detector at the future FAIR facility at\ud GSI will use a Barrel-DIRC for the central region and a Disc DIRC for the forward angular region\ud between 5◦\ud and 22◦\ud . It will be the first time that a Disc DIRC is used in a high performance 4π\ud detector. To achieve this aim, different designs and technologies have been evaluated and tested.\ud This article will focus on the mechanical design and integration of the Disc DIRC with respect to\ud the PANDA environment.
Beam-normal single spin asymmetry in elastic electron scattering off Si and Zr
2020
We report on a new measurement of the beam-normal single spin asymmetry An in the elastic scattering of 570 MeV transversely polarized electrons off $^{28}$Si and $^{90}$Zr at Q2=0.04 GeV2/c2. 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.
Frontend Electronics for high-precision single photo-electron timing
2015
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\ud of the planned PANDA experiment at FAIR. A single photo-electron timing resolution of better\ud than 100 ps RMS is required for the Barrel DIRC to disentangle the complicated patterns created\ud on the image plane. R&D studies have been performed to provide a design based on the TRB3\ud readout using FPGA-TDCs with a typical precision of 10 ps RMS and custom frontend electronics with high-bandwidth pre-amp…
Measurement of the decay η′→π0π0η at MAMI
2018
An experimental study of the η′→π0π0η→6γ decay has been conducted with the best up-to-date statistical accuracy, by measuring η′ mesons produced in the γp→η′p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the η′→π0π0η matrix element are consistent with the most recent results for η′→ππη decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the π+π− mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with t…