20.04.23

J/ψ Measurements with the ALICE Experiment at the LHC

Julian Book

28th Winter Workshop on Nuclear Dynamics

220.04.23

Outline

➤ Physics Motivation

➤ The ALICE Experiment

➤ Prompt and Non-Prompt J/ψ Measurements in pp Collisions

➤ Nuclear Modification in Heavy-Ion Collisions

➤ Summary

➤ Outlook

320.04.23

Motivation: J/ψ in Heavy-Ion Collisions

➤ Quark-Gluon Plasma (QGP): Deconfined state of strongly interacting matter➤ J/ψ suppression proposed as a signature [T.Matsui, H.Satz, Phys.Lett. B178(4),416-422 (1986)]

➤ QGP induced effects in AA➤ Melting due to Debye-screening➤ (Re)combination of uncorrelated ccbar➤ Thermal production (only at LHC)

➤ Suppression at SPS and RHIC (80,40%)

➤ Larger suppression at large rapidity

NA60, Nucl.Phys. A 830:345c-352c (2009)PHENIX, arXiv:1103.6269 (2011)

420.04.23

Motivation: J/ψ in pp Collisions

➤ Provide information on production models (CSM, NRQCD, CEM)➤ Elementary production not yet well understood➤ Crucial reference for nuclear modification in Pb-Pb

➤ Multi-Parton Interations on soft, soft-hard, hard scale?➤ Study pp collisions in different event classes, e.g. impact parameter multiplicity

520.04.23

Inclusive and Prompt J/ψ Measurements in ALICE

Down to pT = 0midrapidity |y|<0.9: ITS + TPC

forward rapidity 2.5 < y < 4.0: ITS + MUON

620.04.23

Proton-Proton Collisions

at

√s = 2.76 and 7 TeV

Energy LHC periodInt. Luminosity

J/ψ e+e- J/ψ μ+μ-

2.76 TeV

2011 1.1 nb-1 19.9 nb-1

7 TeV 2010 5.6 nb-1 15.6 nb-1

720.04.23

Invariant Mass Distributions

Midrapidity |y|<0.9 Forward rapidity 2.5<y<4.0

ALICE Coll., Phys.Lett. B704(2011)442

820.04.23

Inclusive Cross Sections: pT and y Dependence

ALICE Coll., Phys.Lett. B704(2011)442, arXiv:1203.3641

920.04.23

Model Comparison: pT and y Dependence

ALICE Coll., Phys.Lett. B704(2011)442, arXiv:1203.3641

1020.04.23

Contribution from B-hadrons

1.3 < pT < 7 GeV/c ; |y|<0.9

  ATLAS: Nucl.Phys. B850 (2011) 387,LHCb: Eur.Phys.J. C71 (2011) 1645, CMS: Phys.J. C71, (2011) 1575

➤ fraction from B-hadron decays:0.137 +- 0.054(stat) + 0.025 -0.018 (syst)  +0.022 -0.027 (syst polar.)

➤ Strongly pT dependent, rises up to 70% at 40 GeV/c

1120.04.23

Inclusive Cross Sections: Energy Dependence at midrapidity

➤ Strong energy dependence at midrapidity➤ Almost 2x(10x) larger cross sections than at Tevatron (RHIC)

compared to 7 TeV results

ALICE Coll., arXiv:1203.3641 (2012)

1220.04.23

First J/ψ Polarization Measurement at LHC

ALICE Coll., Phys.Rev.Lett. 108, 082001 (2012)M.Butenschoen, B.A. Kniehl arXiv:1201.3862 (2012)

€

W θ ,φ( ) ∝1

3+ λθ1+ λθ cos

2θ + λφ sin2θ cos2φ + λθφ sin2θ cosφ( )

1320.04.23

Charged Particle Multiplicity at Midrapidity

➤ Relative charged particle multiplicity

➤ Up to 5 times the mean multiplicity

➤ Similar significance of J/ψ signal in all intervals

€

dNch /dη = 6.01± 0.01(stat.)−0.12+0.2 (syst.)

ALICE Coll., Eur.Phys.J. C 68: 345–354 (2010)ALICE Coll., arXiv:1202.2816 (2012)(submitted to P.L. B)

1420.04.23

Invariant Mass Distributions

Midrapidity |y|<0.9 Forward rapidity 2.5<y<4.0

low

highmultiplicity

ALICE Coll., arXiv:1202.2816 (2012)(submitted to P.L. B)

1520.04.23

J/ψ Yield as a Function of Charged Particle Multiplicity

➤ Approximately linear increase with midrapidity dNch/dη➤ Similar behaviour in different rapidity regions➤ Enhancement relative to min. bias. yield up to 5(8) at forward (mid-) rapidity➤ PYTHIA shows an opposite trend

ALICE Coll., arXiv:1202.2816 (2012)(submitted to P.L. B)

1620.04.23

Pb-Pb Collisions

at

√sNN = 2.76 TeV

Energy LHC periodInt. Luminosity

J/ψ μ+μ-

2.76 TeV

2010 2.88 μb-1

1720.04.23

Signal in Pb-Pb Collisions at √sNN = 2.76 TeV

Forward rapidity 2.5<y<4.0

Double exponential (Background) + Crystal Ball function (Signals)

1820.04.23

RAA = 0.545 ± 0.032(stat.) ± 0.084(syst.)

➤Less supression at forward rapidity compared to lower √sNN

➤No significant centrality dependence

Nuclear Modification Factor

Centrality dependence

€

RAAi =

YJ /ψi

TAAi ×σ J /ψ

pp

ALICE Coll., arXiv:1202.1383 (2012)(submitted to P.R.L.)

1920.04.23

RAA = 0.545 ± 0.032(stat.) ± 0.084(syst.)

➤Less supression at forward rapidity compared to lower √sNN

➤No significant centrality dependence

➤Stat. Hadronization and transport models can describe the trend in data

Nuclear Modification Factor

Centrality dependence

€

RAAi =

YJ /ψi

TAAi ×σ J /ψ

pp

2020.04.23

➤ Current parametrizations for shadowing affect the RAA by max. 30%

➤ Need for pA measurements

➤ No explicit rapidity dependence

Nuclear Modification Factor

Rapidity dependence

€

RAAi =

YJ /ψi

TAAi ×σ J /ψ

pp

ALICE Coll., arXiv:1202.1383 (2012)(submitted to P.R.L.)

2120.04.23

Summary

➤ Inclusive J/ψ measurements in pp collisions at √s = 2.76 and 7 TeV

results covering a large rapidity area and pT = 0

➤ Polarization in pp collisions at √s = 7 TeV at LHC

in the forward region consistent with no polarization

➤ Fraction of non-prompt J/ψ production at √s = 7 TeV

~14% of J/ψ yield originates from B-hadron decays, strongly pT dependent

➤ Multiplicity dependence of relative J/ψ yields in pp collisions

linear increase of J/ψ yield with midrapidity dNch/dη

➤ Inclusive nuclear modification factor in Pb-Pb collisions at √s = 2.76 TeV

no significant centrality and rapidity dependence

less supression than at RHIC

less supression at low pT

2220.04.23

Outlook

➤ Pb-Pb collisions

➤ RAA in central rapidity

➤ Elliptic flow v2

➤ pA analysis (data end of 2012)

➤ pp collisions

➤ TRD trigger on electrons

Midrapidity |y|<0.9

2320.04.23

BACKUP

2420.04.23

Model Comparison

Direct J/ψ from Hard Processes in PYTHIA

String Interaction Model