Measurement of the slope parameterαfor theη→3π0decay with the Crystal Ball detector at the Mainz Microtron (MAMI-C) (original) (raw)
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Physical Review C, 2010
The γp → ηp reaction has been measured with the Crystal Ball and TAPS multiphoton spectrometers in the energy range from the production threshold of 707 MeV to 1.4 GeV (1.49 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 η-meson production. Our accumulation of 3.8 × 10 6 γp → ηp → 3π 0 p → 6γp events allows a detailed study of the reaction dynamics. The γp → ηp 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 η production at forward angles.
Study of the p ! p reaction with the Crystal Ball detector at the Mainz Microtron (MAMI-C)
The dynamics of the → 30 decay have been studied with the Crystal Ball multiphoton spectrometer and the TAPS calorimeter. Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz microtron MAMI-C and tagged by the Glasgow photon spectrometer were used for -meson production. The analysis of 3 × 106 p → p → 30p → 6 p events yields the value = −0.032 ± 0.003 for the → 30 slope parameter, which agrees with the majority of recent experimental results and has the smallest uncertainty. The 00 invariant-mass spectrum was investigated for the occurrence of a cusplike structure in the vicinity of the +− threshold. The observed effect is small and does not affect our measured value for the slope parameter.
Mechanism of Near-Threshold Production of the η Meson
Physical Review Letters, 2007
Measurements of the analysing power for the pp → ppη reaction have been performed in the close-to-threshold energy region at beam momenta of p beam = 2.010 and 2.085 GeV/c, corresponding to excess energies of Q = 10 and 36 MeV, respectively. The determined analysing power is essentially consistent with zero implying that the η meson is produced predominantly in the swave at both excess energies. The angular dependence of the analysing power, combined with the hitherto determined isospin dependence of the total cross section for the η meson production in nucleon-nucleon collisions, reveal a statistically significant indication that the excitation of the nucleon to the S11(1535) resonance, the process which intermediates the production of the η meson, is predominantly due to the exchange of the π meson between the colliding nucleons.
New determination of the mass of the η meson at COSY-ANKE
Physical Review D, 2012
A value for the mass of the η meson has been determined at the COSY-ANKE facility through the measurement of a set of deuteron laboratory beam momenta and associated 3 He center-of-mass momenta in the dp → 3 He X reaction. The η was then identified by the missing-mass peak and the production threshold determined. The individual beam momenta were fixed with a relative precision of 3 × 10 −5 for values around 3 GeV/c by using a polarized deuteron beam and inducing an artificial depolarizing spin resonance, which occurs at a well-defined frequency. The final-state momenta in the two-body dp → 3 He η reaction were investigated in detail by studying the size of the 3 He momentum ellipse with the forward detection system of the ANKE spectrometer. Final alignment of the spectrometer for this high precision experiment was achieved through a comprehensive study of the 3 He final-state momenta as a function of the center-of-mass angles, taking advantage of the full geometrical acceptance. The value obtained for the mass, mη = (547.873 ± 0.005stat ± 0.027syst) MeV/c 2 , is consistent and competitive with other recent measurements, in which the meson was detected through its decay products.
A precision determination of the mass of the η meson
Physics Letters B, 2005
Several processes of meson production in proton-deuteron collisions have been measured simultaneously using a calibrated magnetic spectrograph. Among these processes, the η meson is seen clearly as a sharp missing-mass peak on a slowly varying background in the p + d → 3 He + X reaction. Knowing the kinematics of the other reactions with well determined masses, it is possible to deduce a precise mass for the η meson. The final result, m(η) = 547.311 ± 0.028(stat) ± 0.032(syst) MeV/c 2 ,
Physical Review C, 2014
The Dalitz decay η → e + e − γ has been measured in the γp → ηp 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 η → e + e − γ. The value obtained for the slope parameter Λ −2 of the η transition form factor, Λ −2 = (1.95 ± 0.15stat ± 0.10syst) GeV −2 , is in good agreement with recent measurements conducted in η → e + e − γ and η → µ + µ − γ decays, as well as with recent form-factor calculations. The uncertainty obtained in the value of Λ −2 is lower compared to results from previous measurements of the η → e + e − γ decay.