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

Masahiro Konno for the PHENIX Collaboration(University of Tsukuba)

1JPS @ Yamagata, 9/21/2008

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)

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PID Spectra in p+p collisions

- 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

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Phenix Preliminary Phenix Preliminary

mT Spectra for identified particles

- 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

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exp(−(mT −m) /Tinv )

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Tinvπ ~ Tinv

K ~ Tinvp ≈ 200MeV

* Feed-down correction not applied. If applied, Tinv increased by ~ 10-15 %

Hard

Soft

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Energy dependence of Tinv

- 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

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Open: p+p/p+pbarClosed: Pb+Pb, Au+Au

- 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.

Mesons

Baryons

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Baryon-meson difference in mT spectra

Baryon/Meson 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). €

p /π ratios

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(Λ+ Λ) /2K ratios

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Open: p+p/p+pbarClosed: Au+Au

- π0 spectra are described over a wide pT range with pQCD calculation within experimental and theoretical uncertainties.

High pT Spectra - pQCD description

p+p 200 GeV p+p 62.4 GeV

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PRD76(2007)051106

xT Scaling in p+p Collisions

- Invariant cross section for single-particle inclusive reaction is given by the general scaling formula:

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E d3σdp3

= 1pTn F(xT )

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xT = 2pT / swhere

- 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.

- Inclusion of QCD into the above equation leads to:

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E d3σdp3

= 1

sn(xT , s )

G(xT )

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≤

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Ref: PL 42B 461(1972), PRD11(1975)1199

xT Scaling for PID Spectra

- 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

Pions Antiprotons

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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

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n(xT ) =log(Yield (xT ,62.4) /Yiled (xT ,200))

log(200 /62.4)

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E d3σdp3

= ( As)n xT

−m

p

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p

Data points: method (1)Lines: method (2)

π0 p pbar

neff 6.45 ± 0.23 6.84 ± 0.47 6.46 ± 0.18

(Fit range: xT = 0.07 – 0.20)

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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.

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RAA =Yield(A + A)

< Ncoll >Yield(p+ p)where <Ncoll> is the number of binary NN collisions

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- 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.

xT Scaling in A+A Collisions

neff vs. Npart

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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 know whether a similar value of neff (as pions, or as in p+p) is obtained or not.

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