2008/04/12APS April Meeting 1 Decomposition of Awayside Components of Dijet Correlation in Au+Au Collisions at √S NN = 200 GeV at PHENIX Chin-Hao Chen (presenter: B. Jacak) Department of Physics and Astronomy Stony Brook University

2008/04/12APS April Meeting 2 Method 200 GeV (Run4) 200GeV (Run5) Inclusive photon – hadron  correlation –Trigger: inclusive photon p T : 2-3 GeV/c Mostly  0 decays Not thermal photons! –Associated: charged hadron p T : 1-2, 2-3 and 3-5 GeV/c trigger partner

2008/04/12APS April Meeting 3 2-D correlations Both near and away side modified! shoulder ridge   rad  Peripheral Au+Au Central Au+Au How is the jet’s momentum redistributed by the medium?

2008/04/12APS April Meeting 4 Yield in  slices: peripheral Au+Au ~ p+p 0<|  |<0.10.1<|  |< <|  |< <|  |<0.7

2008/04/12APS April Meeting 5 Yield in  slices: 0-20% central ridge 0<|  |< <|  |< <|  |<0.50.5<|  |<0.7

2008/04/12APS April Meeting 6 Decomposition method Fit away side jet with sum of three Gaussians to decompose components: Head :punch through jet Shoulder: new peak either side of  (medium response ?!?!) Treat all components as Gaussian in shape Use ZYAM method to fix background level

2008/04/12APS April Meeting 7 shoulder & ridge increase with centrality Yields are very similar!

2008/04/12APS April Meeting 8 Shoulder & ridge p T spectra vs. p+p Both are softer than hard scattering. Ridge harder than shoulder? Shoulder not quite as soft as inclusive hadrons RIDGE SHOULDER

2008/04/12APS April Meeting 9 Momentum flow Weight per trigger yield of each partner p T bins  Ensemble averaged vector sum of associated particles. Vector sum is along the trigger direction e.g. projected on trigger p T direction partner p T trigger p T

2008/04/12APS April Meeting 10 Near & away increase with centrality Number of particles p T Weighted yield

2008/04/12APS April Meeting 11 away/near to ~ cancel acceptance p T is transferred from head  shoulder shoulder to ridge ratio is roughly constant Near = jet 0 <  < 0.1 Near = ridge 0.5<  <0.7

2008/04/12APS April Meeting 12 summary In central collisions, both near and away side are modified. Both ridge and shoulder spectra soften approach inclusive hadron spectra. The transverse momentum in away side is redistributed between head and shoulder. Shoulder and ridge track one another –Similar underlying physics?

2008/04/12APS April Meeting 13 Backup slides

2008/04/12APS April Meeting 14 Jets are modified in Medium Away side peak at  =  suppressed and new peak appears Feature present with both ZYAM & absolute background measure How is the momentum redistributed?

2008/04/12APS April Meeting 15 The nearside enhancement vs centrality Enhancement!

2008/04/12APS April Meeting 16 SpassoT,away/ SpassoT,near When we extend the associated particle pT range, the result still holds!

2008/04/12APS April Meeting 17 Weight the integrated yield with p T asso (along trigger particle direction) both nearside and awayside p T asso is increased Awayside pTasso increases less than AS yields Crossover of “ head ” and “ shoulder ” at N part at Charged associated particles only Not include the trigger particle contribution

2008/04/12APS April Meeting 18 Ratio of Away p T asso / near p T asso Ratio constant with centrality Consistent with p+p value, also with PYTHIA Even though the total vector sum of nearside/awayside both increase, the ratio of the two still hold constant The ratio of the total contribution from “ head ” and “ shoulder ” part is hold, but the contribution from the two is changing. head shoulder Head+shoulder PYTHIA

2008/04/12APS April Meeting 19 Extend to Lower p T asso The ratio still holds when we include softer particles! l p T asso =[ ] GeV/c l p T asso =[ ] GeV/c