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RHIC and AGS Annual Users’ Meeting

Heavy Flavor Workshop, June 2nd 2009

Roberta Arnaldi - INFN Torino (Italy)

Summary on SPS results on heavy quark measurements

Open charm measurement at SPS NA50 and NA60 pA and AA results

J/ production in pA collisions new pA data @ 158 GeV (NA60) definition of the new reference for AA collisions

J/ suppression in AA collisions update of the results based on the new reference curve

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Heavy Quarks at SPS

LMR IMR HMR

Intermediate Mass Region open charm production

High Mass Region charmonia production

Heavy quark measurement at SPS energies:

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Open Charm at SPS

HELIOS3-NA38-NA50

p-A IMR described by DY and Open CharmPb-Pb yields exceed pA extrapolation

centralcollisions

NA50Pb-Pb 158 A

GeV/c<Npart> = 381

Eur.Phys.C14(2000) 442

NA60 In-In

Fit range

DD

DYMass spectrum similar to NA50 (DY+2*Charm extrapolated from pA)

Dimuon offsets wrt interaction vertex show that the excess is prompt charm is not enhanced in A-A with respect to expectations

1.120.17DataPrompt: 2.290.08Charm: 1.160.16Fit 2/NDF: 0.6DD

Prompt

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Open Charm A dependenceRecent results from E866 seem to suggest strong nuclear effects on open charm

M. Leitch – Trento Workshop, May 09

New NA60 pA results soon available.Open charm A-dependence may add further useful information also in the charmonium understanding

E. Scomparin – Trento Workshop, May 09

E866/NuSea Preliminary

Preliminary studies point to an even stronger DD antishadowing with respect to J/

If DD has little final state interactions its should be significantly larger than that of the J/ (initial state energy loss should be the same)

xF

EKS98EPS08

J/

DD

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Charmonia in pA and AA collisions

Study of charmonium production/suppression in pA and AA collisions

• Production models (CSM, NRQCD, CEM, ....)• Initial/final state nuclear effects (shadowing, dissociation,...)• Reference for understanding dissociation in a hot medium

AA collisions

• Color screening and charmonium suppression > 20 year long history

pA collisions

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Experimental landscape

AA collisions

NA38 (M.C. Abreu et al., PLB449(1999)128) S-U 200 GeV/nucleon, 0<y<1NA50 (B. Alessandro et al., EPJC39 (2005)335) Pb-Pb 158 GeV/nucleon, 0<y<, pT<5 GeVNA60 (R. Arnaldi et al., PRL99(2007) 132302) In-In 158 GeV/nucleon, 0<y<1, pT<5 GeV

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

pA collisions

HERAB (I. Abt et al., arXiv:0812.0734) p-Cu (Ti) 920 GeV,-0.34<xF<0.14,pT<5 GeV

E866 (M. Leitch et al., PRL84(2000) 3256) p-Be,Fe,W 800 GeV,-0.10<xF<0.93,pT<4 GeV

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

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

NA60 p-Be,Al,Cu,In,W,Pb,U 158/400 GeV,-0.1<xF<0.35,pT<3 GeV

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absJ/ = 4.2±0.5 mb,

(J//DY)pp =57.5±0.8

• extrapolated to AA assuming

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

pA collisions

Reference for the J/ suppression in AA(cold nuclear matter effects aka nuclear abs.)

• tuned using pA at 400/450 GeV (NA50)

(Glauber analysis)

In-InPb-Pb AA collisions

absJ/ (158 GeV) = abs

J/ (400/450 GeV)

Observed suppression in AA exceeds nuclear absorption

Experimental results before QM09

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

J/ production is studied in p-A collisions

I. Abt et al., arXiv:0812.0734

ApppA

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

• E866/HERAB vs NA50

J/ absorption is parameterized through

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)

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pA and AA collisions

Charmonium absorption in cold nuclear matter: difficult topic because many competing effects contribute

pA collisions

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

p

μ

μJ/

NA60 has collected for the first time pA data at 158 GeV, i.e. the same energy as the AA collisions

• Initial state: shadowing, parton energy loss, intrinsic charm

Charmonium production in pA should provide the reference for AA data.

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

AA collisions

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NA60 pA data

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)

158 GeV: no data available up to now400 GeV: already investigated by NA50 (cross check)

NA60 has collected the following pA data:

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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New NA60 p-A results

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

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A-dependence fitted using the Glauber model

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 400 GeV

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

pA: new NA60 results

ApppA

Very good agreement with the NA50 value

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Comparison between experiments: vs xF Recent results on vs xF from HERA-B, together with older data

from NA50, E866

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 scale with x2 clearly other effects are present

yT esmx /1

yT esmx /2

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Comparison between experiments: abs vs xF

absJ/ calculated from cross

section ratios for HERA-B, E866,NA3

Increase of absJ/ with √s,

but NA3 shows values closer to the high energy experiments (E866/HERA-B)

First attempts of a systematic study of abs dependencies:(most recent C. Lourenco, R. Vogt and H.Woehri, JHEP 0902:014,2009,see also F. Arleo and V.N. Tram, EPJC55(2008)449 ) Hermine’s talk

Interpretation of results not easy many competing effects affect J/ production/propagation in nuclei (shadowing, final state absorption, energy loss,....) need to disentangle the different contributions (E. Scomparin, Trento workshop 2009)

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

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

abs J/ (158 GeV)

158 GeV free proton pdf158 GeV free proton pdfEKS98

Antishadowing correction

We have evaluated (and corrected for) the (anti)shadowing effect expected for our data points, within the EKS98 and EPS08 scheme

Significantly higher than the “effective” values

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Reference for AA data

The cold nuclear matter reference used up to now by NA50/NA60 was based on the following assumptions:

• abs is energy independent

but this may not be the case

New pA results collected at 158 GeV, in the same kinematic and energy range as AA data

First attempts to disentangle initial (antishadowing/energy loss) and final state effects (absorption in nuclear matter)

• all cold nuclear matter effects can be described with an “effective” abs

but, since these effects depend on energy/kinematic domain, it is difficult to compare results e.g. between SPS and RHIC

• pA nuclear effects can be extrapolated to AA

but in AA collisions gluon antishadowing affects both projectile and target

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

New pA analysis should provide a more appropriate reference

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abs J/ (158 GeV) > abs J/ (400 GeV)

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

Results with old and new reference

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 to be included in the extrapolation of the reference from pA to AA

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?

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Comparison with new PHENIX results

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

Tony Frawley’s talk at Trento Heavy Quarkonia Workhop May 2009

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

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Comparison with new PHENIX results (2)

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

The relation between the charged multiplicity and NPart is obtained

AuAu using PHOBOS data(Phys.Rev.C65 061901 (2002)

PbPb using NA50 data(Phys.Lett.B 530 1-4 (2002) 43-55)

Good agreement between PbPb and AuAu

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Conclusions

The determination of cold nuclear matter effects affecting the J/ is fundamental in order to understand J/ dissociation in a hot matter

The PHENIX and SPS result seem to point to a scaling of the suppression as a function of the charged multiplicity

This new reference imply a smaller anomalous suppression with respect to previous estimates

New 158 Gev pA results from NA60 have improved the understanding of this reference

Open charm A-dependence may add further useful information:first results from NA60 soon available

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Backup slides

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Differential distributions: d/dy, d/dxF

158 GeV 400 GeV

• Gaussian fit gives y=0.05±0.05, y=0.51±0.02158 GeV

400 GeV• y-distribution wider at 400 GeV, as expected• peak position not well constrained at 400 GeV• imposing y=-0.2 (NA50 at 400 GeV) y=0.81±0.03 (NA50 got 0.85)

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Comparison with previous experimentsHERA-B (920 GeV)

HERA-BNA50

small displacement of the center of the xF distribution towards negative values, increasing with A (xF<0.01)

NA50 (400 GeV)

strong, A-independent, backward shift (y=0.2, corresponding to xF= 0.045). Incompatible with HERA-B ?

NA60 points (@400GeV) seem to confirm NA50 result, but data probably not precise enough to quantitatively investigate rapidity shift

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pT broadening (Cronin effect) observed by all experiments

NA60 158 GeV

incident parton

cc

A1/3

pT

Differential distributions: dN/dpT

Fit pT2 for various nuclei as

<pT2>= <pT

2>pp+ gN L

<pT2>= <pT

2>pp+ (A1/3-1)

• New NA60 results suggest a decrease at low √s• NA3 result similar to high √s values• Agreement NA60 vs NA50 at 400 GeV

<pT2>pp shows a roughly linear increase vs s

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J/ polarization

Important tool for the study of quarkonium production mechanisms

Debated topic because of inconsistencies between theory and data

Recent studies have pointed out the importance of the choice of the polarization frame (P. Faccioli et al. arXiv:0902.4462, E. Braaten et al arXiv:0812.3727)

• degree of polarization is frame dependent • results comparable only if the same frame is adopted

pprojectileViewed from dimuonrest

frame

ptarget

z axis

xy

reaction plane

decay plane

+

ϕ

pprojectile

Viewed from dimuonrest frame

ptargetzCS

yzGJ

zHE

2cossin

2cos2sincos1

cos d

dσ1 22

d

J/ polarization measured from the angular distribution of the decay μ

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J/ polarization resultsHERA-B (pA @ 920 GeV)

Gottfried-JacksonCollins-SoperHelicity*

clear hierarchy in the values of the decay angular parameters measured in the different frames

|λHE|< |λGJ|< |λCS|

|νHE|> |νGJ|> |νCS|

polarization depends on the J/ pT

no strong dependence on xF

CDF (p-p @ √s =1.8 TeV)E866 (p-Cu @ 800GeV)

Large transverse polarization at high pT predicted by NRQCD NOT seen

PHENIX (pp √s =200GeV)

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NA60 pA J/ polarization results

p-A 158 GeV p-A 400 GeVHECS

First measurement of the full angular distribution

• Preliminary systematic error ~± 0.10 (increasing with pT)

• Large errors for in the CS frame (acc. large only at small |cosCS|)

Helicityλ

Collins-Soper

NA60, 158 GeV E866, 800 GeV NA3, 280 GeVNA60, 400 GeV HERA-B, 920 GeV

Comparison with other experiments:

λCS tends to be negative and larger in absolute value with respect to λHE

Global understanding of measured pattern not yet available

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NA60 In-In J/ polarization results

Results vs. transverse momentum Results vs. centrality

First full measurement of the J/ angular distribution in nuclear collisions

Npart

Npart

Helicity frame

Polarization is rather small everywhere: no pT or centrality dependence

Positive azimuthal coefficient at low pT?

Quantitative predictions needed!

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Cold nuclear matter effects vs. √s

Many competing effects:

Can a suitable combination of these effects generate a √s dependence of at fixed xF ?

• Shadowing• Initial state energy loss• Final state energy loss• Nuclear dissociation

Complicate interpretation of the vs. xF pattern

E. Scomparin, Trento worshop, May 2009

Try to calculate vs xF for various √s

• Use LO CEM formulas (from R. Vogt, PR310 (1999) 197)

• Shadowing (EKS98, EPS08 & GRV98LO pdfs)

• Initial state energy lossGavin-Milana (PRL68(1992)1834)

BDMPS (Arleo, JHEP11(2002)044)

• Nuclear dissociationConstantDepending on √sN

Get from the ratio Pb / Be

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Cold nuclear matter effects vs. √s (2)

158 GeV400 GeV800 GeV

EKS98

assume abs J/ = 0

no initial state energy loss

weak √s-dependence at fixed xF

• almost negligible at midrapidity• at foward rapidity decreases when increasing √s

158 GeV400 GeV800 GeV

012.01

absJ/=0 mb

EKS98

Shadowing

Initial state energy loss (GM)

3/1111 Axx In each collision (prior to

the one creating the cc) the parton looses a fixed fraction of its energy

This model may explain the high xF behaviour, but cannot create a √s-dependence at fixed xF (x1 shift does not depend on proton momentum)

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Cold nuclear matter effects vs. √s (3)

158 GeV400 GeV800 GeV

2/2 fmGeVq

This mechanism is able to produce an effectwhich depends on √s but

• no decrease at high xF

• abnormally high qhat needed (estimate in cold nuclear matter qhat~0.25 GeV/fm2)

Initial state energy loss (BDMPS)

3/21 ~~ A

sEx

p

A simple combination of shadowing+initial state energy loss + constant nuclear dissociation cross section abs

J/ cannot reproduce data on vs xF

• Is it possible to find, using the data sets collected at various energies, a ”universal” abs

J/ vs √sN ?

• Initial energy loss should be studied in more detail• Drell-Yan data to constrain free parameters

inside models (see e.g. F.Arleo,PLB532(2002)231)• How to combine

• Constant energy loss per unit length (squared) • Fixed fraction of energy loss per collision