# Presentation: 501884

## Soft Physics from STARBulk properties 

- Fuqiang Wang
- For the STAR Collaboration

## The STAR Detector

**The STAR Detector**

**Magnet**
**Coils**
**Central **
**Trigger**
**Barrel **
**(CTB)**
**ZCal**
**Time **
**Projection **
**Chamber**
**(TPC)**
**Year 2000**

**Barrel EM Cal (BEMC)**
**Silicon Vertex Tracker (SVT)****Silicon Strip Detector (SSD)**
**FTPC****Endcap EM Cal****FPD**
**TOFp, TOFr**
**FPD**
**Year 2001+**

**PMD**

- _Large acceptance: 2____ coverage at mid-rapidity_

## the Quark-Gluon Plasma

**the Quark-Gluon Plasma**

- To create and study QGP – a state of deconfined, thermalized quarks and gluons over a large volume predicted by QCD at high energy density.

- Lattice QCD prediction:

- _Tools_:
- -  jets & interactions with bulk
- -  elliptic & radial flow
- -  hadron distributions

- F. Karsch, Prog. Theor. Phys. Suppl. 153, 106 (2004)

- _Questions_:
-   energy density?
-   degree of thermalization?
-   deconfinement, DOF, EOS?

- The goal:

- QGP is a bulk,
- soft physics phenomenon.

## outline

**outline**

*Courtesy of S. Bass*

- correlations:
- (1) thermalization?
- (2) is there conical flow?

- elliptic flow:
- does hydro work?
- what EOS?

- hadrons
- hadronic scatterings
- freeze-out

**1**

**2**

**3**

- Initial condition: CGC
- high-Q2 interactions
- medium formation

- hot, dense medium
- expansion
- hadronization

- ratios, spectra:
- freeze-out properties
- fluctuations, etc.

## soft-soft correlations

*See posters, Prindle (#111), *
*Ray(#87) , Trainor (#31)*

- even at low pt, remnants of jet-like structure survive.
- strongly coupled to the medium, elongated along ****.

## hard-soft interactions

- Two sources of particles:
- hard: hard scattering products.
- soft: bulk medium constituents.
- Very different as seen in peripheral.
- Become similar in central.

- <pT> from away jets

- <pT> from medium decay

- Away side <pT> (GeV/c)

- hard-soft: approach thermalization.
- soft-soft (larger x-section): higher degree of thermalization.

- STAR, nucl-ex/0501016.

## hard-soft angular correlations

**hard-soft angular correlations**

- Broader away-side correlations in central Au+Au.
- Novel dip at  in away <pT> for pTtrig<6 GeV/c. Associated hadrons at  appear more equilibrated.

- number
- correlation

- pT-weighted
- correlation

*See talk, J. Ulery (section 3c)*

- pTtrig=4-6 GeV/c
- pTassoc=0.15-4 GeV/c

## correlation functions

****** ****(radian)**

- 4 < pT trig < 6 GeV/c
- 1 < pTassoc < 2.5 GeV/c

- - large angle gluon radiation: Vitev
- - conical flow: Stoecker,Shuryak,Muller
- - jets deflected by medium flow

- 1/Ntrig dN/d()

- 2.5 < pT trig < 4 GeV/c
- 1 < pTassoc < 2.5 GeV/c

*See talk, J. Ulery *
*(section 3c) and*
*poster, M. Horner (#70)*

- broad away-side correlations.
- consistent with flat.

## conical flow? 3-particle correlation

- d+Au and Au+Au
- elongated along
- diagonal: kT effect,
- and deflected jets?
- Distinctive features
- of conical flow are
- not seen in present
- data with these pT
- windows.

- Three regions on away side:
- center =	(, ) ±0.4
- corner =	(+1,+1) ±0.4 x2
- cone =	(+1,-1) ±0.4 x2

- difference in Au+Au
- average signal per radian2:
- center – corner =
-    0.3 ± 0.3 (stat) ± 0.4 (syst)
- center – cone =
-    2.6 ± 0.3 (stat) ± 0.8 (syst)

*See talk, J. Ulery (section 3c)*

## outline

**outline**

*Courtesy of S. Bass*

- elliptic flow:
- does hydro work?
- what EOS?

- hadrons
- hadronic scatterings
- freeze-out

**1**

**2**

**3**

- Initial condition: CGC
- high-Q2 interactions
- medium formation

- hot, dense medium
- expansion
- hadronization

- ratios, spectra:
- freeze-out properties
- fluctuations, etc.

- correlations:
- (1) thermalization?
- (2) is there conical flow?

## elliptic flow v2

**elliptic flow v****2**

- m-dependence: common vT field.
- hydro works: suggests early thermalization.
- soft (QGP) EOS favored: sub-hadronic DOF.

*See talks, X. Cai (section 1)*
*M.D. Oldenburg (section 2a)*
*and poster, J. Speltz (#164)*

- large v2 (even ): strong interactions at early stage
- large v2 of ** **(low hadronic x-sections): partonic collectivity at RHIC.

## Charged hadrons: v2 at 200 GeV in Cu+Cu

- Non-flow effects large at high pT and for lighter systems.
- multiple methods to remove non-flow: 4-particle cumulants, subtraction of pp.
- Significantly smaller v2 in Cu+Cu than in Au+Au.

*See talk, G. Wang (section 2a)*

## constituent quark scaling

**constituent quark scaling**

- Constituent quark DOF.
- Deconfinement?

*See talk: Oldenburg (section 2a)*

- - v2 appears to scale with number of constituent quarks.
- - quark coalescence.

## hadronization via quark coalescence?

- explains
- baryon/meson enhancement
- NCQ scaling of v2.

- No significant difference in angular correlations.
- More work for coalescence approach.

- Molnar, Voloshin, Ko, Fries, Hwa, et al.

- But no intrinsic
- angular correlations.

## outline

**outline**

*Courtesy of S. Bass*

- elliptic flow:
- does hydro work?
- what EOS?

- hadrons
- hadronic scatterings
- freeze-out

**1**

**2**

**3**

- Initial condition: CGC
- high-Q2 interactions
- medium formation

- hot, dense medium
- expansion
- hadronization

- ratios, spectra:
- freeze-out properties
- fluctuations, etc.

- correlations:
- (1) thermalization?
- (2) is there conical flow?

## chemical freeze-out

- hadron-chemistry: particle ratios  chemical freezeout properties

- short lived
- resonances

**T****ch**

******s**

*See poster: J. Speltz (#164)*

**T****ch**** ≈ T****C**** ≈ 165 ± 10 MeV**Chemical freezeout **≈ **hadronization.
**s ~ u, d **Strangeness is chemically equilibrated.

- STAR white paper
- Nucl Phys A757 (05) 102

## time and size

- resonance decays and regeneration: measure kinetic freezeout – life time.

*See talk, S. Salur (section 5a) and *
*posters, C. Markert (#151), D. Mishra (#19)*

*See talks, Z. **Chaj**ę**cki**, P. **Chaloupka *
*(section 4a)*

- Re-scattering and regeneration is needed! Finite time span from chemical to kinetic freeze-out.

- Npart

- HBT: measures freeze-out source sizes (marked by collective flow).

- HBT size (low kT): x2 expansion
- initial  final in Au+Au.
- What is the size at chemical freeze-out?
- may be assessed via - correlations.

## strange baryon spectra

**strange baryon spectra**

- 200 GeV
- Au+Au

- 62.4 GeV
- Au+Au

*See talk, S. Salur *
*(section 5a)*

## kinetic freeze-out

- particle spectra  kinetic freezeout properties, total collective radial flow.

- ,K,p,: Tkin decreases,  increases with centrality.
- ,  (low hadronic x-sections): higher Tkin **≈** Tch, still significant radial flow.
- Rare particles: kinetic freeze-out **≈ **chemical freeze-out **≈ **hadronization

- Blast wave fit

*See poster, J. Speltz (#164)*

## event-by-event fluctuations

**event-by-event fluctuations**

- Phase transition  large event-by-event fluctuations

- where is Koch prediction
- on this graph?

- Smooth √s dependence, no threshold effect.
- Original QGP signal in inclusive net charge fluctuation is excluded. More differential studies are needed.

*See talk, C.A. Pruneau (section 4c) and poster, L. Ray (#87)*

## forward physics

- Photons: centrality independent limiting fragmentation.
- Charged particles: centrality dependent limiting fragmentation.
- Pions follow limiting fragmentation in heavy-ion collisions.

*See talk, B. Mohanty (section 1b)*

- Forward rapidity at RHIC probes CGC.
- CGC will be even more important at LHC (and at mid-rapidity).

- Consistent with the CGC framework.
- RdAu-0 lower than h-: p+ph- is isospin suppressed at large .

## New, precision data from STAR.
Jet-medium interaction: 
strong indication of thermalization processes
distinctive features of conical flow not seen 
Elliptic flow and spectra data show: 
early thermalization
partonic collectivity
relevance of constituent quark DOF
Particle distributions with equilibrium models:
chemical freeze-out ≈ hadronization
finite span from chemical to kinetic freeze-out

- Jet-medium interaction:
- strong indication of thermalization processes
- distinctive features of conical flow not seen
- Elliptic flow and spectra data show:
- early thermalization
- partonic collectivity
- relevance of constituent quark DOF
- Particle distributions with equilibrium models:
- chemical freeze-out **≈** hadronization
- finite span from chemical to kinetic freeze-out

**Summary**

## The STAR Collaboration

- The *STAR* Collaboration

**U.S. Labs:****   ****	**
**	****Argonne,  Lawrence Berkeley,  and Brookhaven National Labs**
**U.S. Universities:****    **
**	****UC Berkeley, UC Davis,  UCLA,  Caltech, Carnegie Mellon, Creighton,  Indiana, Kent State, MIT, MSU,  CCNY, Ohio State, Penn State,  Purdue,  Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale**
**Brazil:****	****    **
**	****Universidade de Sao Paolo**
**China:****	****    **
**	****IHEP - Beijing, IPP - Wuhan, USTC,**
**	****Tsinghua, SINAP, IMP Lanzhou**
**Croatia:****	****    **
**	**** ****Zagreb University**
**Czech Republic:****	****    **
**	**** ****Nuclear Physics Institute**
**England:**
**	****University of Birmingham**

**France:****     **
**	****Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes**
**Germany:****  **
**	****Max Planck Institute – Munich University of Frankfurt**
**India:**
**	****Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC**
**Netherlands:**
**	****NIKHEF/Utrecht**
**Poland:**
**	****Warsaw University of Technology**
**Russia:****  **
**	****MEPHI – Moscow,  LPP/LHE JINR – Dubna,  IHEP – Protvino**
**South Korea:**
**	****Pusan National University**** **
**Switzerland:**
**	****University of Bern**
**	**

**Notes:**
Let me put up the most important slide: the STAR collaboration, 
and I want to thank my STAR colleagues to give me the opportunity to present this talk on their behalf. 
Thank you for your attention.

## ---Backup slides---

## Is there conical flow?

- hard-soft-corr   +   soft-bkgd.

- soft-soft-corr in underlying event.

- flow modulated background:

- 3-particle correlation

*See talk, J. Ulery (section 3c)*

## existing v2 scaling data