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Quarkonia in deconfined matterAcitrezza, September 28th-30th 2011

Roberta ArnaldiINFN, Torino

for the ALICE Collaboration

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• J/ψ production in ultra-peripheral collisions• J/ψ flow

Physics motivations

J/ψ measurement in PbPb collisions @ 2.76 TeV with ALICE

RAA and RCP results

Comparison with results from other experiments

Comparison with models

Prospects:

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Physics motivations Quarkonium suppression is considered since a long time as one ofthe most striking signatures for QGP formation in AA collisions

…but many effects complicate the picture:•cold nuclear matter (cc break-up,shadowing)•cc recombination

Sequential suppression of quarkonium states

thermometer for the temperature reached in heavy ion collisions

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Towards LHC results…

• RHIC: stronger suppression at forward

rapidities• SPS vs. RHIC:not clear trend of the suppression

pattern versus energy

LHC results can shed some light, investigating the role of

• the large charm quark multiplicity

• other quarkonia states (bottomonium)(almost unexplored in HI collisions: STAR ~200ϒ(1S+2S+3S) in AuAu@200GeV)

After SPS and RHIC J/ψ results many questions are still open…

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First LHC PbPb run The first LHC heavy ion run took place in November 2010

Peak luminosity increasing from 3x1023 to 3x1025 Hz/cm2

Similar integrated luminosity for ALICE, ATLAS, CMS ~9 μb-1

PbPb collisions at √s=2.76 TeV

Quarkonium measurement in ALICE

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µ+

µ-

Quarkonium in ALICE can be measured in two ways:

e e

Central Barrel J/ψ e+e-

(|y|<0.9)

Electrons tracked using ITS and TPCParticle identification: TPC (+TOF)

Forward muon arm J/ψμ+μ-

(2.5<y<4)

Muons identified and tracked in the muon spectrometer

Acceptance coverage in both y regions down to zero pT

ALICE results refer to inclusive J/ψ production

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Pb-Pb collisions at √s=2.76TeV

Trigger:Minimum bias trigger (V0A and V0C and SPD)~17 106 MB events collected

Event selection:Rejection of beam gas events (V0 timing)

Negligible EM background in the centrality range (0-80%)

Integrated luminosity ~ 2.7 μb-1

Centrality:Estimate based on a Glauber model fit of the V0 amplitude

Statistics imposes rather wide centrality bins for J/ψ analysis:

J/ψ μ+μ-:0-10,10-20,20-40,40-80%J/ψ e+e-: 0-40, 40-80%

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J/ψ e+e- at mid-rapidity

Visible J/ψ signal, in spite of the low S/B (~0.04-0.3)

Electrons tracking: ITS and TPC

Particle identification: TPC (on-going PID with TRD and TOF)

Cuts:|ηe+e-|<0.8

0-40% 40-80%

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J/ψ μ+μ- at forward rapidity

• to improve the purity of the muon sample, both muons reconstructed in the tracking and trigger chambers should satisfy the trigger algorithm

reduction of hadronic background and fake tracks

• cut on the track position at the end of the front absorber

• 2.5 < yJ/ψ < 4, 2.5<ημ<4, pT J/ψ>0 GeV/c

Event/Track selection:

No identification of J/ψ from B decays scattering in the absorber spoils the muon vertex information

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Signal extraction

• Crystal Ball shape for the signal (tails fixed to pp data, pure MC, MC signal embedded into real events)

• sum of two exponentials for the background• ψ(2S) negligible with this statistics

S/B centrality dependent (~0.1-0.7), but good significance also in most central bin

J/ψ yield extracted from a fit (2-5 GeV/c2) to the invariant mass spectrum assuming

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Alternative signal extraction

Results obtained with different techniques combined to extract <NJ/ψ> and to evaluate systematic uncertainties

Mixed event technique also used to estimate the background•mixed pair invariant mass distribution normalized to data in

(1.5, 2.5) GeV/c2

•fit the background subtracted mass distribution with a Crystal Ball function and a straight line (or exponential) to account for a small residual background

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Centrality dependence of J/ψ parameters

The increase of detectors occupancy with centrality may worsen the reconstruction resolution, affecting the J/ψ shape

centrality dependence of J/ψ parameters is studied embedding a MC J/ψ into a real event

No centrality dependence of J/ψ width and Crystal Ball parameters

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Acceptance x efficiency Two approaches:

Standard Monte-Carlo:

J/ψ y and pT distributions interpolated from Phenix, CDF and LHC data

A x eff = 19.44 ± 0.04 (stat)%

small decreasing (~5%) of the reconstruction efficiency when increasing centrality

MC J/ψ embedded in real event

allows the study of the A x eff centrality dependence

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Nuclear modification factor

in each centrality bin ( )TeVppT

YR

inclJ

iAA

iJi

AA 76.2@ψ

ψ

σ×=

( ) ( ) iMB

iJi

J NAllJBRN

Y×××→

= −+ εψψ

ψwith:

pp reference: measured J/ψ production cross section in pp@√s=2.76 TeV (3 days data taking in March 2011 see talk G. Bruno)

( ) blumisystsyststatTeVppinclJ μσ ψ ).(28.0)(32.0)(13.046.376.2@ ±±±=

%8040%8040 −−=

AAJ

iAA

iJi

CP TY

TYR

ψ

ψ

RAA

RCP

peripheral reference:Warning: 40-80% centrality bin…not really peripheral…

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Systematic uncertainties

sources centrality

0-10% 10-20% 20-40% 40-80% correlated

NJ/ψ 19 % 14 % 17% 14% -

NJ/ψ/NJ/ψ40-80% 12% 8% 7% - -

Acc. inputs - - - - 3%

Trigger eff. - - - - 4%

Tracking eff. 4% 2% 1% 0% 5%

Reco eff. - - - - 2%

Branching ratio - - - - 1%

Cross Section - - - - 13%

<TAA> 4% 4% 4% 6% -

<TAA>i/<TAA>40-80% 6% 5% 4% - -

Total for RAA 20% 15% 17% 15% 15%

Total for RCP 14% 10% 8% - -

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Inclusive J/ψ RAA0-80% = 0.49 ± 0.03 (stat.) ± 0.11 (syst.)

Contribution from B feed-down:~ 10% from pp measurement (LHCb Coll., arXiv:1103.0423)Rough estimation assuming simple Ncoll scaling : ~11% reduction of RAA

0-80%

Error bars:Statistical uncertainties

Empty boxes:Centrality-dependent systematic uncertainties

Blue box:common systematic uncertainties

RAA vs. centrality

Suppression with no strong centrality dependence

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Comparison with PHENIX

*>part<N0 50 100 150 200 250 300 350 400

AA

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4 >0 (preliminary)T

= 2.76 TeV), 2.5<y<4, pNNsALICE (Pb-Pb

>0 (arXiv:1103.6269)T

= 0.2 TeV), 1.2<|y|<2.2, pNNsPHENIX (Au-Au

coll> is weighted by N

part(*) ALICE <N

Large ALICE centrality bins the <Npart> values have been weighted by Ncoll

J/ψ RAA is larger with respect to PHENIX results at forward y Difference increases with centrality

*>part<N0 50 100 150 200 250 300 350 400

AA

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4 >0 (preliminary)T

= 2.76 TeV), 2.5<y<4, pNNsALICE (Pb-Pb

>0 (arXiv:1103.6269)T

= 0.2 TeV), 1.2<|y|<2.2, pNNsPHENIX (Au-Au

>0 (nucl-ex/0611020)T

= 0.2 TeV), |y|<0.35, pNNsPHENIX (Au-Au

coll> is weighted by N

part(*) ALICE <N

J/ψ RAA is compatible with RHIC mid-rapidity result, except for the most central collisions

…but CNM effects may be different at the two energies

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Comparison with CMS results

ALICE RAA is significantly higher than the CMS result, but the covered kinematical region (y and pT) is different

CMS PAS HIN-10-006

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Nuclear shadowing

centrality40-80% 20-40% 10-20% 0-10%

AA

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4>0 (preliminary)

T = 2.76 TeV), 2.5<y<4, pNNsALICE (Pb-Pb

EPS09 (R. Vogt , priv. comm.)

Let’s consider shadowing as the only CNM effect (cc break-up cross section expected to be negligible at LHC energies)

R. Vogt, Phys.Rev.C81:044903, 2010JP. Lansberg, QM2011

Different approaches (J/ψ production through 2 1 or 2 2 partonic processes) and several nPDF adopted

Important shadowing contribution, but nPDF are affected by large uncertainties pA @ LHC (end 2012?)

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Comparison to models

Statistical hadronization:

• Screening by QGP of all direct J/ψ

• CNM (shadowing) on open charm

• Charmonium production at phase boundary by statistical combination of uncorrelated charm quarks

P. Braun-Muzinger, J. Stachel, PLB490 (2000) 196A.Andronic@QM2011, Andronic et al.,PLB571(2003)36

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Comparison to models

• Prompt J/ψ dissociation in QGP• J/ψ regeneration by charm quark

pair recombination• Feed-down from B decays• Shadowing

Parton transport models:R.Rapp, X. Zhao, NPA 859, 114(2011)R.Rapp, X. Zhao, PRC82 064905(2010)

Prediction including:

X.Zhu, P.Zhuang,N.Xu,PLB607(2005)107L.Yan,P.Zhuang,N.Xu,PRL97(2006)232301Y.Liu,Z.Qu,N.Xu,P.Zhuang,PLB678(2009)72P.Zhuang, WE-Heraeus Seminar 2011

• Shadowing and Cronin effect• Prompt J/ψ dissociation in QGP• J/ψ regeneration by charm

quark pair recombination • Feed-down contribution from B

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RCP

Error bars:Statistical uncertainties

Empty boxes:Centrality-dependent systematic uncertainties

RCP is normalized to the centrality bin 40-80%

Statistical uncertainty of the reference bin propagated to the ratioNon centrality-dependent uncertainties cancel out

Values close to 1 reflect the RAA flatness vs. centrality

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Comparison with ATLAS result

centrality40-80% 20-40% 10-20% 0-10%

nor

mal

ized

to 4

0-80

%C

PR

0

0.2

0.4

0.6

0.8

1

1.2

= 2.76 TeVNNsPb-Pb >0 (preliminary)

TALICE, 2.5<y<4, p

>6.5 GeV/c (arXiv:1012.5419)T

ATLAS, |y|<2.5, p

J/ψ RCP larger for ALICE than for ATLAS… but different rapidity and pT coverage can play a role

ALICE:•2.5<y<4•pT > 0

ATLAS:•|y|<2.5•80% of J/ψ with pT>6.5 GeV/c

centrality40-80% 20-40% 10-20% 0-10%

nor

mal

ized

to 4

0-80

%C

PR

0

0.2

0.4

0.6

0.8

1

1.2

= 2.76 TeVNNsPb-Pb >0 (preliminary)

TALICE, 2.5<y<4, p

>0 (preliminary)T

ALICE, |y|<0.8, p>6.5 GeV/c (arXiv:1012.5419)

TATLAS, |y|<2.5, p

Very challenging analysis… error bars are still large. Wait for 2011 high luminosity run!

Inclusive J/ψ RCP can be also measured in ALICE at mid-rapidity in the dielectron channel

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J/ψ in ultra-peripheral collisions Probe gluon distribution in the nuclei (down to x~10-4)

Search for tracks in the central barrel (ITS+TOF) or muon spectrometer, with a veto on V0 detectors

J/ψ e+e- J/ψ μ+μ-

Visible J/ψ signals in ultra peripheral PbPb collisions

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Prospects: J/ψ flow

At LHC, J/ψ regeneration could play an important role and will dominate the J/ψ flow

Several methods explored: here event plane method, using TPC tracks

Study is feasible, now waiting for larger data sample in 2011

Y. Liu, N. Xu, P. Zhuang, Nucl.Phys.A834(2010) 317c

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Summary and outlook

The ALICE experiment has measured the inclusive J/ψ production in PbPb collisions at √sNN = 2.76 TeV at both mid-rapidity and forward rapidity

A deeper understanding requires a precise knowledge of cold nuclear matter effects: waiting for pA at LHC in 2012!

• normalized to J/ψ cross-section in pp at the same energy• shows a clear suppression of the J/ψ yield with respect to

Ncoll scaling• forward values are larger than forward RHIC results• RAA (RCP) values are larger than those measured by CMS

(ATLAS), but the kinematical coverage is different

Next 2011 PbPb run with >5 times Lint (2010) should improve the quality of the measurements, allowing the study of J/ψ flow and production in ultra-peripheral collisions

RAA

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backup

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Comparison RHIC/SPSRAA comparison between SPS and RHIC

…picture not yet clear!

…but recently the pp reference was obtained directly from NA60 pA @ 158 GeV

the comparison looks different!

The initial estimate of the pp reference was obtained from pA data at higher energy, 450 GeV, (and rescaled to 158GeV)

All RAA looked similar!

pp reference is crucial to correctly interpret the results!

CAVEAT: at SPS no pp data taking @ 158GeV need to build the reference extrapolating pA data to A=1

Comparison SPS and RHIC

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front absorber (10λI)

tracking system (10 detection sub-planes, 70μm resolution in the bending plane)

dipole magnet (3Tm)

muon-filter wall (7λI)

trigger chambers(4 planes, programmable pT cut, with pT

μ>0.5GeV/c)

It is designed in order to have:

• large geometrical acceptance to increase dimuon statistics• acceptance down to pT~0 where direct J/ψ production dominates• good mass resolution to separate the ϒ family• tracking/trigger high granularity read-out to cope with the high multiplicity

The muon spectrometer

LHC

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√s G

eV/c

1986 1990 ~2000 2010

2760

200

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RHIC

SPS

Year

Physics motivations Quarkonium suppression is considered since a long time as one ofthe most striking signatures for the QGP formation in AA collisions

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Quarkonium measurement in ALICE

3 sources of J/ψ

• Direct production• Feed down from heavier

charmonium states

• J/ψ from b-hadron decay

Prompt J/ψ

J/ψ from B

feasible in the central barrel, thanks to the good impactparameter resolution (σrφ < 75 μm for pT>1 GeV/c)

forward detection more difficult3-muon eventsB cross section from single muon measurement

ALICE results refer to inclusive J/ψ production

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