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

This study presents preliminary results from the STAR Detector at RHIC, investigating the initial environment for particle production, strangeness production, quark coalescence, and more. The data quality indicates peaks and clear signals for various particles, with baryon/antibaryon ratios, strange hadron ratios, and quark-counting ratios examined. The analysis includes measurements of baryon stopping/transport, pair production processes, energy evolution of baryon ratios, and chemical content determination using particle ratios. The study also explores freeze-out mechanisms, thermal fits, and slope systematics for particle distributions and radial flow. The findings suggest a complex interplay of processes in heavy ion collisions.

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

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

  2. 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

  3. 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 What are we looking for? Baryon / antibaryon ratios Strange hadron / h- ratios Quark-counting ratios Hadron ratios vs. pt Strange baryon ratios Mt slopes

  4. 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

  5. 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

  6. 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

  7. 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) _ _ _ _ - - - - - - - -

  8. 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

  9. 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

  10. Ratios vs pt _ 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!!

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

  12. Simple Model Measure D=1.08± 0.08 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 System consistent with having a de-confined phase

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

  14. 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, Tchand saturation factor

  15. Chemical Fit Results Not a 4-yields fit! s  1 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)

  16. Chemical Freeze-out early universe LEP/ SppS 250 RHIC quark-gluon plasma 200 SPS AGS Lattice QCD deconfinement chiral restauration 150 Chemical Temperature Tch [MeV] thermal freeze-out 100 SIS hadron gas 50 neutron stars atomic nuclei 0 200 400 600 800 1000 1200 0 Baryonic Potential B [MeV] P. Braun-Munzinger, nucl-ex/0007021

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

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

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

  20. 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

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

  22. Radial 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

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

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

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

  26. _ 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

  27. 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-

  28. 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

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

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

  31. 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? What have we learnt so far? 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

  32. SPARE STUFF-not shown

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

  34. 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

  35. Event (Centrality) Selection 5% Central ZDC ZDC Au Au Central Multiplicity Detectors PRL 86, (2001) 402 nch = primary tracks in || < 0.75

  36. Strange particle ratios

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

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

  39. 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.) ¯

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

  41. K0s-K0s Correlations l = 0.7 ±0.5 R = 6.5 ± 2.3 • 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 K0s Correlation will become statistically meaningful once we have ~10M events (aim for this year)

  42. 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

  43. 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 _

  44. 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

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