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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. Introduction. Measure transverse momentum spectra for identified particles as reference to heavy ion data. - PowerPoint PPT Presentation
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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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