# Presentation: 751667

## PID v2 and v4 from Au+Au Collisions at √sNN = 200 GeV at RHIC

- N. Li for the STAR Collaboration
- Lawrence Berkeley National Laboratory, Berkeley
- Institute of Particle Physics, Wuhan, China

## Outline

**Na Li            25th Winter Workshop on Nuclear Dynamics**

- Motivation
- Analysis
- Results
- Summary

## Motivation

- Formation of QGP in high-energy
- nuclear collisions:
- De-confinement
- Collectivity
- Local thermalization
-    ***Important questions ***
-  **We study with dataset of highest statistics**

## Anisotropy Parameters

- spatial
- space
- anisotropy

- momentum
- space
-  anisotropy

** ****Azimuthal correlation with**
**    ****the reaction plane. **
** ****Built up in the early stage,**
**    ****therefore supplies the**
**    ****early information of matter**
**    ****generated in the collision. **

## Motivation (cont.)

**Na Li            25th Winter Workshop on Nuclear Dynamics**

**Study the PID dependence of v****2**** and v****4.**

***R. S. Bhalerao et.al PLB 627, 49; ***
***Borghini and Ollitrault, PLB 642, 227 ***

**Study Number-of-Quark scaling.**
**           *****Range?***
**v****4****/v****2****2 ****: a probe of ideal hydro behavior. **

***STAR: ******Phys. Rev. C 77 (2008) 54901***

## Anisotropy Parameter v2

- Anisotropy Parameter v2

-  Baryon and meson elliptic flow follow the number of
-    quark ( *N**q* ) scaling.
-  Indicates that partonic flow builds up at RHIC.

***STAR: ******Phys. Rev. C 77 (2008) 54901***

** ****How about the**
**    ****higher order**
**    ****anisotropic flow**
**    ****such as v****4****? **

## Anisotropy Parameter v2 v4

- Anisotropy Parameter v2 v4

***Peter Kolb, PRC 68, 031902***

***STAR:  ******Aihong Tang,  Proc.***
***24******th****** Winter Workshop on Nuclear Dynamics***

**v****4 :  ****4****th**** harmonic**
** ****If system reaches local thermal equilibrium, according to ideal hydro dynamic calculation, v****4****/v****2****2 ****approaches 0.5 at high p****T ****region.**
** ****Directly related to the degree of thermalization of the medium.**

## Dataset and Cuts

**Na Li            25th Winter Workshop on Nuclear Dynamics**

**Tracks used for TPC event plane:****         **
**No. of fit hits > 15**
**No. of fit hits/No. of possible hits >0.52**
**0.1 < p****T**** < 2.0 GeV/c**
**|**** ****η**** ****| < 1.0**

**Tracks used for FTPC event plane:****         **
**6 =< No. of fit hits < 12**
**No. of fit hits/No. of possible hits > 0.52**
**0.1 < p****T**** < 2.0 GeV/c**
**2.5< |**** ****η**** ****| < 4.0**

## TPC Event Plane

**Na Li            25th Winter Workshop on Nuclear Dynamics**

**2****nd**** harmonic event plane**

**Detector bias is removed by applying**
**   ****phi weights to the tracks. **
** ****Phi weights are generated by**
**    ****inverting the normalized phi**
**    ****distributions of detected tracks for a**
**    ****large event sample.**

- (c)

## FTPC Event Plane

***J.Barrette et al. Phys. Rev. C56 (1997)3254 ***

** ****The event plane distribution is**
**    ****not flat after phi weight**
**    ****correction due to several**
**    ****acceptance effect of FTPC.**
** ****Add additional shift correction.**
** ****Large ****η **** gap is used to reduce**
**    ****the non-flow effect. **

## Invariant Mass Method

**Na Li            25th Winter Workshop on Nuclear Dynamics**

***Borghini*** ***et al. Phys. Rev. C70 (2006)4905 ***

**Assume**

- KS0

- STAR preliminary

- STAR preliminary

## Pion and Proton Identification

**Na Li            25th Winter Workshop on Nuclear Dynamics**

**TPC: pi/K ~ 0.7 GeV/c pi+K/p ~1.1 GeV/c**
**          ****pi/p ~ > 3GeV/c relativistic rise**

**Cuts used for identification:**
**No. of fit hits > 15**
**No. of fit hits/No. of possible hits >0.52**
**p****T ****< 1 (GeV/c)       -2 < n****σ****π (p)**** < 2**
**p****T ****> 2.5 (GeV/c)****    ****0 < nσ****π **** < 1**
**                              ****-1 < nσ****p****  < 0 ****	**

* **M. Shao, et al., Nuclear Instruments and Methods in Physics Research A 558 (2006) 419-429*

**pion purity: over 95%**
**proton purity: 70%**
**     ****The effect on proton v****2**** will be about 10%.**

**Using Run 4 data result**

## v2 {TPC} and v2 {FTPC} 

- v2 {TPC} and v2 {FTPC}

** **v2**(p****T****) have been measured for ********, p, K****S****0**** and ********.**
** **
** ****Non-flow effect reduced considerably by using the**
**    ****FTPC event plane.**

**Au+Au 200GeV (minibias)**

**Notes:**
minibais result for centrality 0-80%

## Number of Quark (Nq) Scaling

- Number of Quark (Nq) Scaling

** ****The number of quark scaling ****for ********, K****S****0**** and ******** ****holds**
**    ****up to ****(m****T ****– m)**/**n****q**** ~ 1 GeV/****c****2****. **
** ****Protons seem to deviate from the scaling at lower p****T.**** **

## v4 {TPC} 

- v4 {TPC}

** ****v****4****(p****T****) has been measured for ********, K****S****0**** and ********.**
**  **
** ****The *****N******q***** scaling ****for v****4**** is ****observed at ****(m****T ****- m)/n****q ****< 1 GeV/****c****2****,**
**    ****similar to that of v****2.****       ****	****   **

## Test of Ideal Hydro Predictions

**Na Li            25th Winter Workshop on Nuclear Dynamics**

** ****v****4**** /v****2****2  ****is about 1 at p****T**** ~ 2 GeV/c, larger than the value**
**    ****0.5 expected from ideal fluid calculations.**

## Summary

** ****FTPC event plane is used in STAR in order to reduce the **
**    ****non-flow effect. Run 7 high statistics data used in this**
**    ****analysis.**
** ****Proton and anti-proton seems to deviate from the**
**    ****number of quark scaling at ****(m****T ****- m)/n****q ****~ 1 GeV****/****c****2**** .**
** ****The number of quark scaling has been observed for v****4**** at**
**    ****(m****T ****- m)/n****q ****< 1 GeV****/****c****2****. **
** ****Mesons and baryons (********, K****S****0**** and ********) ****have similar v****4****/(v****2****)****2**
** ****   ****ratios. It is close to unity at p****T ****> 1 GeV/c, higher than**
**    ****ideal hydrodynamic model predictions.**** **

## BACK UP

**BACK UP**

## Number of Quark (Nq) Scaling

- Number of Quark (Nq) Scaling