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

1. 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

2. QCD phase diagram M.Stephanov, hep-ph/0402115v1 (March 2006) Predictions (models, lattice) for location of CP: 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 mB and T QM 2008, Jaipur, India, February 2008

3. Beam Energy Scan at RHIC: sNN ~ 5-50 GeVexperimental window to QCD phenomenologyat 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 QM 2008, Jaipur, India, February 2008

4. “sQGP” at RHIC top energy RHIC At RHIC: LHC • mT-NQ scaling • partonic collectivity • deconfinement RHIC experiments in agreement hot and dense matter with partonic collectivity has been formed at RHIC QM 2008, Jaipur, India, February 2008

5. Some indications at lower energies – NA49 at SPS NA49 PRC 40A GeV proton v2 non-monotonic K+/p+ behavior,“horn”, but dynamical fluctuations quite monotonic…? collapse of proton v2 - signature of phase transition (Stoecker,Shuryak), but result depends on analysis technique … ? inconclusive QM 2008, Jaipur, India, February 2008

6. Access to large range of mB 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 QM 2008, Jaipur, India, February 2008

7. RHIC run 10 (fall 2009) (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 QM 2008, Jaipur, India, February 2008

8. STAR experience with Low Energy RHIC running see D. Cebra talk observed apparent rates of collisions surprisingly high (?!) to do: (1) understand background (2) optimize triggering 2001: 19.6 GeV Au+Au 2004: 22.4 GeV Cu+Cu 2007: 9 GeV Au+Au 2008: 9 (5?) GeV Au+Au STAR TPC image of 9 GeV Au+Au, taken on June 7, 2007 (run 8158119, ev.44), figure from Jeff Langraf QM 2008, Jaipur, India, February 2008

9. 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 ? QM 2008, Jaipur, India, February 2008

10. STAR experiment readiness for Low Energy Run STAR will measure : yields and particle ratios T vs mB, particle spactra (pt, rapidity, …), strangeness production (K/p, 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) QM 2008, Jaipur, India, February 2008

11. 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 QM 2008, Jaipur, India, February 2008

12. Triggering 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 ?) QM 2008, Jaipur, India, February 2008

13. Particle Identification in STAR log10(dE/dx) log10(p) TOF completed in 2010 • TOF alone: (p,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) PID capabilities (stat.) cover a broad range: ~ 0.2 – 12 GeV/c QM 2008, Jaipur, India, February 2008

14. Reaction Plane Determination v1 Kejun Wu v2 Good reaction plane resolution – a new detector under consideration QM 2008, Jaipur, India, February 2008

15. Summary • The unique RHIC energy scan program will map the QCD diagram in sNN =5-50 GeV, (corresponding to mB ~ 600-150 MeV) • systematic study of collective dynamics and fluctuations with p, L, X, W, p, K, K*, r, f... • turning off partonic activities (e.g. v2 of f, W, D – no NQ scaling, quenching ->0, …) • STAR detector with 2p 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 QM 2008, Jaipur, India, February 2008

16. THANKS ! QM 2008, Jaipur, India, February 2008