Total and differential cross sections for photoproduction of η mesons from 12 C, 40 Ca, 93 Nb, and nat Pb have been obtained up to 790 MeV incident photon energy at the Mainz Microtron (MAMI) with the TAPS spectrometer. The absorption cross section σ ηN abs = (30 ± 2.5 ± 6)mb of η mesons in nuclear matter and the absorption length λ η = (2.0 ± 0.2 ± 0.4) fm are extracted. No significant depletion of the S 11 (1535) strength in the η photoproduction on nuclei is observed.
THE TOTAL SIG WAS PARAMETRIZED BY A**POWER.
The production of η′ (958) and φ (1020) mesons has been studied very close to threshold in the inclusive p d → 3 He X reaction. The complicated phase space acceptance problem caused by rapidly changing kinematics close to threshold has been carefully treated. The measured averaged squared amplitudes | f | 2 at threshold are 0.9 and 2.4 nb/sr for the η′ and φ meso Our results are in remarkable agreement with predictions of a two-step model, which uses existing π − p → n X data as input. However the ratio of φ to ω production seems at variance with naïve expectations based on the Okubo-Zweig-Iizuka rule.
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In explosive stellar hydrogen burning, the hot CNO cycles and the rp-process are mainly linked by the reaction sequence 15 O(α, γ) 19 Ne(p,γ) 20 Na. Using intense 19 Ne radioactive beams, both the 19 Ne(p,γ) and the 19 Ne(d,n) reaction have been studied. Upper and lower limits for the 19 Ne(p,γ) reaction rate have been deduced, allowing to conclude that the 15 O(α,γ) reaction is most likely the bottleneck reaction.
Two target were used: polyethylene foil (C=CH2) and static gas cell (C=H2).Two different detection set-ups have been designed: the Solid State Nuclear Tra ck Detector (C=SSNTD) method and the Solenoid and Telescope (C=STAR) method.
Proton-proton elastic scattering has been measured over the angular range 7 to 16 mrad at centre-of-mass energies of 31, 45 and 53 GeV using the CERN Intersecting Storage Rings. The results indicate that the diffraction peak has continued to shrink with increasing energy, but not as fast as suggested by the results at lower energies.
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The annihilation p p → Φγ has been investigated with the Crystal Barrel detector at LEAR for antiprotons stopped in liquid hydrogen. The observed branching ratio BR ( p p → Φγ = (1.7 ± 0.4) · 10 −5 is almost two orders of magnitude higher than expected from the OZI-rule. As a by-product, the branching ratios BR ( p p → K L K S ) = (9.0 ± 0.6) · 10 −4 and BR ( p p → Φπ 0 ) = (5.5 ± 0.7) · 10 −4 have been measured.
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The study of the K + total cross sections on a wide range of nuclei has revealed important modifications of the free-space K + -nucleon interaction when the nucleon is embedded in a nucleus. Data indicating such an effect were first obtained in a comparison of the total cross sections on carbon and deuterium. In this letter we report new measurements on 6 Li, silicon, and calcium, and demonstrate that the previously reported modifications occur quite generally.
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Total neutron cross-sections were determined for He, Li, Be, C, Al, Fe, Cu and Pb at an average neutron momentum of 10 GeV/ c . The results agree very well with total proton-neuclei cross-sections at 20 GeV/ c . The interaction radii inferred from the cross-sections are in remarkable agreement with the half-density radii as obtained from electron scattering.
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Using data from the NA32 experiment at CERN we have studied the Λ + c decays containing a Σ + among the decay products. The interactions of 230 GeV π − with a Cu target were analysed using a precise vertex telescope (charge-coupled devices and silicon microstrip detectors) and the ACCMOR spectrometer. We have found eleven Λ + c →Σ + π + π − , one Λ + c →Σ + K + K − , two Λ + c →Σ + K + π − and one Λ + c →Σ + π + π − π + π − decays practically without any backgroun d. We have measured the branching ratios with respect to the Λ + c →pK − π + channel.
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We present a study of the inclusive η production based on 300 000 hadronic Z 0 decays. The measured inclusive momentum distribution can be reproduced by parton shower Monte Carlo programs and also by an analytical QCD calculation. Comparing our results with low energy e + e − data, we find that QCD describes both the shape and the energy evolution of the η spectrum. The comparison of η production rates in quark- and gluon-enriched jet samples does not show statistically significant evidence for more abundant production of η mesons in gluon fragmentation.
Differential cross section for inclusive eta production, normalized to the total hadronic cross section.
Differential cross section for inclusive eta production, normalized to the total hadronic cross section.
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