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Charmonia in Heavy Ion Collisions

Strongly Interacting Matter Under Extreme ConditionsHirschegg, 17-23 January 2010

Roberta ArnaldiINFN Torino (Italy)

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Outline

Charmonia suppression in AA collisions is already a 25 years long story

SPS RHIC LHC

17 GeV/c 200 GeV/c 5.5 TeV/c√s

years 1990 ~2000 20101986

Last year, new high precision data (HERA-B, NA60, PHENIX/STAR) have been presented

improvements in the understanding of the charmonium behavior, taking advantage of the different energy and kinematics exploited domains

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Physics motivation: AA collisions

Study of charmonium production/suppression in pp, pA and AA collisions

AA collisions

• Charmonia suppression has been proposed, more than 20 years ago, as a signature for QGP formation

• Sequential suppression of the resonances is a thermometer of the temperature reached in the collisions

T/TC

J/(1S)

c(1P)

’(2S)

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Physics motivation: pp, pA collisions

allow the understanding the J/ behaviour in the cold nuclear medium complicate issue, because of many competing mechanisms:

pp collisions

provide information on production models (CSM, NRQCD, CEM…)

provide a reference for the study of charmonia dissociation in a hot medium approach followed at SPS and similarly at RHIC (with dAu data)

pA collisions

provide a reference for nuclear collisions results

Final state: cc dissociation in the medium, final energy loss

p

μ

μJ/

Initial state: shadowing, parton energy loss, intrinsic charm

(not covered by this talk)

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Fixed target experiments

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AA collisions

NA38 S-U 200 GeV/nucleon, 0<y<1 (M.C. Abreu et al., PLB449(1999)128)

NA50 Pb-Pb 158 GeV/nucleon, 0<y<, pT<5 GeV (B. Alessandro et al., EPJC39 (2005)335)

NA60 In-In 158 GeV/nucleon, 0<y<1, pT<5 GeV (R. Arnaldi et al., PRL99(2007) 132302, Nucl. Phys. A 830 (2009) 345)

pA collisions

HERAB p-Cu (Ti) 920 GeV,-0.34<xF<0.14,pT<5 GeV

(I. Abt et al., arXiv:0812.0734) E866 p-Be,Fe,W 800 GeV,-0.10<xF<0.93,pT<4 GeV

(M. Leitch et al., PRL84(2000) 3256) NA50 p-Be,Al,Cu,Ag,W,Pb,400/450 GeV,-0.1<xF<0.1,pT<5 GeV (B. Alessandro et al., EPJC48(2006) 329)

NA3 p-p p-Pt, 200 GeV, 0<xF<0.6, pT<5 GeV (J. Badier et al., ZPC20 (1983) 101)

NA60 p-Be,Al,Cu,In,W,Pb,U 158/400 GeV,-0.1<xF<0.35,pT<3 GeV (E. Scomparin et al., Nucl. Phys. A 830 (2009) 239)

Fixed target experimental landscape(Relatively) large amount of fixed-target data (SPS, FNAL, HERA)

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Fixed target experimental resultsAnomalous J/ suppression in AA is evaluated wrt to a reference obtained extrapolating, from pA to AA, the CNM effects affecting the J/

In-InPb-Pb

absJ/ = 4.2±0.5 mb,

(J//DY)pp =57.5±0.8 (Glauber analysis)

Observed suppression in AA exceeds nuclear absorption

AA collisions

• extrapolated to AA at 158 GeV assuming

• obtained from pA at 400/450 GeV (NA50)

In the NA50 approach:all initial/final CNM effects are described through an effective abs. cross section abs

J/

absJ/ (158 GeV) = abs

J/ (400/450 GeV)

(J//DY)pp rescaled from 450/400 to 158 GeV

• Onset of the suppression at Npart 80• Good overlap between Pb and In

pA collisions

~e−ρLσabs

(R. Arnaldi et al., PRL99(2007) 132302)

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Cold nuclear matter effects

I. Abt et al., arXiv:0812.0734

ApppA

• E866 vs HERAB (similar √s) agreement in the common xF range

• E866/HERAB vs NA50

These effects can be quantified, in pA collisions, in two ways:

decreases when decreasing √s

Satisfactory theoretical description still unavailable!

Strong xF dependence of

(R. Vogt, Phys. Rev. C61(2000)035203, K.G.Boreskov A.B.Kaidalov JETP Lett. D77(2003)599)

Because of the dependence on xF and energy the reference for the AA suppression must be obtained under the same kinematic/energy domain as the AA data

To understand the J/ dissociation in the hot matter created in AA collisions, cold nuclear matter effects have to be under control

absLpppA Ae ~

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New NA60 pA data

NA60 has collected pA data (using 7 different targets):

158 GeV: no data available up to now. First pA data at the same energy as AA collisions400 GeV: already investigated by NA50 (cross check)

A-dependence of the relative cross sections is fitted using the Glauber model and abs is extracted

shadowing neglected, as usual (but not correct!) at fixed target

abs J/ (158 GeV) = 7.6 ± 0.7 ± 0.6 mbabs J/ (400 GeV) = 4.3 ± 0.8 ± 0.6 mb

Using

(158 GeV) = 0.882 ± 0.009 ± 0.008 (400 GeV) = 0.927 ± 0.013 ± 0.009

ApppA

Very good agreement with the NA50 value

E. Scomparin et al., Nucl. Phys. A 830 (2009) 227

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Comparison between experiments: vs xF

NA60 pA results can be compared with values from other experiments

In the region close to xF=0, increase of with √s

NA60 158 GeV: smaller , hints of a decrease

towards high xF ?

NA60 400 GeV very good agreement with

NA50

Systematic error on for the new NA60 points ~0.01

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Comparison between experiments: vs x1,2

pattern vs x1 at lower energies resembles HERA-B+E866 but systematically lower

shadowing effects and nuclear absorption scale with x2 (V. Tram and F. Arleo, arXiv:0612043) clearly other effects are present

yT esmx /1

yT esmx /2

2

21~

x

xms JNJ

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Kinematical dependence of nuclear effects

need to disentangle the different contributions

Size of shadowing-related effects may be large and should be taken into account when comparing results at different energies

• anti-shadowing (with large uncertainties on gluon densities!)• final state absorption…

158 GeV free proton pdf158 GeV free proton pdfEKS98

Interpretation of results not easy many competing effects affect J/ production/propagation in nuclei

with antishadowing (EKS) = 9.3± 0.7± 0.7 mbwithout antishadowing: 7.6± 0.7± 0.6 mb

abs J/ (158 GeV)

Significantly higher than the “effective” value

C. Lourenco et al., arXiv:09013054

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Kinematic dependence of nuclear effects (2)Apart from shadowing, other effects not very well known, as parton energy loss, intrinsic charm may complicate the picture even more

First attempts of a systematic study recently appeared (C. Lourenco, R. Vogt and H.Woehri, JHEP 0902:014,2009, INT Seattle workshop 2009, F. Arleo and Vi-Nham Tram Eur.Phys.J.C55:449-461,2008, arXiv:0907.0043 )

No coherent picture from the data no obvious scaling of or abs with any kinematical variable

Clear tendency towardsstronger absorption at low √s

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Reference for AA dataa precise reference for the J/ behavior in AA collisions can be determined

abs shows an energy/kinematical

dependencereference now obtained from 158 GeV pA data (same energy/kinematical range as the AA data, contrarily to what was done in the past)

B. Alessandro et al., EPJC39 (2005) 335

R. Arnaldi et al., Nucl. Phys. A (2009) 345

In-In analysis based on another centrality estimator (number of tracks) ongoing, to check the observed pattern

AA collisions shadowing affects not only the target, but also the projectile

proj. and target antishadowing taken into account in the reference determination

R.A., P. Cortese, E. Scomparin Phys. Rev. C 81, 014903

Using the new reference:

• Central Pb-Pb: still anomalously suppressed• In-In: almost no anomalous suppression?

In-In 158 GeV (NA60)Pb-Pb 158 GeV (NA50)

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Collider experiments

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Collider experimental landscape

Experiments

PHENIX J/e+e- |y|<0.35 & J/+- |y| [1.2,2.2] STAR J/e+e- |y|<1

pp, dA collisions

pp 200 GeV/nucleon PHENIX, PRL 98, 232002 (2007) STAR, Phys. Rev. C 101 041902 (2009) dAu 200 GeV/nucleon PHENIX, Phys.Rev.C 77 024912 (2008) Nucl.Phys.A 830 (2009) 227

Data from RHIC, waiting for high energy LHC collisions…

All data have been collected with the same collision energy (√s = 200 GeV) and kinematics

AA collisions

Au-Au 200 GeV/nucleon PHENIX, PRL 98 232301 (2007) Nucl.Phys.A 830 (2009) 331Cu-Cu 200 GeV/nucleon PHENIX, PRL 101 122301 (2008) STAR, Phys. Rev. C 101 041902 (2009)

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pp experimental results

RHIC J/ results are usually provided as in terms of nuclear modification factor

The pp reference, used up to now, is based on Run 5 improvement expected from new Run 6 high statistics data

pp results should help to • understand the J/ production mechanism• provide a reference for AA collisions (RAA)

arXiv:0904.0439

ppJcoll

AAJ

AA dNN

dNR

C.L. da Silva, Nucl. Phys. A 830 (2009) 227

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AA experimental results

The Npart dependence of RAA for CuCu and AuAu is consistent

PRL 101, 122301 (2008)

J/ suppression is stronger at forward rapidity wrt. to midrapidity

Phys. Rev. Lett 98, 232301 (2007)

AuAu

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BackwardMid Forward

CNM effects from dAuIn a similar way as at SPS, CNM effects are obtained from dAu data

RdAu is fitted with a theoretical calculation assuming

y

Phys. Rev. C 77, 024912 (2008)

RHIC data exploit different x2 regions corresponding to shadowing (forward and midrapidity) anti-shadowing (backward rapidity)

• nuclear modified PDF distibutions• breakup

The result is the extrapolated to AA

results from dAu Run 3 do not allow to draw conclusions on AA results, because of the large breakup

error

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CNM effects from dAu (2)Furthermore CNM effects may depend on the assumed J/ production mechanisms (E. Ferreiro et al. arXiv:0809.4684)

intrinisic (gg J/) extrinsic (gg J/ + g) (emission of a hard gluon)

J/ produced through different partonic processes involve gluons in different x2 region different shadowing corrections

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The Run8 dAu dataNow high statistics dAu data (Run8 ~ 30x Run3) are available

a single value of break-up cannot reproduce the RCP ratios

A new approach has been proposed, to evaluate CNM effects(T. Frawley ECT*,INT quarkonium,Joint Cathie-TECHQM workshop)

RCP vs. centrality is fitted for each y bin with

a breakup for each y range a shadowing parameterization

EKS98: 0,1,…4,…mb

RCP flat vs centrality at backward rapidity, but falls at forward y

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RAA/RAA (CNM)

the trend at high y is similar to the one observed by E866 the suppression beyond CNM

effects is found to be similar at y=0 and at y=1.7 There is essentially no dependence of

these results on the shadowing model used to parameterize the dAu RCP

Result is then extrapolated to AA

(T. Frawley Joint Cathie-TECHQM workshop)

midrapidity

backward y forward y

breakup shows a strong rapidity dependence

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Comparison with SPS results vs NPart

Measured/Expected SPS results are compared with RHIC RAA results normalized to RAA(CNM)

Both Pb-Pb and Au-Au seem to depart from the reference curve at NPart~200

For central collisions more important suppression in Au-Au with respect to Pb-Pb

Systematic errors on the CNM reference are shown for all points

still some model dependence also in this approach: Cu results are fitted using breakup from dAu, since dCu data do not exist

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Comparison with SPS results

Results are shown as a function of the multiplicity of charged particles (~energy density, assuming SPS~RHIC)

Comparison can also be done in terms of * Bjorken energy density

energy density evaluation is based on several assumptions

A

dydET

0

dET/d from WA98 data for SPS data no dET/d for CuCu, so AuAu data at the same NPart are used

complicate issue, in particular when comparing results from different experiments

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Interpretation of the resultsSeveral theoretical models have been proposed in the past, starting from the following observations

• RAA at forward y is smaller than at midrapidity• RAA at RHIC and SPS are similar, in spite of the very different √s

Different approaches proposed:

SPS RHIC LHC

s (GeV) 17.2 200 5500

Ncc ≈ 0.2 ≈10 ≈100-200

1) Only J/ from ’ and c decays are suppressed at SPS and RHIC

The 2 effects may balance: suppression similar to SPS

2) Also direct J/ are suppressed at RHIC but cc multiplicity high

J/ regeneration ( Ncc2) contributes to the J/ yield

same suppression is expected at SPS and RHIC results do not seem to reflect the sequential suppression

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RecombinationModels including J/ regeneration qualitatively describe the RAA data

(X. Zhao, R. Rapp arXiv:0810.4566, Z.Qu et al. Nucl. Phys. A 830 (2009) 335)

J/ elliptic flow J/ should inherit the positive heavy quark flow

J/ y distribution should be narrower wrt pp

J/ pT distribution should be softer (<pT

2>) wrt pp

Results are not precise enough to assess the amount of regeneration

Indirect way some distributions should be affected by regeneration

Direct way for quantitative estimate accurate measurement of charm

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High pT J/ in Cu-Cu

RCuCu up to pT = 9 GeV/c suppression looks roughly constant up to high pT

PHENIX (minimum bias) STAR (centrality 0-20% & 0-60%)

RCuCu =1.4±0.4±0.2 (pT>5GeV/c) RAA increases from low to high pT

Difference between high pT results, but strong conclusions limited by poor statistics

Both results in contradiction with AdS/CFT+Hydro

Increase at high pT already seen at SPS

NA50: Pb-Pb

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Statistical hadronizationJ/ production by statistical hadronization of charm quarks (Andronic, BraunMunzinger, Redlich and Stachel, PLB 659 (2008) 149)

• charm quarks produced in primary hard collisions• survive and thermalize in QGP • charmed hadrons formed at chemical freeze-out (statistical laws)• no J/ survival in QGP

yA. Andronic et al. arXiv:0805.4781

Good agreement between data and model

Recombination should be tested on LHC data!

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LHC perspectives

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Quarkonium physics at LHC

Factor 10 (100) increase in charmonia (bottomonia) with respect to RHIC

Bottomonium physics will be accessible

High charm quark multiplicity (NCC~100)

J/ regeneration (not yet well defined at RHIC) might become dominant

New scenarios will be accessible, thanks to the high beam energy

Pb ions will be accelerated (√s=5.5 TeV)p collisions will be also studied (√s=7 – 14 TeV)

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Charmonium performances @ LHCCharmonia measurements will be carried out by all the LHC experiments under different kinematical conditions

LHCbCMSATLASALICE

Comparison of J/ measurement in central PbPb collisions

Acc

(M)

S/BpT

ALICE(+-) ALICE(e+e-) ATLAS(+-) CMS(+-)

2.5<<4 -0.9<<0.9 -2.7<<2.7 -2.4<<2.4

70 MeV 30 MeV

0.13 (7)

>0 GeV/cindirect id.

1.2 (5)

>0 GeV/c

yes yes? yes?

>2 GeV/c >2 GeV/c

35 MeV

1.2

70 MeV

0.15

prompt/displ.

Simulations with dNch/d~2500-5000

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ALICEALICE is the LHC experiment dedicated to nucleus-nucleus collisions

Central Barrel:-0.9<<0.9e+e- decay channel

Forward Muon Arm2.5<<4+- decay channel

Quarkonium production will be measured in the central barrel and in the forward muon spectrometer in p-p and Pb-Pb collisions

Quarkonium physics that will be addressed:

Suppression of in AA collisions to study the created medium

Differential distributions (y,pT,polarization) to constrain production models to provide a reference for AA

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Quarkonium in central Pb-Pb

Central rapidity Forward rapidity

• e- identification in TPC+TRD• integrated J/ acceptance ~29%

• identified in a Muon Spectrometer• integrated J/ acceptance ~4.6%

J/

N. 200 103 103

M MeV/c2 30 80

S/B 1.2 1.1

S/√(S+B) 245 21

J/ (2S)

N. 130 103 3.7 103 1.3 103

M MeV/c2 70 100 100

S/B 0.2 0.01 1.7

S/√(S+B) 150 7 29

J/ and significances not so different smaller statistics compensated by background reductionWorst situation for the ’ statistics , but much larger background

Quarkonium in central Pb-Pb collisions (106 s running time, L=51026cm-2 s-1)

Simulations with dNch/dy~3000 Simulations with dNch/dy~8000

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With the expected statistics (~7 105 J/ in 1 month of data taking): J/ suppression can be studied as a function of centrality and pT (up to ~10GeV/c), allowing the discrimination between the different theoretical scenarios J/ polarization study will be performed as a function of pT

Quarkonium in Pb-Pb

A fraction of the J/ produced at LHC comes from the B hadron decay useful to evaluate the beauty production cross section need to be disentangled to study prompt J/ production

At midrapidity prompt and secondary J/ can be discriminated thanks to the vertexing capabilities.At forward y J/ from B can be determined only indirectly

Higher charmonia states (’, c) can be measured cleaner signal for theory feasible in pp, much more complicate in Pb-Pb because of the lower significance

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First ALICE dimuons!

First dimuons seen in ALICE in pp at √s=900GeV, even if out of the ~20 observed dimuons… not yet a J/!

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ConclusionsJ/ suppression is a good signature for QGP studies

J/ behaviour in cold nuclear matter is already a complicate issue: many competing initial/final state effects

Many steps forward thanks to new high precision data

but for a correct evaluation of anomalous effects, cold nuclear matter effects have to be under control

Signal of anomalous suppression has been observed at SPS and RHIC

Important to understand J/ behaviour from lower to higher energy in a coherent scenario

New LHC data will soon be available!

They will help to discriminate among the different processes (suppression, regeneration…) affecting the J/

In the future, the “J/ picture” will be enriched by the results from CBM, exploring a baryon rich matter, and maybe from a NA60-like experiment filling the gap between FAIR and top SPS energy

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Backup

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NA60 pA data

NA60 has collected pA data:

158 GeV: no data available up to now. First pA data at the same energy as AA collisions400 GeV: already investigated by NA50 (cross check)

3-day long data taking, largely motivated by the need of a reference sample taken in the same conditions of In-In (NA60) and Pb-Pb (NA50) data useful to enlarge the vs xF systematics

bulk of the NA60 p-A data taking results released up to now

• sub-sample with same exp. set-up used at 158 GeV• useful as a cross-check (same energy/kinematic domain of the large statistics data sample collected by NA50)

Kinematical window where acceptance is >0 for all targets

• 3.2 < ylab < 3.70.28 < ycm < 0.78 (158 GeV)

-0.17 < ycm < 0.33 (400 GeV)

• | cos CS | <0.5

158 GeV

400 GeV

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all targets simultaneously on the beam

beam luminosity factors Niinc cancel out

(apart from a small beam attenuation factor) no systematic errorsBeBe

tBe

incBe

JBe

AAtA

incA

JA

JBe

JA

ANN

N

ANN

N

arg

/

arg

/

/

/

each target sees the vertex spectrometer under a (slightly) different angle

acceptance and reconstruction efficiencies do not completely cancel out

Estimate of nuclear effects through relative cross sections:

Efficiency map(4th plane, sensor 0)

These quantities, and their time evolution, are computed for each target separately

DY

J/, ’

DD

Comb.bck.

p-Pb

NJ/ 2 103Not enough DY statistics to extract (as in NA50) B J//DY target by target

New NA60 pA results

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Comparison between experiments: abs vs xF

absJ/ calculated from cross section

ratios for HERA-B, E866,NA3

As already observed for , there is:

• a strong xF dependence• a √s dependence…but NA3 shows values closer to the high energy experiments (E866/HERA-B)

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Results with old and new referenceabs J/ (158 GeV) > abs J/ (400 GeV)

Anomalous suppression in In-In is quite small ( 10%)

new reference

In-In 158 GeV (NA60)Pb-Pb 158 GeV (NA50)

published results

B. Alessandro et al., EPJC39 (2005) 335R. Arnaldi et al., PRL99 (2007) 132302

smaller anomalous suppression expected with respect to previous results

In-In analysis based on another centrality estimator (number of tracks) ongoing, to check the observed pattern

Anomalous suppression in Pb-Pb up to 30%

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Antishadowing contribution

In AA collisions the initial state effects (shadowing) affect not only the target, but also the projectile

Even in absence of anomalous suppression, the use of the standard reference (no shadowing) induces a 5-10% suppression signal sizeable effect

Using the new reference (shadowing in the projectile and target)

• Central Pb-Pb: still anomalously suppressed• In-In: almost no anomalous suppression?

proj. and target antishadowing taken into account in the reference determination

R.A., P. Cortese, E. Scomparin Phys. Rev. C 81, 014903

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CNM effects from dAu

As discussed for SPS data, a good knowledge of the initial/final state effects in nuclear matter helps to understand the J/ behaviour in AA

CNM effects at RHIC energies can be inferred from dAu data, using different approaches

1st method

• RdAu is fitted with a theoretical calculation assuming a shadowing parameterization and a breakup common to the whole y range.

• The result is the extrapolated to AA

y

Phys. Rev. C 77, 024912 (2008)

• Since breakup is common, results in the two y ranges strongly depend on nPDF

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CNM effects from dAu

2nd method

• RdAu data are fitted with a theoretical model including a breakup for each y range and shadowing parameterization

• Results are limited by the low Run 3 statistics

3rd methodNpart

PRL 101, 122301 (2008)

• The approach is based on a combination of RdAu data at different y, to predict CNM RAA for AuAu

• The method works only for AuAu, since RdAu is used directly

• Results at different y are independent, but they again suffer the Run 3 low statistics

J. Phys. G34, S955 (2007)

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abs vs. y

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High pT J/ @ SPS

pT (GeV/c)

RC

P 33-47%

NA60: In-In @ 158 GeV

NA50: Pb-Pb @ 158 GeV

pT (GeV/c)

RC

P 0-1.5%

pT dependence of the J/ suppression already investigated at SPS energies:

strong pT dependence of RCP

only the low pT J/ψ are suppressed !

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First Upsilon results @ RHIC

PHENIX, STAR pp @ √s=200GeV

PHENIX Au-Au @ √s=200GeV

STAR dAu @√s=200GeV

Cross section follows CEM expectations

RdAu = 0.98 ± 0.32 ± 0.28

RAuAu [8.5,11.5] < 0.64 at 90% C.L.

very low statistics

as expected from CNM + sequential melting

PHENIX

Upsilons suppressed:

consistent with Nbin scaling

in the future:

Upcoming 50 pb-1 200 GeV p+p run (5.6 pb-1 in run6 p+p)

RHIC II: high luminosity → separation of 1S, 2S, 3S states

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…and more results on…

STAR: arXiv:0904.0439

Small bck contribution allows the study of high pT J/ - hadron azimuthal correlations

STAR pp @ √s=200GeV

from the comparison with model calculations BJ/ fraction = 13% ±5%

PHENIX pp @ √s=200GeV

• v2 = –10 ± 10 %@ |y|<0.35 & –9.3 ± 9.2 %@1.2<|y|<2.2

• does not allow to differentiate between different models

in the measure pT range

J/ azimuthal flow measurement limited by statistics

PHENIX AuAu@√s=200GeV

N(J/) = 9.9 4.1 1.0

First measurement of J/ψ photoproduction in ultraperipheral collisions cross section (7633(stat)11(syst) b) consistent with theoretical predictions

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Sequential melting

In a color screening suppression scenario, a sequential melting, starting from the most loosely bound charmonia state, is expected

can the c and ’ feed down account for the observed J/ suppression?

are other mechanisms (e.g. color glass condensate) needed to explain the different suppression at midrapidity vs forward rapidity?

are the SPS and RHIC J/ suppression in the hot medium similar enough to justify this assumption?

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RecombinationIn a dense medium, J/ may be formed by a c and a c belonging to a different initial cc pair 2

ccNN J

regeneration is expected to be more important at midrapidity

A good accuracy in the open charm cross section measurement should help to quantify the importance of this process

Thews Eur.Phys.J C43, 97 (2005)

Grandchamp, Rapp, BrownPRL 92, 212301 (2004)

RHIC patterns are qualitatively reproduced

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RecombinationModels including J/ regeneration qualitatively describe the RAA data

(X. Zhao, R. Rapp arXiv:0810.4566)

J/ elliptic flow J/ should inherit the positive heavy quark flow

J/ y distribution should be narrower wrt pp

J/ pT distribution should be softer (<pT

2>) wrt pp

Results are not precise enough to assess the amount of regeneration

Regeneration should affect several distributions: