Identified Charged Hadron Production in p+p Collisions at √s = 62.4 and 200 GeV

1. Identified Charged Hadron Production in p+p Collisions at √s = 62.4 and 200 GeV Masahiro Konno for the PHENIX Collaboration (University of Tsukuba) JPS @ Yamagata, 9/21/2008

2. Introduction • Measure transverse momentum spectra • for identified particles as reference to heavy ion data. • - Experiment: RHIC-PHENIX • - Data: p+p at √s = 62.4 and 200 GeV • Study the properties of hadron production in p+p collisions • - Inverse slope parameter in mT spectra • - Particle ratios • - xT scaling, its exponent neff • Compare them with data taken at different collision energies • Compare them between p+p and heavy ion data (Au+Au, Cu+Cu)

3. PID Spectra in p+p collisions Phenix Preliminary Phenix Preliminary • Measured pT spectra for π, K, p with √s = 62.4 and 200 GeV p+p data • PHENIX TOF counter used for particle identification • Proton and antiproton spectra measured up to pT = 4 GeV/c

4. mT Spectra for identified particles Hard Soft • mT spectra fitted with an exponential function • to extract the inverse slope parameter (Fit range: mT-m ~0.3-1.0 GeV). • mT scaling roughly applicable: • Two components (soft, hard) to be taken into account * Feed-down correction not applied. If applied, Tinv increased by ~ 10-15 %

5. Energy dependence of Tinv Open: p+p/p+pbar Closed: Pb+Pb, Au+Au • Compiled Tinv in p+p (p+pbar) and A+A data • Tinv(p+p) < Tinv(A+A) for π/K/p • Clear energy dependences seen in (anti-)proton for both p+p and A+A

6. Baryon-meson difference in mT spectra Mesons Baryons • mT scaling in yield is roughly applicable within an order of magnitude. • By scaling arbitrarily at mT~ 1-1.5 GeV, the spectra are split into meson and baryon • groups. The harder meson spectra indicate that meson production requires only • a quark pair in fragmentation, while baryon production requires a diquark pair.

7. Open: p+p/p+pbar Closed: Au+Au Baryon/Meson Ratios ratios ratios • Baryon/meson ratios increase with collision energy even in p+p collisions. • Λ/K ratios at high energies are surprisingly high as in heavy ion collisions. • This could be due to NLO contribution, bulk effect such as coalescence, and so on. • First measure particle ratios in p+p at LHC energy (√s = 14 TeV).

8. High pT Spectra - pQCD description PRD76(2007)051106 p+p 200 GeV p+p 62.4 GeV - π0 spectra are described over a wide pT range with pQCD calculation within experimental and theoretical uncertainties.

9. xT Scaling in p+p Collisions • Invariant cross section for single-particle inclusive • reaction is given by the general scaling formula: where • Inclusion of QCD into the above equation leads to: • - n(xT,√s) equals 4 in lowest order calculations as in • QED. Measured values of n(xT,√s) in p+p collisions are • in the range from 5 to 8 due to higher order effects. • The data points deviate from the xT scaling • for pT 2 GeV/c, which is interpreted as a transition • from hard to soft processes in particle production. Ref: PL 42B 461(1972), PRD11(1975)1199

10. xT Scaling for PID Spectra Pions Antiprotons • xT scaling works for both of pions and (anti-)protons at √s = 62.4 and 200 GeV • Next compare the xT-scaling power neff between pions and (anti-)protons

11. p Estimation of neff • xT-scaling power n is a function of xT and √s. • Effective value of n(xT,√s), neff, is obtained • by the following two methods: • (1) Taking the ratio of yields between different • energies (e.g. √s = 62.4, 200 GeV) • (2) Fit xT distributions with a common function Data points: method (1) Lines: method (2) (Fit range: xT = 0.07 – 0.20)

12. pT Spectra in A+A Collisions • In central Au+Au collisions, hadron yields are suppressed at high pT • compared to those in p+p collisions. • - The suppression is thought to be a final state effect (parton energy loss). • Au+Au and Cu+Cu RAA show a similar dependence on Npart. where <Ncoll> is the number of binary NN collisions

13. xT Scaling in A+A Collisions neff vs. Npart • The assumptions is that structure and fragmentation functions scale with xT for A+A. • The π0’s show xT scaling with the same number of n as in p+p in any systems, while • (anti-)protons show xT scaling with similar value for peripheral only. In central, they • show a larger value of n – due to baryon enhancement at 2-3 GeV/c in 62.4 GeV A+A. • - The effective energy loss should scale ΔpT/pT = const., leading to constant RAA.

14. Summary • Identified charged hadron pT spectra measured in p+p collisions • at √s = 62.4 and 200 GeV (Phenix preliminary) for reference of heavy ion data • mT scaling tested with p+p and A+A data • Inverse slope parameter: Tinv(p+p) < Tinv(A+A) for π, K, p • Tinv increases with collision energy √sNN. • (Anti-)protons increase quickly than pions and kaons for both p+p and A+A • - Baryon-meson difference of the yields seen in mT spectra • xT scaling tested with p+p and A+A data • xT scaling works for pions and (anti-)protons in p+p collisions (62.4, 200 GeV) • - In heavy ion data, π0’s show xT scaling with the same number of neff as in p+p • for both central and peripheral collisions (Au+Au, Cu+Cu). • - (Anti-)protons show xT scaling with similar value for peripheral. In central, • they show a larger value of neff. This is consistent with the observed baryon • enhancement at intermediate pT region (2-4 GeV/c). • - Need to measure (anti)proton spectra higher pT to knowwhether a similar • value of neff (as pions, or as in p+p) is obtained or not.