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 dNch/dη in pp collisions at √s = 7 TeV 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.