Jana Bielcikova (Yale University) for the STAR Collaboration 23 rd Winter Workshop on Nuclear...

Jana Bielcikova (Yale University) for the STAR Collaboration

23rd Winter Workshop on Nuclear Dynamics February 12-18, 2007

Two-particle correlations with strange baryons and mesons at

RHIC

Jana Bielcikova 23rd Winter Workshop on Nuclear Dynamics

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Outline:

• Physics motivation• Correlations with identified strange trigger

particles (Λ, Λ and K0

S) in d+Au and Au+Au collisions

• Correlations with identified strange associated particles

(Λ, Λ and K0S) in central Au+Au collisions

• Summary


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RCP:• intermediate pT : baryon/meson splitting independent of strangeness content• high pT (pT > 5 GeV/c) : all particles have similar RCP and appear to show similar suppression •large enhancement of baryon/meson ratio in central Au+Au relative to p+p collisions - reaches maximum at pT~3 GeV/c

• jet fragmentation is not a dominant source of particle production

Baryon/meson anomaly at intermediate pT


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Parton recombination at intermediate pT

• in vacuo fragmentation of a high momentum quark to produce hadrons competes with in medium recombination of lower momentum quarks to produce hadrons

•6 GeV/c particle via : fragmentation from high pT

meson - 2 quarks at pT~3 GeV/c baryon - 3 quarks at pT~2 GeV/cRecombination produces more baryons than mesons at intermediate pT

R.J. Fries et al., PRL 90 (202303) 2003V. Greco et al., PRL 90 (202302) 2003

baryon

meson


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Jet-like correlations at RHIC

central Au+Au collisions @ 200 GeV:

• disappearance of away-side correlations observed at intermediate pT

• d+Au and p+p similar -> jet suppression is a final state effect

• lowering associated pT :

- resurrects correlated yield at away side

- near and away-side yields are enhanced with respect to d+Au

0.15<pT(assoc)<4.0 GeV/c4 <pT(trig)<6 GeV/c 2 GeV/c <pT(assoc)<pT(trig)


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Correlations with identified particles

provide additional information on:• baryon/meson enhancement • medium modification of jet shape • particle production mechanisms

coalescence/recombination mechanisms

and/or (modified) fragmentation of high-pT partons?

parton

hadrons

hadrons

Λ, Λ, K0S, γ … ?

Λ, Λ, K0S, γ … ?

parton


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Correlations at near-side

a.u.

pTtrig=3-6 GeV/c, 1.5 GeV/c <pT

assoc< pTtrig

Au+Au central @ 200 GeV

ridge

ridge

jetjet+ridge

after v2 subtraction

jetridge

v2 + away-side peak h-h

Au+Au: long-range correlations at near side (“the ridge”)

Near-side yield : Δɸ (J+R) = Δɸ (J) + Δɸ (R) Jet yield : Δɸ (J) = Δɸ (|Δη| < 0.7) - Δɸ (|Δη| > 0.7) Ridge yield : Δɸ (R) = Δɸ (J+R) - Δɸ(J)


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before elliptic flow subtraction

Correlations with strange particle triggers in Au+Au at 200 GeV

Selection criteria:• 3.0 GeV/c < pT

trigger < 3.5 GeV/c • 1 GeV/c < pT

associated < 2 GeV/c• || < 1

Correlation function:• normalized per trigger particle• corrected for reconstruction efficiency of associated charged particles• acceptance corrected

STAR preliminarySTAR preliminary

STAR preliminarySTAR preliminarySTAR preliminarySTAR preliminary

STAR preliminarySTAR preliminary

trigger: baryon/meson baryon/antibaryon

after elliptic flow subtraction (using ZYAM method) Ajitanand et al, PRC72 (2005) 011902

systematic errors due to v2 uncertainty ~ 30%


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• steep increase of near-side yield with centrality in Au+Au• ratio of yields in central Au+Au/d+Au ~ 4-5

-> “jet” yield is independent of centrality and agrees with d+Au (effects of merged tracks under study)

JetJet + Ridge

-> “ridge” yield increases with centrality ridge of K0

S < ridge of Λ

Ridge

Centrality dependence of near-side yield

Jet


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pTtrigger dependence of jet and ridge

yields

• near-side associated yield is ridge dominated at intermediate pT

• jet yield: - increases steeply with pT

trigger

- smaller for Λ-triggers than for K0S-triggers ?

- baryon jet is wider than meson jet - effects of merged tracks under study • jet/ridge ratio increases with pT

trigger

Jet + Ridge Ridge Jet


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pT-distribution of associated particles

Trigger particle T(ridge) MeV T (jet) MeV

h+/- 438 ± 4 (stat.) 478 ± 8

K0S 406 ± 20 (stat.) 530 ± 61

Λ 416 ± 11 (stat.) 445 ± 49

STAR preliminary“jet” sloperidge slopeinclusive slope

J. Putschke (STAR), QM’06

h-h correlationspT

associated>2GeV/c

• Ridge spectra similar to particles from the bulk• Jet spectra are harder(T increases steeply with pT

trig)


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central-to-peripheral ratio (“ICP”): - ~ 3 at pT

associated = 1 GeV/c - decreases slowly with pT

associated

- jet yield is independent of centrality “ICP” is driven by long-range Δη correlations

• qualitative agreement with the parton recombination model BUT!• quantitative agreement requires same centrality and pT selection• check required on how well the “ridge” is reproduced by the model

• call for predictions for identified particles

What does a parton recombination model predict?

jet

ReCo: R. Hwa, Z.Tan: PRC72 (057902) 2005


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Particle composition in the ridge

/K0S ratio:

in the ridge: ~ 1.0 similar to that from inclusive pT spectra in the jet: ~ 0.5 consistent with p+p

|Δη|<2.0 |Δη|<0.7

STAR preliminary STAR preliminary


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What is the origin of the ridge ? 1) Parton radiation and its coupling to the longitudinal flow

• gluon bremsstrahlung of hard-scattered parton parton is shifted to lower pT

• radiated gluon contributes to broadening

2) Medium heating + parton recombination Chiu & Hwa Phys. Rev. C72:034903,2005

• hard parton passing through the medium enhanced thermal parton distribution (ΔT=15 MeV) recombination of thermal partons forms a pedestal (ridge)

• pedestal is not a part of the jet • enhanced baryon/meson ratio

3) Radial flow + trigger bias S.Voloshin, nucl-th/0312065, Nucl. Phys. A749, 287 (2005)

4) Longitudinal broadening of quenched jets in turbulent color field

A. Majumder, B. Mueller, S.A.Bass, hep-ph/0611135

• plasma instabilities in expanding medium broadening of jet cone

wide ridge in rapidity at low pTassoc

Armesto et al, PRL 93 (2004)


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Correlations with strange trigger particles:

- system size: strong increase (~4-5) of the near-side yield in central Au+Au in comparison to d+Au collisions due to long-range Δη correlations (“ridge”).

Ongoing studies of correlations in Cu+Cu. - ridge yield: steep increase with centrality, slope of pT spectra similar to that of “bulk”

- jet yield: consistent with d+Au, constant with centrality, increasing with pT

trigger

Correlations with strange associated particles:

B/M ratio in the ridge: close to the bulk

B/M ratio in the jet: consistent with p+p

The data qualitatively agree with recombination picture, but more detailed

comparisons are needed to draw final conclusions.

Summary


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BACKUP


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Analysis method

raw data correlation mixed events correlation corrected data correlation

h-K0S, 3 < pT

trig < 6 GeV/c, 2 < pTassoc < 3 GeV/c

ridge jetAu+Au, 0-10%

Jana Bielcikova (Yale University) for the STAR Collaboration 23 rd Winter Workshop on Nuclear...

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