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

This article presents the preliminary results from the STAR detector at RHIC regarding strange particle production. It explores various aspects such as chemical content, resonance flow, freeze-out conditions, and previous strangeness highlights.

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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. STAR STRANGENESS! (Preliminary) K+ W-+ L̅ W̅+ f K0s L X- X̅+ K*

  4. Introduction Chemical content – Yields When is Strangeness Produced –Resonances Flow – How much and when does it start? Thermal Freeze-out –Radii and Inverse slopes Chemical Freeze-out - Ratios

  5. Previous Strangeness Highlights WA97 Multi- Strange Particles appear to freeze out at a cooler temperature/ earlier or have less flow

  6. The Phase Space Diagram TWO different phase transitions at work! – Particles roam freely over a large volume – Masses change Calculations show that these occur at approximately the same point Two sets of conditions: High Temperature High Baryon Density Lattice QCD calc. Predict: Deconfinement transition Chiral transition Tc ~ 150-170 MeV ec ~ 0.5-0.7 GeV/fm

  7. STAR Pertinent Facts Field: 0.25 T (Half Nominal value) (slightly worse resolution at higher p, lower pt acceptance) TPC: Inner Radius – 50cm (pt>75 MeV/c) Length – ± 200cm ( -1.5< h < 1.5) Events: ~300,000 “Central” Events –top 8% multiplicity ~160,000 “Min-bias” Events

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

  9. Triggering/Centrality • “Minimum Bias” ZDC East and West thresholds set to lower edge of single neutron peak. ~30K Events |Zvtx| < 200 cm • “Central” CTB threshold set to upper 15% REQUIRE: Coincidence ZDC East and West REQUIRE: Min. Bias + CTB over threshold

  10. Particle ID Techniques - dE/dx dE/dx dE/dx PID range: ~ 0.7 GeV/c for K/ ~ 1.0 GeV/c for K/p

  11. High Pt K+ & K- Identification Via “Kinks” m+/- nm K+/-

  12. Particle ID Techniques - Topology X+ Decayvertices Ks p + + p - L  p + p - L  p + p + X-  L + p - X+L + p + W  L + K- L Vo “kinks”: K  + 

  13. Finding V0s proton Primary vertex pion

  14. In case you thought it was easy… Before After

  15. Particle ID Techniques Combinatorics K* combine all K+ and p- pairs (x 10-5) f from K+ K- pairs dn/dm m inv (GeV) background subtracted Breit-Wigner fit Mass & width consistent w. PDG m inv dn/dm K+ K- pairs same event dist. mixed event dist. m inv Combinatorics Ks p+ + p-f  K+ + K- L  p + p-L  p + p+

  16. Particle Freeze-out Conditions time 3. freeze-out Kinetic Freezeout: elastic scattering stops 2. hot / dense 1.formation ChemicalFreezeout: inelastic scattering stops

  17. _ p/p Ratio Ratio is flat as function of pt and y Slight fall with centrality Phys. Rev. Lett March 2001 Ratio = 0.65 ±0.03(stat) ±0.03(sys)

  18. Strange Baryon Ratios Reconstruct: Reconstruct: _ _ ~0.006 X-/ev, ~0.005 X+/ev ~0.84 L/ev, ~ 0.61 L/ev Ratio = 0.82 ± 0.08 (stat) Ratio = 0.73 ± 0.03 (stat) STAR Preliminary

  19. 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

  20. Anti-baryon/Baryon Ratios versus s _ _ ¯ _ _ _ _ _ Baryon-pair production increases dramatically with s – still not baryon free Pair production is larger than baryon transport STAR preliminary 2/3 of protons from pair production , yet pt dist. the same – Another indication of thermalization

  21. L and L̅ from mixed event Studies _ L/L= 0.77  0.07 (stat) Good cross-check with standard V0 analysis. Low pt measurement where there is no V0 analysis High efficiency (yields are ~10X V0 analysis yields) Background determined by mixed event STAR preliminary The ratio is in agreement with “standard” analysis

  22. K+/K- vs pt

  23. K+/K- Ratio - Nch Kinks dE/dx STAR preliminary STAR preliminary • K+/K-= 1.08±0.01(stat.)± 0.06(sys.) (dE/dx). (The kink method is systematically higher.) • K+/K- constant over measured centrality.

  24. K-/p-Ratios STAR preliminary K-/p-ratio is enhanced by almost a factor of 2 in central collisions when compared to peripheral collisions SPS

  25. 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

  26. _ K0* and K0* Identification First measurement in heavy ion collisions Short lifetime (ct =4fm) – sensitive to the evolution of the system?

  27. K0*/h- Represents a 50% increase compared to K0*/p measured in pp at the ISR. Aim to measure in pp ourselves this year.

  28. Comparing to SPS K+/K-(kink) = 1.2 ± K+/K-(dE/dx) = 1.08 ±0.01 (stat.)± 0.06 (sys.) K-/p- =0.15 ± 0.02 (stat.) 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.) ¯

  29. 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

  30. 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)

  31. Chemical Freeze-out early universe LEP/ SppS 250 RHIC quark-gluon plasma 200 SPS AGS Lattice QCD deconfinement chiral restauration Chemical Temperature Tch [MeV] 150 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

  32. “Kink” Rapidity Distribution Mid-y K+ dN/dy = 35 ±3(stat.)±5(sys.) Mid-y K- dN/dy = 30±2.5(stat.)±4(sys.)

  33. “Kink”mt Distributions

  34. K- Inverse Slope Results Kink dE/dx Increasing centrality h- mid rapidity dN/dh

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

  36. Radial Flow: mt - slopes versus mass Naïve: T = Tfreeze-out + m  r 2 where  r  = averaged flow velocity • Increased radial flow at RHIC ßr (RHIC)  ßr (SPS/AGS) = 0.6c = 0.4 - 0.5cTfo (RHIC)  Tfo (SPS/AGS) = 0.1-0.12 GeV = 0.12-0.14 GeV

  37. f Identification STAR Preliminary

  38. Radial Flow and the f STAR Preliminary Central collisions NA49 – 290 MeV NA50 – MeV Doesn’t follow “radial flow systematics” early kinetic freezeout?

  39. 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

  40. Mapping out “Soft Physics” Regime Net-baryon  0 at mid-rapidity! ( y = y0-ybeam ~ 5 ) Chemical parameters Chemical freeze-out appears to occur at same ~T as SPS Strangeness saturation similar to SPS Kinetic parameters Higher radial flow than at SPS Thermal freeze out same as at SPS f The f does not seem to flow with the other particles. Reduced rescattering for the kaons from f decay and/or f feels less flow Conclusions More than we ever hoped for after the first run !!!

  41. This Year – RICH,TOF Patch, SVT, FTPC RICH and TOF: Increase K identification in pt over a limited geometric acceptance Centered at mid-rapidity they provide complimentary pt coverage TOF patch 0.3< pt <1.5 GeV/c RICH 1.1 < pt < 3.0 GeV/c Overlaps with the TPC kink and dE/dx measurement kink pt < 5 GeV, dE/dx pt < 0.8 GeV SVT: Increased efficiency for all strange particles and resonaces due to improved tracking Should measure spectra for all particles this year. HBT with strange particles Exotica FTPC: Strange particles at high y

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