Charged Particle High pt Spectra at PHENIX Jiangyong

Charged Particle High pt Spectra at PHENIX Jiangyong Jia For the PHENIX Collaboration @

QGP and Charge Particle High pt Physics M. Gyulassy, I. Vitev, X. N. Wang PRL 86 (2001) 2557 l Hard parton fragments carries information of QGP l l l Suppression of high pt spectra Strong centrality dependence In which pt and centrality? X. N. Wang PRC 63 (050821)01 @ APS 04/21/2002 2 Jiangyong Jia

PHENIX Setup l Global Observables l event characterization h ZDC, BBC l Charged Particles l tracking & momentum East arm DC, PC 1, PC 3 l 1. 4 M minimum bias events l More background rejection power by new tracking subsystem l ~170 events total(92 minimum bias) l spectra can be measured independently in west and east arms @ APS 04/21/2002 3 Jiangyong Jia

High pt Charged Hadron Spectra at 130 Ge. V/c PHENIX preliminary l Centrality dependence of charged particle production l Charged hadron spectra in bins of centrality show a gradual loss in concavity as they evolve from peripheral to central collisions. l The loss in concavity is consistent with the effect one might expect from suppression @ APS 04/21/2002 4 Jiangyong Jia

Change in Shape l Local inverse slope characterize the spectra shape l It is more convenient to calculate Mean pt above a pt cut p. T - p. Tmin l Centrality dependencies at high pt region are clearly different from low pt region Hydrodynamic collective flow at low pt. Suppression at high pt. PHENIX preliminary @ APS 04/21/2002 5 Jiangyong Jia

Comparison with NN references I l RAA for 5 centrality bin l Peripheral RAA 1 l Central RAA saturates ~ 0. 6 at pt >2 Ge. V/C l Changes in behavior in 30 -60% bin. PHENIX preliminary @ APS 04/21/2002 6 Jiangyong Jia

Comparison with NN references II l Normalized by N collision Soft and hard production have different scaling behavior: RAA and RAA(part/2) PHENIX preliminary l 2 Normalized by N participate Ratio for central are the same for 3 pt intervals reflects the saturation of RAA at high pt l look at ratio vs centrality for three high pt-intervals @ APS 04/21/2002 With increasing pt, RAA(part/2) saturates at successively lower Npart, most of this changes occurs in the range of Npart below 100 -150 which sits within 30 -60% centrality bin. 7 Jiangyong Jia

Run 2 analysis status 4 92 million minimum bias + 80 million level 2 triggered events 4 Momentum resolution dp/p < 1%p(3. 5% for Run 1) 4 West arm (DC PC 1 PC 2 PC 3), No random association background 6 Open issue : background from decay and photon conversion at pt > 6 Ge. V/c ~6 million events n 0 -5% n 5 -15% n 15 -30% n 30 -60% n 60 -80% n 80 -93% £minimum bias Uncorrected Raw Spectra @ APS 04/21/2002 8 Jiangyong Jia

Conclusion and outlook l Charged particle momentum spectra have been measured for different centrality selection up to 5 Ge. V/c at 130 Ge. V l l Particle production is suppressed at high pt relative to binary NN scaling. At pt>2 Ge. V/c, inverse slope decreases with centrality, the trend is opposite at low pt. For pt>2 Ge. V/c , RAA in central collisions saturates at 0. 6. At high pt, RAA(part/2) saturates at 3 for Npart >150. l In Run 2, PHENIX tracking detectors are fully operational l 92 million MB Au - Au (plus 80 million level 2 events) l ~ 200 million MB Proton - Proton events l Momentum resolution dp/p< 1%p(Ge. V/c) l Need to address background problem at pt>6 Ge. V/c l Expect accurate measurement of RAA at high pt @ APS 04/21/2002 9 Jiangyong Jia

Proton Contamination @ APS 04/21/2002 10 Jiangyong Jia

gradual onset of suppression with centrality and p. T @ APS 04/21/2002 11 Jiangyong Jia

Phys. Rev. Lett. , (2001) CERN - SPS X. N. Wang soft/hard transition? @ APS 04/21/2002 12 Jiangyong Jia

Slides not to be shown n 0 -5%/60 -80% n 0 -5%/80 -92% @ APS 04/21/2002 13 Jiangyong Jia

Ratio of 6 centrality bin / minimum bias x 1. 5 x 10 @ APS 04/21/2002 14 Jiangyong Jia

@ APS 04/21/2002 15 Jiangyong Jia

p/p ratio m. T scaling p. QCD measured soft/hard transition @ p. T APS 04/21/2002 16 Jiangyong Jia