Flow Measurement in PHENIX Masahiro Konno (Univ. of Tsukuba) for the PHENIX Collaboration

Outline Physics Motivation Method, PHENIX detector Single Particle Spectra: - p/ ratios - Npart Scaling of p/ in Au+Au, Cu+Cu - RAA in Au+Au, Cu+Cu Elliptic Flow: - Scaling properties of v2 Summary

Single Particle Spectra

Physics Motivation - Baryon Enhancement - RAA p/ ratio Au+Au 200 GeV PRC 74, 024904 (2006) PRL 91, 172301 (2003) p/ ratio Au+Au 200 GeV . - 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. - Several models try to reproduce the data. What is the origin of (anti-)proton enhancement at intermediate pT(2~5 GeV/c) ? A systematic study at intermediate pT is necessary over different collisions systems. 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.

PHENIX detector - - EM Calorimeter (PID) TOF (PID) - Central Arm Detectors Centrality and Reaction Plane determined on an E-by-E basis. PID (particle identification) is a powerful tool to study hadron production. Aerogel Cherenkov (PID) Aerogel Cherenkov (ACC) Time of Flight (TOF) p (p) ID up to 7 GeV/c - p (p) ID up to 4 GeV/c - Drift Chamber (momentum meas.) p K+ Tracking detectors (PC1,PC2,PC3) π+ Veto for proton ID

pT spectra (Cu+Cu √sNN = 200 GeV) Phenix preliminary (Anti-) protons ACC - Cu+Cu is a smaller system compared to Au+Au. pT reach extended for (anti-)protons with fine centrality bins. <= (1) Aerogel Cherenkov, (2) Enough statistics in Au+Au/Cu+Cu NOTE: No weak decay feed-down correction applied.

pT spectra (p+p √s = 200 GeV) Phenix preliminary TOF High statistics 200 GeV p+p data. More than10 times statistics used compared to previous Run3 p+p analysis. The p+p data provides baseline spectra to heavy ion data, and it is important to quantify in-medium nuclear effects in heavy ion collisions at RHIC. NOTE: No weak decay feed-down correction applied.

p/ vs. pT Au+Au 200 GeV ACC p/ p/ - p/ (pbar/) ratios seem to turn over at intermediate pT, and be close to the value of fragmentation at higher pT. - Clear peak in central events than that in peripheral. - Indicating a transition from soft to hard at intermediate pT. NOTE: - No weak decay feed-down correction applied. - p+p data (PRC 74, 024904 (2006))

p/ vs. pT Cu+Cu 200 GeV ACC p/ p/ Phenix preliminary p/ p/ Baryon enhancement observed in Cu+Cu at 200 GeV. - pT dependence in Cu+Cu is similar to that in Au+Au. => How about the magnitude as a function of centrality? see Next. NOTE: No weak decay feed-down correction applied.

p/ vs. Npart1/3 3.0 - 4.0 GeV/c 4.0 - 5.0 GeV/c 2.0 - 3.0 GeV/c Cu+Cu 200 GeV vs. Au+Au 200 GeV p/ vs. Npart1/3 pT Phenix preliminary 3.0 - 4.0 GeV/c 4.0 - 5.0 GeV/c 2.0 - 3.0 GeV/c 0.6 - 1.5 GeV/c 1.0 - 2.0 GeV/c Phenix preliminary - Centrality dependence in Cu+Cu looks similar to that in Au+Au (Npart scaling at same sqrt(sNN)!). - Even though overlap region has a different geometrical shape. - Slight difference in the magnitude seen. TOF (<3 GeV/c) ACC (>3 GeV/c) NOTE: No weak decay feed-down correction applied.

p/ vs. pT (Low pT) - Radial flow - TOF (Anti-)protons Phenix preliminary Phenix preliminary - Radial flow: transverse expansion of the system - At low pT, p/ shows weak and decreasing Npart dependence because inverse slope (from mT exponential fitting) also shows it. NOTE: No weak decay feed-down correction applied.

p/ vs. pT (Intermediate pT) TOF, ACC - Radial flow (ex. blast-wave fit) - Au+Au 200 GeV Spectra for heavier particles has a convex shape due to radial flow. Using Blast-wave fitting, try to estimate p/ ratio as a function of pT. NOTE: No weak decay feed-down correction applied. (hydro p)/(hydro ) (hydro p)/(real ) Hydrodynamic contribution for protons is one of the explanations (baryon enhancement). - Other contribution is also needed: Recombination, Jet fragmentation Central Peripheral

p/ vs. pT (Intermediate pT) ACC - Quark Recombination - p/ Phenix preliminary Now, we find a similar trend. ACC TOF 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… Fries, R et al PRC 68 (2003) 044902 Greco, V et al PRL 90 (2003) 202302 Hwa, R et al PRC 70(2004) 024905 etc. NOTE: No weak decay feed-down correction applied.

p/ vs. pT Cu+Cu 62 GeV vs. Au+Au 62 GeV TOF Phenix preliminary - Again, look at centrality dependence of p/ ratios. - Similar tendencies as at 200 GeV.

p/ vs. Npart1/3 Cu+Cu 62 GeV vs. Au+Au 62 GeV TOF Phenix preliminary Npart scaling of p/ also at 62 GeV in Au+Au/Cu+Cu. NOTE: No weak decay feed-down correction applied.

p/ vs. Npart1/3 ,(dET/dy)1/3 Au+Au 200 GeV vs. Au+Au 62 GeV TOF Phenix preliminary Phenix preliminary No Npart scaling of p/ (pbar/) in Au+Au between 62 GeV and 200 GeV. dET/dy scaling of pbar/ seen. => Proton production (at this pT range) at 62 GeV is partly from baryon transport, not only pair production. Nuclear stopping is still large at 62 GeV. NOTE: No weak decay feed-down correction applied.

(dET/dy)/Npart vs. Npart Phenix preliminary R. Armendariz (2006) - Transverse energy density is a connection key.

* No weak decay feed-down correction applied. Beam energy dependence of p/ T. Chujo (QM ‘06) - p/+ ratio : decreasing as a function of sNN. p/- ratio : increasing as a function sNN. Suggesting a significant contribution of baryon transport at lower energies. * No weak decay feed-down correction applied.

* No weak decay feed-down correction applied. Beam energy dependence of p/ Antiproton is a good probe to study the excitation function. * No weak decay feed-down correction applied.

RAA vs. pT TOF Phenix preliminary Similar Npart dependence NOTE: Systematic errors (~10%) for overall normalization not shown. Similar Npart dependence for Au+Au / Cu+Cu. (Npart scaling of RAA) - Cronin effect in peripheral Proton, antiproton are enhanced at 1.5 - 4 GeV/c for all centralities. (enhancement > suppression) - Suppression is seen for pions, kaons. NOTE: No weak decay feed-down correction applied.

Elliptic Flow

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 Py Pz v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane Px

KET Scaling of v2 A. Taranenko (QM ‘06) Large elliptic flow observed. nucl-ex/0608033 KET ~ mT–m0 at y ~ 0 PHENIX preliminary 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.

No.-of-Constituent-Quarks Scaling of v2 nucl-ex/0608033 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

Eccentricity Scaling of v2 At mid rapidity, v2 (pt,M,b,A)/n~ F(KET/n)*ε(b,A)? ε(b,A): integral elliptic flow of charged hadrons KET : transverse kinetic energy n: number of quarks

Eccentricity Scaling of v2 M. Shimomura (JPS ‘06) 2.0-4.0 GeV/c 1.0-2.0 GeV/c 0.2-1.0 GeV/c - ε(b,A)/v2(b,A) ~ 3.1+/-0.2 v2/eccentricity vs. Npart has different slopes for different pT. Black: 200GeV Red: 62.4GeV

Energy and System Size dependence of v2 Black AuAu 200GeV Red AuAu 62.4GeV Green CuCu 200GeV Blue CuCu 62.4GeV 0.2-1.0 GeV/c 1.0-2.0 GeV/c v2 is not scaled by Npart.

Energy and System Size dependence of v2 Black AuAu 200GeV Red AuAu 62.4GeV Green CuCu 200GeV Blue CuCu 62.4GeV 0.2-1.0 GeV/c 1.0-2.0 GeV/c 2.0-4.0 GeV/c v2 looks rather scaled by eccentricity.

Summary pT reach of PID (especially for p, pbar) extended with: (1) High statistics Au+Au/Cu+Cu data (2) New PID detector (Aerogel) (Anti-)Proton enhancement is observed in Au+Au/Cu+Cu collisions at 200/62 GeV. p/ ratios: (1) Indicating a transition from soft to hard production at intermediate pT. (2) Npart scaling (dET/dy scaling) over different collision systems. (3) Recombination + radial flow would explain the pT, Npart dependencies. - PID v2: (1) KET scaling, NCQ scaling (2) Eccentricity scaling - Systematic study of PID spectra, elliptic flow (and jet correlations) for different collision systems can provide information to understand the hadron production mechanisms.

Backup slides

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.

v2 of phi meson v2 vs KET – is a good way to see if v2 for the φ follows that for mesons or baryons v2 /n vs KET/n scaling clearly works for φ mesons as well

No.-of-Constituent-Quarks Scaling of v2 PHENIX Preliminary KET/n scaling works for the full measured range with deviation less than 10% from the universal scaling curve