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

Grazyna Odyniec QM 2008, Jaipur, India, February QCD phase diagram M.Stephanov, hep-ph/ v1 (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:

Grazyna Odyniec QM 2008, Jaipur, India, February 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

Grazyna Odyniec QM 2008, Jaipur, India, February “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

Grazyna Odyniec QM 2008, Jaipur, India, February 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…?

Grazyna Odyniec QM 2008, Jaipur, India, February 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

Grazyna Odyniec QM 2008, Jaipur, India, February RHIC run 10 (fall 2009)  s NN [p ft ] GeV [GeV/c]  B [MeV] [Hz] Days/ Mevent # events# beam days 4.6 [9.6]570395M [18.8]470745M [27.9] M [37.7] M [71.0] M [161]220> M [391]150> M1.5 (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: CERN (starting in 2010): 10, 20, 30, 40, 80, 158 GeV/c

Grazyna Odyniec QM 2008, Jaipur, India, February STAR TPC image of 9 GeV Au+Au, taken on June 7, 2007 (run , 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

Grazyna Odyniec QM 2008, Jaipur, India, February 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 ?

Grazyna Odyniec QM 2008, Jaipur, India, February 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)

Grazyna Odyniec QM 2008, Jaipur, India, February 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

Grazyna Odyniec QM 2008, Jaipur, India, February Triggering impact parameter GeV BBC InnerBBC OuterBBC InnerBBC Outer 0<b< <b< <b< b> 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 ?)

Grazyna Odyniec QM 2008, Jaipur, India, February 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

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

Grazyna Odyniec QM 2008, Jaipur, India, February Summary The unique RHIC energy scan program will map the QCD diagram in  s NN =5-50 GeV, (corresponding to  B ~ 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 > PID –low energy e-cooling at RHIC extremely beneficial

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

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

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