J/ψ Production in pPb Collisions at the LHC

Zhang, Hong-FeiThird Military Medical University

Contents

• Quark-gluon Plasma (QGP) and J/ψ Production Suppression

• Cold Nuclear Matter (CNM) Effects• Introduction to Non-relativistic QCD (NRQCD)• J/ψ Production in pPb Collisions at the LHC• Summary and Outlook

Quark-gluon Plasma (QGP) and J/ψ Production Suppression

Nuclear at High Density

• At low density, the nucleons in a nuclear are distinguished.• With increasing density, the nucleons start to overlap.• Free quarks exist in this kind of matter.• It is a new state of matter, which is called Quark-gluon Plasma

(QGP).

Phase Diagram of QCD Matter

Quarkonium in QGP

• Quarks in QGP are deconfined.• Strong interactions are suppressed.• Quarkonium suppression is a signature of QGP

matter .

Cold Nuclear Matter (CNM) Effects

Quarkonium Suppression via CNM Effects

• Not all the quarkonium suppression is due to QGP formation.

• J/ψ production in proton-nuclear (pA) collisions in forward rapidity region, where no QGP is expected, is also suppressed with respect to scaled proton-proton (pp) collisions.

• One should first distinguish CNM effects to confirm the hot nuclear matter (HNM) effects.

• High-precision prediction of CNM effects is necessary.

Possible CNM effects

• Parton distribution function (PDF) shadowing and anti-shadowing

• Cronin effect• Initial state energy loss• Heavy quark energy loss• Absorption effects in pA collisions

PDF Shadowing (EPS09)

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Cronin Effect

• The partons are not restricted to collinear direction

• Initial-state scattering provide the partons with transverse momentum

• A simple normalized Gaussian form of distribution of kT is assumed

High pt Heavy Quarkonium Production

• For high pt heavy quarkonium production, Cronin effect can be neglected.

• We don’t consider energy loss and absorption, and provide a baseline for CNM effects study.

• In high pt region, perturbative calculation works.

Introduction to Non-relativistic QCD (NRQCD)

Difficulties in the calculations of heavy quarkonium related processes

• Color-singlet (CS) model was the first generally used calculation scheme after the discovery of heavy quarkonia.

• For J/ψ and ψ(2S) production at hadron colliders, theoretical predictions via CS model was 1~2 orders smaller than experimental data at the Tevatron.

• For some P-wave quarkonia decays, even at leading order, divergences do not cancel.

J/ψ and ψ(2S) production at the TevatronPrompt production of J/ψ and ψ(2S) at the Tevatron, with √s=1.8TeV, and |η|<0.6. The solid line correspond to theoretical prediction based on CS model.PRL 79, 572 (1997)

Nonrelativistic Quantum Chromodynamics (NRQCD)

• NRQCD was proposed in 1994 and solved the two puzzles.

• In NRQCD framework, the cross section can be factorized into the summation of products of a short-distance coefficient and a long-distance matrix element (LDME),

• These terms are expanded in v (the relative velocity of the quark and anti-quark in the quarkonium). CS model only counts one of the leading-order terms in v.

n

HnnH Odfd

Predictions of J/ψ production at hadron colliders via NRQCD

J/ψ production at the Tevatron.

NRQCD prediction can explain the experiment.

Success of NRQCD

J/ψ (ψ(2S)) Production at the Tevatron

J/ψ (ψ(2S)) Production at the LHC

Summary

• NRQCD is one of the most successful models for heavy quarkonium productions and decays.

• It reconciles experimental data from different experiment collaborations.

• The number of free parameters is few.• It can provide precise knowledge of heavy

quarkonium production.

J/ψ Production in pPb Collisions at the LHC

In Collaboration with Professor Zhang, Ben-Wei

Why Next-to-leading Order (NLO)?

• Three parts contribute to prompt J/ψ production: direct part, contributions from χc and ψ(2S) feeddown.

• Leading order (LO) calculation can reproduce direct part and ψ(2S) feeddown part in high precision, however, fails in χc feeddown predictions.

χc1 Production at LO and NLO (ATLAS)

χc2 Production at LO and NLO (ATLAS)

χc Production at LO and NLO (LHCb)

Selection of Experimental Data

• In low pt region, resummation is required, and relativistic correction is non-linear. We adopt pt>7GeV data.

• For large rapidity region, a new scale emerges: E(J/ψ)/pt=0.5*exp(y). We adopt 1.5<y<3.0 data.

pt Distribution

We present dσ/dpt predcitions comparing to experimental data from

LHCb.

rpA as a Function of pt

tpp

tpAtpA dpAd

dpdpR

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Summary

• NLO NRQCD predictions can almost explain LHCb data for 1.5<y<2.0, 2.0<y<2.5, 2.5<y<3.0 and 1.5<y<4.0 at large pt.

• For large rapidity region, fixed order calculation is not good, further investigation is required to make definite conclusions.

• For large rapidity region, final state energy loss might play a role in the discrepency between theory and experiment.

Summary and Outlook

Summary

• At high temperature and density, QGP is expected to form.

• Quarkonium suppression is a signature of QGP formation.

• Not all the suppression is due to HNM effects.• High-precision prediction of heavy

quarkonium production in pA collisions is necessary.

Summary

• We calculate J/ψ production rate in pPb collisions at the LHC at NLO level within NRQCD framework.

• NLO NRQCD predictions can almost explain LHCb data at small rapidity and large transverse momentum.

• Suppression ratios are also studied.

Outlook

• Resummation is required for large rapidity region.

• More experimental data for high transverse momentum are expected.

• Small-x evolution provides an opportunity to the study of small pt region phenomenology.

• A small room is left for CNM effects other than PDF shadowing.