Abstract
We report measurements of the inclusive J/ψ yield and average transverse momentum as a function of charged-particle pseudorapidity density dNch/dη in p–Pb collisions at sNN=5.02TeV with ALICE at the LHC. The observables are normalised to their corresponding averages in non-single diffractive events. An increase of the normalised J/ψ yield with normalised dNch/dη, measured at mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward rapidity, a saturation of the relative yield is observed for high charged-particle multiplicities. The normalised average transverse momentum at forward and backward rapidities increases with multiplicity at low multiplicities and saturates beyond moderate multiplicities. In addition, the forward-to-backward nuclear modification factor ratio is also reported, showing an increasing suppression of J/ψ production at forward rapidity with respect to backward rapidity for increasing charged-particle multiplicity.
Highlights
Quarkonium states, such as the J/ψ meson, are prominent probes of the deconfined state of matter, the Quark–Gluon Plasma (QGP), formed in high-energy heavy-ion collisions [1]
The relative yields at mid-rapidity and backward rapidity keep growing with the relative multiplicity in p–Pb collisions to the observation in pp collisions at 7 TeV [37]
We recall that the explored Bjorken x ranges in the forward rapidity region are in the domain of shadowing/saturation, and that a variety of models [12,13,49,20,21] are fairly successful in describing the recent centrality-integrated and differential measurements of ALICE [19,34], which correspond in terms of our relative multiplicities to dNch/dη/ dNch/dη 2.5 at most
Summary
Quarkonium states, such as the J/ψ meson, are prominent probes of the deconfined state of matter, the Quark–Gluon Plasma (QGP), formed in high-energy heavy-ion collisions [1]. A fair agreement is observed between data and models including nuclear shadowing [12] or saturation [20,21]; models including a contribution from coherent energy loss in CNM [13] describe the data These measurements are relevant with respect to J/ψ production in Pb–Pb collisions at the LHC [5, 7], currently understood to be strongly influenced by the presence of a deconfined medium. Recent measurements of the ψ (2S) state in p–Pb collisions have revealed a larger suppression than that measured for J/ψ production [24,25] Such an observation was not expected from the available predictions based on CNM effects. A measurement of the forward-to-backward J/ψ nuclear modification factor ratio is presented
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