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

The ALICE Collaboration reports the measurement of the relative J/ψ yield as a function of charged particle pseudorapidity density dN ch/dη in pp collisions at √s=7TeV at the LHC. J/ψ particles are detected for p t>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 (dN J/ψ/dy)/〈 dN J/ψ/dy〉 with (dN ch/dη)/〈 dN ch/dη〉 is observed in both rapidity ranges, where dN ch/dη is measured within |η|<1 and p t>0. In the highest multiplicity interval with 〈 dN ch/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.