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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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R sultats r cents du rhic

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
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 modifications Di-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
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 dyn k
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
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
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
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
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
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



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


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/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 dyn p
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.