A Strange Perspective – Preliminary Results from the STAR Detector at RHIC

The STAR Collaboration Brazil: Universidade de Sao Paolo China: IHEP - Beijing, IPP - Wuhan England: University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute – Munich University of Frankfurt Poland: Warsaw University, Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR–Dubna, IHEP-Protvino U.S. Labs: Argonne, Berkeley, Brookhaven National Labs U.S. Universities: Arkansas, UC Berkeley, UC Davis, UCLA, Carnegie Mellon, Creighton, Indiana, Kent State, MSU, CCNY, Ohio State, Penn State, Purdue,Rice, Texas A&M, UT Austin, Washington, Wayne State, Yale Spokesperson: John Harris Institutions: 36 Collaborators: 415 Students: ~50

What are we looking for? What is the initial environment like for particle production? Net baryon density What happens during the initial particle production? Strangeness production Quark coalescence? Are re-interactions significant? Rescattering of hadrons Equilibration of strangeness Radial flow Baryon / antibaryon ratios Strange hadron / h- ratios Quark-counting ratios Hadron ratios vs. pt Strange baryon ratios Mt slopes

Data Quality 1: Peaks _ ~0.84 L/ev, ~ 0.61 L/ev ~0.006 X-/ev, ~0.005 X+/ev _ ~1.6 K0s/ev Clear peak

Data Quality 2: Resonances First measurement in heavy ion collisions STAR Preliminary K* f _ K* Mass and width are consistent with PDG book convoluted with TPC resolution

Data Quality 3: Lifetime check Star Preliminary L Star Preliminary K0s Lifetime : 8.03 ±0.05 (stat)cm PDG Value : 7.89 cm Lifetime : 2.64 ±0.01(stat)cm PDG Value : 2.68 cm

Baryon Stopping/Transport Anti-baryons - all from pair production Baryons - pair production + transported B/B ratio =1 - Transparent collision B/B ratio ~ 0 - Full stopping, little pair production Measure p/p, L/L , K-/K+ (uud/uud) (uds/uds) (us/us) _ _ _ _ - - - - - - - -

STAR B/B Ratios Ratio approaching 1.0 as strangeness content increases However still some baryon number being transported from beams Ratios calculated for central events at mid-rapidity, averaged over experimental acceptance in pt

Energy Evolution of B/B Ratio Production of baryons through pair processes increases dramati-cally with s – still not baryon free (ISR) STAR preliminary Pair-process production is larger than baryon transport

Ratios vs pt 0.60.02 (stat.) 0.06 (sys.) 1.1± 0.05 (stat.) _ L/L 0.60.02 (stat.) 0.06 (sys.) 1.1± 0.05 (stat.) 0.73 ± 0.03 (stat.) pt Baryon pt distribution the same as anti-baryon 2/3 of protons from pair processes , yet pt dist. the same as antiprotons Much Rescattering!!

K+/K- Ratio - Nch K+/K- constant over measured centrality

Simple Model Assume fireball passes through a deconfined state can estimate particle ratios by simple quark-counting models No free quarks so all quarks have to end up confined within a hadron Predict D=1.12 Predict D=1.12 D=1.08± 0.08 Measure System consistent with having a de-confined phase

Energy Evolution Revisited RHIC/STAR (Au+Au) SPS/NA44 (S+S) SPS/NA49 (Pb+Pb) AGS/E866 (Au+Au) (ISR) STAR preliminary K-/K+ ratios exhibit similar behavior to p/p as net baryon number drops and p absorption lessens _

Particle Ratios and Chemical Content mj= Quark Chemical Potential T = Temperature Ej – Energy required to add quark gj– Saturation factor Use ratios of particles to determine m, Tch and saturation factor

Chemical Fit Results s (RHIC) < 0.004 GeV Not a 4-yields fit! 2  1.4 Thermal fit to preliminary data: Tch (RHIC) = 0.19 GeV  Tch (SPS) = 0.17 GeV q (RHIC) = 0.015 GeV << q (SPS) = 0.12-0.14 GeV s (RHIC) < 0.004 GeV  s (SPS) Chem Fit

Chemical Freeze-out early universe quark-gluon plasma hadron gas Baryonic Potential B [MeV] Chemical Temperature Tch [MeV] 200 250 150 100 50 400 600 800 1000 1200 AGS SIS LEP/ SppS SPS RHIC quark-gluon plasma hadron gas neutron stars early universe thermal freeze-out deconfinement chiral restauration Lattice QCD atomic nuclei P. Braun-Munzinger, nucl-ex/0007021 Production systematic

Kinetic Freeze-out and Radial Flow Want to look at how energy distributed in system. Look in transverse direction so not confused by longitudinal expansion Look at mt = (pt2 + m2 ) distribution A thermal distribution gives a linear distribution dN/dmt  e-(mt/T) mt 1/mt d2N/dydmt Slope = 1/T Slope = 1/Tmeas ~ 1/(Tfo+ mo<vt>2) If there is transverse flow

Kaon Slope Systematics K0s e(-mT/T) STAR Preliminary T~290+-5 MeV

Inverse slope for f and L e(-mt/T) _ L L T=352+-7 MeV Similar slopes for similar masses

L Inverse Slope Systematics Note spectra are not feed-down corrected Fits are e(-mt/T) Centrality % T (MeV) 0-5 342 ± 9 ± 20 5-10 336 ± 9 ± 20 10-20 328 ± 7 ± 20 20-35 331 ± 8 ± 20 35-75 295 ± 7 ± 19 L T=300-350 MeV |y|<0.5 Some indication that one slope fit is not appropriate at low and high mt

mt slopes vs. Centrality Tp = 190 MeV TK = 300 MeV Tp = 565 MeV mid-rapidity Increase with collision centrality  consistent with radial flow.

Radial Flow? Fitting to p indicates high flow. STAR Preliminary Fitting to p indicates high flow. Fitting to L and f “same” as SPS. What’s going on? L L L Depends on fit range

mT dist. from Hydrodynamic type model b s s Ref. : E.Schnedermann et al, PRC48 (1993) 2462 1/mT dN/dmT (a.u.) flow profile selected (r =s (r/Rmax)0.5)

Fits to the hydro. model Tth [GeV] 1/mT dN/dmT (a.u.) mT - m [GeV/c2] - K- p  solid : used for fit K- p  - <r > [c] Tth [GeV] 0 0.4 STAR Preliminary ßr (RHIC) = 0.52c Tfo (RHIC) = 0.13 GeV explosive radial expansion at RHIC  high pressure

The Global picture Seems to be a limiting Tfo As colliding energy goes up energy goes into higher and higher transverse flow.

h-, L and L pT distributions _ h-, L and L pT distributions Evidence that B/M ratio > 1 at high pT Consequence of radial flow ? or novel baryon dynamics ? STAR Preliminary

f, L, L fractions of h- STAR Preliminary Note: spectra are not feed-down corrected and L yields are from fits to Boltzmann; h- yields are power law fits _ L= (0.042 0.001)h- All ratios are flat as functions of centrality f = (0.02 0.002)h-

K-/p- Ratios K-/p- ratio is enhanced by almost a factor of 2 in central collisions when compared to peripheral collisions STAR preliminary Similar dependence on centrality was seen in SPS and AGS data Energy dependence of the ratio reflects the changing baryon chemical potential. SPS

K0*/h- Represents a 50% increase compared to K0*/p measured in pp at the ISR. More evidence of Strangeness Enhancement?

F/h- Ratios Relative production of f increasing with collision energy in heavy ion collisions. STAR preliminary p+p collisions HI collisions Strangeness Enhancement?

What have we learnt so far? What is the initial environment like for particle production? Net baryon density What happens during the initial particle production? Strangeness production Quark coalescence? Are re-interactions significant? Rescattering of hadrons? Radial flow? Still a significant amount of baryon number around Increasing fraction of particle production with energy, but not centrality? Reasonable predictor Little pt dependence, significant rescattering? Slope dependence of mt fit range- Large flow

SPARE STUFF-not shown

Interpreting the mt spectra _ (x2) p 1/mT dN/dmT (a.u.) STAR Preliminary mT – m0 (GeV/c2)

K0*/h- Represents a 50% increase compared to K0*/p measured in pp at the ISR. Strangeness Enhancement? Also look at K*/K From spin counting K*/K = vector meson/meson = V/(V+P) = 0.75 e+e-(LEP)K*/K = 0.32 ±0.02 pp (ISR)K*/K = 0.6 ± .09 ± .03 Au-Au (STAR) 0.42

Event (Centrality) Selection PRL 86, (2001) 402 nch = primary tracks in || < 0.75 ZDC Au Central Multiplicity Detectors

Strange particle ratios

The STAR Detector (Year-by-Year) Magnet Time Projection Chamber Coils FTPCs Silicon Vertex Tracker * Vertex Position Detectors year 2001, + TOF patch TPC Endcap & MWPC ZCal ZCal installation in 2003 Endcap Calorimeter Central Trigger Barrel Barrel EM Calorimeter year-by-year until 2003, RICH * yr.1 SVT ladder Year 2000,

Identified pbar/p Ratio X.N.Wang, Phys.Rev.C 58 (1998) 2321 pbar/p ratio Identified pbar/p Ratio Two Detectors TPC RICH RICH will extend ratio to 5 GeV/c with improved statistics Ratio constant as function of Pt pbar/p ratio

Comparing to SPS K+/K-(dE/dx) = 1.08 ±0.01 (stat.)± 0.06 (sys.) f/h- = 0.021 ± 0.001 (stat.)± 0.004 (sys.) K*/h- = 0.06 ± 0.006 (stat.)± 0.01 (sys.) K*/h- = 0.058 ± 0.006 (stat.)± 0.01 (sys.) ¯ p/p = 0.6  0.02 (stat.)  0.06 (sys.) ¯ ¯ / = 0.73 ± 0.03 (stat.) X/X = 0.82 ± 0.08 (stat.) ¯

SVT Performance Noise 1ch=2mV Cosmic Ray Event–L3 Trigger Threshold at 4mV 6% live Hits from Au-Au Event

K0s-K0s Correlations No coulomb repulsion No 2 track resolution Few distortions from resonances K0s is not a strangeness eigenstate - unique interference term that provides additional space-time information l = 0.7 ±0.5 R = 6.5 ± 2.3 K0s Correlation will become statistically meaningful once we have ~10M events (aim for this year)

Preliminary L̅/ Ratio L/L= 0.73  0.03 (stat) _ Central events |y|<0.5 Ratio is flat as a function of pt and y

Strangeness Highlights (2) Multi-Strange Particles appear to freeze out at a cooler temperature/ earlier or have less flow SPS AGS AGS and SPS > 1 Need to consider p absorption _

Previous Strangeness Highlights Enhancement W > X > L > h SPS s=17GeV WA97 |s| Evidence of strangeness enhancement between pA and AA collisions at the SPS – Not reproducible by models