Is there a strange baryon/meson dependence in

correlations in STAR?

Marek Bombara for the STAR Collaboration (University of Birmingham)

Strangeness in Quark Matter, Levoča, Slovakia, 24.06. 2007

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Outline

Introduction•Why correlations?•Why a strange baryon/meson correlations?•How do we make correlations?

ResultsConclusions

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Why correlations?

• angular correlations: info about jet-like structures (jet and ridge)

• practical: jets are indistinguishable from the bulk (in STAR TPC)

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Why a strange baryon/meson correlations?

• good source of baryons (), antibaryons () and mesons (K0) - various quark compositions

• correlations with identified particles: helpful for understanding particle production mechanism at intermediate pT (recombination and fragmentation)

• practical: for high/intermediate pT region in STAR experiment the purity/statistics ratio is best in comparison to others particles

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associated) - trigger) associated) - trigger)

How do we make correlations?1) Pick up track (for h-h) or V0 (for strange particle-h) with pT in

2-6 GeV/c (trigger particle) - we assume that track/V0 is related to jet leading particle

2) Pick up tracks from the same event with pt 1.5<pTasso< pTtrig (associated particle)

3) Calculate angular (azimuthal, and polar, correlations

associated

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Results

awayside

sameside

dAu

AuAu

Sameside peak broader in and peak sits atop a ridge!

What we have seen in unidentified h-h correlations:

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What causes the ridge and jet broadening?

• Radiated gluon contributes to ridge and broadening (N. Armesto, C.A. Salgado, U.A. Wiedemann, Phys. Rev. Lett. 93, 2004)

• Coalescence of quarks from the medium (C.B. Chiu, R.C. Hwa, Phys. Rev. C 72, 2005)

• Collective flow combined with jet-quenching (S.A. Voloshin, Nucl. Phys. A749, 2005)

• Turbulent color fields (A. Majumder, B. Mueller, S.A.Bass, hep-ph/0611135)

• Anisotropic QGP (P. Romatschke, Phys.Rev. C 75, 014901, 2007)

In vacuo (pp)fragmentation

static mediumbroadening

flowing mediumanisotropic shape

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Dip in the centre of the jet peak

∆ projection∆ projection

Intensive analysis showed that dip is a consequence of missing pairs whose tracks are crossed in TPC. Those pairs are instead probably reconstructed as merged tracks.

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• The position and depth of the dip depends on pT and helicity of trigger and associated particle

• Could be more pronounced for V0-h correlations (3 tracks for merging)

• How to correct?1) Anti-merging cut - calculation of fraction

of merged hits of two tracks2) Mirror image method - replacement of

dip region on one side (for specific helicities combination) with unaffected region from other side (used in this analysis)

3) Calculation of pair reconstruction efficiency with MC simulations

h_tr = -1

h_as = 1

h_tr = 1

h_as = 1h_tr = -1

h_as = -1

genuine merging, most visible for low pt triggers

h_tr = 1

h_as = -1

Closer look at the dip…. 5 dips!

h_tr - helicity of trigger

h_as - helicity of associated

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Study of jet and ridge with identified strange trigger particles

• Pair-wise detector acceptance• Single particle reconstruction efficiency• Combinatorial background modulated by elliptic flow • Track merging

• 16 million central AuAu (√sNN = 200 GeV) events

Input

Correlations corrected for

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Yields definition

Jet yield = (JR) - (R)

Ridge yield = 2* (R)

JR

R2

R1

R=R1+R2

Jet+Ridge region (JR) = || < 1

Ridge region (R) = 1<||<2

Assumption: Ridge is flat in all region!

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∆ projectionspTtrigger h-h -h -h K0-h

2.5-3.0GeV/c

4.5-6.0GeV/c

3.5-4.5GeV/c

3.0-3.5GeV/c

2.0-2.5GeV/c

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∆ projectionspTtrigger h-h -h -h K0-h

2.5-3.0GeV/c

4.5-6.0GeV/c

3.5-4.5GeV/c

3.0-3.5GeV/c

2.0-2.5GeV/c

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∆ projectionspTtrigger h-h -h -h K0-h

2.5-3.0GeV/c

4.5-6.0GeV/c

3.5-4.5GeV/c

3.0-3.5GeV/c

2.0-2.5GeV/c

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∆ projectionspTtrigger h-h -h -h K0-h

2.5-3.0GeV/c

4.5-6.0GeV/c

3.5-4.5GeV/c

3.0-3.5GeV/c

2.0-2.5GeV/c

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Jet widths

• Jet is broadening in ∆ with decreasing pTtrig

• Smaller broadening is seen for ∆

∆ projection projection

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PTtrig dependence

• Jet yield is increasing with pTtrig

• Ridge yield dependence?• No trigger species dependence

Jet Ridge

J. Bielcikova, QM’06 J. Bielcikova, QM’06

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System size dependence

• Jet yield doesn’t depend on centrality• Ridge yield increases with centrality

RidgeJet

J. Bielcikova, QM’06 J. Bielcikova, QM’06

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PT distribution of associated particles

• Ridge pT distribution similar to medium

• Jet distribution harder

STAR preliminary

“jet” sloperidge slopeinclusive slope

J. Putschke, QM’06

h-h correlationspT

associated>2GeV/c

J. Bielcikova, QM’06

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Conclusions

• No observation of strange baryon/meson trigger differencies in angular correlations

• Jet peak broadened in ∆, increasing with pTtrig, constant with centrality

• Ridge (long ranged ∆ correlation) increasing with centrality, associated spectra similar to inclusive

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Backup slides

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No anti-merging cut

h-h, 2.25<p_tr<2.50, 1.5<p_as<p_tr, 0-10%

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Anti-merging cut applied

h-h, 2.25<p_tr<2.50, 1.5<p_as<p_tr, 0-10%

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Mirror image

h-h, 2.5<p_tr<3.0, 1.5<p_as<p_tr, 0-10%