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:
Collaborators: 415
Students: ~50

3. 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

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 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!!

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

12. 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

13. 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 _

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, Tch and saturation factor

15. 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) = GeV
<< q (SPS) = GeV
s (RHIC) < GeV
 s (SPS)
Chem Fit

16. 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/
Production systematic

17. 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

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

19. Inverse slope for f and L
e(-mt/T) _ L L
T= 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)
± 9 ± 20
± 9 ± 20
± 7 ± 20
± 8 ± 20
± 7 ± 19 L
T= MeV
|y|<0.5
Some indication that one slope fit is not appropriate at low and high mt

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

22. 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

23. 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)

24. 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]
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_
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= ( )h-
All ratios are flat as functions of centrality
f = ( )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
Relative production of f increasing with collision energy in heavy ion collisions.
STAR preliminary
p+p collisions
HI collisions
Strangeness Enhancement?

31. 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

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

36. Strange particle ratios

37. 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,

38. 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

39. Comparing to SPS
K+/K-(dE/dx) = 1.08 ±0.01 (stat.)± (sys.)
f/h = ± (stat.)± (sys.)
K*/h = 0.06 ± (stat.)± (sys.)
K*/h = ± (stat.)± (sys.)
p/p = 0.6  0.02 (stat.)
 0.06 (sys.)
/ = ± 0.03 (stat.)
X/X = ± 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 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)

42. Preliminary L̅/ Ratio
L/L=  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