STAR Helen Caines The Ohio State University Stony Brook – Nucl. Seminar May 2001 A Strange Perspective – Preliminary Results from the STAR Detector at RHIC

Helen Caines Stony Brook 2001 STAR The STAR Collaboration 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 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 Institutions: 36 Collaborators: 415 Students: ~50 Spokesperson: John Harris

Helen Caines Stony Brook 2001 STAR STAR STRANGENESS! K0sK0s  K+K+ (Preliminary) ̅̅   ̅̅  ̅̅ 

Helen Caines Stony Brook 2001 STAR Introduction When is Strangeness Produced – Resonances Chemical content – Yields Thermal Freeze-out – Radii and Inverse slopes Flow – How much and when does it start? Chemical Freeze-out - Ratios

Helen Caines Stony Brook 2001 STAR Previous Strangeness Highlights Multi- Strange Particles appear to freeze out at a cooler temperature/ earlier or have less flow WA97

Helen Caines Stony Brook 2001 STAR 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: T c ~ MeV  c ~ GeV/fm Deconfinement transition Chiral transition

Helen Caines Stony Brook 2001 STAR STAR Pertinent Facts Field: 0.25 T (Half Nominal value) (slightly worse resolution at higher p, lower pt acceptance) TPC: Inner Radius – 50cm (p t >75 MeV/c) Length – ± 200cm ( -1.5  1.5) Events: ~300,000 “Central” Events –top 8% multiplicity ~160,000 “Min-bias” Events

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

Helen Caines Stony Brook 2001 STAR Triggering/Centrality “Minimum Bias” ZDC East and West thresholds set to lower edge of single neutron peak. ~30K Events |Z vtx | < 200 cm “Central” CTB threshold set to upper 15% REQUIRE: Coincidence ZDC East and West REQUIRE: Min. Bias + CTB over threshold

Helen Caines Stony Brook 2001 STAR Particle ID Techniques - dE/dx dE/dx PID range: ~ 0.7 GeV/c for K /  ~ 1.0 GeV/c for K/p dE/dx

Helen Caines Stony Brook 2001 STAR High P t K + & K - Identification Via “Kinks”  +/- K +/- 

Helen Caines Stony Brook 2001 STAR Particle ID Techniques - Topology Decay vertices K s   + +  -   p +  -   p +  +  -   +  -  +  +  +    + K -   “kinks”: K     + VoVo

Helen Caines Stony Brook 2001 STAR Finding V0s proton pion Primary vertex

Helen Caines Stony Brook 2001 STAR In case you thought it was easy… BeforeAfter

Helen Caines Stony Brook 2001 STAR Particle ID Techniques Combinatorics K s   + +  -   K + + K -   p +  -   p +  + Combinatorics  from K + K - pairs K + K - pairs m inv same event dist. mixed event dist. background subtracted dn/dm Breit-Wigner fit Mass & width consistent w. PDG K* combine all K + and  - pairs (x ) m inv (GeV)

Helen Caines Stony Brook 2001 STAR Particle Freeze-out Conditions time 3. freeze-out 1. formation Chemical Freezeout: inelastic scattering stops 2. hot / dense Kinetic Freezeout: elastic scattering stops

Helen Caines Stony Brook 2001 STAR p/p Ratio _ Phys. Rev. Lett March 2001 Ratio = 0.65 ±0.03(stat) ±0.03(sys) Ratio is flat as function of p t and ySlight fall with centrality

Helen Caines Stony Brook 2001 STAR Strange Baryon Ratios Ratio = 0.73 ± 0.03 (stat) ~0.84  /ev, ~ 0.61  /ev _Reconstruct: Ratio = 0.82 ± 0.08 (stat) Reconstruct: ~0.006   /ev, ~0.005   /ev _ STAR Preliminary

Helen Caines Stony Brook 2001 STAR Preliminary  ̅ /  Ratio  = 0.73  0.03 (stat) _ Ratio is flat as a function of p t and y Central events |y|<0.5

Helen Caines Stony Brook 2001 STAR ¯ _ _ _ _ _ _ _ Anti-baryon/Baryon Ratios versus  s STAR preliminary Baryon-pair production increases dramatically with  s – still not baryon free 2/3 of protons from pair production, yet pt dist. the same – Another indication of thermalization Pair production is larger than baryon transport

Helen Caines Stony Brook 2001 STAR  and  ̅ from mixed event Studies Good cross-check with standard V0 analysis. Low p t 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  = 0.77  0.07 (stat) _

Helen Caines Stony Brook 2001 STAR K + /K - vs p t

Helen Caines Stony Brook 2001 STAR K + /K - Ratio - N ch dE/dx Kinks K + /K - = 1.08±0.01(stat.)± 0.06(sys.) (dE/dx). (The kink method is systematically higher.) K + /K - constant over measured centrality. STAR preliminary

Helen Caines Stony Brook 2001 STAR K - /  - Ratios K - /   ratio is enhanced by almost a factor of 2 in central collisions when compared to peripheral collisions STAR preliminary SP S

Helen Caines Stony Brook 2001 STAR Simple Model Assume fireball passes through a deconfined state can estimate particle ratios by simple quark-counting models D=1.12 No free quarks so all quarks have to end up confined within a hadron Predict D=1.08± 0.08 Measure System consistent with having a de-confined phase

Helen Caines Stony Brook 2001 STAR K 0 * and K 0* Identification First measurement in heavy ion collisions Short lifetime (c  =4fm) – sensitive to the evolution of the system? _

Helen Caines Stony Brook 2001 STAR K 0 */h - Represents a 50% increase compared to K 0* /  measured in pp at the ISR. Aim to measure in pp ourselves this year.

Helen Caines Stony Brook 2001 STAR Comparing to SPS K + /K - (kink) = 1.2 ± K + /K - (dE/dx) = 1.08 ±0.01 (stat.) ± 0.06 (sys.) K - /    = 0.15 ± 0.02 (stat.) K*/h - = 0.06 ± (stat.) ± 0.01 (sys.) K*/h - = ± (stat.) ± 0.01 (sys.) p/p = 0.6  0.02 (stat.)  0.06 (sys.) ¯  /  = 0.73 ± 0.03 (stat.)  ± 0.08 (stat.) ¯ ¯ ¯

Helen Caines Stony Brook 2001 STAR Particle Ratios and Chemical Content  j = Quark Chemical Potential T = Temperature E j – Energy required to add quark  j – Saturation factor Use ratios of particles to determine  T ch and saturation factor

Helen Caines Stony Brook 2001 STAR Chemical Fit Results Not a 4  -yields fit!  s  1  2  1.4 Thermal fit to preliminary data: T ch (RHIC) = 0.19 GeV  T ch (SPS) = 0.17 GeV  q (RHIC) = GeV <<  q (SPS) = GeV  s (RHIC) < GeV   s (SPS)

Helen Caines Stony Brook 2001 STAR P. Braun-Munzinger, nucl-ex/ Chemical Freeze-out Baryonic Potential  B [MeV] Chemical Temperature T ch [MeV] 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

Helen Caines Stony Brook 2001 STAR “Kink” Rapidity Distribution Mid-y K + dN/dy = 35 ±3(stat.)±5(sys.) Mid-y K - dN/dy = 30±2.5(stat.)±4(sys.)

Helen Caines Stony Brook 2001 STAR “Kink” m t Distributions

Helen Caines Stony Brook 2001 STAR K - Inverse Slope Results Kink dE/dx h - mid rapidity dN/d  Increasing centrality

Helen Caines Stony Brook 2001 STAR T  = 190 MeV T  = 300 MeV T p = 565 MeV mid-rapidity m t slopes vs. Centrality Increase with collision centrality  consistent with radial flow.

Helen Caines Stony Brook 2001 STAR Radial Flow: m t - slopes versus mass Naïve: T = T freeze-out + m   r  2 where   r  = averaged flow velocity  Increased radial flow at RHIC ß r (RHIC)  ß r (SPS/AGS) = 0.6c = c T fo (RHIC)  T fo (SPS/AGS) = GeV = GeV

Helen Caines Stony Brook 2001 STAR  Identification STAR Preliminary

Helen Caines Stony Brook 2001 STAR Radial Flow and the  Doesn’t follow “radial flow systematics”  early kinetic freezeout? Central collisions STAR Preliminary NA49 – 290 MeV NA50 – MeV

Helen Caines Stony Brook 2001 STAR K 0 s -K 0 s Correlations  = 0.7 ±0.5 R = 6.5 ± 2.3 No coulomb repulsion No 2 track resolution Few distortions from resonances K 0 s is not a strangeness eigenstate - unique interference term that provides additional space-time information K 0 s Correlation will become statistically meaningful once we have ~10M events

Helen Caines Stony Brook 2001 STAR Conclusions Mapping out “Soft Physics” Regime  Net-baryon  0 at mid-rapidity! (  y = y 0 -y beam ~ 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   The  does not seem to flow with the other particles. Reduced rescattering for the kaons from  decay and/or  feels less flow More than we ever hoped for after the first run !!!

Helen Caines Stony Brook 2001 STAR This Year – RICH,TOF Patch, SVT, FTPC RICH and TOF: Increase K identification in p t over a limited geometric acceptance Centered at mid-rapidity they provide complimentary pt coverage TOF patch 0.3< p t <1.5 GeV/c RICH 1.1 < p t < 3.0 GeV/c Overlaps with the TPC kink and dE/dx measurement kink p t < 5 GeV, dE/dx p t < 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