STAR STRANGENESS! K0sK0s    K+K+ (Preliminary)         

What do we measure? K + (us) 494MeV  + +  c  cm K 0 s (ds) 498MeV  +  + c  cm  uds) 1116MeV p+  - c  cm   (dss) 1321MeV  +  - c  cm   (sss) 1672MeV  +K - c  cm  0 (ss) 1020MeV K + +K + c  cm + anti-particles + other more exotic resonances (  (1520)!)

What do we measure (2)? Particle yields How much is created? Spectra (dN/dy, dN/dp t, d 2 N/dydp t ) Where and when are they created and what are the dynamics? Particle ratios What are the chemical potentials? Interferometry How large is the source and how long did it exist?

T fireball < T c  Hadron gas Hard to make S  0 particles  + N   + K (E thresh  530MeV)  + K   +  (E thresh  1420MeV) Mtm phase space suppressed Need to create 3 qq pairs (initially there are no q) with similar momenta in a region already containing many quarks. Why are we interested in Strangeness production? T fireball >T c  QGP Easy to make s quarks E=2m s (  300MeV) Free gluons g-g fusion - dominate s s creation faster reaction time than qq Pauli blocking may aid creation of s s quarks ( probably not true at high T, too many states). ¯ ¯ ¯ ¯ ¯ ¯

What is the best thing to measure? While K’s carry ~70% of the strangeness they are easily produced in the final stage reactions as the hadrons in the expanding gas interact and already show an enhancement over N-N collisions at energies too low to form a QGP.  Want to look at the yields of multi-strange (anti-)baryons  production suppressed in Hadron Gas because a) need large energy to create b) need to create u d s where there are already many ud c) need to create them in the same mtm phase space Looking at the particle ratios  p  tells you the s/u ratio -> 1 if there is chemical equilibration ¯ ¯¯¯ ¯ ¯ ¯¯

Evidence for Strangeness Enhancement - WA97 results

Strange particle ratios AGS > 1 and is higher than SPS. Seems to be a clear strangeness enhancement between pA and AA collisions at the SPS

Where are the strange particles produced? If heavy ion collisions were just N-N reaction superpositions  (uds) concentrated in the baryon rich projectile regions  (uds), K 0 s (ds) peaked at mid-rapidity due to their sea-quark content PROBLEM! What if there is any stopping? Baryon-rich projectile and baryon-free “fire-ball” region become merged Have to separate fire-ball creation from that merely due to associated production

Stopping and the net  distribution We expect that the net  yield should follow the net p yield. However there is a distinct “bump” about mid-rapidity in the  distribution that is not observed in the p. Is this NEW physics? Or is it evidence of feed-down into the  channel that has yet to be corrected properly. NA49 have recently obtained  and  results which may help answer this question

Freeze out “Temperature” vs Mass From two particle correlation studies you can extract  2 /T from R . ~50% transverse kinetic energy goes into radial flow. -> Very important for any global thermo-chemical analysis T prop = 120 ±10MeV  = 0.5 N.B  (Na49) T=305 MeV  (Na50) T=213 MeV Also 3x smaller yield

K +/-  +/- +  K +, K - High P t identification via “Kink”Analysis

Finding V0s

STAR TPC Acceptance for B=0.25T (Half Field )

  — The peaks in their glory 332K Events |z|<50cm, |y|=0.5, GeV/c 0.16/event 0.13/event

154K MinBias Events |z|<50cm, |y|=0.5, GeV/c And there’s more /event0.2/event

STAR STRANGENESS! K0sK0s    K+K+ (Preliminary)         

In case you thought it was easy… Before

And Voila!!!! After

Large peaks at 2 o’clock and 8 o’clock TPC pad row “floating” Fine way to calibrate a detector.. Now in ExB “Hell”

Baryons distributions carry information related to –stopping and particle production –baryon chemical potential –thermal equilibrium p/p ratio should be sensitive Last call for RHIC predictions (nucl-th/ ) at  s NN = 200 GeV : –Quark Coalescence:  p/p = 0.6 –Fireball:  p/p = –Hijing:  p/p = 0.8 –RQMD:  p/p = 0.5 

 p/p: centrality and p t dependence No strong p t dependence Weak centrality dependence more stopping and/or other process ? 85%  centrality  6% Ratio for 0.3 < |y| < 0.4

 /  preliminary  = 4 MeV 332K min bias Events 0 < p t < 2.3 GeV/c 0.5<y<0.5 ¯

p/ p E p/ p NA49  WA97 p/ p STAR  STAR AGSSPS RHIC STAR Preliminary  /  ratio Anti-Baryon/Baryon Ratio Preliminary:  /  = 0.70  0.05 (stat)  0.2 (syst) p/p = 0.65  0.03 (stat.)  0.06 (sys.) ¯

Conclusion Stay tuned for QM2001!!!!