Résultats récents du RHIC

Guy Roche, LPC-Clermont. Etretat, 20-23 Septembre 2010.

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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.

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

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Cold nucl. matter: in d+Au

Consistent with Nbin scaling. Cold Nuclear Matter effects (shadowing) are rather small.

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Cold nucl. matter: in d+Au

RdA 0.78 0.28(stat.) 0.20(sys.)

in Au+Au 200 GeV

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4.6 significance, 95 Signal counts in 8 < m < 11 GeV/c2 Includes , Drell-Yan + bb Analysis in progress

Summary

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High-pT J/ψmeasurement 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 Collisions.

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From Olga Evdokimov for the STAR colaboration, ICHEP 2010.

Angular pair-correlationsAngular pair-correlations

84-93%

28-38%

74-84%

18-28%

64-74% 55-64% 46-55%

9-18% 5-9% 0-5%

proton-proton

ηΔφΔ

refρ

Δρ

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.

STAR Preliminary

Di-jets through correlationsDi-jets through correlations

trig1trig2

assoc.Trig1 is highest pT particle in event with 5-10 GeV/cTrig2 (pT > 4 GeV/c) is back-to-back with Trig1Associated particles pT > 1.5 GeV/c.

200 GeV Au+Au and d+Au.

same-side away-side

associated particlepT spectraSTAR Preliminary

No evidence of medium modifications Di-jets observed - all tangential?

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Jet-energy calibrarionJet-energy calibrarion

Direct γ-hadron correlations

rich sample has lower near-side yields compared to those of the

0 different bias

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

is this due to tangential emission?

STAR Preliminary

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Inclusive jet measurementsInclusive jet measurements

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

• 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,

ffb bNaNN )(

From Terence J Tarnowsky for the STAR collaboration, Winter Workshop on Nuclear Dynamics 2010.

F-B Multiplicity Correlations

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N = # of hadrons

2

2

22ff

bf

ff

bfbf

D

D

NN

NNNNb

3) Correlations and fluctuations.

F-B Correlations

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• 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.

Phys.Rev.Lett.103:172301,2009

Characterize Fluctuations

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• NA49 uses the variable dyn

• Measure deviation from Poisson behavior using dyn

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

dyn sign data2 mixed

2 data2 mixed

2

is relative width of K / distribution

dyn,K NK NK 1 NK

2 N N 1 N

2 2NKN

NK N

dyndyn 2

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

Excitation Function for σdyn,K/π

Phys.Rev.Lett.103:092301,2009

• 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. • : 0.2 < pT < 0.6 GeV/c

•K: 0.2 < pT < 0.6 GeV/c

4) Forward and central flow.

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

v2, v4 h± Results

• 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)

arXiv:1003.5586

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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.

0-60% Centrality

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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

arXiv:1005.1627

arXiv:1005.1627

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Heavy Flavor v2 Results

arXiv:1005.1627

• 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.

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Model Comparisons

arXiv:1005.1627

• 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.

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

Rapidity Separated Correlations : Widths.

No significant broadening

between p+p and d+Au within

large experimental uncertainties

assoc 0, = 3.4

trig or h+/-, = 0

2.0 < pT,trig< 3.0 GeV/c

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Rapidity Separated Correlations : IdA .

assoc 0, = 3.4

trig or h+/-, = 0

peripheral central

0.45 < pT,assoc < 1.59 GeV/c

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

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Forward/Forward Correlations : p+p .

• Show per-trigger correlation functions, i.e. 1/NtrigdN/d()– Area of away-side peak represents conditional yield without efficiency correction– More work needed to determine uncorrelated background level– Conditional yields, widths not shown

Data points mirrored for >

Trigger particle pT > 2 GeV/c

Associate particle pT > 0.875 GeV/c

trig cluster = 3.4

assoc 0, = 3.4

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p+p vs d+Au Central .

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

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p+p vs d+Au Peripheral .

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

6) W/Z measurements.

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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

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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

+ -

•90+% of signal is kept (red histograms)•Factor ~5 reduction in jet dominated region

E < 2GeV

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

2009 Results

STAR Preliminary Run 9

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-

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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

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Summary &Outlook from STARSummary &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• dyn,p/ displays strong system size dependence for small dN/d.

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

• Interpretation still under study.

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Inclusive jet ratiosInclusive jet ratios

RAAJet> RAA

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

Significant ratio suppression wrt. pp

→ medium induced ET broadening

RAA of pions ~ 0.2

R=0.4R=0.4

RA

AJe

t

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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.