J/ψ production as a function of charged particle multiplicity in pp collisions at s=7TeV

Abstract

The ALICE Collaboration reports the measurement of the relative J/ψ yield as a function of charged particle pseudorapidity density dNch/dη in pp collisions at s=7TeV at the LHC. J/ψ particles are detected for pt>0, in the rapidity interval |y|<0.9 via decay into e+e-, and in the interval 2.5<y<4.0 via decay into μ+μ- pairs. An approximately linear increase of the J/ψ yields normalized to their event average (dNJ/ψ/dy)/〈 dNJ/ψ/dy〉 with (dNch/dη)/〈 dNch/dη〉 is observed in both rapidity ranges, where dNch/dη is measured within |η|<1 and pt>0. In the highest multiplicity interval with 〈 dNch/dη(bin)〉 =24.1, corresponding to four times the minimum bias multiplicity density, an enhancement relative to the minimum bias J/ψ yield by a factor of about 5 at 2.5<y<4 (8 at |y|<0.9) is observed. © 2012 CERN.