1. Grazyna Odyniec 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. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 2 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:

3. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 3 Beam Energy Scan at RHIC:  s NN ~ 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: (1) properties of hypothesized sQGP (2)boundary between hadronic and partonic phases (3)possible critical point

4. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 4 “sQGP” at RHIC top energy LHC RHIC RHIC experiments in agreement (1)m T -NQ scaling (2)partonic collectivity (3)deconfinement At RHIC: hot and dense matter with partonic collectivity has been formed at RHIC

5. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 5 Some indications at lower energies – NA49 at SPS 40A GeV proton v 2 NA49 PRC 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…?

6. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 6 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

7. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 7 RHIC run 10 (fall 2009)  s NN [p ft ] GeV [GeV/c]  B [MeV] [Hz] Days/ Mevent # events# beam days 4.6 [9.6]570395M45 6.3 [18.8]470745M20 7.6 [27.9]4101325M10 8.8 [37.7]380201.55M7.5 12 [71.0]300540.55M2.5 18 [161]220>1000.255M1.5 28 [391]150>1000.255M1.5 (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

8. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 8 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 STAR experience with Low Energy RHIC running see D. Cebra talk

9. Grazyna Odyniec 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 ?

10. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 10 STAR experiment readiness for Low Energy Run STAR will measure : yields and particle ratios T vs   particle spactra (p t, rapidity, …), strangeness production (K/ , multistrange, …), fluctuations and correlations (including forward-backward corr), flow (v 1,v 2,v 4, …) 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)

11. Grazyna Odyniec 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) t 0 for TOF is under discussion to achieve those goals, we need: (1)triggering (2)PID (TOF completed by 2010) (3)reaction plane determination but rates without low energy e-cooling: ~5 Hz at 4.6 GeV; with e-cooling much better

12. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 12 Triggering impact parameter AuAu @ 5 GeVAuAu @ 8.75 GeV BBC InnerBBC OuterBBC InnerBBC Outer 0<b<35271254 3<b<611302157 6<b<922353940 b>94430668 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 ?)

13. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 13 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) log 10 (p) log 10 (dE/dx) TOF completed in 2010 PID capabilities (stat.) cover a broad range: ~ 0.2 – 12 GeV/c

14. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 14 Reaction Plane Determination Kejun Wu Good reaction plane resolution – a new detector under consideration v1v1 v2v2

15. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 15 Summary The unique RHIC energy scan program will map the QCD diagram in  s NN =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. v 2 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

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

17. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 17 ETRA SLIDES

18. Grazyna Odyniec QM 2008, Jaipur, India, February 2008 18 Triggering at low energies: e.g.BBC&&CTB(TOF)