J/J/µµ++µµ–– measurement in measurement in Cu+Cu collision at Cu+Cu collision at √s = √s = 200 GeV200 GeVRapidity dependence

Andry Rakotozafindrabe – LLR Andry Rakotozafindrabe – LLR

For the PHENIX collaborationFor the PHENIX collaborationQuark Matter 05Quark Matter 05

Budapest, August 2005Budapest, August 2005

The J/ is a promising hard probe to study the hot and dense matter created in relativistic heavy ion collisions:

large charm quark mass J/ produced in the early stages of the collision only hard enough to resolve sub-hadronic scales

Most theoretical models indicate that producing a quark-gluon plasma will result in changes to the J/ yield:

its dissociation requires harder gluons than those present in hadrons possible only in a deconfined medium

J/ will be suppressed by color screening in a deconfined medium at ~1.2 Tc (Matsui and Satz, Phys.

Lett. B178, 416) coalescence/recombination models rather predict an enhancement of the J/ yield at RHIC energy (Grandchamp, Rapp and Brown, Phys.Rev.Lett. 92:212301 (2004), Thews, Schroedter, Rafelski, Phys. Rev. C63, 054905 (2001))

NA50 (CERN) experiment: anomalous J/ suppression in Pb+Pb collisions, in excess of the normal suppression expected from the nuclear absorption (NA50 Collaboration, Phys. Lett. B477 (2000) 28)

Physics motivations in the J/Physics motivations in the J/ yield measurementyield measurement

Cu+Cu 200 GeV data taking: triggers and

level2 filtering

Vol

ume of

dat

a

50 Tb50 Tb

2.5 Tb2.5 Tb

173 Tb

500 Mb500 Mb

Minimum Bias trigger: BBC

Level1 trigger: MuID Deep-DeepLevel1 trigger: MuID Deep-Deep

ReconstructionReconstruction

Level2 filtering: Level2 filtering: MuTrMuTr + MuID + MuID New !

• fast online reconstruction of 1D road in MuID• di-road accepted if last MuID gap reached (with a minimum number of hit gaps) • reconstruction of 2D road in MuID reconstruction of 2D road in MuID used as seed for MuTr track findingused as seed for MuTr track finding• rough track momentum estimate rough track momentum estimate invariant mass cut for tracks pairs invariant mass cut for tracks pairs at 2at 2 GeV/c² GeV/c²

Using Monte Carlo J/ generated by PYTHIA over 4π embed the J/ within muon arm acceptance into real minimum bias Cu+Cu data use a realistic detector response apply to them the same triggers and signal extraction method as the ones applied to the data

Acc*eff(Acc*eff(ii) is the probability for a J/) is the probability for a J/ thrown by thrown by PYTHIA in a given bin PYTHIA in a given bin ii to survive the whole to survive the whole process followed by the dataprocess followed by the data

Getting acceptance*efficiency Getting acceptance*efficiency correction factorscorrection factors

Acc*eff vs rapidity for the range 1.2 < |y| < 2.2 and integrated over all centralities (statistical error only).

Acc*eff vs rapidity (4 bins) and for 4 slices in centrality (0-20%, 20-40%, 40-60% 60-94%) for North (top) and South (bottom) muon arms (statistical error only).

Systematic errors:

5% from track/pair cuts and uncertainities in pT, y and z-vertex input distribution

8% from run to run variation (mainly due to the varying number of dead FEM in MuTr).

35°35°

10°

12° MuTr

MuID

BBC

South Muon arm : -2.2 < y <-1.2

North Muon arm : 1.2 < y <2.4

MuTr : tracking and momentum measurement with cathode strip chambers

MuID:muon identification with penetration depth/momentummatching.

BBC : particle production measurement in 3.0 < |η| < 3.9. Luminosity monitor + vertex measurement.

J/ measurement is done via the decay channel: J/ µ+µ–

data presented here = forward (backward) rapidities only

Muon Arms:0 < < 2 |p| > 2 GeV

PHENIX Muon PHENIX Muon ArmsArms

RRCPCP vs |y| per centrality slice vs |y| per centrality slice Systematic of Glauber calculation for peripheral is shown as a band.

RRcpcp useful because: useful because: removes uncertainities due to p+p referenceremoves uncertainities due to p+p reference

We can see:We can see: most central (0-20%) Rmost central (0-20%) Rcpcp distribution significantly below the peripheral (40-60%) distribution significantly below the peripheral (40-60%)

RRcpcp distribution distribution

Going Going from the most peripheral to the most central bin, afrom the most peripheral to the most central bin, a suppression suppression (increasing with centrality)(increasing with centrality) of the J/ of the J/ production is observed.production is observed.This suppression is indeed clearly seen on the centrality This suppression is indeed clearly seen on the centrality dependence of the J/dependence of the J/ yield per binary collision (see the yield per binary collision (see the poster by D. Silvermyr for more information):poster by D. Silvermyr for more information):

Theoretical expectations: rapidity dependence of the nuclear modification RTheoretical expectations: rapidity dependence of the nuclear modification RAAAA

The AA/pp ratio with the EKS98 parametrization as a function of y for octet absorption for Cu+Cu at 200 GeV. The curves are σabs = 0 (solid), 1 (dashed), 3 (dot-dashed) and5~mb (dotted).

Due to cold nuclear effects

To have a proper baseline for charmonium suppression in AA collisions, one need to carefully understand/predict cold nuclear matter effects in charmonium production :

absorption (final-state effect)where the formed cc pre-resonance pair is broken by interactions with primary target/projectile nucleons

shadowing (initial-state effect)where the free nucleon structure function is modified by the nuclear environnement, and hence affects heavy quark production

theoretical predictions on RAA vs rapidity by R. Vogt (nucl-th/0507027):

Cuts: Event cuts

• |Z-vertex| < 30 cm Pair cuts

• 2.6 < mass < 3.6 GeV/c²• 1.2 < |rapidity| < 2.2

Level2-like cut Track cuts

• pz < 0 (>0) to match the studied arm• determined using Monte Carlo J/ embedded in real data:

• cut on pair approach to BBC vertex• cut on track quality• cuts on the matching between MuID road and MuTr track

Signal extractionSignal extraction

Combinatoric background from uncorrelated di-muon:

Nbgd = 2√(N++. N– –)

Signal = number of counts within J/ invariant mass region 2.6 – 3.6 GeV/c² after substracting Nbgd to the distribution of opposite sign dimuons

Systematic errors: ~10% from varying fits of background subtracted signal. Also account for physical background that can be included into previous counting.

–1.95 < y < –1.70

Di-muon invariant mass distribution

Predicted by recombination model

J/ formed by recombination will exhibit a narrower rapidity spectra. Since recombination process is larger for central collisions, the width of the rapidity distribution of all J/ should decrease with increasing centrality:

If large number of c and c are produced in nucleus collision, then the probability of c and c incoherent recombination will no longer be negligible (off-diagonal recombination in a deconfined medium). This could be the case at RHIC energy.

Thews (nucl-th/0505055):

initially produced diagonal cc pairformation using allall cc pairs which can recombine in themedium

Predicted rapidity spectra of J/ in Au+Au at 200 GeV (pQCD calculation). Diagonal pair = cc pair coming from the same hard collision.

Close-up: RClose-up: RAAAA at |y| =2 vs at |y| =2 vs

centralitycentrality

Data is compared to predictions at y = 2 from cold nuclear matter effects (Vogt, Data is compared to predictions at y = 2 from cold nuclear matter effects (Vogt, nucl-th/0507027, nucl-th/0507027, σσabsabs = 3 = 3 mb and EKS98 parametrization at y=2, showing mb and EKS98 parametrization at y=2, showing

shadowing dependance vs centrality). The shadowing dependance vs centrality). The most central point seems to be most central point seems to be underpredicted: underpredicted: is there anyis there any additionnal suppression mechanism? additionnal suppression mechanism?

Summary:

Baseline cold nuclear matter effects seems to describe RAA dependence with rapidity for the centrality slices. But most central bin looks underpredicted: hint of additionnal suppression mechanism? J/ yield distribution with rapidity does not seem to get narrower with increasing centrality: this is expected in model where only recombination is taken into account.

J/J/ yield per centrality slice yield per centrality slice vs vs

rapidityrapidity

Recombination model predicts a narrowing of the Recombination model predicts a narrowing of the distribution with centrality (Thews, nucl-th/0505055). distribution with centrality (Thews, nucl-th/0505055). Data indicate Data indicate no significant change in the shape with no significant change in the shape with increasing centralityincreasing centrality. But, this model takes into . But, this model takes into account recombination account recombination onlyonly, and no other effect like , and no other effect like cold nuclear matter effect. cold nuclear matter effect.

Jij

iMB

Jij

µµ Ay

NNJCuCu

dy

dNB

.)( for rapidity bin i,

centrality bin j

errors (shadowing + errors (shadowing + σσabsabs = 1 = 1 mb dot curve, shadowing + mb dot curve, shadowing + σσabsabs = 3 mb dashed curve). = 3 mb dashed curve).

Nuclear modification factor RNuclear modification factor RAAAA vs rapidity vs rapidity

per centrality sliceper centrality slice

RAA at forward |y| are computed using reference dimuon p+p data fitted with a Gaussian. This fit serves as an interpolation to the available p+p points in the dimuon channel. Substantial Substantial uncertainty due to chosen fituncertainty due to chosen fit 20% added in quadrature to systematics.

RAA

PHENIX Preliminary

The study of the nuclear modification factor as a The study of the nuclear modification factor as a function of the rapidity exhibits afunction of the rapidity exhibits a similar pattern similar pattern between the different centrality bins.between the different centrality bins.A A comparisoncomparison of the data of the data with with thethe curves from curves from cold nuclear matter predictionscold nuclear matter predictions (Vogt, (Vogt, nucl-th/0507027) shows a possible agreement nucl-th/0507027) shows a possible agreement with the general trend of these curves within our with the general trend of these curves within our largelarge

dydNN

dydNR

JppColl

JAA

AA