# Presentation: 312230

## STAR physics program and technical challenges with the RHIC Au+Au energy scan 

*Grazyna Odyniec/LBNL*
*for STAR collaboration*
***                  ******QM 2008****, Jaipur, *
*                       **India, February 2008*

- Outline :
- HI - study exp. QCD phase diagram
- BES at RHIC Program
- Experimental questions

## QCD phase diagram

*M.Stephanov, hep-ph/0402115v1 (March 2006)*

- dense & hot medium
- deconfined phase (partonic dof)
- continuous transition (crossover)
- critical point (CP)
- hadron gas

- Search for CP needs measurements over a _broad range of ____B__ and T_

- Predictions (models, lattice) for location of CP:

## Beam Energy Scan at RHIC: sNN ~ 5-50 GeVexperimental window to QCD phenomenology at finite temperature and and baryon number density

- At RHIC : indications of sQGP found
- but remain _unknown_:
-  properties of hypothesized sQGP
- boundary between hadronic and partonic phases
- possible critical point

## “sQGP” at RHIC top energy

- LHC

- RHIC

-  RHIC experiments _in agreement_

- mT-NQ scaling
- partonic collectivity
- deconfinement

- At RHIC:

***hot and dense matter with ***_***partonic collectivity***_*** ***
***has been formed at RHIC***

## Some indications at lower energies – NA49 at SPS

- collapse of proton v2 - signature of phase transition (Stoecker,Shuryak), but result depends on analysis technique ... ?

- _inconclusive_

- non-monotonic K+/+ behavior,“horn”, but  dynamical fluctuations quite monotonic...?

## Access to large range of  and T

- Beam Energy Scan (BES)  at RHIC + SPS + FAIR

- RHIC:
- advantage of _collider geometry_ !

- At fixed target geometry:
- detector acceptance changes with energy
- track density at mid-y increases fast with energy
- -> technical difficulties in tracking

## RHIC run 10 (fall 2009)

| sNN [pft]
GeV [GeV/c] | B [MeV] | <BBC Rate> 
[Hz] | Days/
Mevent | # events | # beam days |
| --- | --- | --- | --- | --- | --- |
| 4.6   [9.6] | 570 | 3  | 9  | 5M | 45  |
| 6.3  [18.8]  | 470 | 7  | 4  | 5M | 20  |
| 7.6  [27.9]   | 410 | 13  | 2  | 5M | 10 |
|  8.8  [37.7] | 380 | 20  | 1.5  | 5M | 7.5  |
|  12  [71.0] | 300 | 54  | 0.5  | 5M  | 2.5  |
| 18  [161] | 220 | >100  | 0.25  | 5M  | 1.5  |
| 28  [391] | 150 | >100  | 0.25  | 5M  | 1.5  |

- (1) Large energy range  accessible
- (2) Collider geometry (acceptance won’t change with S, track density varies slowly)
- (3) STAR detectors well suited (large acceptance), tested & understood

- STAR PAC 2007 Strawman proposal:

- Note: NA61 @ CERN (starting in 2010): 10, 20, 30, 40, 80, 158 GeV/c

## STAR experience with Low Energy RHIC running

*STAR TPC image of 9 GeV Au+Au, taken on June 7, 2007 (run 8158119, ev.44), figure from Jeff Langraf*

- 2001:  19.6 GeV Au+Au
- 2004:  22.4 GeV Cu+Cu
- 2007:     9 GeV Au+Au
- 2008:   9 (5?) GeV Au+Au

- observed apparent rates of collisions surprisingly high (?!)
- _to do_: (1) understand background
-           (2) optimize triggering

- see D. Cebra talk

## Analysis of 9 GeV run data (June 2007)

- Preliminary conclusions very optimistic, but
- 	.... in 2500 events on tape fewer than 1 % vertex candidates were found
- During 2008 d+Au run a contribution to the BBC coincidence rate from _beam-background coincidence_ was identified:

- - background can explain almost entire event rate during the low energy test
-  actual event rate is unknown and could be very low
-  time for physics program may be underestimated
- BBC alone is not a good measure of luminosity for the low energy run -> new run: **BBC&&CTB(TOF)**
**                                                                                                                         ****trigger ** ?

##     STAR experiment readiness for Low Energy Run

- _STAR will measure_ :  yields and particle ratios       **T vs **************
- 		particle spactra (pt, rapidity, ...),
- 		strangeness production (K/, multistrange, ...),
- 		fluctuations and correlations (including forward-backward corr),
- 		flow (v1,v2,v4, ...) with charged and identified particles,
- 		HBT radii,
- 		(if statistics adequate - possibly charm, jets/high pt, ...)
-              _Search for_ : - disappearance of partonic activities
- 	               - fluctuations, correlations

-  turn _on and off_ signature of deconfinement
-                                                                    (-> simulations showing sensitivity-work in progress)

## Experimental challenges at low energy run 

- _under discussion_:
- new detector (RPSD) to (1) determine reaction plane
-  and (2) t0 for TOF is under discussion

- _to achieve those goals_, we need:
- triggering
- PID (TOF completed by 2010)
- reaction plane determination

- but rates without low energy e-cooling: ~5 Hz at 4.6 GeV; with e-cooling _much_ better

## Triggering

| impact parameter | AuAu @ 5 GeV |  |  | AuAu @ 8.75 GeV |  |
| --- | --- | --- | --- | --- | --- |
|  | BBC Inner | BBC Outer |  | BBC Inner | BBC Outer |
| 0<b<3 | 5 | 27 |  | 12 | 54 |
| 3<b<6 | 11 | 30 |  | 21 | 57 |
| 6<b<9 | 22 | 35 |  | 39 | 40 |
| b>9 | 44 | 30 |  | 66 | 8 |

- BBC is sensitive down to single MIP hitting the detector
- BBC Upgrade: 1 PMT for each tile (important at low energies)
- BBC can _effectively trigger_ for low energy runs   (-> centrality from reference multiplicity), but one needs to worry about background -> new test run March 2008  (BBCx&&CTB/TOF ?)

## Particle Identification in STAR

- TOF alone: (,K) up to 1.6 GeV/c, p up to 3 GeV/c
- TOF+TPC(dE/dx, topology) up to 12 GeV (NIMA **558** (419) 2006)

- TOF completed in 2010

-  PID capabilities (stat.) cover a broad range: ~ 0.2 – 12 GeV/c

## Reaction Plane Determination

- Kejun Wu

- Good reaction plane resolution –
- a _new detector_ under consideration

- v1

- v2

## Summary

- The unique RHIC energy scan program will map the QCD diagram
- 	in sNN =5-50 GeV, (corresponding to B ~ 600-150 MeV)
- systematic study of collective dynamics and fluctuations with p, , , , , K, K*,, 
- turning off partonic activities (e.g. v2 of ,  D – no NQ scaling, quenching ->0, ...)
- STAR detector with 2 acceptance is ready to carry out this program
- can trigger on low energy events (tests)
- full TOF in 2010  -> PID
- low energy e-cooling at RHIC extremely beneficial

## THANKS !

**THANKS !**

## ETRA SLIDES

**ETRA SLIDES**

##       Triggering at low energies: e.g.BBC&&CTB(TOF)