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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%