1. STAR: recent results and future physics program
Olga Barannikova
for the STAR Collaboration

2. Not in this talk: Overview of strangeness production from STAR
STAR Preliminary
Strangeness production in light vs. heavy systems
Collision geometry effects on strangeness production at RHIC …
See talk by Anthony Timmins this afternoon…
Strangeness production in light and heavy systems continues to challenge our understanding of QCD in heavy-ion collisions…
Collision geometry key factor in mid-rapidity strangeness production at RHIC
EPOS vs. AMPT
Predictions for multi-strange particles follow similar trends..
STAR Preliminary 2
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

3. Not in this talk: Recent heavy flavor results from STAR
J/ spectra in 200 GeV pp and Cu+Cu  RAA measurements
Azimuthal correlations for HF
J/  -hadron, e-D0, …
 capabilities in pp and Au+Au …
See talk by Zhangbu Xu on Tuesday
• J/y spectra in 200 GeV p+p collisions at STAR
1. Extend the pT range up to ~14 GeV/c
2. Spectra can be described by CEM and CSM.
3. High pT J/y follows xT scaling with n=5.6
4. Spectra at high pT can be used to constrain B production
• J/y-hadron azimuthal correlation in p+p
1. no significant near side correlation
Expect strong near-side correlation from BJ/y+X 26
Can be used to constrain J/y production mechanism
2. Away-side spectra consistent with h-h correlation
indicates gluon or light quark fragmentation
J/  -hadron azimuthal correlation in pp
• non-photonic (rejection - 70%) e-D0 azimuthal correlations in p+p collisions- (Bottom contribution to non-photonic electrons is significant at pT> 5 GeV/c (~50%))
relative bottom contribution
• J/y RAA from 200 GeV Cu+Cu collisions at STAR
1. Extend RAA from pT = 5 GeV/c to 10 GeV/c
2. Indication of RAA increasing at high pT
STAR Preliminary:
The Cu+Cu data consistent with
no suppression at high pT:
RAA(pT > 5 GeV/c) = 0.9 ± 0.2
- Low-pT RAA ~ (PHENIX)
- Most models expected decrease
RAA at high pT.
J/-h 3
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

4. University of Illinois at Chicago
In this talk…
Outline:
Selected recent STAR results on medium properties
Collectivity and Thermalization
Particle production and Parton propagation
Energy density & Energy loss
Near-term program
Physics plans and goals for upcoming runs
Summary 4
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

5. University of Illinois at Chicago
Thermalization
Differential v2 studies
No participant-eccentricity scaling
Fitting function: H-J Drescher et al. PRC 76, (2007)
CGC e: A.Adil et al. PRC 74, (2006)
With the assumption that parton cross section (σ) is same for all ID’d particles,
a universal trend of approaching hydro limit is established.
Anti-correlation found between σ and Cs.
Good constraint on EoS
Dense medium flowing with minimal shear viscosity
Sizeable v2 for f mesons, nq scaling  partonic nature
Assuming same parton σ for all hadrons  universal trend toward hydro limit
v2 / e ~ 30% below ideal hydro (even central collisions)
Knudsen number K is not 0 as for ideal hydro
Ideal Hydro? 5
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

6. Angular pair correlations
Au+Au 200 GeV
STAR Preliminary
STAR Preliminary
STAR Preliminary
STAR Preliminary
Fit function =
!! per-particle quadrapole : universal trend above 13 GeV
Soft component: Longitudinal Fragmentation(“strings”) 1D Gaussian, US pairs HBTpeak at origin, LS pairs
Hard component: Minijets2D Gaussian at origin, away-side peak actually cos(φΔ)
62 and 200 have the same shape, • Substantial amp. change with energy
Nu = <Nbin> / <Npart/2>
per-particle quadrapole : universal trend above 13 GeV +
soft
hard 6
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

7. University of Illinois at Chicago
Low pT ridge
Same-side evolution
83-94%
55-65%
ηΔ width
STAR Preliminary
46-55%
0-5%
200 GeV
62 GeV
STAR Preliminary
Transverse particle density
peak amplitude
peak η width
Little shape change from peripheral to 55% centrality
Large change within ~10% centrality
What causes this rapid transition?
Smaller change from transition to most central
Sharp transition in both amplitude and width at ρ ~ 2.5
Similar ρ-trends at 62 and 200 GeV 7
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

8. Intermediate pT ridge Production mechanisms p+p / p++p-
Au+Au 0-10%
STAR preliminary
3 < pt,trig< 4 GeV/c
pt,assoc. > 2 GeV/c
pTtrig > 4.0 GeV/c
2.0 < pTAssoc < pTtrig
Au+Au: 2 < pTtrig < 3 GeV/c
Cu+Cu: 3 < pTtrig < 6 GeV/c
p+p / p++p-
Weak dependence of ridge yield on pT,trig  Relative contribution reduces with pT,trig
Strong deta-dphi asymmetry suggests coupling to longitudinal flow
Baryon/meson ratio in ridge close to inclusive, in jet close to p+p
Different production mechanisms for ridge and jet?
Jet+ridge yields follow similar trend in pT for all trigger types
Production mechanisms for jet and ridge are different

9. University of Illinois at Chicago
Dh-Dh correlations
No acceptance
3<pTTrig<10 GeV/c 1<pTAsso<3 GeV/c
No apparent substructure – no gluon fragments/flow coupling?
No cross-like term –
ridge and cone decoupled?
STAR Preliminary
d+Au
deta-deta structure: central peak + uniform
Note absence of excess along axes: no jet+ridge events?
Au+Au
0-12%
STAR Preliminary 9
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

10. Charge-ordering in Dh-Dh
Charge-ordering in Jet
No ordering in Ridge
Ridge (T- A+ ) = Ridge (T+ A+)
Ridge (T+ A-) = Ridge (T- A- )
STAR Preliminary
Tlike,AAlike : Only ridge
Tunlike,AAlike: Jet + Ridge
Use charge-ordering for Jet-Ridge separation
2*(AAlikeTunlike – AAlikeTlike )
STAR Preliminary
STAR Preliminary 10
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

11. University of Illinois at Chicago
Path-length effects 0º
90º
in-plane fS=0
out-of-plane fS=90o
3<pTtrig<4GeV/c
1 < pTasso < 1.5GeV/c
STAR Preliminary
20-60%
Jet peak shows little changes from d+Au to central Au+Au collisions
Ridge decreases from in-plane to out-of-plane
Ridge |Dh|>0.7
STAR Preliminary 11
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

12. Jet-energy calibration
Direct g - hadron correlations
Direct  0
Associated yield/Ntrig
STAR Preliminary
QCD Compton Scattering
suppression similar to
inclusives in central collisions
The away-side yield per trigger of direct gamma triggers shows smaller value
compared to pi0 triggers which is consistent with
partons loose energy “dense medium” and then fragment.
1st measurement of away-side
-h correlations
Suppression similar level as
Note : Ejet = E
p0 -triggers are from higher energy parton, and more surface-biased
Away-side yield results consistent with in-medium parton energy loss scenario 12
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

13. Full jet reconstruction
In Au+Au collisions!
Will allow direct measurements of jet spectra and fragmentation functions in AA
STAR Preliminary
STAR Preliminary
No apparent modification with respect to pp!?
To do:
need to understand trigger bias
ξ not yet corrected for jet energy shift due to quenching
STAR Preliminary 13
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

14. University of Illinois at Chicago
The “QCD factory”
STAR – new advances in studies of medium properties,
new questions
Dense QCD medium, strong coupling with parton Eloss
Differential qualitative studies of the medium:
precise jet FF measurements,
energy loss, “ridgeology”,
colour-charge effects
? Conventional hydro picture, initial eccentricity ?
? Mechanisms of jet-medium interactions ?
Systematically study the partonic medium properties at RHIC
RHIC stochastic cooling +STAR detector upgrades:
High precision measurements, strong pQCD tests 14
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

15. University of Illinois at Chicago
STAR: the near future
Longitudinal and transverse spin programs
- Study proton intrinsic properties
Forward programs
- Study low-x properties and search for CGC
Tagged forward protons
- Study elastic and inelastic process
- Investigate gluonic exchanges and search for gluonic matter
RHIC beam energy scan
- Search for critical point
- Chiral symmetry restoration 15
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

16. Search for QCD Critical Point
Strategy:
Search for disappearance of dense medium effects
Search for onset of de-confinement
Evolution of the system is attracted to the critical point
Focusing causes broadening of signal region
Scan plan:
Hydro predicts that the evolution of the system is attracted to the critical point.
Focusing causes broadening of signal region - No need to run at exactly Critical Point energy 16
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

17. Energy scan test run Au+Au collisions at 9 GeV: Non-central Collision17
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

18. University of Illinois at Chicago
Key measurements
Hadron ratios and fluctuations
STAR advantages:
Large acceptance: full azimuthal coverage and |y|<1.0
Extended particle identification: (TPC, ToF, EMC)
Same detector – same systematics 18
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

19. University of Illinois at Chicago
The STAR Upgrade
MTD
EMC barrel
MRPC ToF barrel
Ready for run 10
EMC End Cap
RPSD
FMS
FPD
TPC
PMD
Complete
Ongoing
DAQ1000
Ready for run 9
HFT
FGT
R&D 19
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

20. University of Illinois at Chicago
For more details:
STAR Highlights on Strangeness Production - Anthony Timmins
STAR Highlights on Heavy Quark Production - Zhangbu Xu
Parallel Talks:
Non-photonic electron yields in p+p Collisions at 200 GeV with reduced detector material in STAR -- Fu Jin
First results from Au+Au collisions at 9.2 GeV in STAR -- Lokesh Kumar
System size, energy and centrality dependence of strange hadron elliptic flow at STAR -- Hiroshi Masui
Anisotropic flow: indications for incomplete thermalization -- Yuting Bai
Strange hadron production in 62 GeV collisions at RHIC -- Marcelo Munhoz
Thermal production of particles at RHIC–Jun Takahashi 20
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

21. University of Illinois at Chicago
Back Up 21
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

22. Angular pair correlations
Pair densities ρ(η1-η2,φ1-φ2) for all possible pairs in same and mixed events.
Correlation measure: 22
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago

23. 3-particle correlation in 
STAR TPC acceptance for
3-particle correlation in 
(||<1 and full azimuth)
T : Trigger particle
A1: First Associated particle
A2: Second Associated particle
In medium radiation + Longitudinal flow
Jet fragmentation in vacuum
N.Armesto et.al Phys.Rev.Lett.
93(2004)
Transverse flow boost
Turbulent color field.
Momentum Kick
C.Y. Wong hep-ph:
S.A.Voloshin, Phys.Lett.B. 632(2006)490
E.Shuryak, hep-ph:
A.Majumder et.al
Phys. Rev. Lett.99(2004)042301 23
October 6-10, 2008
Olga Barannikova
University of Illinois at Chicago