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Soft Hadron Production at RHIC

Soft Hadron Production at RHIC. Masahiro Konno (University of Tsukuba). 金野正裕（筑波大学）. <. ~. Outline. A Picture of Relativistic Heavy Ion Collisions Motivation (this talk) RHIC-PHENIX Single spectra at low p T ( 2 GeV/c) Single spectra at Intermediate p T (2~5 GeV/c)

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Soft Hadron Production at RHIC

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  1. Soft Hadron Production at RHIC Masahiro Konno (University of Tsukuba) 金野正裕（筑波大学）

  2. < ~ Outline • A Picture of Relativistic Heavy Ion Collisions • Motivation (this talk) • RHIC-PHENIX • Single spectra at low pT ( 2 GeV/c) • Single spectra at Intermediate pT(2~5 GeV/c) • Elliptic flow • Jet modification in the medium • Summary Results

  3. Z phenix (05) Bjorken energy density: x5 ! Well above ec (~1 GeV/fm3) from lattice QCD if assuming t = 1 fm/c. Picture of Relativistic Heavy Ion Collisions Space-time evolution • the created system lasts for only ~10 fm/c. time 4. Cooling, Freeze-out 3. Hadronization 2. Thermalization & QGP 1. Hard scattering

  4. Motivation Why soft particle production important to heavy ion collisions? => Soft particle production dominates the bulk yield. Through this study, we can know bulk properties of the system including collective flow. Hadrons interact strongly so it is a probe to know the evolution of the system and medium effect to hadronization. Useful Observables: - Single particle spectra - Azimuthal anisotropy of particle emission - Modification of jet shape/yield in the medium

  5. RHIC-PHENIX EM Calorimeter (PID) TOF (PID) - Central Arm Detectors (magnetic spectrometer) - Event Characterization detectors • Centrality and Reaction Plane • determined on an Event-by-Event basis. Aerogel Cherenkov (PID) Drift Chamber (momentum meas.) Tracking detectors (PC1,PC2,PC3)

  6. - - p (p) ID up to 8 GeV/c p (p) ID up to 4 GeV/c • PID is a powerful tool • to study hadron production! PID detectors (PID = Particle Identification) Aerogel Cherenkov No Cut p K+ Time of Flight (TOF) π+ Aerogel Veto Clear Proton Line!

  7. Single spectra (low pT) pT spectra for /K/p (mid rapidity) PRC 69, 034909 (2004) • <pT>: <K<p (mass dependence) • consistent with radial flow picture. Spectra for heavier particles has a convex shape due to radial flow. Tkin ~ 100 MeV <vT/c> ~ 0.5 particle spectra (blast wave fit) => kinetic freeze-out properties.

  8. Single spectra (low pT) Statistical mode fit particle ratios (statistical model) => chemical freeze-out properties. Tch ~160 MeV, gs ~1.0 • Hadron yields and spectra are consistent with • thermal emission from a strongly expanding • source (radial flow driven by pressure gradient). • The observed strangeness production is • consistent with complete chemical equilibrium. nucl-th/0405068

  9. Single spectra (intermediate pT) Nuclear Modification Factor RAA Au+Au 200 GeV nucl-ex/0603010 • High-pT suppression due to parton energy loss • in the medium (jet quenching). • The suppression patterns depend on particle type. • Protons are enhanced, while pions and kaons are suppressed.

  10. Baryon Enhancement p/ ratio PRL 91, 172301 (2003) Elliptic flow (v2) • - p/ ratio ~1 for central Au+Au at intermediate pT(2-4 GeV/c). • Larger than expected from jet fragmentation (measured in pp, e+e-). • Baryon / Meson difference at intermediate pT. • (on RAA (nuclear modification factor), v2 (elliptic flow)etc.) What is the origin of (anti-)proton enhancement at intermediate pT?

  11. Quark Recombination p/ Fries, R et al PRC 68 (2003) 044902 Greco, V et al PRL 90 (2003) 202302 Hwa, R et al PRC 70(2004) 024905 At intermediate pT, recombination of partons may be a more efficient mechanism of hadron production than fragmentation. A number of models predicted a turnover in the B/M ratio at pT just above where the available data finished… => pT spectra and particle ratio (Baryon/Meson) at higher pT provide most basic tool to study the hadronization mechanism.

  12. pT spectra for (anti-)protons Using Aerogel Cherenkov detector pT reach extended for (anti-)protons with fine centrality bins.

  13. p/ p/ vs. pT p/ * No feed-down correction. - p/ (pbar/) ratios seem to turn over at intermediate pT, and close to the value of fragmentation at higher pT. - Indicating transition from soft to hard at intermediate pT.

  14. p/ p/ vs. pT (centrality dependence) p/ * No feed-down correction. * p+p data (nucl-ex/0603010) - p/ ratios look to have a peak at intermediate pT(2-4 GeV/c). - Clear peak in central events than that in peripheral.

  15. Beam energy dependence in Cu+Cu • p/+ ratio :decreasing as a function of sNN. • p/- ratio: increasing as a function sNN. • Cu+Cu 22.5 GeV central data reaches the p+p values. • Cu+Cu 62.4 GeV central data is higher than that in 22.5 GeV. Suggesting a significant contribution of incoming protons (not produced protons) in lower energies Cu+Cu.

  16. Beam energy dependence of net protons nucl-ex/0313023 nucl-ex/0410003 SPS AGS - The shape of net proton distribution change dramatically with beam energy. - pbar/ ratio could be a good indicator of thermalization.

  17. RdAu vs. RAuAu preliminary preliminary Pions suppressed by a factor of ~5 with respect to protons Proton Cronin effect larger by ~30% • - In d+Au Particle type dependence: , K < p • (recombination in d+Au?) • Cronin effect (in d+Au) cannot account for the huge gap between • protons and pions in central Au+Au collisions.

  18. Elliptic Flow • Overlap region is like ellipsoid • at the beginning of collision. • Spatial anisotropy of the system • followed by multiple scattering of • particles (pressure gradient) in the • evolving system • - Spatial anisotropy => momentum anisotropy Z Reaction plane Y X Pz Py v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane Px

  19. Elliptic Flow M. Issah, A. Taranenko, nucl-ex/0604011 PHENIX preliminary • KET ~ mT–m0 • at y ~ 0 • Large elliptic flow observed. • - Mass ordering seen at low pT (<1.5 GeV/c). • KET scaling (for hadronic flow) vanish this mass • dependence but give clear splitting of meson/baryon v2.

  20. Elliptic Flow M. Issah, A. Taranenko, nucl-ex/0604011 PHENIX preliminary • Species dependence of v2 well accounted for • by scaling v2 and pT (KET) with # of quarks. • Evidence of partonic flow! v2 is developed before • hadrons form. v2q(pT) = v2h(pT/n)/n, v2q(KET) = v2h(KET/n)/n

  21. KET and Nq scaling works for . • Thermal s recombined to form .  meson -- A test of recombination ( -> KK) H.Masui CIPANP06 •  RAA looks like 0 rather than • proton even if mass() ~ mass(p). • Suggest that it’s not mass effect • (radial flow). • Mass ordering at pT <2 GeV/c. • For pT >2 GeV/c, v2 favors quark • composition rather than mass centrality: 20-60%

  22. Interests: - Mapping of momentum of trigger/partner. - Shape of away-side jet - Study the composition of the jets <= Focus on this. Jet modification in the medium • In heavy ion collisions, we expect: • (1) Scattered partons travel through the medium. • (2) Partons loose their energy because of a large gluon density. • (3) Suppression of high-pT leading particles. Observables: - Single spectra RAA -- to look at yield suppression - Angular correlation -- to look at jet modification Jet partons interact with the medium via the strong force. So jet can be a probe of the medium.

  23. C() Method of Jet study • Using two-particle correlation function. • Should treat large combinatorial back • ground (flow, decay) in heavy ion collisions. • Use mixed events for correction of pair acceptance.

  24. PHENIX Preliminary Jets at intermediate pT Meson vs. Baryon associated partner (for fixed Hadron trigger) W.Holzmann HardProbes06 • Particle species dependence of jet modification • BTW, how can hadrons at intermediate pT show • jet-like structure? => pickup of soft quarks by jets?

  25. Jet Associated Identified Conditional Yield Meson vs. Baryon associated partner (for fixed Hadron trigger) • Different pT trends of associated meson and baryon yields.

  26. Jet Associated Baryon to Meson Ratio Meson vs. Baryon associated partner (for fixed Hadron trigger) - Near-side: like p+p, Away-side: Larger B/M ratio. - Baryon/meson ratio can be an indicator for the degree of thermalization (density of comoving constituents) in a jet.

  27. < ~ • The medium created in heavy ion collisions: • (1) has bulk properties like collective flow, thermalization • (2) induce the jet modification. • Recombination models seem to be matched • to the experimental observations (B/M difference) : • (1) particle ratios (p/ etc.) • (2) Consistent quark scaling of v2 etc. • p/ ratio indicates a transition from soft to hard • production at intermediate pT. • Soft particle production (flow, recombination, etc.) • observed at low ~ intermediate pT ( 5 GeV/c). Summary Systematic study (especially for colliding species, √s) with enhanced PID capabilities.

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