# Presentation: 123936

## Directed flow of identified particles from Au+Au Collisions at RHIC

**Jiayun Chen**
***Institute of Particle Physics, Central China Normal Uni.***
***Brookhaven National Lab.***

## Outline

**Motivation**
**Data sample, **
**   ****Proton selections,**
**   ****& V0**** ****reconstruction**
**Event plane reconstruction**
**V****1 ****result**
**Discussion and Summary**

- Flow-meeting 07.1.4.

## Motivation

*p**t*

- Higher harmonics

- Anisotropic flow

- Directed flow (*v*1)

- Elliptic flow (*v*2)

**Motivation**

- Flow-meeting 07.1.4.

## Motivation 

**Motivation**

***Brachmann, Soff, Dumitru, et. al. , PRC 61 (2000) 024909.***
***L.P. Csernai, D. Roehrich                PLB 458, 454 (1999)      ***
***M.Bleicher and H.Stocker,               PLB 526,309(2002)***

- Anti-flow/3rd flow component, with QGP  *v**1* flat at middle rapidity.

- Directed flow (v1) and phase transition

- Flow-meeting 07.1.4.

## Motivation

- RQMD v2.4

***R.Snellings, H.Sorge, S.Voloshin, F.Wang, N. Xu, PRL (84) 2803(2000) ***

- Positive space-momentum correlation, no QGP necessary  *v**1* wiggle.

- Directed flow (*v**1*) and baryon stopping

- Flow-meeting 07.1.4.

## freeze-out of multi-strange hadrons
- at higher
  temperature Tfo
- with lower 
  collective
  velocity T
less interaction of strange hadrons with non-strange hadrons
sensitivity to the early, partonic stage

- freeze-out of multi-strange hadrons
**- at higher**
**  ****temperature T****fo**
**- with lower **
**  ****collective**
**  ****velocity ********T******
**less interaction of strange hadrons with non-strange hadrons**
**sensitivity to the early, partonic stage**

***Nucl. Phys. A757, 102 (2005)***

- Flow-meeting 07.1.4.

## Proton & Antiproton Selection

**Proton & Antiproton Selection**

- Common cut:
- |Primary Vertex|           < 30cm
- No. Dedx Points           > 10
- No. fit Points                 > 20
- No. fit Points/No. Max  [0.52,1.05]
- Global DCA                  < 1.0cm
- nSigma                         [-2.5,2.5]
- Proton:       0.4  < pT <1.0 (GeV/c)
- Antiproton: 0.15< pT <1.0 (GeV/c)
***DataSet:***
***62GeV  Au+Au Minimum Bias***
***200GeV Au+Au Minimum Bias***

**STAR Preliminary**

- Flow-meeting 07.1.4.

## V0s reconstruction

**cuts:**
**Distance of closest approach(DCA) **
**         ****between daughters                          < 0.8cm**
**DCA of V0 to Primary Vertex (PV)       < 0.5cm**
**Daugter’s DCA to PV                            > 0.8 cm**
**decay length                                          > 6.0cm**
**daughter’s Tpc Hits                              > 15**

**0.48<mass<0.51**

**1.11<mass<1.12**

**1.11<mass<1.12**

- Flow-meeting 07.1.4.

## Event Plane reconstruction

-     the event plane vector        and the event plane angle            from the nth  harmonic of the particle’s azimuthal distribution are defined by the equations:
-          -- the azimuthal angle of the ith particle in the event plane determination
-          -- weights

- Flow-meeting 07.1.4.

## Flattening Event Plane

**Flattening**** Event Plane**

**Step 1:**
- Apply weight which can be
- determined with the inverse
- of the bin content in the raw 
- distribution.
**Step 2:**
- Make corrections to the event
- plane angle itself, & flatten
- the event plane distribution.
- The corrected event plane
- angle is

***E877 Collaboration,  J. Bareeette et al, Phys.Rev.Lett.70,2996(1993) ***

**FTPC Event Plane distribution**

**ZDCSMD Event Plane distribution**

- Flow-meeting 07.1.4.

## After the flatness of FTPC & ZDCSMD Full EP. 
The final event plane used is defined by the sum of 

Where 

or 

weight is from resolution

- The final event plane used is defined by the sum of
- Where
- or
- weight is from resolution

**Combined ****Event Plane**

- Flow-meeting 07.1.4.

## Resolution of FTPC,ZDCSMD,{FTPC,ZDCSMD}(62GeV Au+Au)

- The event plane resolution is enhanced by
- combining EP of FTPC & ZDC-SMD with proper weight.

**STAR Preliminary**

- Flow-meeting 07.1.4.

## Proton & Antiproton v1 vs. Rapidity(62GeV)

* **Proton         0.4<p**T**<1.0 (GeV/c) *
-     v1=ay  dv1/dy = -0.4± 1.1
* **Antiproton   0.15<p**T**<1.0 (GeV/c) *
-     v1=ay   dv1/dy =  1.3± 1.5

**30%-60%**

**with combined RP**

**STAR Preliminary**

** ****Proton v****1**** is less than 1%,**
** ****Antiproton v****1**** is less than 2%.**

**30%-60%**

**STAR Preliminary**

- Flow-meeting 07.1.4.

## Proton & Antiproton v1 vs. Rapidity(200GeV)

**Proton & Antiproton v****1**** *****vs.***** Rapidity(****200GeV****)**

-  *Proton            0.4<p**T**<1.0 (GeV/c) *
-     v1=ay    dv1/dy = -2.6± 2.9
-  *Antiproton      0.15<p**T**<1.0 (GeV/c) *
-     v1=ay     dv1/dy =  3.1± 3.1

**with combined RP**

**STAR Preliminary**

**30%-60%**

- Flow-meeting 07.1.4.

## v1=ay   dv1/dy =-3.2±1.7

- v1=ay   dv1/dy =-3.2±1.7

**K****s**** v****1**** *****vs.***** Rapidity(62GeV)**

**STAR Preliminary**

- Flow-meeting 07.1.4.

## Work in progress.

****** ****& ******** ****v****1**** *****vs.***** Rapidity**

**STAR Preliminary**

**STAR Preliminary**

- Flow-meeting 07.1.4.

## Summary

- The event plane resolution is enhanced by combining EP of FTPC & ZDC-SMD with proper weight;
- Au+Au 62.4GeV/c
- Proton v1 is less than 1%.
- AntiProton v1 is less than 2%.
- Made an attempt to study directed flow of K0S & , .
- Looking forward to analyzing run VII’s data (~60M MB events).

- Flow-meeting 07.1.4.