A precision determination of the mass of the η meson

2016

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 → 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, Preprint submitted to Elsevier Science 19 November 2013 is significantly lower than that found by the recent NA48 measurement, though it is consistent with values obtained in earlier counter experiments.

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.

MESON 2002 - Proceedings of the 7th International Workshop on Production, Properties and Interaction of Mesons, 2003

By means of the COSY-11 detection system, using a stochastically cooled proton beam of the Cooler Synchrotron COSY and a hydrogen cluster target, we have performed a high statistics measurement of the pp → ppη reaction at an excess energy of Q = 15.5 MeV. The experiment was based on the four-momentum determination of both outgoing protons. This permits to identify pp → ppη events and to derive the complete kinematical information of the ηpp-system allowing for subsequent investigations of the ηp interaction. The observed spectrum of the invariant mass of the protonproton system deviates strongly from the phase-space distribution revealing the influence of the final-state-interaction among the outgoing particles or nontrivial features of the primary production mechanism.

International Journal of Modern Physics A, 2007

Information about the production mechanism of the η meson in proton-proton collisions can be inferred by confronting the experimental studies on the analysing power for the pp → ppη reaction with the theoretical predictions of this observable. The determined analysing powers for Q=10 MeV and Q=36 MeV are consistent with zero. Results show that the predictions of pure pseudoscalar meson exchange model fairly describe the experimental data, while the predictions of pure vector meson exchange dominance model disagree with the data at the level of 4.3 σ.

Physics Letters B, 1982

A high precision measurement of the T-meson mass has been performed at the storage ring VEPP-4 using the MD-1 detector. The resonance depolarization method has been used for the absolute calibration of the beam energy that allowed to improve the accuracy of T-mass measurement by a factor of ten. The following mass value has been obtained: M = 9459.7-+ 0.6 MeV.

Physical Review C, 1999

The pp → ppη ′ reaction is investigated within a relativistic meson-exchange model of hadronic interactions. We explore the role of nucleonic and mesonic, as well as the N * resonance currents, in producing η ′ mesons. In order to learn more about the production mechanisms, new measurements in the energy region far from the threshold are required. PACS: 13.60Le, 25.10+s,

Physical Review Letters, 2008

We measure the mass of the η ′ meson using ψ(2S)→π + π − J/ψ, J/ψ → γη ′ events acquired with the CLEO-c detector operating at the CESR e + e − collider. Using three decay modes, η ′ →ρ 0 γ, η ′ →π + π − η with η→γγ, and η ′ →π + π − η with η→π + π − π 0 , we find M η ′ =957.793±0.054±0.036 MeV, in which the uncertainties are statistical and systematic, respectively. This result is consistent with but substantially more precise than the current world average.

Physics Letters B, 2000

The production of η mesons has been measured in the proton-proton interaction close to the reaction threshold using the COSY-11 internal facility at the cooler synchrotron COSY. Total cross sections were determined for eight different excess energies (ǫ) in the range from ǫ = 0.5 MeV to ǫ = 5.4 MeV.

Physics Letters B, 2012

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Physical Review D, 2011

The decay width and mass of the Ds1(2536) + meson are measured via the decay channel D + s1 → D * + K 0 S using 385 fb −1 of data recorded with the BABAR detector in the vicinity of the Υ(4S) resonance at the PEP-II asymmetric-energy electron-positron collider. The result for the decay width is Γ(D + s1 ) = 0.92 ± 0.03 (stat.) ± 0.04 (syst.) MeV. For the mass, a value of m(D + s1 ) = 2535.08 ± 0.01 (stat.) ± 0.15 (syst.) MeV/c 2 is obtained. The mass difference between the D + s1 and the D * + is measured to be m(D + s1 ) − m(D * + ) = 524.83 ± 0.01 (stat.) ± 0.04 (syst.) MeV/c 2 , representing a significant improvement compared to the current world average. The unnatural spin-parity assignment for the D + s1 meson is confirmed.