STAR 1 APS Spring Meeting - April malisa Recent results from STAR M.A. Lisa, for the STAR Collaboration

STAR 2 APS Spring Meeting - April malisa Outline Year-1 data (Au+Au  s=130 GeV)  hadro-chemistry driving dynamical physics and consistent low p T ? central collisions  radial flow two-particle correlations   HBT  K-  correlations  balance functions non-central collisions  elliptical flow  HBT vs reaction-plane low-p T summary driving “high” p T ?  spectra compared to pp collisions  elliptical flow  two-particle correlations Summary

STAR 3 APS Spring Meeting - April malisa Particle ID in STAR pions kaons protons deuterons electrons STAR dE/dx dE/dx PID range:  (dE/dx) =.08] p  ~ 0.7 GeV/c for K /   ~ 1.0 GeV/c for  p/p RICH PID range: GeV/c for K /  GeV/c for  p/p RICH “kinks”: K     + VoVo Decay vertices K s   + +  -   p +  -   p +  +  -   +  -   +  +  +    + K - Topology Combinatorics K s   + +  -   K + + K -   p +  -   p +  +    + +  -   p +  -   from K + K - pairs K + K - pairs m inv same event dist. mixed event dist. background subtracted dn/dm

STAR 4 APS Spring Meeting - April malisa Vector meson production in Ultra-peripheral collisions Signal region: p T <0.15 GeV  0 P T 00 Au  qq b > 2R  electromagnetic interactions d  /dp T consistent with predictions for coherent  0 production

STAR 5 APS Spring Meeting - April malisa Kaon Spectra at Mid-rapidity vs Centrality Exponential fits to m T spectra: K+K+ K-K- (K + +K - )/2 KsKs STAR preliminary 0-6% 11-18% 26-34% 45-58% 58-85% Centrality cuts 0-6% 11-18% 26-34% 45-58% 58-85% Centrality cuts 0-6% 11-18% 26-34% 45-58% 58-85% Centrality cuts Good agreement between different PID methods

STAR 6 APS Spring Meeting - April malisa Statistical Thermal Model: Fit Results  b driven by  p/p, K - /K + T driven by p/ 

STAR 7 APS Spring Meeting - April malisa Something different vs p T ? Particle/Antiparticle Ratios STAR Preliminary Within the errors no or very small p T dependence (as one might expect from simply flow) see talk by B. Norman

STAR 8 APS Spring Meeting - April malisa p T spectra: Flavor Dependence Enhancement at ~2 GeV is not specific to baryons  mass effect  simplest explanation: radial flow)

STAR 9 APS Spring Meeting - April malisa Thermal motion superimposed on radial flow Fits by M. Kaneta Hydro-inspired “blast-wave” thermal freeze-out fits to , K, p,  T th = 107 ± 8 MeV hydro predictions reproduce early p T spectra preliminary

STAR 10 APS Spring Meeting - April malisa Hydro attempts to reproduce data R out R side R long : model waits too long before emitting K T dependence approximately reproduced  correct amount of collective flow Right dynamic effect / wrong space-time evolution???  the “RHIC HBT Puzzle” generic hydro model emission timescale too long

STAR 11 APS Spring Meeting - April malisa Blastwave: radii vs p T STAR data blastwave: R=13.5 fm,  freezeout =1.5 fm/c Magnitude of flow and temperature from spectra can account for observed drop in HBT radii via x-p correlations, and R o <R s …but emission duration must be small Four parameters affect HBT radii p T =0.4 p T =0.2 K K

STAR 12 APS Spring Meeting - April malisa From R long :  t kinetic  = 8-10 fm/c Simple Sinyukov formula (S. Johnson) –R L 2 =  t kinetic  2 T/m T  t kinetic  = 10 fm/c (T=110 MeV) B. Tomasik (~3D blast wave) –  t kinetic  = 8-9 fm/c

STAR 13 APS Spring Meeting - April malisa Kaon – pion correlation: dominated by Coulomb interaction Smaller source  stronger (anti)correlation K-p correlation well-described by: Blast wave with same parameters as spectra, HBT But with non-identical particles, we can access more information… STAR preliminary

STAR 14 APS Spring Meeting - April malisa Initial idea: probing emission-time ordering Catching up: cos  0 long interaction time strong correlation Ratio of both scenarios allow quantitative study of the emission asymmetry Moving away: cos  0 short interaction time weak correlation Crucial point: kaon begins farther in “out” direction (in this case due to time-ordering) purple K emitted first green  is faster purple K emitted first green  is slower

STAR 15 APS Spring Meeting - April malisa measured K-  correlations - natural consequence of space-momentum correlations clear space-time asymmetry observed C+/C- ratio described by: –“standard” blastwave w/ no time shift Direct proof of radial flow-induced space-momentum correlations Kaon = 0.42 GeV/c Pion = 0.12 GeV/c STAR preliminary

STAR 16 APS Spring Meeting - April malisa Balance functions: How they work For each charge +Q, there is one extra balancing charge –Q. Charges: electric, strangeness, baryon number Bass, Danielewicz, Pratt (2000)

STAR 17 APS Spring Meeting - April malisa Balance functions - clocking the evolution Model predictions l Wide  early creation of charges l nn, e + e - collisions l Narrow  late hadronization / (Q)GP l central RHIC? Pythi a (wide ) Bjorken (narrow) Bass, Danielewicz, Pratt (2000)

STAR 18 APS Spring Meeting - April malisa Balance Functions in STAR STAR Preliminary  Pairs Peripheral collisions approach Hijing (NN) Clear narrowing for central collisions In Bass/Danielewicz/Pratt model, central data consistent with: T chem ~ 175 MeVT kinetic ~ 110 MeV  t chem  = 10 fm/c  t kinetic  = 13 fm/c

STAR 19 APS Spring Meeting - April malisa p T (GeV/c) Noncentral collision dynamics hydro evolution hydro reproduces v 2 (p RHIC for p T < ~1.5 GeV/c system response (pressure): x-space  p-space anisotropy again: correct p-space dynamical effect freezeout shape  evolution duration? STAR preliminary see talk of J. Fu v2v2 flow of neutral strange particles PID beyond p T =1 GeV/c

STAR 20 APS Spring Meeting - April malisa Blast-wave fit to low-p T v 2 (p T,m) STAR, PRL (2001) spatial anisotropy indicated consistent with out-of-plane extended source (but ambiguity exists)  p =0°  p =90° R side (large) R side (small) possible to “see” via HBT relative to reaction plane? expect large R side at 0  small R side at 90  2 nd -order oscillation

STAR 21 APS Spring Meeting - April malisa Out-of-plane extended source ~ short system evolution time STAR preliminary Same blastwave parameters as required to describe v 2 (p T,m), plus two more: –R y = 10 fm  = 2 fm/c Both p-space and x-space anisotropies contribute to R(  ) –mostly x-space: definitely out-of-plane calibrating with hydro,  freezeout ~ 7 fm/c R os 2 - new “radius” important for azimuthally asymmetric sources

STAR 22 APS Spring Meeting - April malisa RHIC 130 GeV Au+Au Disclaimer: all numbers (especially time) are approximate Low-p T dynamics — one (naïve?) interpretation: rapid evolution and a “flash” K-  K * yield

STAR 23 APS Spring Meeting - April malisa Physics at “high” p T (~6 GeV/c) hadrons q q leading particle suppressed leading particle suppressed hadrons q q leading particle leading particle Jets modified in heavy ion collisions -Parton Energy loss in dense nuclear medium -Modification of fragmentation function 1) high-pT suppression relative to NN (especially in central collisions) 2) finite, non-hydro v 2 due to energy loss (non-central collisions) see talk of J. Klay y Jet 1 Jet 2 x

STAR 24 APS Spring Meeting - April malisa Inclusive spectra preliminary Statistical errors only

STAR 25 APS Spring Meeting - April malisa Power law fits Power Law: “pQCD inspired” Fits wide range of hadronic spectra: ISR  Tevatron Good fits at all centralities (  2 /ndf~1) Smooth dependence on centrality most peripheral converges to Nucleon- Nucleon reference (UA1) (p 0, n highly correlated) STAR preliminary

STAR 26 APS Spring Meeting - April malisa Central collisions: suppression of factor 3 (confirms PHENIX) Peripheral collisions: “enhancement” consistent with zero (uncertainties due to and NN reference) Smooth transition central  peripheral preliminary low p T scales as

STAR 27 APS Spring Meeting - April malisa Azimuthal anisotropy - theory and data Preliminary p T <2 GeV: good description by hydrodynamics p T >4 GeV: hydro fails but finite v 2 finite energy loss  finite v 2 at high p T sensitive to gluon density y Jet 1 Jet 2 x model: Gyulassy, Vitev and Wang, (2001) Low p T : parameterized hydro High p T : pQCD with GLV radiative energy loss

STAR 28 APS Spring Meeting - April malisa V2 centrality dependence Preliminary all centralities: finite v 2 at high p T

STAR 29 APS Spring Meeting - April malisa But are we looking at jets? - 2 Particle Correlations Trigger particle p T >4 GeV/c, |  azimuthal correlations for p T >2 GeV/c short range  correlation: jets + elliptic flow long range  correlation: elliptic flow  subtract correlation at |      NB: also eliminates the away-side jet correlations extracted v 2 consistent with reaction-plane method what remains has jet-like structure  first indication of jets at RHIC! preliminary 0-11%

STAR 30 APS Spring Meeting - April malisa STAR vs UA1 UA1: Phys. Lett. 118B, 173 (1982) (most events from high E T trigger data) UA1: very similar analysis (trigger p T >4 GeV/c) But sqrt(s)=540 GeV, |  |<3.0 preliminary

STAR 31 APS Spring Meeting - April malisa Brief Summary chemistry: wide range of particle yields well-described by thermal model T chem ~ 170 MeV  b ~ 45 MeV p T dependence of yields (e.g. baryon dominance) consistent with radial flow dynamics at p T < 2 GeV/c “real” model (hydro) reproduces flow systematics, but not HBT finger-physics analysis of probes sensitive to time: short system evolution, then emission in a flash T chem ~ 170 MeVT kin ~ 110 MeV t chem ~ 10 fm/ct kin ~ 13 fm/c naïve? unphysical? useful feedback to modelers? dynamics at p T > 2 GeV/c hydro picture breaks down preliminary jet signal observed evidence for medium effects at high p T

STAR 32 APS Spring Meeting - April malisa THE END

STAR 33 APS Spring Meeting - April malisa Ratios driving the thermal fits Plots from D. Magestro, SQM2001

STAR 34 APS Spring Meeting - April malisa Blast Wave Mach I - central collisions  R  s Ref. : E.Schnedermann et al, PRC48 (1993) 2462 flow profile selected (  t = s (r/R max ) n ) mtmt 1/m t dN/dm t T fo A tt 2-parameter (T fo,  t ) fit to m T distributions

STAR 35 APS Spring Meeting - April malisa Blastwave Mach II - Including asymmetries R tt –Flow Space-momentum correlations = 0.6 (average flow rapidity) Assymetry (periph) :  a = 0.05 –Temperature T = 110 MeV –System geometry R = 13 fm (central events) Assymetry (periph event) s 2 = 0.05 –Time: emission duration  = emission duration analytic description of freezeout distribution: exploding thermal source

STAR 36 APS Spring Meeting - April malisa Comparison to Hijing Ratio of integrals over correlation peak: 1.3 Hijing fragmentation is independent of quenching

STAR 37 APS Spring Meeting - April malisa High-p T highlights Qualitative change at 2 GeV Jet-like structure

STAR 38 APS Spring Meeting - April malisa measured K-  correlations - natural consequence of space-momentum correlations clear space-time asymmetry observed C+/C- ratio described by: –static (no-flow) source w/  t K  -  t   =4 fm/c –“standard” blastwave w/ no time shift We “know” there is radial flow  further evidence of very rapid freezeout Direct proof of radial flow-induced space-momentum correlations Kaon = 0.42 GeV/c Pion = 0.12 GeV/c STAR preliminary