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High-p T identified particle spectra in p+p collisions at 200 GeV

High-p T identified particle spectra in p+p collisions at 200 GeV. Outline: Motivation Analysis Preliminary results Future work & Summary. Yichun Xu (for the STAR collaboration). Motivation.

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High-p T identified particle spectra in p+p collisions at 200 GeV

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  1. High-pT identified particle spectra in p+p collisions at 200 GeV Outline: • Motivation • Analysis • Preliminary results • Future work & Summary Yichun Xu (for the STAR collaboration)

  2. Motivation • Extend the identified hadron spectra study to higher pT range and test the applicability of pQCD in p+p collisions. • Baseline for study of color charge effect of parton energy loss in heavy ion collisions. Proton spectra in STAR is limited to 7GeV/c with current statistics from minimum bias p+p collisions.[1] In Au+Au, it can be extended to 12GeV/c now. [2] [2] Phys. Rev. Lett. 97 (2006) 152301 [1] Phys. Lett. B 637 (2006) 161 8/17/2008, Hot Quark, Colorado

  3. trigger ∆φ ∆φ Experiment and Data set Data set: EMC Triggers in run5 pp @ 200GeV Jet Patch trigger: ETtot>7.8 GeV TPC Cuts: pT>0.2 GeV/c, |h| < 0.5, Azimuthal angle |∆φ|>π/2 • Time Projection Chamber (TPC) • Electro-Magnetic Calorimeter (EMC) • Shower Maximum Detector (SMD) 8/17/2008, Hot Quark, Colorado

  4. STAR preliminary STAR preliminary 4.0<pT<4.5GeV/c w/ EMC cut dE/dx re-calibration, why? Where Bπ is the expected mean dE/dx of pion from Bichsel function of ionization energy loss in TPC. 8/17/2008, Hot Quark, Colorado

  5. s = 0.87 STAR preliminary Raw Yield STAR preliminary Peak positions of charged particles are fixed by parameters from re-calibration. 8/17/2008, Hot Quark, Colorado

  6. STAR preliminary STAR preliminary Results (1)—pion spectra PYTHIA (V6.205, MSEL=1) and GEANT are used to get trigger enhancement to correct spectra in triggered events. 8/17/2008, Hot Quark, Colorado

  7. Simon, private communication STAR preliminary Results (2)—proton spectra Our data will provide the best constraint on Fragmentation Function! AKK 2008 [1] is constrained by BRAHMS pbar/p ratio [2] (y=2.95, pT<5 GeV/c). [1] arXiv:0803.2768 , [2]Phys. Rev. Lett. 98, 252001 (2007) 8/17/2008, Hot Quark, Colorado

  8. STAR preliminary Results(3)--Comparison with NLO STAR preliminary • DSS, KKP and AKK2008 predict pionspectra very well, but PYTHIA under-predict pion production. • Only DSS can describe proton production. 8/17/2008, Hot Quark, Colorado

  9. Results(4)--Ratios PYTHIA describe all ratios very well, DSS over-predicts anti-proton, and AKK2008 over-predicts proton and under-predicts anti-proton. 8/17/2008, Hot Quark, Colorado

  10. Results(5)—compare with d+A, A+A p-/p+ : isospin conservation Pbar/p: are similar in three systems. p(+-)/p+(-) at intermediate pT: are consistent with coalescence prediction. p (+-)/p+(-) at high pT: indicate more quark jet contribution to proton in p+p than in A+A. 8/17/2008, Hot Quark, Colorado

  11. EMC module STAR preliminary Future work:EMC as hadron trigger detector STAR preliminary A factor of 100 enhancement Given pT=5 GeV/c, ~5.6M HT1 triggered events are equivalent to L(0.64 pb-1)*s(30mb) * effTrg(3%)/effTrk(90%) ~ 0.6B events. 8/17/2008, Hot Quark, Colorado

  12. STAR preliminary KS->p+p Reconstruct KS with triggered pion It can reach 10 GeV/c while it only arrive 5 GeV/c in minimum bias events . Constrain K/p ratio and check hadron yields. Good method to reconstruct resonance at high pT. 8/17/2008, Hot Quark, Colorado

  13. Summary • Extend pion and proton spectra to pT ~15 GeV/c. • p-/p+, pbar/p & p(pbar)/p+(-) ratios are consistent with results from minimum-bias events within error. • DSS, KKP and AKK2008 describe pion yields very well, but only DSS predictions are consistent with proton production. • p-/p+ and pbar/p ratios are consistent with PYTHIA, which under-predicts the individual yields of p+ and p-. • Decrease of pbar/p ratio indicates a significant quark jet contribution to baryon. 8/17/2008, Hot Quark, Colorado

  14. Thanks! 8/17/2008, Hot Quark, Colorado

  15. Backup 8/17/2008, Hot Quark, Colorado

  16. STAR preliminary STAR preliminary V0 (KS&L) -- p&p dE/dx MKs(0.485,0.505) ML(1.112,1.118) STAR preliminary 8/17/2008, Hot Quark, Colorado

  17. Fit function: Re-calibration STAR preliminary No obvious color charge effect of parton energy loss in heavy ion collision. 8/17/2008, Hot Quark, Colorado

  18. NLO differences • KKP: e+e- data, no charge difference • AKK: derived from KKP, including p,n,KS,L etc. • AKK2008: including STAR data, and constrained by including BRAHMS pbar/p ratio. • DSS: e+e- data, including STAR data points. EMC & SMD cuts: 0.3<p/E<1.5,nh>=2,nf>=2, |zdist|<2, |fdist|<0.01 8/17/2008, Hot Quark, Colorado

  19. STAR preliminary STAR preliminary 8/17/2008, Hot Quark, Colorado

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