# Presentation: 889442

## STAR highlights and

**STAR highlights and**
**physics update of the FTPCs   **
**Joern Putschke**

## Outline

**The FTPCs at STAR**** **
**Jet quenching (initial/final state ?)**** **
**Flow measurements**
**Directed Flow v****1**
**Elliptic Flow v****2**** **
**Charged particle spectra**
**Au+Au analysis**
**d+Au analysis**

## RHIC

## The STAR detector

## The Forward TPCs

**2 FTPCs **
**2.5 < |********| < 4.0**
**6 azimuthal sectors (~60 deg.) with 10 rows in z- direction **
**Electron drift radial and perpendicular to the magnetic field**
**Spatial res. ******** 0.1 mm**
**Two track res. ******** 1.5 mm**

## Heavy Ion Collision (animation)

## Heavy Ion Collisions

- 1) Initial condition:	2) System evolves:	3) Bulk freeze-out:
-  Baryon transfer	- parton/hadron expansion	- hadronic dof
- - ET production	- final state interactions	- inel. interactions cease:
-  Partonic dof		  particle ratios, Tch, B
-  		- elas. interactions cease
- 		  particle spectra, Tth, <T>

## Collision Geometry

**Notes:**
The sketch on the left shows an example for a non central collision. The overlap region with the participating nucleons is shown in orange, while the remnants of two Au nuclei travel along the z-axis. There is no direct measure of an impact parameter – the initial distance of the center of both nuclei -. One can define the collision centrality the number of produced particles in the final state, where in the highest multiplicities are produced in the most central collisions.  The measured multiplicity distribution shown on the right can then be divided in different centrality bins. 

## Azimuthal distributions in Au+Au

**Azimuthal distributions in Au+Au**

## Is suppression an initial or final state effect? 

## Azimuthal distributions

- Near-side: p+p, d+Au, Au+Au similar
- Back-to-back: Au+Au strongly suppressed relative to p+p and d+Au

- Suppression of the back-to-back correlation in central Au+Au is a final-state effect

## Motivation of flow measurements

**Equation of State of nuclear matter under extreme****conditions unknown**** **
**Investigation of „early times“ in the evolution****of the hot, dense central collision region possible**** **
**FTPCs allow substantial extension of TPC****measurements (sign of elliptic flow / directed flow)**

## Definition of anisotropic flow

- Anisotropic flow  any correlationwith respect to the reaction plane

## Directed flow v1 at RHIC 

**Directed flow v****1**** at RHIC **

* *First measurement of directed flow at RHIC
* *Correlation* *of directed and elliptic flow axes shows that v2 is in the reaction plane
-  Consistent with a “limiting fragmentation” hypothesis.

## v2 measurements in the FTPCs 

## v2 comparison with Hydro

-  v2 at low pt reach Hydro limit => collective motion
-  v2 at high pt in qualtiative agreement with “jet-quenching” scenario

## FTPC track finding efficiencies

- FTPC track finding eff. flat over selected pt and  range
- for all centrality classes (expect ~90% for dAu).

**20k AuAu minbias embedded ********-  (5% of total FTPC mult.) with flat p****t**** dist.**** **

## FTPC momentum resolution

-  FTPC momentum resolution around 15%, degrades to 40% at =3.5 and pt=1 GeV/c
-  FTPC  resolution better than 0.02 units
-  Systematic underestimation of pt up to 5% at =3.5 for 0.1<pt<1 GeV/c

## Pseudorapidity distribution in Au+Au

- Good agreement between PHOBOS and FTPC dN/d dist.
- applying constant eff. corrections depending on centrality.

- 200k minbias AuAu events

**dots = PHOBOS [Phys. Rev. Lett. 91,052303 (2003)]**

## <pt> as a function of centrality

- <pt> increases with centrality and seems to saturate at high centrality.
- Consistent picture with <pt> vs. centrality at mid-rapidity and Hydro.

## d+Au pt spectra

- 200k minbias dAu events corrected for vertex-finding efficiency
- Centrality selection with TPC multiplicity

**FTPC west = d-side**
**FTPC east = Au-side**

**(power-law fit)**

## d+Au particle density asymmetry

-  charged particle asymmetry clearly visible in the FTPCs
-  Saturation model (CGC) inconsistent with data
-  qualitative agreement with microscopic HIJING model

## d+Au RCP in the FTPCs

| centrality [%] | <Nbin> |
| --- | --- |
| 0-20 | 15 |
| 20-40 | 10.2 |
| 40-100 | 4 |
| minbias | 7.5 |

- Strong centrality dependence at d-side for RCP visible.
- Could be explained by the “stopping” of the deuteron.

## Summary

**Strong suppression of the back-to-back correlations (and the inclusive yields) in central Au+Au collisions are due to *****final-state interactions***** with the *****dense medium***** generated in such collisions**** **
**Directed flow (v****1****) measurement confirms *****in-plane***** elliptic flow (v****2****)**** **
**v****2 ****reaches Hydro limit at low p****t**** and indicates a pressure driven collective expansion at the early stage of a heavy ion collision**** **
**v****2**** at high p****t**** in qualitative agreement with *****jet-quenching***** scenario**
**Centrality dependence of <p****t****> at mid- and forward rapidity follows the same behaviour and consistent with Hydro expectations**** **
**Charged particle density asymmetry measurements in d+Au disfavor parton saturation model => consistent picture with back-to-back correlation observations in d+Au**

## The STAR FTPC group

**The STAR FTPC group**

**Volker Eckardt**
**Maria Mora Corral**
**Joern Putschke**
**Norbert Schmitz**
**Janet Seyboth**
**Peter Seyboth**
**Frank Simon**

**Weissmies (4023m), Switzerland [2003]**

## backup slides 

## Inclusive yield relative to binary-scaled p+p

- Suppression of the inclusive yield
- in central Au+Au is a final-state effect

-  d+Au : enhancement
-   Au+Au: strong suppression
-  pT=4 GeV/c:
- cent/minbias = 1.110.03
-  central collisions enhanced wrt minbias

## Event plane angle correlations FTPC & FTPC+TPC

## Particle ratios

- Evidence for _thermal equilibrium_ at high temperature and density.
- RHIC increasing ****s: same temperature, decreasing baryon density.

**Particle ratios**

## FTPC pion acceptance