J/psi Production as a Function of Charged Particle Multiplicity in pp Collisions at sqrt{s} = 7 TeV

TL;DR

This study measures how J/psi particle production varies with charged particle multiplicity in proton-proton collisions at 7 TeV, revealing a roughly linear increase and significant enhancement at high multiplicities.

Contribution

It provides the first detailed measurement of J/psi yields as a function of event multiplicity in pp collisions at the LHC, highlighting the multiplicity dependence of quarkonium production.

Findings

J/psi yields increase linearly with charged particle multiplicity.

At high multiplicity, J/psi production is enhanced by a factor of up to 8.

The results suggest a strong correlation between soft particle production and quarkonium yields.

Abstract

The ALICE collaboration reports the measurement of the inclusive J/psi yield as a function of charged particle pseudorapidity density dN_{ch}/deta in pp collisions at sqrt{s} = 7 TeV at the LHC. J/psi 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 mu+mu- pairs. An approximately linear increase of the J/psi yields normalized to their event average (dN_{J/psi}/dy)/<dN_{J/psi}/dy> with (dN_{ch}/deta)/<dN_{ch}/deta> is observed in both rapidity ranges, where dN_{ch}/deta is measured within |eta| < 1 and p_t > 0. In the highest multiplicity interval with <dN_{ch}/deta(bin)> = 24.1, corresponding to four times the minimum bias multiplicity density, an enhancement relative to the minimum bias J/psi yield by a factor of about 5 at 2.5 < y < 4 (8 at |y| < 0.9) is observed.