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Inclusive spectra of protons emitted in the interaction of 12 C-projectiles at an energy of 3.6 GeV/nucleon and C, Cu, Sn and Pb target nuclei were measured. The analysis of the experimental data suggests that in all these interactions the main contribution to proton cross sections in the investigated kinematic region is due to emission from a moving source with a rapidity which differs greatly from the target nucleus rapidity, y t , as well as from that of the effective fireball. The properties of this source such as the excitation energy depend only slightly on the combination of the colliding nuclei.
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Charmonium production in p – A collisions is a unique tool for the study of the interaction of bound c c states in nuclear matter. It can provide details on the basic features of the resonance formation mechanism and, in particular, on its non-perturbative aspects. In this Letter, we present an experimental study of charmonia and Drell–Yan production in proton–nucleus collisions at 450 GeV/ c . The results are analyzed in the framework of the Glauber model and lead to the values of the nuclear absorption cross-section σ abs pA for J / ψ and ψ ′. Then, we compare the J / ψ absorption in proton–nucleus and sulphur–uranium interactions, using NA38 data. We obtain that, for the J / ψ , σ abs pA and σ abs SU are compatible, showing that no sizeable additional suppression mechanism is present in S–U collisions, and confirming that the anomalous J / ψ suppression only sets in for Pb–Pb interactions.
The J/PSI production cross section times the branching ratio to MU+ MU- pernucleon-nucleon collision for the differential nuclear targets.
The PSI(3685) production cross section times the branching ratio to MU+ MU-per nucleon-nucleon collision for the differential nuclear targets.
The Drell Yan cross section, divided by the mass number A, and multiplied by the isospin correction factors in the mass interval 2.9 to 4.5 GeV.
The production of ${\rm J}/\psi$ and
The J/PSI production cross sections, per target nucleon, times the di-muon branching ratio for the two data samples.
The PSI(3685) production cross sections, per target nucleon, times the di-muon branching ratio for the two data samples.
J/PSI production cross section times the di-muon branching ratio for the BEtarget as a function of the Feynman X bin.
The total cross section of hadron photoproduction on C, Cu and Pb nuclei is measured for six energy values in the range 12–30 GeV. The obtained cross-section values for C and Cu nuclei have a weak energy dependence at high energies (above 20 GeV). The cross section for the Pb nucleus is somewhat higher in comparison with that expected, and energy dependence is not observed. The A -dependence of the effective number of hadrons agrees with VDM predictions.
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A-EFFECTIVE/A = SIG(GAMMA A)/(Z*SIG(GAMMA P) + (A-Z)*SIG(GAMMA N)) WHERE SIG(GAMMA P) = (98.7 +- 3.6) + (65 +- 10)/SQRT(P) MUB, SIG(GAMMA N) = SIG(GAMMA P) - (18.3 +- 6.1)/SQRT(P) MUB AND A IS 12, 64 AND 207 FOR THESE NUCLEI.
The NA50 collaboration has measured J/ψ , ψ′ and Drell Yan pair production in Pb Pb interactions at 158 GeV/ c per nucleon at the CERN SPS. Final results from the 1995 run and preliminary ones from the higher statistics 1996 run are presented. A anomalous J/ψ suppression (relative to the Drell-Yan process) has been observed with respect to the suppression pattern established in experiments NA38 and NA51 with proton, oxygen and sulfur beams. The 1996 data allow a detailed study of the suppression pattern in the Pb Pb sample itself, showing a discontinuity around an E T value (the neutral transverse electromagnetic energy) of 50 GeV. The ψ′ is also suppressed relative to Drell-Yan, with a pattern very similar to the one observed in S U collisions. Finally, the p T distributions of dimuons are presented. The average p T 2 of the J/ψ in Pb Pb collisions does not increase any more with E T above 100 GeV.
ET - neutral transverse energy in the electromagnetic calorimeter, etarap=1.1-2.3.