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STAR Physics Overview and Future Upgrades

STAR Physics Overview and Future Upgrades. Tim Hallman. International CCAST Summer School and Workshop On QCD and RHIC Physics Beijing, China August 9-14, 2004. Time Projection Chamber. FTPCs (1 + 1).

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STAR Physics Overview and Future Upgrades

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  1. STAR Physics Overview and Future Upgrades Tim Hallman International CCAST Summer School and Workshop On QCD and RHIC Physics Beijing, China August 9-14, 2004

  2. Time Projection Chamber FTPCs (1 +1) Vertex Position Detectors The STAR Detector Magnet Silicon Vertex Tracker * Coils TPC Endcap & MWPC ZCal ZCal ZCal BBCs Endcap Calorimeter Central Trigger Barrel + TOF patch + TOFr Barrel EM Calorimeter

  3. Au on Au Event at sNN = 130 GeV Central Event

  4. What does (will) STAR Measure ? J/y, D, W f X L p, K, D, p d, K*, L(1520), Σ* partonic scatterings? early thermalization? Initial Condition -initial scatterings - baryon transfer - ET production - parton dof System Evolves -parton interaction - parton/hadron expansion Bulk Freeze-out - hadron dof - interactions stop Q2 time All of these particles (and more): yields/spectra/correlations

  5. STAR has produced a wealth of data from the first RHIC runs: Time for a critical evaluation of the evidence regarding formation of a QGP in RHIC Collisions ! Jamie Dunlop (BNL) Huan Huang (UCLA) Peter Jacobs (LBNL) Mike Lisa (Ohio State U.) Raimond Snellings (NIKHEF) Steve Vigdor (Indiana U. -- Chair) Nu Xu (LBNL) Zhangbu Xu (BNL) Focus group to help shape STAR’s discussion of: Predicted Signatures of the QGP Bulk Properties Hard Probes Open Issues (experimental and theoretical)

  6. QGP  a (locally) thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons, so that color degrees of freedom become manifest overnuclear,rather than merely nucleonic, volumes. • We do not require: • non-interacting quarks and gluons • 1st- or 2nd-order phase transition • evidence of chiral symmetry restoration Our def’n is consistent with that of the community large, but contrasts with other recent def’ns and the assertion that “it must have a QGP because” it is: Start by Defining QGP : Approximately thermalized matter at energy densities so large that the simple degrees of freedom are quarks and gluons. This energy density is that predicted by LGT for the existence of a QGP,  2 GeV/fm3.

  7. Lattice QCD Still Predicts a RAPID Transition! The most realistic calcs.  no discontinuities in thermodynamic proper-ties @ RHIC conditions (i.e., no 1st- or 2nd-order phase transition), but still crossover transition with rapid evolution vs. temperature near Tc 160 – 170 MeV. in entropy density, hence pressure in chiral condensate in heavy-quark screening mass

  8. P. Kolb, J. Sollfrank, and U. Heinz, Phys. Rev. C. C62 054909 (2000). Early Expectations of an Interesting Energy-Dependence: Early mixed-phase hydro evolution …  Soft EOS dip in v2(sNN)? Energy density 

  9. But What We Observe (at least in the soft sector) Appears Smooth : HBT parameters Charged particle pseudo-rapidity density pT-integrated elliptic flow, scaled by initial spatial eccentricity pT-integrated elliptic flow No exp’tal smoking gun!  Rely on theory-exp’t comparison  Need critical evaluation of both! Theory must eventually explain the smooth energy- and centrality-dependences.

  10. Soft Sector: Evidence for Thermalization and EOS with Soft Point? Hydro calculations: Kolb, Heinz and Huovinen • Systematic m-dependence of v2(pT) suggests common transverse vel. field • mT spectra and v2 systematics for mid-central collisions at low pT are well (~20-30% level) described by hydro expansion of ideal relativistic fluid • Hydro success suggests early thermalization, very short mean free path • Best agreement with v2 and spectra for therm < 1 fm/c and soft (mixed-phase- dominated) EOS ~ consistent with LQCD expectations for QGP  hadron

  11. How Unique & Robust is Hydro Account in Detail? P. Kolb, J. Sollfrank, and U. Heinz, Phys. Rev. C. C62 054909 (2000). • Are we sure that observed v2 doesn’t result alternatively from harder EOS (no transition) and late thermalization? • How does sensitivity to EOS in hydro calcs. compare quantitatively to sensitivity to other unknown features: e.g., freezeout treatment (compare figures at right), thermaliz’n time, longitudinal boost non-invariance, viscosity? • What has to be changed to understand HBT (below), and what effect will that change have on soft EOS conclusion? Sharp freezeout  dip Hydro+RQMD  no dip? Hydro vs. STAR HBT Rout/Rside Teaney, Lauret & Shuryak

  12. Soft Sector: Hadron Yield Ratios Strangeness Enhancement Resonances STAR PHENIX • pT-integrated yield ratios in central Au+Au collisions consistent with Grand Canonical stat. distribution @ Tch = (160 ± 10) MeV, B  25 MeV, across u, d and s sectors. • Inferred Tch consistent with Tcrit (LQCD)  T0 >Tcrit . • Does result point to thermodynamic and chemical equilibration, and not just phase-space dominance?

  13. Intermediate pT: Hints of Relevant Degrees of Freedom • For 1.5 < pT <6 GeV/c, see clear meson vs. baryon (rather than mass-dependent) differences in central-to-mid-central yields and v2. • v2/nq vs. pT /nq suggestive of constituent-quark scaling. If better established exp’tally, would give direct evidence of degrees of freedom relevant at hadronization, and suggest collective flow @ constituent quark level. • N.B. Constituent quarks  partons! Constituent quark flow does not prove QGP

  14. Questions for Coalescence Models Duke-model recomb. calcs. Duke-model recomb. calcs. • Can one account simultaneously for spectra, v2 and di-hadron  correlations at intermediate pT with mixture of quark recombination and fragmentation contributions? Do observed jet-like near-side correlations arise from small vacuum fragmentation component, or from “fast-slow” recombination? • Are thermal recomb., “fast-slow” recomb. and vacuum fragment-ation treatments compatible? Double-counting, mixing d.o.f., etc.? • Do coalescence models have predictive power? E.g., can they predict centrality-dependences?

  15. Hard Sector: Quantitative Indication of Early Gluon Density PHENIX • Inclusive hadron and away-side cor-relation suppression in central Au+Au, but not in d+Au, clearly establish jet quenching as final-state phenomenon, indicating very strong interactions of hard-scattered partons or their fragments with dense, dissipative medium produced in central Au+Au.

  16. Questions for Parton Energy Loss Models • pQCD parton energy loss fits to observed central suppression  dNgluon/dy ~ 1000 at start of rapid expansion, i.e., ~30-50 times cold nuclear matter gluon density.How sensitive is this quantitative conclusion to: assumptions of factorization in-medium and vacuum fragmentation following degradation; treatments of expansion and initial-state cold energy loss preceding hard collision? • Can pQCD models account for orientation- dependence of dihadron correlation? Should be sensitive to both path length and matter expansion rate variation with (R). • ~pT-independence of measured RCP unlikely that hadron absorption dominates jet quenching.

  17. Gluon Saturation: a QCD Scale for Initial Gluon Density + Early Thermaliz’n Mechanism? Saturation model curves use optical Glauber sNN = 130 GeV Au+Au • Does the high initial gluon density inferred from parton E loss fits demand a deconfined initial state? Can QCD illuminate the initial conditions? • Assuming initial state dominated by g+g below the saturation scale (con- strained by HERA e-p), Color Glass Condensate approaches ~account for RHIC bulk rapidity densities  dNg/dy ~ consistent with parton E loss. • How robust is agreement, given optical vs. MC Glauber ambiguity in calcu -lating Npart , and assumption of ~one charged hadron per gluon? • CGC applies @ SPS too? If not, why is measured dNch/d(sNN) so smooth?

  18. The Five Pillars of RHIC Wisdom Ideal hydro Early thermalization + soft EOS Statistical model Quark recombination  constituent q d.o.f. …suggest appealing QGP-based picture of RHIC collision evolu-tion, BUT invoke 5 distinct models, each with own ambigu-ities, to get there. u, d, s equil-ibration near Tcrit pQCD parton E loss CGC Very high inferred initial gluon density Very high anticipated initial gluon density

  19. Hydro: 0, freezeout, boost-invariance ambigs. Statisticalmodel: equilib’n or phase space? LQCD: CPU limitations; applic’y to dynamic matter? Gluon saturation: universal scale estab-lished? Quark recomb.: predictive power? Parton E loss: untested assump-tions The State of RHIC Theory A theoretical patchwork, with parameters adjusted independ-ently at each successive stage! Emerging description of beautiful evolution from one new state of matter to another! AND/ OR In order to rely on theory for compelling QGP discovery claim, we need:greater coherence; fewer adjusted parameters; quantitative estimates of theoretical uncertainties; quantitative PREdictions whose subsequent comparison to experiment is “make-or-break”.

  20. Summary on QGP Search • RHIC’s major advances from runs 1-3: • Extended reach in energy density appears to reach simplifying conditions in central collisions --~ideal fluid expansion; approx. local thermal equilibrium. • Extended reach in pT gives probes for behavior inaccessible at lower energies –jet quenching; ~constituent quark scaling. • Bottom Line: In the absence of a direct “smoking gun” signal of deconfinement revealed by experiment alone, a QGP discovery claim must rest on the comparison with a promising, but still not yet mature, theoretical framework. In this circumstance, clear predictive power with quantitative assessments of theoretical uncertainties are necessary for the present appealing picture to survive as a lasting one.

  21. Critical Future Exp’t Needs: Short-Term (some data already in the bag from run 4) Establish v2 scaling more definitively: better statistics, more particles (incl. , , resonances), include  correlations in recomb.-model fits. Establish that jet quenching is an indicator of parton, not hadron, E loss:higher pT; better statistics dihadron correlations vs. reaction plane; away-side punchthrough? charmed meson suppression? Extend RHIC Au+Au meas’ments down toward SPS energy, search for possible indicators of a rapid transition in measured properties: determine turn-on of jet suppression vs. s; pp reference data crucial. Measure charmonium yields + open charm yields and flow, to search for signatures of color screening and partonic collectivity: charmed hadrons in chem. equil.? Coalescence vs. frag-mentation? D-meson flow; J/ sup-pression? (eventually  , other “onia”) Measure hadron correlations with far forward high-energy hadrons in d+Au: search for monojet signature of interaction with classical gluon field.

  22. Some Critical Future Exp’t Needs: Longer-Term Develop thermometers for the early stage of the collision, when thermal equilibrium is first established:direct photons ( HBT for low E), thermal dileptons. Quantify parton E loss by measurement of mid-rapidity jet fragments tagged by hard direct photon, a heavy-quark hadron, or a far forward energetic hadron: constrain E loss of light quarks vs. heavy quarks vs. gluons in bulk matter. Test quantitative predictions for elliptic flow in U+U collisions: Considerable extrapolation away from Au+Au  significant test for hydro predictive power @ RHIC. Measure hadron multiplicities, yields, correlations and flow at LHC & GSI, and compare to quantitative predictions based on models adjusted to work at RHIC: test viability and falsifiability of QGP-based theoretical framework. Devise tests for the fate of fundamental QCD symmetries in RHIC collision matter: chiral & UA(1) restoration? CP violation? Look especially at the strongly affected particles opposite a high-pT hadron tag.

  23. RHIC II Physics in STAR • Detailed studies of the fundamental properties of the new high temperature, high density (QGP) matter at RHIC • Is it equilibrated? • Does it behave collectively? • What are its early temperature and pressure? • What is its gluon density? • What is the quark mass dependence of partonic energy loss? • Does it exhibit the properties of a classical plasma? • Studying the deconfinement and chiral transitions, and the hot, superdense states preceding the formation of a plasma of quarks and gluons to: • Test lattice predictions of the properties and behavior of bulk QCD matter • Study the nature of chiral symmetry breaking and how it is related to the masses of the hadrons • Study the nature of a possible saturated gluon state in cold nuclei at low momentum fraction (Bjorken x) • Search for broken/restored symmetries the QGP may provide access to (e.g. strong CP, parity) • Understanding the contributions to the nucleon spin • The helicity preference of gluons inside a proton • The origin of the proton sea • The transversity distribution for quarks in a proton

  24. RHIC II STAR Physics: What’s Needed Sensitivity to rare probes and improved background rejection for plasma radiation; also characterization of the bulk matter QGP is NOT rare in these collisions, but signals of early-time phenomena ARE! To test and extend QCD theory and its predictions STAR will: • use hard (short wavelength) probes such as • Inclusive jets and direct photons • back to back jets (correlation of leading particles) • direct gamma + leading hadron from jet • flavor tagged jets • measurement of spectra and yields for the Upsilon family of states to measure the differential energy loss for gluon, light quark and heavy quark probes which couple differently to the medium • measure very large samples of “soft physics” events to study • heavy quark thermalization • heavy baryon / meson (open charm) elliptic flow • spectrum of extended hadronic matter (resonances) • broken / restored symmetries (e.g., cp violation, chiral restoration)

  25. High pT hadrons in coincidence withg One thing apparent right away: rare probes need higher luminosity Quantitative measurements of partonic energy loss Measurement of the gluon density via direct  + jet and flavor-tagged jets to study the quark mass dependence of energy loss AuAu (b = 0), s1/2 = 200 GeV • Leading hadrons are very rare: only • ~0.1% of jets fragment hard enough • that hadrons are above incoherent • background • cross section for  + jet coincidences • (central Au+Au): • Eg=10 GeV: 6 nb/GeV • Eg=15 GeV: 0.6 nb/GeV • 50 weeks of Au+Au @ RHIC I design: • 10 nb-1 !!  luminosity upgrade • needed to access this physics! dN/dyd2pT (y=0) (GeV-2c-3) PT (GeV/ c)

  26. The STAR Future Plan: Short Form • Physics Bullets: • Determine degree of thermalization and collectivity • in partonic matter formed in RHIC collisions • Test QCD (for variety of parton types) and • determine the fate of its fundamental symmetries in • bulk partonic matter • Map the contributions of gluons and sea • antiquarks of different flavor to the spin of the • proton • Probe the large gluon densities at low momentum • fraction in heavy nuclei TOF Barrel Pixel Vertex DAQ/FEE upgrade RHIC-II Inner/ endcap tracking Forward calorimeter upgrade GEM R&D development for possible next Generation TPC Tracker is ongoing

  27. Upgrades planned to carry out the future STAR program • A Barrel MRPC TOFPID information for > 95% of kaons and protons in the STAR acceptance; clean e± ID down to 0.2 GeV/c extended scientific reach for key observables • A micro-vertex detectorprecise (~5 m) hit position close to the primary vtx  D’s ,flavor- tagged jets • A DAQ/ TPC FEE Upgradenew architecture / FEE  > 1 khz of events available at L3; effective integration of 10 x more data • Development of GEM tech. Preparation for a compact, fast, next generation TPC needed for 40 x L • Forward Tracking Upgrade W charge sign identification • Forward Calorimeter Upgrade: Jet reconstruction at high pseudorapidity: CGC monojet search in d(p) + A; isolation of fragmentation effects in large pp  0 production single-spin transverse asymmetries • High Luminosity 10 - 50 times the luminosity (10 nb-1) integrated at RHIC up to 2010

  28. The STAR Barrel TOF MRPC Prototype Prototype Tray Construction at Rice University MRPC design developed at CERN, built in China 28 MRPC Detectors; 24 made at USTC FEE Neighbor CTB Tray EMC Rails   70 ps, 2 meter path Strong team including 6 Chinese Institutions in place Completed Prototype 28 module MRPC TOF Tray installed in STAR Oct. ‘ 02 in place of existing central trigger barrel tray

  29. The STAR Barrel TOF MRPC Prototype Prototype modules met all performance specs in the STAR environment and produced important physics on PID’d Cronin Effect MRPC TOF + TPC  clean e± ID down to 0.2 GeV/c Proposal reviewed and approved by STAR and BNL Management Submitted to DOE

  30. Example of Recent and Projected Progress • Combination of TOF +Vertex permits STAR to study low-mass dilepton pair spectrum: access to leptonic decays of vector mesons (chiral symmetry) • MRPC TOF + TPC  clean e± ID down to 0.2 GeV/c (from run 4 data!) • Addition of Vertex suppress dominant  conversion bkgd. by large factor! STAR Simulations STAR Simulations

  31. Track Residual: AuAu Prod 62 GeV: “Local” SVT Spatial Resolution STAR Vertex Tracking, Now and in the Future Earlier (initial) work on pp (40% increase in yield) • Dedicated effort for next several months to achieve • approx.design spatial resolution globally on the detector • → Significant higher yield for low momentum particles • → Significantly higher yield for multiply strange baryons • (e.g. a factor of ~ 2 for the Ω) • Event-by-event charm & bottom requires an order of • magnitude smaller (5 μm) resolution than SVT design p+p  KºS + X  s = 200 Gev TPC TPC + SVT

  32. Open charm Charm quark yield Reconstructing D0 Charm hadron chemistry Reconstructing D+, Ds+, … Charm hadron flow Constructing D0 spectra Open beauty Identifying B mesons Identifying heavy quark jets Physics provided by the STAR mVertex detector STAR Future Physics and Planned Upgrades Number of events required for inclusive charm studies reduced by a factor of ~ 100 Thin silicon ladders under tension Event by Event Charm/Bottom Not Possible Without It !

  33. Pythia p-p 200 GeV Au-Au Thermal* D+/ D0 0.33 0.455 Ds+/ D0 0.20 0.393 Lc+/ D0 0.14 0.173 J/Y/D0 0.0003 0.0004 An additional Requirement: Upgraded Detector Capability for Open Charm Open charm: a probe of initial conditions, and possible equilibration at early times D0 K, d+Au D± K, Au+Au Yield and Spectra carry Important information STAR Preliminary Chemistry carries important information Do c quarks thermalize? For high statistics inclusive, MRPC TOF and silicon μvtx buy a factor of ~ 100 reduction (!)

  34. Forward pT reconstruction:- • True pT = 30 GeV • Range in: 1 <  < 2 Reconstructed pT for various detector configurations: Recent Progress: Integrated Tracking Upgrade Simulated Forward pT Resolution =-1 =1 • Inner (Si strip) + forward (GEM) tracking detector concept should eliminate incorrect sign reconstructions for W daughters in endcap region Simulated configuration: • Inner configuration: 3 silicon layers (50 μm spatial resolution) • Outer configuration: 2 triple GEM layers (100 μm spatial resolution)

  35. STAR Forward Meson Spectrometer Conceptual Design • Physics Motivation: • probing gluon saturation in p(d)+A • collisions via… • large rapidity particle production (p0,h,w,h’,g,K0,D0) detected through all g decays. • di-jets with large rapidity interval (Mueller-Navelet jets) • disentangling dynamical origins of • large xF analyzing power in p+p • collisions. Df=2p 2.2<h<4

  36. STAR DAQ/FEE upgrade–DAQ1000 • GOAL: increase STAR’s rate capability to equivalent of 1 kHz min-bias Au+Au  ~820 MB/s instantaneous (~300 MB/s time-averaged?) • IMPLEMENTATION: (1) replace TPC FEE with version based on ALICE ALTRO chip; (2) replace TPC DAQ system with one based on storage of only cluster information extracted in fast hardware; (3) upgrade EMC Level 2 Receiver Boards and use for other new subsystems as well. • MILESTONES: • FY04 Run: deploy Fast Cluster Finder algorithm ( DAQ100) and cluster storage only in software as proof-of-principle; handle clustered event building with 4 Linux-based EVB work stations • FY04 R&D: implement a Row Computing Slice (RCS) incorporating FCF in hardware (FPGA, DSP, …); design generic new DAQ Receiver Board; prototype ALTRO-based FEE • FY05 Run: implement new Receiver Board for BEMC/EEMC Level 2 triggering • FY05 R&D: design ALTRO  DAQ interconnect; prototype DAQ fiber interconnect & network system

  37. STAR Future Physics and Planned Upgrades The Scope & Scientific Merit of Proposed R&D / Upgrade Plan SystemR&D Constr/CostBenefit to STAR Barrel MRPC TOF ‘ 04  ‘06 ‘ 06  ’08 E x E PID information for ~ 95% of kaons and TOF ~$300k $4.7M protons in acc; extended pT for resonances + $2.5M in- kind  v2; D’s; E x E PID’d correlations; e ± ID Inner vtx ‘04  ‘06 ‘07 (?)  exclusive charm/bottom , enrichment factor of 100 $965k $~5M 100 for inclusuive open charm, flavor- tagged jets Forward/Inner Tracker TBD ~ $8MCharge sign for W± ( presently 500 GeV run ~ 200) DAQ Upgrade ’05 – ‘08 (?)  1 kz  L3; D’s;  & D v2, cp, parity, Direct  HBT ( Plus Level III) $~1M ($2M) FEE Upgrade ‘’06 –’08? 1 kz  L3; D’s; , D, cp, parity, Direct  HBT $1-2 M Forward HCAL TBD ‘06 (?) (Mono) jets at high η; transverse spin studies (AN) $1-2M GEM TPC ‘ 05  ’09 ‘10  Compact, fast TPC;robust $900k ~ 20M(?) tracking for high Q2 physics at 40 x L R&D on these projects has begun

  38. Conclusions on Future Upgrades STAR proposes a future program of QCD studies of unprecedented breadth and depth to study – the quark mass dependence of partonic energy loss – collective behavior in partonic systems – the nature of chiral symmetry breaking and how is it related to the masses of the hadrons – the nature of a possible saturated gluon state in cold nuclei at low Bjorken x – the helicity preference of gluons inside a proton; the origin of the proton sea; the transversity distribution for quarks in a proton This physics program requires: a Barrel MRPC TOF detector to extend STAR’s PID a micro vertex detector to enable measurement of D’s and flavor-tagged jets a DAQ / FEE upgrade to allow 1 khz to L3 to integrate needed event samples a tracking upgrade to afford good forward charge sign determination a forward hadron calorimeter Development of GEM technology to insure the possibility of robust tracking for the 40 x L era STAR has embarked on this plan; work is in progress

  39. The Feasibility of the Future STAR program 31 scientific papers published (25 PRL, 4 PRC, 2 PLB); 12 submitted (3 PRL, 4 PRC; 10 in progress) 18 technical papers published ~ 2000 Citations 40 Ph.D’s granted STAR is a vibrant, strong collaboration with a proven track record which can successfully carry out this program

  40. The STAR Collaboration: 50 Institutions, ~ 500 People U.S. Labs: Argonne, Lawrence Berkeley, and Brookhaven National Labs U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale Brazil: Universidade de Sao Paolo China: IHEP - Beijing, IPP - Wuhan, USTC, Tsinghua, SINR, IMP Lanzhou Croatia: Zagreb University Czech Republic: Nuclear Physics Institute England: University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute – Munich University of Frankfurt India: Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC Netherlands: NIKHEF Poland: Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP – Protvino Switzerland: University of BERN

  41. Recent Simulation Progress • Microvertex detector makes b-quark jet tagging possible! • Trigger B decay event on pT > 4 GeV/c e± detected in EMC • Search for hadron-electron vertex with DCA(e-h) < 150 m from B  e± + h + X decay • First look at background looks very encouraging! • Simulations assume: pe > 4 GeV/c, ph > 0.7 GeV/c • Allow for 50% of EMC- Identified e± to be mis- identified h± • Extract signed DCA of e-h vertex from event vertex, where DCA > 0 for displacement along pe pT ~ 15 GeV/c: s (Au+Au) ~ 20mb/Gev 10 nb-1yields 200K b-bar pairs 

  42. TPC Tracking in the STAR Future Plan What about existing TPC operation at High Luminosity ? • Initial Study by TPC Evaluation & Study Group • 40 x • Track Eff (Central)  • Pt Resolution  • DCA Distortion (SC) ongoing study • Gated Grid Operation at > 1 Khz  • Laser calibration stabilized  • Questions Under Study • Full understanding of space charge effects • (event-by-event) • Wire aging with increase gated grid rate? • Sources/fluctuations of space charge • First indications are pretty good that TPC should work well at 4 x present luminosity •  Space charge will likely require a TPC replacement for 40x era; also aging? Event-by-Event space charge correction • The ongoing GEM development will: • lay the foundation for a possible future high rate, compact TPC with shorter drift /trigger capability • develop important technology which may needed elsewhere in STAR (e.g. forward tracking)

  43. Angular correlations of hard and soft hadrons in STAR explore transverse momentum balance opposite a high-pT particle, in the light of jet quenching (F. Wang): STAR PRELIMINARY { s = 200 GeV Au+Au results: Assoc. particles: 0.15 < pT < 4 GeV/c Closed symbols  4 < pTtrig < 6 GeV/c Open symbols  6 < pTtrig < 10 GeV/c { NN Away side not jet-like! In central Au+Au, the balancing hadrons are greater in number, softer in pT, and distributed ~statistic-ally [~ cos()] in angle, relative to pp or peripheral Au+Au.  away-side products approach equilibration with bulk medium traversed. STAR PRELIMINARY STAR PRELIMINARY • away-side products approach equilibration with bulk medium traversed !

  44. near away away Collimatedregion away side: whole: |Df-p|<2.0 collimated: |Df-p|<0.35 Scientific Conjecture: The data suggest the away side products approach equilibrium with the bulk medium traversed Suggests a means to study particles (e.g. leptonic decays of vector mesons such as the Φ) that have an increased probability of having been produced in a bulk medium which may be deconfined, and/or in which chiral symmetry is restored. Differences between yields and spectra, branching ratios, flavor composition… for products 180° versus 90° from the tagged high pt particle may provide access e.g. to the study of chiral symmetry φ e+ e- Spectroscopy of the away-side soft fragmentation may be as interesting as the high pT tag

  45. Studying the fundamental nature of QCD: Strong CP Violation: STAR Future Physics and Planned Upgrades QCD “should ” include CP violation, but experimentally,  = 0 Under certain conditions around a de-confining phase transition, regions of space may be formed which behave as if   0 - spontaneous CP violation. (Kharzeev et al) No Helicity Correlations  EC• HC  0  Helicity Correlations EC• HC  0  Simple momentum space asymmetry probably not good enough  look at e-by-e helicity balance of fermions () and search for fluctuation (too many positive helicity ) N /(N +N) Estimated need: several hundred million events! (efficiency dependent) Finch, Majka, Sandweiss et al.

  46. High Luminosity RHIC Physics • What about RHIC in the era of the LHC ? • The center of mass energy at LHC will exceed that at RHIC by • a factor of ~ 30 • - longer lifetime of QGP state • - larger dynamic range for hard probes • - higher Q2 for study of jets, heavy flavor • - higher multiplicity, more complex final state • RHIC is a dedicated facility ~ 30 weeks of physics running per • year  Studies pp, pA, AA, e-A as a function of s, A, B, , • - unprecedented QCD studies • - detailed understanding of “initial conditions” at RHIC • - complete mapping of the spin dependent parton structure • of the proton • Complete understanding of the matter at RHIC is essential! • The LHC survey phase will begin near the end of the decade

  47. Soft-Hard Correlations: Partial Approach Toward Thermalization? Leading hadrons { s = 200 GeV Au+Au results: Assoc. particles: 0.15 < pT < 4 GeV/c Closed symbols  4 < pTtrig < 6 GeV/c Open symbols  6 < pTtrig < 10 GeV/c { NN Medium STAR PRELIMINARY Away side not jet-like! In central Au+Au, the balancing hadrons are greater in number, softer in pT, and distributed ~statistically [~ cos()] in angle, relative to pp or peripheral Au+Au.  away-side products seem to approach equilibration with bulk medium traversed, making thermalization of the bulk itself quite plausible.

  48. Angular correlations of hard and soft hadrons in STAR explore transverse momentum balance opposite a high-pT particle, in the light of jet quenching (F. Wang): { s = 200 GeV Au+Au results: Assoc. particles: 0.15 < pT < 4 GeV/c Closed symbols  4 < pTtrig < 6 GeV/c Open symbols  6 < pTtrig < 10 GeV/c { NN STAR PRELIMINARY STAR PRELIMINARY Away side not jet-like! In central Au+Au, the balancing hadrons are greater in number, softer in pT, and distributed ~statistic-ally [~ cos()] in angle, relative to pp or peripheral Au+Au.  away-side products approach equilibration with bulk medium traversed. STAR PRELIMINARY

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