1 Jet Structure of Baryons and Mesons in Nuclear Collisions Why jets in nuclear collisions? Initial state What happens in the nuclear medium? Medium modification of jet fragmentation PHENIX Collaboration Barbara Jacak Stony Brook University Aug. 16, 2004
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Jet Structure of Baryons and Mesons in Nuclear Collisions
Jet Structure of Baryons and Mesons in Nuclear Collisions. Why jets in nuclear collisions? Initial state What happens in the nuclear medium? Medium modification of jet fragmentation. PHENIX Collaboration Barbara Jacak Stony Brook University Aug. 16, 2004. why jets in nuclear collisions?. - PowerPoint PPT Presentation
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Jet Structure of Baryons and Mesons in Nuclear Collisions
Why jets in nuclear collisions? Initial state What happens in the nuclear medium? Medium modification of jet fragmentation
But observed enhancement can be explained by recombination of thermal quarks from an expanding quark gluon plasma. NOT Jet-like!
Jet-likeNot suppressed!!?
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So, do jet analysis in Au+Au
Trigger:hadron with pT > 2.5 GeV/cIdentify as baryon or mesonBiased, low energy, high z jets!
Plot of associated partnersCount associated lower pT
particles for each trigger “conditional yield”Near side yield: number of jet associated particles from same jet in specified pT binAway side yield: jet fragments from opposing jet
trigger2 particle correlationsnear side < 90°Partner from same jet
away side > 90° opposing jet
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Subtract the underlying event
CARTOON
flow
flow+jet dNNtrig d
includes ALL triggers(even those with no
associated particles inthe event)
jetUnderlying event isbig! Collective flow causes another correlation in them:
B(1+2v2(pTtrig)v2(pT
assoc)cos(2))
associated particles with non-flow angular
correlations -> jets!
Treat as 2 Gaussians
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combinatorial background large in Au+Au!
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2 particle correlations
Select particles with pT= 2.5-4.0GeV/c
Identify them as mesons or baryons viaTime-of-flight
Find second particle with pT = 1.7-2.5GeV/c
Plot distribution of the pair opening angles
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jet partner equally likely for trigger baryons & mesons
Same side: slight decrease with centrality for baryonsLarger partner probability than pp, dAu
Away side: partner rate as in p+p confirms jet source of baryons!“disappearance” of away-side jet for both baryons and mesons
intermediate pT baryons ARE from jets
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What’s going on?
Thermal quark recombination
Radiated gluons are collinear (inside jet cone)
Increases partner yield
Fries, Bass & Muellernucl-th/0407102
Meson triggerbaryon
Dilutes jet partner yield
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Jet partner distribution on trigger side
Corrected to full jet yieldPartner spectrum flatter, indicates jet sourcePartners soften in most central collisions