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					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
                   Jet Properties at RHIC

           Au  Au  jets                      p  p  jets




    Measure jets in “simple” system (p+p).
    Use this information to measure jets in complex system (Au+Au).
May 2003                                                        Mike Miller
                           Jets in Au+Au: Angular Correlations
                           Select high-pT portion                  Particles from same
                            of event (pT>2 GeV)                    jet are close in angle
Py (GeV/c)




                                                                   Particles from di-jets are
             4




                                                                   ~180 deg. apart
             3
             2
             0 1




                                                                1) Approximate jet axis by
                                                                leading particle (trigger )
             -4 -3 -2 -1




                                                                2) Study  of associated
                                                                particles w.r.t. trigger
                           -4 -3 -2 -1   0 1   2    3   4   Px (GeV/c)
May 2003                                                                                    Mike Miller
           Jets in p+p: Direct Identification
 Cluster final state
  (charged!) hadrons from        distance measure:
  a common “parent”              R   2   2
  quark/gluon.

 Reconstruct momentum
 of quark/gluon
 Implemented, tested,
 using 4 jet-finding
 algorithms

  Remember: only charged particles!
May 2003                                             Mike Miller
           Di-jet Angular Distributions
           di-jet  from s =200 GeV p+p (Run II)



                            ptjet1  ptjet1 
                      kt                     sin( 
                                   2        
               Raw STAR Preliminary

                       pt  6GeV
                          jet




                 Increase jet pT, tighten di-jet peak
                 Measure Nuclear kT in d+Au
May 2003                                                    Mike Miller
                                          Jet-Event Shape and Size
           <Total pT> (Arbitrary Units)              ptall tracks vs. leading jet


                                                              s =200 GeV p+p (Run II)
                                                             RawRaw STAR Preliminary
                                                                STAR Preliminary




                                           Within lead jet     Transverse region         Within away side jet




            Measure pt ,                                 N charge ,    p    t     in jet and w.r.t. thrust axis
            Measure underlying event  dAu jet energy correction!
May 2003                                                                                                           Mike Miller
           “Fragmentation” of Charged Jets
                                                      p track
             What about “Correlation” jets?        z  t jet
                                                       pt

                                                  Slope depends on jet-
                                                       algorithm



                                                 Events with pT>4 GeV
            s =200 GeV p+p (Run II)              track
           Raw STAR Preliminary                  All jets with at least
                                                 one 2<pT<6 GeV track

                Selecting Jets with large Fragmentation Bias!
May 2003                                                         Mike Miller
                      What Does this Mean?
  1.   At high jet-pT, leading particle
       collinear with jet axis
  2.   Correlation jets: leading particle
       carries ~80% of reconstructed
                                                                            pttrigger
       charged particle jet pT.                                   pTjet   
                                                                               zc
                                                 Mean trigger
             Leading particle is a good         fragmentation
           approximation of jet direction


   Leading particle is easily related to jet
                     pT


             Defines the pQCD scale            Defines jet pT of away-side partner!
May 2003                                                                      Mike Miller
                    Jets In d+Au Collisions
No background subtraction          p+p: Adler et al., PRL90:082302 (2003), STAR

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
May 2003                                                                     Mike Miller
           Jets In Least Violent Au+Au Collisions
                                     Au+Au, p+p: Adler et al., PRL90:082302 (2003), STAR

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           “Near side” jet: consistent
          systems                       in all 3 systems
May 2003                                                                        Mike Miller
           Jets In Most Violent Au+Au Collisions
                                     Au+Au, p+p: Adler et al., PRL90:082302 (2003), STAR

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
May 2003                                                                        Mike Miller
                    Conclusions
      1. p+p: pT>4 GeV particles are good
         approximation of jet direction, momentum
      2. d+Au: no suppression of away-side jet in
         central collisions
      3. 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
May 2003                                        Mike Miller
           What’s Coming from STAR?
      1. p+p: Run III data with E.M. Calorimeter
         0<<1. Identified jets including 0.
      2. d+Au: Same!
      3. Au+Au: Run IV with expanded
         calorimeter and extensive high-pT
         triggered data.
             Measure vacuum, in-medium
             “fragmentation” functions!

May 2003                                           Mike Miller
           Backup slides




May 2003                   Mike Miller
           The STAR Detector




May 2003                       Mike Miller
             d+Au “Centrality” Tagging
   FTPCE multiplicity: -3.8<<-2.8
  (Au fragmentation direction)
   ZDCW: single deuteron spectator                              FTPCE
                             ZDCW
                                        Au                         d
                   Uncorrected
                   FTPCE multiplicity
                            minbias

                                        FTPCE multiplicity: defines
       single deuteron                  “centrality” in d+Au events
          spectator



May 2003                                                       Mike Miller
                                           Jet-Event Shape and Size
            ptall tracks vs. leading jet from s=200 GeV p+p
            <Total pT> (Arbitrary Units)




                                                                 Raw STAR Preliminary




                                            Within lead jet   Transverse region         Within away side jet




             Measure pt ,                                 N charge ,   p   t     in jet and w.r.t. thrust axis
             Measure underlying event  dAu jet energy correction!
May 2003                                                                                                          Mike Miller
           Why Jets? Energy Loss in Dense Matter
                                         Thick plasma (Baier et al.):
                                                           C R s 2 ~
                                             EBDMS             ˆ
                                                                 qL v
                                                             4
                                                    2

                                             q
                                             ˆ          S  glue
                                                     Debye
       Gluon Bremsstrahlung
                                                glue
                                                                   2 E jet 
                                  CR  d glue  , r  Log 2 
    Thin plasma
                         EGLV          3
                                        S                          L
    (Gyulassy et al.):                                                     
 Strong dependence of energy loss on gluon density glue:
    • measure E  measure gluon density at early hot, dense
    phase
May 2003                                                                 Mike Miller
           “Fragmentation” of Charged Jets
            How does the slope change as a      p track
                 function of jet pT?         z  t jet
                                                 pt




                                             Fragmentation slope
                                              scales with jet pT
                                                beyond 6 GeV
                   Raw STAR Preliminary




May 2003                                                  Mike Miller
           “Fragmentation” of Charged Jets
            What fraction of (reconstructed)      p track
            jet pT does each particle carry?   z  t jet
                                                   pt




                                               Slope depends on jet-
                                                    algorithm

                    Raw STAR Preliminary




May 2003                                                      Mike Miller
           Di-jet Angular Distributions
              di-jet  from s =200 GeV p+p



                           ptjet1  ptjet1 
                     kt                     sin( 
                                  2        
              Raw STAR Preliminary

                      pt  6GeV
                         jet




                Increase jet pT, tighten di-jet peak
                Measure Nuclear kT in d+Au
May 2003                                                   Mike Miller

				
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