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Michael L. Miller Yale University For the STAR Collaboration

Multiparticle Correlations and Charged Jet Studies in p+p , d+Au , and Au+Au Collisions at s NN =200 GeV. Michael L. Miller Yale University For the STAR Collaboration. Jet Properties at RHIC. Measure jets in “simple” system ( p+p ).

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Michael L. Miller Yale University For the STAR Collaboration

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  1. Multiparticle Correlations and Charged Jet Studies in p+p, d+Au, and Au+Au Collisions at sNN=200 GeV. Michael L. Miller Yale University For the STAR Collaboration

  2. Jet Properties at RHIC Measure jets in “simple” system (p+p). Use this information to measure jets in complex system (Au+Au).

  3. Particles from same jet are close in angle Select high-pT portion of event (pT>2 GeV) Py (GeV/c) Particles from di-jets are ~180 deg. apart -4 -3 -2 -1 0 1 2 3 4 Px (GeV/c) -4 -3 -2 -1 0 1 2 3 4 Jets in Au+Au: Angular Correlations

  4. Jets in p+p: Direct Identification • Cluster final state (charged!) hadrons from a common “parent” quark/gluon. • Reconstruct momentum of quark/gluon • Implemented, tested, using 4 jet-finding algorithms Remember: only charged particles!

  5. Raw STAR Preliminary Di-jet Angular Distributions • Increase jet pT, tighten di-jet peak • Measure Nuclear kT in d+Au

  6. <Total pT> (Arbitrary Units) Raw STAR Preliminary Raw STAR Preliminary Within lead jet Transverse region Within away side jet Jet-Event Shape and Size

  7. Slope depends on jet-algorithm Events with pT>4 GeV track All jets with at least one 2<pT<6 GeV track Raw STAR Preliminary “Fragmentation” of Charged Jets What about “Correlation” jets? Selecting Jets with large Fragmentation Bias!

  8. Leading particle is a good approximation of jet direction Defines the pQCD scale Defines jet pT of away-side partner! Mean trigger fragmentation What Does this Mean? • At high jet-pT, leading particle collinear with jet axis • Correlation jets: leading particle carries ~80% of reconstructed charged particle jet pT. Leading particle is easily related to jet pT

  9. p+p: Adler et al., PRL90:082302 (2003), STAR Jets In d+Au Collisions • No background subtraction • Central: top 20% of -3.8<η<-2.8 uncorrected multiplicity • underlying event: p+p< d+Au minbias < d+Au central • near-side: correlation strength and width similar • away-side: d+Au peak broader but with little centrality dependence Back-to-back jets are not suppressed in central d+Au

  10. Au+Au, p+p: Adler et al., PRL90:082302 (2003), STAR Jets In Least Violent Au+Au Collisions • Au+Au: Subtract background from combinatorics, flow • d+Au: no suppression in central collisions  use min. bias. • d+Au: subtract underlying event. “away side” jet: consistent in all 3 systems “Near side” jet: consistent in all 3 systems

  11. Au+Au, p+p: Adler et al., PRL90:082302 (2003), STAR Jets In Most Violent Au+Au Collisions • Au+Au: Subtract background from combinatorics, flow • d+Au: no suppression in central collisions  use min. bias. • d+Au: subtract underlying event. “away side” jet: p+p d+AuAu+Au “Near side” jet: consistent in all 3 systems

  12. Conclusions • p+p: pT>4 GeV particles are good approximation of jet direction, momentum • d+Au: no suppression of away-side jet in central collisions • Au+Au: strong suppression of away-side jet in central collisions. Combined: Strong back-to-back suppression in central Au+Au cannot be fully explained by initial state physics

  13. What’s Coming from STAR? • p+p: Run III data with E.M. Calorimeter 0<<1. Identified jets including 0. • d+Au: Same! • Au+Au: Run IV with expanded calorimeter and extensive high-pT triggered data. Measure vacuum, in-medium “fragmentation” functions!

  14. Backup slides

  15. The STAR Detector

  16. FTPCE ZDCW Au d Uncorrected FTPCE multiplicity minbias single deuteron spectator d+Au “Centrality” Tagging • FTPCE multiplicity: -3.8<h<-2.8 (Au fragmentation direction) • ZDCW: single deuteron spectator • FTPCE multiplicity: defines “centrality” in d+Au events

  17. Jet-Event Shape and Size <Total pT> (Arbitrary Units) Raw STAR Preliminary Within lead jet Transverse region Within away side jet

  18. Thick plasma (Baier et al.): Gluon Bremsstrahlung Thin plasma (Gyulassy et al.): • Strong dependence of energy loss on gluon density glue: • measure DE measure gluon density at early hot, dense phase Why Jets? Energy Loss in Dense Matter

  19. “Fragmentation” of Charged Jets How does the slope change as a function of jet pT? Fragmentation slope scales with jet pT beyond 6 GeV Raw STAR Preliminary

  20. “Fragmentation” of Charged Jets What fraction of (reconstructed) jet pT does each particle carry? Slope depends on jet-algorithm Raw STAR Preliminary

  21. Di-jet Angular Distributions Raw STAR Preliminary • Increase jet pT, tighten di-jet peak • Measure Nuclear kT in d+Au

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