STAR Plans for Low Energy Running

1. STAR Plans for Low Energy Running Paul Sorensen for QCD at High Temperature — BNL — July, 2006

2. RBRC workshop

3. M. Stephanov: hep-ph/0402115 location of the critical point

4. Ejiri, et.al. Taylor Expansion Gavai, Gupta Taylor Expansion Fodor, Katz Lattice Re-weighting M. Stephanov: hep-ph/0402115 location of the critical point

5. Ejiri, et.al. Taylor Expansion Fodor, Katz Lattice Re-weighting M. Stephanov: hep-ph/0402115 Gavai, Gupta B Lower Limit B √sNN ——————————————————— 180 MeV 25 GeV 420 MeV 7.5 GeV 725 MeV 4.5 GeV ——————————————————— Cleymans, et.al. location of the critical point

6. C. Nonaka Focusing by the hydro evolution could cause many initial conditions to cross the critical point region: broadening the signal region Correlation lengths expected to reach at most 2 fm  pT<0.5 GeV/c (Berdnikov, Rajagopal and Asakawa, Nonaka): reduces signal amplitude We shouldn’t count on sharp discontinuities focusing

7. The Horn STAR Preliminary experimental indications?

8. STAR and NA49 Measurements larger k/ fluctuations could be due cluster formation at 1st order p.t. (Koch, Majumder, Randrup) critical point could be above √sNN~15 GeV large possible increase in dv2/dpT seen between 17 and 62.4 GeV (but not between 62.4 and 200) experimental indications?

9. C. Pruneau QM05 STAR: 5% Central Au+Au PHENIX ||<0.35, =/2 CERES 2.0<  <2.9 large increase in dv2/dpT seen between 17 and 62.4 GeV (but not between 62.4 and 200) same shape for alternative variable dyn experimental indications?

10. Some Key Measurements • yields and particle ratios  T and B •elliptic flow v2 collapse of proton flow? •k/, p/, pT fluctuations  the critical point signal •scale dependence of fluctuations  source of the signal •v2 fluctuations  promising new frontier? focus

11. STAR’s Ability to Achieve yields: triggering and centrality determination elliptic flow: event-plane resolution k/, p/:efficiency, pid, andsystematics scale dep.: statistics v2 fluct.: statistics, statistics I don’t discuss machine performance or projected number of weeks etc. outline

12. BBC BBC • Designed and built for these measurements • “The Solenoidal Tracker at RHIC (STAR) will search for signatures of quark-gluon plasma (QGP) formation and investigate the behavior of strongly interacting matter at high energy density. The emphasis will be on the correlation of many observables on an event-by-event basis… This requires a flexible detection system that can simultaneously measure many experimental observables.” • STAR Conceptual Design Report (July 1992) STAR Detector

13. UrQMD Beam Rapidity BBC Inner  dN/d BBC Outer   T. Nayak Potential problem: losing acceptance in trigger detectors Simulations show that particles will impinge on the Beam-Beam-Counters acceptance for triggering

14. BBC Inner: 3.3 to 5.0 BBC Outer: 2.1 to 3.3 Number of particles striking the STAR Beam-Beam Counters (UrQMD Simulations). (scintillator tiles) Simulations indicate that STAR’s BBCs will be adequate for triggering Centrality can be taken from reference multiplicity  expected number of particles is larger than what is used for p+p collisions triggering

15. log10(dE/dx) log10(p) PID capabilities over a broad pT range: TPC dE/dx, ToF, Topology, EMC, etc. no anticipated obstacles to measuring particle spectra and ratios (T and B) but… some fluctuation analyses need track-by-track I.D. particle identification

16. Surprisingly: • v2 at SPS may be similar to RHIC v2 (when comparison is made with same centrality and within same y/ybeam interval) • ~15% difference (when systematic errors are taken into account) • but larger <pT> • Scanning < 62.4 GeV with • advanced analysis techniques • more ideal detector • has potential for discovery v2 motivation slide

17. NA49 PRC 40A GeV proton v2 • collapse of proton v2: signature of phase transition (H. Stöcker, E. Shuryak) • but resultdepends on analysis technique • difference between v2{4} and v2{2} depends on non-flow andfluctuations • is itnon-flow or fluctuations?A signature of the critical point? • STAR can clarify with updated analysis techniques and a more ideal detector v2 motivation slide

18. better resolution means smaller errors than NA49 • (given the same number of events) • NA49 flow PRC used less than 500k events per energy • STAR will excel in these measurements • Quark-number scaling and  v2 accessible • (requires 2x No. Events as 200 GeV) • Estimates made using: • v2 from NA49 measurements • estimate the dN/dy using 1.5*Npart/2 • use tracks with |y|<0.5 (should be able to do better) • simulate events STAR NA49 event-plane resolution

19. precise v2 measurements require knowledge of: • non-flow g (non-event-plane correlations) and v2(e-by-e v2 fluctuations) • Q distribution depends on v2, v2 and g(Qx=∑cos(2) and Qy=∑sin(2)) • potential for discovery: v2 fluctuations near the critical point • but measurement relies on the tail of the distribution and needs statistics simulations simulations large v2 small v2 v2 = 0 v2 = 0 v2 fluctuations

20. no clear fluctuation signal seen at k/ horn UrQMD: matches p/ but not k/ what to make of the energy dependence? K/ fluctuations

21. proton z = ln{dE/dx} - ln{Bethe-Bloch} pion protons kaon kaons efficiency z for kaons pions electrons momentum p (GeV/c) transverse momentum pT (GeV/c) O. Barannikova, J. Ulery mis-identification K K/ (K+1)/(-1) or (K-1)/(+1) K/ fluctuations can be distorted electron contamination pions leptons that look like kaons mixed events can’t compensate kaon decays:K+ + (c=3.7 m) tracking efficiency < 50% PID cuts reduce efficiency another 50% kaon detection isn’t great: ToF will help(but a new start-time detector is needed) statistical and systematic errors depend on # of events and detector upgrades K/ fluctuation: challenges

22. Simulations Counts (K++K-)/(++-) • 100k central 40 AGeV Au+Au events: statistical errors only • with ToF 5% (relative) without 11% (relative) • but systematic errors are dominant • particle mis-identification changes the width of the distribution • 1% K swapping: width 10% 2% swapping: width 20% K/ fluct. error estimate

23. PHENIX: Phys. Rev. Lett. 93, 092301 (2004) STAR Preliminary all charged tracks (CI) like-sign - unlike-sign (CD) • full acceptance is important: elliptic flow could enhance apparent pT fluctuations in measurements without 2 coverage (but it’s difficult to compare) • differential analyses are often essential for correct interpretation pT fluctuations

24. pT fluctuations

25. fluctuations correlations residual /ref (GeV/c)2 variance excess scale = full STAR acceptance D. Prindle, L. Ray, T. Trainor • correlations lead to fluctuations • variance excess can be inverted to pT angular correlations /ref • elliptic flow, near/away-side and medium response components revealed • reveals origins of the pT fluctuations signal • at RHIC v2, mini-jets, medium-response: what about at 7.6 GeV? fluctuation inversion

26. clear potential for discovery • ,p v2 more precise/accurate with ~half the events used by NA49 • pT and particle ratio fluctuations (address systematics) • event-by-event v2 fluctuations • Part of the interesting range may lie above RHIC injection energy • RHIC covers a unique B range • ————————————————————————————— • real potential exists with only 100k events but we should be sure we have enough data • “after we do the scan we don’t want to end up with all the same uncertainties!” • paraphrasing R. Stock (RBRC workshop) conclusion

27. thanks

28. lost regions • some low pT particles can make it in • inner BBC tiles may not be useful • STAR detector acceptance • TPC: =1 • =40.4 (0.705 rad) • FTPC: =2.5 =4.0 • =9.39 =2.1 • BBC • inner: =3.3 =5.0 • =4.2 =0.77 • BBC • outer: =2.1 =3.3 • =14 =4.2 BBC Acceptance

29. STAR detector acceptance TPC: =1 =40.4 (0.705 rad) FTPC: =2.5 =4.0 =9.39 =2.1 BBC inner: =3.3 =5.0 =4.2 =0.77 BBC outer: =2.1 =3.3 =14 =4.2 For this energy the TPC will cover |y|<1.0 while NA49 covered -0.4<y<1.8 We should have similar multiplicities but the STAR acceptance will be more uniform acceptance √sNN=8.8 GeV

30. Gavai, Gupta 2005 Taylor Expansion location of the critical point

31. S. Voloshin Hydrodynamic interpretation still evolving as analyses progress Energy dependence plays an important role in our interpretations v2 motivation slide

32. M. Stephanov: hep-ph/0402115 location of the critical point

33. Questions remain regarding validity/stability of all lattice results for non-zero B location of the critical point