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تسجيل مستخدم جديدDetermination of the total width of the eta meson
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Taking advantage of both the low-emittance proton-beam of the Cooler Synchrotron COSY and the high momentum precision of the COSY-11 detector system, the mass distribution of the eta meson was measured with a resolution of 0.33 MeV/c^2 (FWHM), improving the experimental mass resolution by almost an order of magnitude with respect to previous results. Based on the sample of more than 2300 reconstructed pp --> pp eta events the total width of the eta meson was determined to be 0.226 +- 0.017(stat.) +- 0.014(syst.) MeV/c^2.
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Using 13.4 $fb^{-1}$ of data collected with the CLEO detector at the Cornell Electron Storage Ring, we have observed 300 events for the two-photon production of ground-state pseudo-scalar charmonium in the decay $eta_c$ -> $K_S K^{mp} pi^{pm}$. We ha
ve measured the $eta_c$ mass to be (2980.4 +- 2.3 (stat) +- 0.6 (sys)) MeV and its full width as (27.0 +- 5.8 (stat) +- 1.4 (sys)) MeV. We have determined the two-photon partial width of the $eta_c$ meson to be (7.6 +- 0.8 (stat) +- 0.4 (sys) +- 2.3 (br)) keV, with the last uncertainty associated with the decay branching fraction.
The excitation function and momentum distribution of $eta^prime$ mesons have been measured in photon induced reactions on $^{12}{}$C in the energy range of 1250-2600 MeV. The experiment was performed with tagged photon beams from the ELSA electron ac
celerator using the Crystal Barrel and TAPS detectors. The data are compared to model calculations to extract information on the sign and magnitude of the real part of the $eta^prime$-nucleus potential. Within the model, the comparison indicates an attractive potential of -($37 pm 10(stat)pm10(syst)$) MeV depth at normal nuclear matter density. Since the modulus of this depth is larger than the modulus of the imaginary part of the $eta^prime$-nucleus potential of -($10pm2.5$) MeV, determined by transparency ratio measurements, a search for resolved $eta^prime$-bound states appears promising.
The excitation function and momentum distribution of {eta} mesons have been measured in photoproduction off 93^Nb in the energy range of 1.2-2.9 GeV. The experiment has been performed with the combined Crystal Barrel and MiniTAPS detector system, usi
ng tagged photon beams from the ELSA electron accelerator. Information on the sign and magnitude of the real part of the {eta}-Nb potential has been extracted from a comparison of the data with model calculations. An attractive potential of -(41 pm 10(stat) pm 15(syst)) MeV depth at normal nuclear matter density is deduced within model uncertainties. This value is consistent with the potential depth of -(37 pm 10(stat) pm 10(syst)) MeV obtained in an earlier measurement for a light nucleus (carbon). This relatively shallow {eta}-nucleus potential will make the search for {eta}-nucleus bound states more difficult.
Using the Crystal Barrel(CB)/TAPS detector system at the ELSA accelerator facility in Bonn the eta photoproduction off nuclei (C, Ca, Nb and Pb) was studied via the hadronic decay channel eta -> pi^0pi^0eta . Recent results on the in-medium propertie
s of the eta-meson, derived from the transparency ratio measurements, are presented. The absorption of the eta-meson in nuclear matter is compared to the properties of other mesons (eta, omega).
The photoproduction of eta-mesons off different nuclei has been measured with the CBELSA/TAPS detector system for incident photon energies between 1500 - 2200 MeV. The transparency ratio has been deduced and compared to theoretical calculations descr
ibing the propagation of eta-mesons in nuclei. The comparison indicates a width of the eta -meson of the order of Gamma= 15-25 MeV at rho =rho_0 for an average momentum p_{eta} = 1050 MeV/c, at which the eta-meson is produced in the nuclear rest frame. The inelastic eta N cross section is estimated to be 3 - 10 mb. Parameterizing the photoproduction cross section of eta-mesons by sigma(A) = sigma_0 A^{alpha}, a value of alpha = 0.84pm0.03 has been deduced.
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