Charmonium production in Pb [sbnd]Pb interactions at 158 GeV/ c per nucleon

L Ramello ,P Rato-Mendes,P Bordalo,I Chevrot,M Bedjidian,A Piccotti,P Macciotta,N Willis,M Mac Cormick,T Chambon,A Baldit,C Vale,D Jouan,T.L Karavitcheva,A Musso,E Chiavassa,C Gerschel,M Atavan,A.A Grigorian,J Fargeix,M Gallio,L Kluberg,S Mehrabyan,C Baglin,F Bellaiche,O Drapier,M.C Abreu,R Hakobyan,V Boldea,P Petiau,M Gonin,S Serci,C Quintans,J Castor,P Saturnini,A Guichard,A Romana,M Masera,P Force,Y Le Bornec,P Sonderegger,S Ramos,R Haroutunian,X Tarrago,B Chaurand,A De Falco,N De Marco,F.F Guber,L Riccati,Y.K Gavrilov,J Astruc,G Puddu,S Mourgues,G Dellacasa,A Devaux,F Ohlsson-Malek,C Racca,V Capony,C Lourenço ,W.l Prado Da Silva ,M Idzik ,N Topilskaya ,C Soave ,A Kurepin ,F Fleuret ,S Constantinescu ,J.r Pizzi ,H Gulkanyan ,S Filippov ,A Bussière ,Luca Casagrande ,C Alexa ,S Beolè ,E Scomparin ,E Vercellin ,M Golubeva ,B Cheynis ,R Shahoyan ,M P Comets ,S Diţă ,S Silva ,A Masoni ,J.‐Y Grossiord ,P Giubellino ,R Arnaldi ,Sabrina Sartori ,A Marzari‐Chiesa ,P Temnikov ,J Cruz ,C Cicalò ,G L Usai ,B Alessandro ,B Espagnon

doi:10.1016/s0375-9474(98)00360-1

Abstract

Abstract 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.

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