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Résultats récents du RHIC. Outline : (1) heavy quarkonia production; (2) jet – medium interactions in heavy ion collisions; (3) correlations and fluctuations; (4) forward and central flow; (5) searching for gluon saturation;

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Résultats récents du RHIC

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Résultats récents du RHIC

Outline : (1) heavy quarkonia production;

(2) jet – medium interactions in heavy ion collisions;

(3) correlations and fluctuations;

(4) forward and central flow;

(5) searching for gluon saturation;

(6) W/Z measurements.

Guy Roche, LPC-Clermont.

Etretat, 20-23 Septembre 2010.


1) heavy quarkonia production.

From Daniel Kikota for the STAR colaboration, ICHEP 2010.

baseline:  in p+p 200 GeV

Consistent with CEM, (inconsistent with CSM: ~ 2)

Consistent with world data trend


Cold nucl. matter:  in d+Au

Cold nucl. matter:  in d+Au

Consistent with Nbin scaling.

Cold Nuclear Matter effects (shadowing) are rather small.


 in Au+Au 200 GeV

4.6 significance, 95 Signal counts in 8 < m < 11 GeV/c2

Includes , Drell-Yan + bb

Analysis in progress



  • High-pT J/ψmeasurement in p+p - a crucial test of quarkonia production

    in QCD.

  •  (B  J/ψ / J/ψ = (13 ± 5)% for pT > 5 GeV/c.

  • No J/ψ suppression at high-pT in Cu+Cu 200GeV: RAA ~ 1

  •  First  cross section measurements at RHIC energies:

    • - p+p results consistent with Color Evaporation Model

    • - d+Au: RdAu = 0.78 ± 0.28 (stat.) ± 0.20 (sys.)


(2) jet – medium interactions in heavy ion


From Olga Evdokimov for the STAR colaboration, ICHEP 2010.

Angular pair-correlations














STAR Preliminary

Evolution of several correlation structures is observed

Shown are 200 GeV minimum bias Au+Au data.

Similar analysis performed for 200 GeV Cu+Cu, and 62 GeV Au+Au and Cu+Cu data.





Di-jets through correlations

Trig1 is highest pT particle in event with 5-10 GeV/c

Trig2 (pT > 4 GeV/c) is back-to-back with Trig1

Associated particles pT > 1.5 GeV/c.

200 GeV Au+Au and d+Au.



associated particle

pT spectra

STAR Preliminary

  • No evidence of medium modificationsDi-jets observed - all tangential?


Jet-energy calibrarion

Direct γ-hadron correlations

STAR Preliminary

  • Similar medium effect on the away-side of 0 and dir

  •  is this due to tangential emission?

  • rich sample has lower near-side

  • yields compared to those of the

  • 0 different bias


Inclusive jet measurements

Central Au+Au: background correction leads to a factor of 2 uncertainty in cross-section


3) Correlations and fluctuations.

From Terence J Tarnowsky for the STAR collaboration, Winter Workshop on

Nuclear Dynamics 2010.

F-B Multiplicity Correlations

  • Predicted in context of Dual Parton Model [DPM] (and Color Glass Condensate [CGC]).

  • Test of multiple elementary [partonic] scattering.

  • Linear expression relating Nb and Nf (forward and backward multiplicity), found in hadron-hadron experiments (ex. UA5),

  • “b” is correlation strength.

    • Function of √s and A.

    • Coefficient can be

      expressed as,

N = # of hadrons


F-B Correlations

  • Central 200 GeV Au+Au collisions show a strong long-range correlation.

  • Most peripheral Au+Au have negligible LRC, as does pp.

  • HIJING and Parton String Model (PSM) do not agree w/ Au+Au data.

  • Multiparton interaction in central Au+Au collisions.

  • See talk by M. Skoby.



Characterize Fluctuations

  • NA49 uses the variable dyn

  • Measure deviation from Poisson behavior using dyn

  • It has been demonstrated (for K/p and p/p) that,


Excitation Function for σdyn,K/π

STAR central Au+Au (0-5%) collisions with SPS central Pb+Pb collisions (0-3.5%).


  • Large decrease in fluctuations as function of energy from NA49.

  • Fluctuations measured by STAR approximately constant as function of energy from 19.6-200 GeV.

  • p : 0.2 < pT < 0.6 GeV/c

    • K: 0.2 < pT < 0.6 GeV/c


4) Forward and central flow.

From Eric Richarson for the PHENIX collaboration, RHIC & AGS Annual Users Meeting June 7-11, 2010 BNL.

  • RP detectors with different  ranges yield similar signal

  • Signal varies v2 (v4)

    • mid-central ~5% (10%)

    • central/peripheral 10% (20%)

  • Signals agree within systematic errors (v2 = 10%, v4 = 20%)

  • Indicates reliable measurement largely free of  and pT dependent non-flow effects within the measured range (pT = 0.5 - 2.4 GeV/c)

v2, v4 h± Results



0-60% Centrality

v2, v4 h± Results

  • Fig (a) & (b)

    • v2 and v4 signal have similar shape

  • Fig (c) - v4/(v2)2

    • Ratio independent of pT within 0.5-3.6 GeV/c

    • v4/(v2)2 ≈ 0.8 for ~50<Npart<200, which is greater than ideal hydro (dot-dot)

    • adding eccentricity fluctuations within hydro model fits data better (dash-dash)

    • Even better fit when  added to hadron gas phase and small  added to QGP phase (dot-dash)

    • Ratio significantly increases Npart > ~200

    • Additional fluctuations needed to match central data (solid)

    • Fit with data implies a small /s

Data gives strong indication of hydrodynamic behavior in matter created at RHIC

These precision measurements should provide stringent constraints for models.


Heavy Flavor v2 Analysis Footnotes


  • Run-4, ~700M evts

  • Measured heavy flavor using single electrons from semileptonic decays (~10% branching ratio)

  • Tracking done using DC, PC, RICH and EMCal

  • RICH is primary electron identifier

  • Photonic electron bkgrd subtracted using “cocktail method” where background v2 was estimated using a Monte Carlo simulation with input from measured data

  • Photonic cocktail included electrons from 0 and  decays and  conversions and direct 

  • Electron v2 from K decays was also subtracted



Heavy Flavor v2 Results

  • Positive v2 at low pT - indicates heavy quarks (mainly charm) couple with the medium.

  • Shape similar to lighter quarks except at highest pT.

  • Although errors are large at high pT the signal appears to fall significantly from peak. This indicates a change in energy loss mechanism or a growing contribution from the bottom quark.



Model Comparisons

  • All models include quark coalescence

  • Models that best describe low pT data are:

    • Greco et al. with charm flow

    • Zhang et al. with larger charm quark parton-scattering cross section ( = 10 mb)

    • van Hees et al. with resonance interactions

  • Indicates

    • heavy quarks participate in the medium

    • Coalescence and resonance are large contributors to HF v2 at low pT



5) searching for gluon saturation.

From Beau Meredith for the PHENIX collaboration, DIS Conference, Florence, Italy, April 19-23, 2010.

Rapidity Separated Correlations : Widths.

2.0 < pT,trig< 3.0 GeV/c

trigp0or h+/-, h = 0

assoc p0, h = 3.4

No significant broadening

between p+p and d+Au within

large experimental uncertainties


Rapidity Separated Correlations : IdA .

0.45 < pT,assoc < 1.59 GeV/c

trigp0or h+/-, h = 0

assoc p0, h = 3.4

Increasing suppression of IdA reaches a factor 2 for central events indicating di-jet suppression




Forward/Forward Correlations : p+p .

  • Show per-trigger correlation functions, i.e. 1/NtrigdN/d(Df)

    • Area of away-side peak represents conditional yield without efficiency correction

    • More work needed to determine uncorrelated background level

    • Conditional yields, widths not shown

Trigger particle pT > 2 GeV/c

Associate particle pT > 0.875 GeV/c

Data points mirrored for Df > p

trigclusterh = 3.4

assoc p0, h = 3.4


p+p vs d+Au Central .

Decorrelation and/or suppression seem to get stronger for central d+Au collisions.


p+p vs d+Au Peripheral .

Peripheral d+Au collisions are more similar to p+p collisions




6) W/Z measurements.

From Mickey Chiu for the PHENIX collaboration, RHIC and AGS Users Meeting, June 7-11, 2010.

Comparison To Measured spectra

Data and MC driven BG estimation:

EMCal cluster distribution after subtracting cosmic background

 (Conversion + Accidental)

 Tracking Acceptance

  • (NLO Hadrons thru Geant + FONLL c/b)

  • Normalization from fit to 10-20 GeV


  • The same scale factor for PYTHIA was used for W/Z shape.

  • W-e- signal has fewer counts than W+e+ signal as expected


Isolation cut

  • Signature of a W event is that it is isolated

  • Sum up energy in a cone around electron and in cone on opposite hemisphere

E < 2GeV



  • 90+% of signal is kept (red histograms)

  • Factor ~5 reduction in jet dominated region


STAR Preliminary Run 9

From Joe Seele for the STAR collaboration, RIKEN BNL Research Center Workshop, June 24-25, 2010.

2009 Results

In 2009 STAR recorded its first 500 GeV data set and extracted its first mid-rapidity AL measurement.

Achieved S/B~11 for the W+ and S/B~6 for W-


Expected Data

RHIC is planning to run 500 GeV polarized p+p collisions in a multi-year effort to constrain the polarization of the anti-quarks in the proton

Calculations assume the demonstrated S/B (6 and 11) for the mid-rapidity projections and S/B~1 for the forward and backward rapidity projections


Back-up slides


Summary &Outlook from STAR:

  • Jet quenching discovered at RHIC has been extensively studied for years:

    • Modification of angular shapes, production rates, transverse momentum and energy distributions

  • Evolution of jet studies in HI:

    • Inclusive hadron measurements → di-hadron correlations → multi-particle correlations → full jets

  • Outlook:

    • Towards “theory-ready” (partonic) energy loss measurements

    • Disentangling experimental biases


ndyn,p/p, STAR and NA49

  • ndyn,p/pdisplays strong system size dependence for small dN/dh.

  • Fit is to STAR Cu+Cu 22.4 GeV data only.

  • Interpretation still under study.


Inclusive jet ratios



RAA of pions ~ 0.2

RAAJet> RAAp: recover larger fraction of cross-section, but not all

Significant ratio suppression wrt. pp

→ medium induced ET broadening


Excitation Function for σdyn,p/π

  • Solid points are data from STAR or NA49.

  • Open black points are HSD prediction from Konchakovski, et. al. arXiv:0906.3229.

  • Open red points are UrQMD run locally with STAR acceptance.


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