0000000000309210
AUTHOR
D. Mekterovic
New determination of theηtransition form factor in the Dalitz decayη→e+e−γwith the Crystal Ball/TAPS detectors at the Mainz Microtron
The Dalitz decay eta -> e(+) e(-) gamma has been measured in the gamma p -> eta p reaction with the Crystal Ball and TAPS multiphoton spectrometers, together with the photon-tagging facility at the Mainz Microtron MAMI. The experimental statistic used in this work is one order of magnitude greater than in any previous measurement of eta -> e(+) e(-) gamma. The value obtained for the slope parameter Lambda(-2) of the eta transition form factor, Lambda(-2) = (1.95 +/- 0.15(stat) +/- 0.10(syst)) GeV-2, is in good agreement with recent measurements conducted in eta -> e(+) e(-) gamma and eta -> mu(+) mu(-) gamma decays, as well as with recent form-factor calculations. The uncertainty obtained i…
Double pion photoproduction off nuclei - Are there effects beyond final-state interaction?
Photoproduction of $\pi^{0}\pi^{0}$ and $\pi^{0}\pi^{\pm}$ pairs from nuclei has been measured over a wide mass range ($^2$H, $^{7}$Li, $^{12}$C, $^{40}$Ca, and $^{\rm nat}$Pb) for photon energies from threshold to 600 MeV. The experiments were performed at the MAMI accelerator in Mainz, using the Glasgow photon tagging spectrometer and a 4$\pi$ electromagnetic calorimeter consisting of the Crystal Ball and TAPS detectors. A shift of the pion-pion invariant mass spectra for heavy nuclei to small invariant masses has been observed for $\pi^0$ pairs but also for the mixed-charge pairs. The precise results allow for the first time a model-independent analysis of the influence of pion final-sta…
Accurate Test of Chiral Dynamics in the \boldmath$\vec{\gamma} p \rightarrow \pi^0p$ Reaction
A precision measurement of the differential cross sections $d\sigma/d\Omega$ and the linearly polarized photon asymmetry $\Sigma \equiv (d\sigma_\perp - d\sigma_\parallel) \slash (d\sigma_\perp + d\sigma_\parallel)$ for the $\vec{\gamma} p \rightarrow \pi^0p$ reaction in the near-threshold region has been performed with a tagged photon beam and almost $4\pi$ detector at the Mainz Microtron. The Glasgow-Mainz photon tagging facility along with the Crystal Ball/TAPS multi-photon detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the $S$- and all three $P$-wave amplitudes for the first t…
Coherent photoproduction of η-mesons off 3He – search for η-mesic nuclei
Coherent photoproduction of $\eta$-mesons off $^3$He, i.e. the reaction $\gamma ^3{He}\rightarrow \eta ^3{He}$, has been investigated in the near-threshold region. The experiment was performed at the Glasgow tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS detector. Angular distributions and the total cross section were measured using the $\eta\rightarrow \gamma\gamma$ and $\eta\rightarrow 3\pi^0\rightarrow 6\gamma$ decay channels. The observed extremely sharp rise of the cross section at threshold and the behavior of the angular distributions are evidence for a strong $\eta {^3{He}}$ final state interaction, pointing to the existence of a resonant …
Photoproduction of $\eta$ $\pi$ pairs off nucleons and deuterons
Quasi-free photoproduction of $\pi\eta$-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the $\pi\eta$ and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions $\gamma p\rightarrow p\pi^0\eta$, $\gamma n\rightarrow n\pi^0\eta$, $\gamma p\rightarrow n\pi^+\eta$, and $\gamma n\rightarrow p\pi^-\eta$ from nucleons bound inside the deuteron. For the $\gamma p$ initial state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of $…
Photoproduction of π0-pairs off protons and off neutrons
Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of π0π0 pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections…
Measurement of theγp→K0Σ+reaction with the Crystal Ball/TAPS detectors at the Mainz Microtron
The gamma p -> K-0 Sigma(+) reaction has been measured from threshold to E-gamma = 1.45 GeV (W-CM = 1.9 GeV) using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. In the present experiment, this reaction was searched for in the 3 pi(0)p final state, by assuming K-S(0) -> pi(0)pi(0) and Sigma(+) -> pi(0)p. The experimental results include total and differential cross sections as well as the polarization of the recoil hyperon. The new data significantly improve empirical knowledge about the gamma p -> K-0 Sigma(+) reaction in the measured energy range. The results are compared to previous measurements and model predict…
The isospin structure of photoproduction of πη pairs from the nucleon in the threshold region
Abstract Photoproduction of πη-pairs from nucleons has been investigated from threshold up to incident photon energies of ≈ 1.4 GeV. The quasi-free reactions γ p → p π 0 η , γ n → n π 0 η , γ p → n π + η , and γ n → p π − η were for the first time measured from nucleons bound in the deuteron. The corresponding reactions from a free-proton target were also studied to investigate final-state interaction effects (for neutral pions the free-proton results could be compared to previous measurements; the γ p → n π + η reaction was measured for the first time). For the π 0 η final state coherent production via the γ d → d π 0 η reaction was also investigated. The experiments were performed at the …
Neutron Skin ofPb208from Coherent Pion Photoproduction
Information on the size and shape of the neutron skin on (208)Pb is extracted from coherent pion photoproduction cross sections measured using the Crystal Ball detector together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections, the half-height radius and diffuseness of the neutron distribution are found to be c(n)=6.70±0.03(stat.) fm and a(n)=0.55±0.01(stat.)(-0.03)(+0.02)(sys.) fm, respectively, corresponding to a neutron skin thickness Δr(np)=0.15±0.03(stat.)(-0.03)(+0.01)(sys.) fm. The results give the first successful extraction of a neutron skin thickness with an electromagnetic p…
Measurement of the $^{1}H$($\vec{\gamma}$, $\vec{p}$)$\pi^{0}$ reaction using a novel nucleon spin polarimeter
We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon, pioneering a novel polarimetry technique with wide application to future nuclear and hadronic physics experiments. The commissioning measurement of polarization transfer in the $^{1}H$($\vec{\gamma}$,$\vec{p}$)$\pi^{0}$ reaction in the range $0.4<E_{\gamma}<1.4$ GeV is highly selective regarding the basic parameterizations used in partial wave analyses to extract the nucleon excitation spectrum. The new data strongly favor the recently proposed Chew-Mandelstam formalism.
Search for the charge-conjugation-forbidden decayω→ηπ0
A new upper limit of 2.3x10{sup -4} on the branching ratio of the decay {omega}{yields}{eta}{pi}{sup 0} has been obtained using the Crystal Ball multiphoton spectrometer at the Mainz Microtron MAMI. This decay is forbidden by charge-conjugation invariance of the strong and electromagnetic interactions. We have also obtained the upper limit of 2.3x10{sup -4} for the forbidden decay {omega}{yields}3{pi}{sup 0} and the upper limit of 2.4x10{sup -4} for {omega}{yields}2{pi}{sup 0}.
Determination of the η-transition form factor in the γp→pη→pγe+e− reaction
The Dalitz decay η→γe+e− has been measured using the combined Crystal Ball and TAPS photon detector setup at the electron accelerator MAMI-C. Compared to the most recent transition form-factor measurement in the e+e− channel, statistics have been improved by one order of magnitude. The e+e− invariant mass distribution shows a deviation from the QED prediction for a point-like particle, which can be described by a form-factor. Using the usual monopole transition form-factor parameterization, F(m2)=(1−m2/Λ2)−1, a value of Λ−2=(1.92±0.35(stat)±0.13(syst)) GeV−2 has been determined. This value is in good agreement with a recent measurement of the η Dalitz decay in the μ+μ− channel and with rece…
Beam-Helicity Asymmetries in Double-Pion Photoproduction off the Proton
Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels $\vec{\gamma}p\to \pi^{+}\pi^0n$, $\vec{\gamma}p\to \pi^{0}\pi^0p$ and $\vec{\gamma}p\to \pi^{+}\pi^{-}p$ . The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of $\pi^0$ mesons were detected in a $~4\pi$ electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction d…
Accurate Test of Chiral Dynamics in theγ→p→π0pReaction
A precision measurement of the differential cross sections dσ/dΩ and the linearly polarized photon asymmetry Σ≡(dσ⊥-dσ∥)/(dσ⊥+dσ∥) for the γp→π0p reaction in the near-threshold region has been performed with a tagged photon beam and almost 4π detector at the Mainz Microtron. The Glasgow-Mainz photon tagging facility along with the Crystal Ball/TAPS multiphoton detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the S- and all three P-wave amplitudes for the first time and provide the most stringent test to date of the predictions of chiral perturbation theory and its energy region of a…
Photoproduction of $ \pi^{0}$ -pairs off protons and off neutrons
Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of $\pi^0\pi^0$ pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557~MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400~MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cros…
Measurement of the beam-helicity asymmetry I⊙ in the photoproduction of π0-pairs off the proton and off the neutron
Abstract Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of neutral pion pairs in the reactions γ → p → p π 0 π 0 and γ → d → ( n ) p π 0 π 0 , γ → d → ( p ) n π 0 π 0 off free protons and off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced from bremsstrahlung of longitudinally polarized electrons and tagged with the Glasgow magnetic spectrometer. Decay photons from the π 0 mesons, recoil protons, and recoil neutrons were detected in the 4π covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. After kinematic reconstruction of…
Search forBs0→μ+μ−andB0→μ+μ−Decays with CDF II
A search has been performed for B{sub s}{sup 0} {yields} {mu}{sup +}{mu}{sup -} and B{sup 0} {yields} {mu}{sup +}{mu}{sup -} decays using 7 fb{sup -1} of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider. The observed number of B{sup 0} candidates is consistent with background-only expectations and yields an upper limit on the branching fraction of {Beta}(B{sup 0} {yields} {mu}{sup +}{mu}{sup -}) < 6.0 x 10{sup -9} at 95% confidence level. We observe an excess of B{sub s}{sup 0} candidates. The probability that the background processes alone could produce such an excess or larger is 0.27%. The probability that the combination of background and the expe…
Measurement of thett¯production cross section inpp¯collisions ats=1.96 TeVusing soft electronb-tagging
The authors present a measurement of the t{bar t} production cross section using events with one charged lepton and jets from p{bar p} collisions at a center-of-mass energy of 1.96 TeV. A b-tagging algorithm based on the probability of displaced tracks coming from the event interaction vertex is applied to identify b quarks from top decay. Using 318 pb{sup -1} of data collected with the CDF II detector, they measure the t{bar t} production cross section in events with at least one restrictive (tight) b-tagged jet and obtain 8.9{sub -1.0}{sup +1.0}(stat.){sub -1.0}{sup +1.1}(syst.) pb. The cross section value assumes a top quark mass of m{sub t} is presented in the paper. This result is cons…
Incoherent neutral pion photoproduction on 12C.
We present the first detailed measurement of incoherent photoproduction of neutral pions to a discrete state of a residual nucleus. The C-12(gamma,pi(0))C-12(4.4 MeV)* reaction has been studied with the Glasgow photon tagger at MAMI employing a new technique which uses the large solid angle Crystal Ball detector both as a pi(0) spectrometer and to detect decay photons from the excited residual nucleus. The technique has potential applications to a broad range of future nuclear measurements with the Crystal Ball and similar detector systems elsewhere. Such data are sensitive to the propagation of the Delta in the nuclear medium and will give the first information on matter transition form fa…
Experimental study of theγp→ηpreaction with the Crystal Ball detector at the Mainz Microtron (MAMI-C)
The gamma p - = W >= 1.87 GeV). Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz Microtron MAMI-C and momentum analyzed by the Glasgow tagging spectrometer were used for the eta-meson production. Our accumulation of 3.8 x 10(6) gamma p -< eta p -< 3 pi(0) p -< 6 gamma p events allows a detailed study of the reaction dynamics. The gamma p -< eta p differential cross sections were determined for 120 energy bins and the full range of the production angles. Our data show a dip near W = 1680 MeV in the total cross section caused by a substantial dip in eta production at forward angles. The data are compared to predictions of previous SAID and MAID partial-wave analyses a…
Photoproduction of theωmeson on the proton near threshold
An experimental study of omega photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The gamma p -> omega p differential cross sections are measured from threshold to the incident-photon energy E-gamma = 1.40 GeV (W = 1.87 GeV for the center-of-mass energy) with 15-MeV binning in E-gamma and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the omega N scattering length alpha(omega p) is provided.
Measurement of theH1(γ⃗, p⃗)π0Reaction Using a Novel Nucleon Spin Polarimeter
We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon. The measurement pioneers a novel polarimetry technique, which can be applied to many other nuclear and hadron physics experiments. The commissioning reaction of $^{1}H(\mathrm{\ensuremath{\gamma}P\vec},\text{ }\mathrm{pP\vec}){\ensuremath{\pi}}^{0}$ in the range $0.4l{E}_{\ensuremath{\gamma}}l1.4\text{ }\text{ }\mathrm{GeV}$ validates the technique and provides essential new data to constrain the excitation spectrum of the nucleon.
Photoproduction ofπ0Mesons off Neutrons in the Nucleon Resonance Region
Precise angular distributions have been measured for the first time for the photoproduction of π0 mesons off neutrons bound in the deuteron. The effects from nuclear Fermi motion have been eliminated by a complete kinematic reconstruction of the final state. The influence of final-state-interaction effects has been estimated by a comparison of the reaction cross section for quasifree protons bound in the deuteron to the results for free protons and then applied as a correction to the quasifree neutron data. The experiment was performed at the tagged photon facility of the Mainz Microtron MAMI with the Crystal Ball and TAPS detector setup for incident photon energies between 0.45 and 1.4 GeV…
First measurement of the circular beam asymmetry in the γ→p→π0ηp reaction
Abstract The circular photon asymmetry for π 0 η photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the Δ ( 1700 ) D 33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D 33 amplitude.
"dcs09" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.7891 GeV
"dcs02" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.7319 GeV
"dcs13" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.8192 GeV
"dcs04" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.7490 GeV
"dcs05" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.7568 GeV
"dcs19" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.8657 GeV
"dcs06" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.7645 GeV
"dcs11" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.8045 GeV
"dcs12" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.8119 GeV
"tcs" of "Photoproduction of the omega meson off the proton near threshold"
Total cross section as a function of c.m. energy W.
"dcs17" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.8504 GeV
"dcs01" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.7245 GeV
"dcs20" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.8720 GeV
"dcs18" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.8581 GeV
"dcs16" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.8424 GeV
"dcs07" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.7729 GeV
"dcs03" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.7401 GeV
"dcs14" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.8269 GeV
"dcs10" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.7968 GeV
"dcs08" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.7811 GeV
"dcs15" of "Photoproduction of the omega meson off the proton near threshold"
Differential cross section at W= 1.8348 GeV