RCNP 研究会, 10/29-30/ 金野正裕（筑波大学） RHIC における陽子反陽子生成の系統的測定

RCNP 研究会, 10/29-30/ RHIC Findings (1) Jet Quenching - In central Au+Au collisions, hadrons are suppressed at high p T. - The suppression is a final state effect (parton energy loss). - Away-side jet peak disappeared in central Au+Au collisions.

RCNP 研究会, 10/29-30/ Particles & Medium Effects - Suppression/Enhancement has particle-type dependence. => Baryon/Meson difference in yields and emission patterns at intermediate p T (2-5 GeV/c). 0 Baryon enhancedB/M Splitting of v 2 RHIC Findings (2)

RCNP 研究会, 10/29-30/ Hadron Production in RHI Collisions Hadronization Interactions in the medium Low-p T (soft) Thermal emission Quark recombination Thermalization Collective flow High-p T (hard)Jet fragmentation Hard scattering Jet quenching - There are multiple hadronization mechanisms at intermediate p T. - The relative contributions and particle-type dependence are not yet fully understood. Understanding Baryon/Meson difference at intermediate p T. => What is the origin?

RCNP 研究会, 10/29-30/ Aerogel Cherenkov,TOF-W (PID) EM Calorimeter (PID) TOF-E (PID) Drift Chamber (momentum meas.) Pad Chambers (tracking) PHENIX detector - Beam Beam Counter - Zero Degree Calorimeter Global detectors:

RCNP 研究会, 10/29-30/ Particle Identification Time of Flight (  ~120 ps) Aerogel Cherenkov (n=1.011) Veto for proton ID “New” Time of Flight (  ~90 ps) MRPC typeScint.+PMT type detector upgrade

RCNP 研究会, 10/29-30/ Proton and Antiproton p T spectra p T reach extended up to 6 GeV/c for p(  p) with fine centrality bins. (1) Aerogel Cherenkov (2) High statistics NOTE: No weak decay feed-down correction applied. Au+Au  s NN = 200 GeVCu+Cu  s NN = 200 GeV p+p  s NN = 200 GeV

RCNP 研究会, 10/29-30/ Freeze-out Properties

RCNP 研究会, 10/29-30/ Particle Yield dN/dy at mid rapidity - Particle yields are (roughly) scaled with N part btw. Au+Au and Cu+Cu. - dN/dy(Cu+Cu) >~ dN/dy(Au+Au) at smaller N part. - Statistical model describes their ratios with few parameters (T,  ). Au+Au/Cu+Cu/p+p (  s NN = 200 GeV) Au+Au/Cu+Cu/p+p (  s NN = 62.4 GeV)  K p

RCNP 研究会, 10/29-30/ Clear hadron mass dependence: larger for heavier particles. => Consistent with radial flow picture. - increases with N part. it is clearly seen for (anti)proton. Mean Transverse Momentum  K p Au+Au/Cu+Cu/p+p (  s NN = 200 GeV) Au+Au/Cu+Cu/p+p (  s NN = 62.4 GeV)

RCNP 研究会, 10/29-30/ Blast-wave model is a parameterization within a simple boost-invariant model with transverse collective flow. p T spectra reflecting thermal freeze-out temperature and transverse flow at final state. * Ref: PRC48(1993)2462 (* Resonance decay feed-down correction not applied. Instead, tighter p T fitting range used.  ; GeV/c K; GeV/c, p/pbar; GeV/c) Spectra for heavier particles has a convex shape due to radial flow.  2 map Blast-wave Model Fit T fo ~120 MeV,  T ~0.7

RCNP 研究会, 10/29-30/ : increasing with N part. - N part scaling of between Au+Au and Cu+Cu. - Almost same at √s NN = 62.4, 200 GeV. ~0.5 Transverse Flow Velocity Au+Au/Cu+Cu/p+p (  s NN = 200 GeV) Au+Au/Cu+Cu/p+p (  s NN = 62.4 GeV)

RCNP 研究会, 10/29-30/ T fo : decreasing with N part. - N part scaling of T fo between Au+Au and Cu+Cu. - Almost same T fo at √s NN = 62.4, 200 GeV. T fo ~120 MeV Kinetic Freeze-out Temperature Au+Au/Cu+Cu/p+p (  s NN = 200 GeV) Au+Au/Cu+Cu/p+p (  s NN = 62.4 GeV)

RCNP 研究会, 10/29-30/ Summary - Freeze-out properties Characterizing bulk properties: - Chemical freeze-out - Kinetic freeze-out => Hadron production at low p T : “Thermal emission + Radial flow” Scaling properties between different systems: - Chemical/kinetic freeze-out properties show similarities between different collision systems. - N part scaling of freeze-out properties (Au+Au, Cu+Cu), * even though the overlapped region has a different shape. => System volume N part is a control parameter. * Particle yield: (Cu+Cu) > (Au+Au) at smaller N part - Similarity at  s NN = 200 and 62.4 GeV.

RCNP 研究会, 10/29-30/ Baryon Enhancement

RCNP 研究会, 10/29-30/ (Anti-)proton enhancement observed/confirmed in 200 GeV Au+Au/Cu+Cu. - Larger than expected from jet fragmentation (measured in pp, e + e - ). - p/  (  p/  ) ratios turn over at 2~3 GeV/c,and fall towards the ratio in p+p. Baryon enhancement at  s NN = 200 GeV p/  p/p/

RCNP 研究会, 10/29-30/ Au+Au  s NN = 200 GeV  /K 0 s STAR, nucl-ex/ Strange Baryon enhancement Baryon enhancement seen in strange.

RCNP 研究会, 10/29-30/ Baryon enhancement at  s NN = 62.4 GeV p/  p/p/ - (Anti-)proton enhancement observed/confirmed in 62.4 GeV Au+Au/Cu+Cu. - Similar p T dependence as at 200 GeV.

RCNP 研究会, 10/29-30/ Cu+Cu vs. Au+Au (200 GeV) - N part scaling of p/  (  p/  ) at same √s NN. - The ratios are controlled by the initial overlap size of colliding nuclei, even though overlap region has a different geometrical shape. p/  ratio vs. N part 1/3 Cu+Cu vs. Au+Au (62.4 GeV)

RCNP 研究会, 10/29-30/ Comparison with p+p spectra (reference) in binary collision scaling. - Proton, antiproton are enhanced at GeV/c for all centralities. - Suppression is seen for , K. Nuclear Modification Factor R AA

RCNP 研究会, 10/29-30/ Proton is enhanced for all centralities, while  /K are suppressed. Comparison of R AA in Au+Au/Cu+Cu Pion R AA (p T =2.25 GeV/c)Proton R AA (p T =2.25 GeV/c) R AA (Cu+Cu) > R AA (Au+Au)

RCNP 研究会, 10/29-30/ (Cu+Cu: b=0.0 fm, Au+Au: b=8.6 fm) ~117 Comparison of Au+Au and Cu+Cu ~100 Cu+Cu: good resolution at smaller N part Glauber model calculation Even though N coll -N part relation is almost same between Au+Au and Cu+Cu, the geometrical overlap shape is different. - R AA (Cu+Cu) > R AA (Au+Au) - Geometrical shape : Au+Au more deformed - No. of N-N scatterings per N : narrow peak in Cu+Cu

RCNP 研究会, 10/29-30/ Beam energy dependence

RCNP 研究会, 10/29-30/ Beam energy dependence of enhancement - p/  + ratio : decreasing as a function of  s NN. -  p/  - ratio : increasing as a function  s NN. -Antiproton is a good probe to study the baryon enhancement. * No weak decay feed-down correction applied. p/  p/p/

RCNP 研究会, 10/29-30/ No N part scaling of p/  (  p/  ) in Au+Au between 62.4 and 200 GeV. - Transverse energy density dE T /d  scaling of p/  is favored. - dE T /d  is a connection key between different √s NN. p/  ratio vs. (dE T /d  ) 1/3 Proton production at 62.4 GeV is partly from baryon number transport, not only proton-antiproton pair production.

RCNP 研究会, 10/29-30/ Energy loss per nucleon: 73±6 GeV Net proton distribution it drastically changes with beam energy. BRAHMS, PRL 93 (2004)

RCNP 研究会, 10/29-30/ Au+Au/Cu+Cu/p+p (  s NN = 200 GeV) Au+Au/Cu+Cu/p+p (  s NN = 62.4 GeV) Chemical Potential -  q (200 GeV) : ~8 MeV, independent of N part -  q (62.4 GeV) : increasing with N part => more baryon stopping at central

RCNP 研究会, 10/29-30/ Summary - Baryon enhancement Baryon enhancement: - Proton and antiproton enhancement confirmed at intermediate p T (2-5 GeV/c) in Au+Au/Cu+Cu. A turnover of p/  ratio seen at p T = 2-3 GeV/c. - In terms of binary collision scaling, (anti)protons are enhanced while pions/kaons are suppressed. Low energy 62.4 GeV data: - At lower energy 62.4 GeV, proton production seems to be more affected by baryon number transport process. => Antiproton is a good indicator of the baryon enhancement. Scaling properties between different systems: - N part scaling of p/  (  p/  ) - dE T /d  scaling of  p/ 

RCNP 研究会, 10/29-30/ Two-component model (Soft+Hard)

RCNP 研究会, 10/29-30/ high-p T particles low-p T particles Particle production in expanding matter z-axis time x-axis time

RCNP 研究会, 10/29-30/ Soft component : Thermal emission + Radial flow - Described by Blast-wave model - N part scaling seen - Thermal distribution extrapolated up to high p T Hard component : Jet fragmentation + Jet suppression - Measured p+p spectra - N coll scaling - Constant suppression factor (power-law distribution & fractional energy loss) Two-component Model (Soft+Hard)

RCNP 研究会, 10/29-30/ Hard component (in p+p) at high p T depends on  s. - In Au+Au, suppression effect should be taken into account. Hard component in p+p and Au+Au p+p  s NN = 200 GeV 200 GeV 62.4 GeV Au+Au 200 GeV (pi0: diamond, h+h-: circle)

RCNP 研究会, 10/29-30/ Pion p T spectra Au+Au 200 GeV ++ -- Soft LineHard Line Reproduce the measured pion p T spectra.

RCNP 研究会, 10/29-30/ Pion fraction vs. p T Au+Au 200 GeV ++ -- Soft Hard Residual

RCNP 研究会, 10/29-30/ Proton p T spectra Au+Au 200 GeV p pp Soft LineHard Line Reproduce the measured proton p T spectra.

RCNP 研究会, 10/29-30/ Proton fraction vs. p T Au+Au 200 GeV p pp Soft Hard Residual R AA vs. N part

RCNP 研究会, 10/29-30/ Proton p T spectra Au+Au 200 GeV p pp Soft LineHard Line Using pion’s R AA for suppression factor.

RCNP 研究会, 10/29-30/ Proton fraction vs. p T Au+Au 200 GeV p pp Soft Hard Residual Need 3rd component ?

RCNP 研究会, 10/29-30/ Fraction of soft and hard components ++ -- p pp - Both soft and hard components are necessary to reproduce the hadron spectra at intermediate p T (2-5 GeV/c). - Soft component is extended to higher p T in central. - Intermediate p T : Hard pions vs. Soft protons - Cross point (S=H) vs. p T -

RCNP 研究会, 10/29-30/ Summary - Two-component model Two-component model: - Reproduce the measured p T spectra for pions and protons with a consistent way. - Identify crossover region from soft to hard hadron production at intermediate p T (2-5 GeV/c). Baryon/Meson difference: - Intermediate pT: “Hard” pions vs. “Soft” protons - Origin of baryon enhancement is radial flow. It pushes heavier particles to higher p T. Baryon/Meson difference is trivial?

RCNP 研究会, 10/29-30/ Quark Flow vs. Hadron Flow

RCNP 研究会, 10/29-30/ Quark recombination - One of the hadronization mechanisms. - Recombination of thermal quarks in local phase space: q  q  Meson, qqq  Baryon - At intermediate p T, (recombination) > (fragmentation) because quark distribution is thermal: ~exp(-m T /T). - At high p T, fragmentation (power-law shape) would be dominant. Fries, R et al PRC 68 (2003) Greco, V et al PRL 90 (2003) Hwa, R et al PRC 70(2004)

RCNP 研究会, 10/29-30/ p/  vs. p T - Baryon enhancement & quark number scaling of v 2 explained by “Quark recombination” - v 2 at quark level => Collective flow at quark level Applicability of quark recombination model - In a simple recombination picture, radial flow cannot be distinguished between hadron and quark phases. => Can we separate hadron flow and quark flow ? v 2 /n vs. KE T /n

RCNP 研究会, 10/29-30/ Ideal gas: P=(1/3)  - Entropy conservation - Longitudinal expansion & Transverse expansion z x y 1+1D Adiabatic Expansion  bj vs. N p - cooling curves - t fo fixed at 10 fm/c at most central T scaled with (  bj ) 1/4 at t = 1 fm/c Cooling stopped at T fo

RCNP 研究会, 10/29-30/ More central collisions freeze-out later at lower temperature. - Consistent with freeze-out condition: (t)=R(t) - Even if quark phase is created before hadronization, hadronic scattering should be taken into account. Freeze-out Time & Temperature Freeze-out time vs. N p - As expected, T fo is lower than T ch. Different centrality dependences. - T fo dropping is consistent with 1+1D adiabatic expansion. Freeze-out temperature vs. N p

RCNP 研究会, 10/29-30/ Conclusions - Systematic measurement of proton and antiproton p T spectra (Au+Au, Cu+Cu, p+p at  s NN = 200/62.4 GeV) - Proton and antiproton enhancement confirmed at intermediate p T (2-5 GeV/c). - Antiproton is a good indicator for study of the baryon enhancement. - p/  ratio & freeze-out properties show N part scaling between Au+Au and Cu+Cu at same  s NN. The Initial volume (~N part ) of colliding nuclei is a control parameter. - Baryon enhancement is caused by transverse radial flow - p T and centrality dependences are described by two-component model. - Intermediate p T (2-5 GeV/c): hard pions vs. soft protons - Chemical/Kinetic Freeze-out temperatures provide a hint for further expansion at hadronic stage.