Heavy Quark Workshop, Dec Future of STAR Measurements in the Heavy Quark Sector James C. Dunlop Brookhaven National Laboratory

Heavy Quark Workshop, Dec Outline Physics motivation: what remains to be learned in the heavy quark sector? Current detector and upgrade strategy/timeline Limitations of current detector and how upgrades remove these STAR: nucl-ex/ , nucl-ex/ , nucl-ex/

Heavy Quark Workshop, Dec A central question: the relative yield of c and b Djordjevic et al, nucl-th/ Armesto et al, private comm. The observed suppression of non-photonic electons (NPEs) is not presently understood! Attempts to reproduce it have completely changed the paradigm for the energy loss of light and heavy quarks Resolving this is a crucial next step

Heavy Quark Workshop, Dec Further measurements of NPEs alone won’t solve the problem The relative yield of charm and bottom is highly uncertain The collisional and radiative energy loss for the two is predicted to be different The charm spectra must be measured directly to untangle the two contributions (Bears on the interpretation of the suppression for light quarks as well) The low end The high end M. Djordjevic et al

Heavy Quark Workshop, Dec Moore and Teaney, PRC 71(2005) Hees and Rapp, PRC 71(2005) Charm or “charm resonance” interact with the medium via scattering:  Its phase space shape may be changed at low pT (<3-5 GeV/c)  Charm could pick up elliptic flow from the medium Measurements of charm pT spectra and elliptic flow may give us a hint that the partonic matter might be thermalized Kinetic Equilibration: Spectra and Flow at low p T

Heavy Quark Workshop, Dec Chemical Equilibration: Open Charm Yields No thermal creation of c or b quarks; m(c) = 1.1GeV >> T c and b quarks interact with lighter quarks  thermal recombination ? –D s + /D 0 very sensitive –J/  suppression vs recombination ? –Precision necessary for J/  dilepton baseline Pythia p-p 200 GeV Au-Au Thermal* D + /D D s + /D  c + /D J/  /D No suppression

Heavy Quark Workshop, Dec Yields and Spectra of the onium states (J/ , Upsilon, and excited states) to measure the thermodynamics of deconfinement through varying dissociation temperatures RHI C Upsilon rate ~  J/  l To date: Only an upper limit from ~30 ub -1, year 4 This physics requires luminosity upgrade 10 Temperature and density: Onium To deeply probe the plasma through studies of (Debye) screening length l ~ 1 /gT and map in-medium QCD potential Study vs. Pt Study vs. centrality Study in lighter systems Study vs. a control ( the Upsilon)

Heavy Quark Workshop, Dec STAR Detectors

Heavy Quark Workshop, Dec Upgrades relevant to heavy flavor Barrel Electromagnetic Calorimeter (EMC): High pt e –¾ barrel of run 5 has been instrumented to full azimuthal coverage, -1 <  < 1, for next RHIC run: COMPLETE Barrel Time of Flight (TOF): Particle ID (e, hadrons) –Current prototype patches to be upgraded to full azimuth, -1 <  < 1. –Project is funded and proceeding Forward Meson Spectrometer (FMS): CGC studies –Full azimuthal EM Calorimetry 2.5 <  < 4.0 –Possibility of charm measurements in this region –Project is proceeding: complete by next d+Au run Data acquisition upgrade (DAQ1000): Data rate 10x –Upgrade TPC readout an order of magnitude, ~double effective Luminosity –Target for completion: RHIC run in 2008 Heavy Flavor Tracker (HFT): Displaced vertices –High precision (<10 um) measurements for displaced vertices –Goal: standalone detector in place for RHIC run in 2009

Heavy Quark Workshop, Dec STAR (Central) Coverage 120 Barrel EMC Tracking (TPC,SVT,SSD) Tracking (degraded) TOF Endcap EMC     Tracking (TPC,SVT,SSD,HFT)

Heavy Quark Workshop, Dec From recent STAR PAC Talk: STAR will make much, much more effective utilization of AuAu beams in the timeframe once several key upgrades have come on-line llllll RHIC Upgrade Timeline

Heavy Quark Workshop, Dec e  K p |1/  – 1| < 0.03 Electron ID - TOF e  K p TOF measures particle velocity TPC measures particle energy loss The cut |1/  -1|<0.03 excludes kaons and protons TPC dE/dx further separates the electron and pion bands

Heavy Quark Workshop, Dec hadrons electrons 1.TPC: dE/dx for p > 1.5 GeV/c Only primary tracks (reduces effective radiation length ) Electrons can be discriminated well from hadrons up to 8 GeV/c Allows to determine the remaining hadron contamination after EMC 2.EMC: a)Tower E ⇒ p/E b)Shower Max Detector (SMD) Hadrons/Electron shower develop different shape Use # hits cuts 85-90% purity of electrons (p T dependent) h discrimination power ~ electrons  Kp d hadronselectrons Electron ID - EMC

Heavy Quark Workshop, Dec Triggering Capabilities from the EMC EMC provides a Level 0 high-p T electron trigger –Runs for every RHIC crossing (10 MHz) –Multiple E T thresholds in prescale ladder For this plot, 2.5 and 5 GeV –Enhancement proven to be >1000 for p T > 5 GeV/c Utilizes full RHIC Luminosity (modulo deadtime, currently ~50%) More sophisticated triggers: –Upsilon Limited only by luminosity ~15K Upsilon in 30 nb -1 –J/Psi Needs TOF for discrimination in Au+Au

Heavy Quark Workshop, Dec STAR Preliminary TOF spectra measured in p+p, d+Au, Au+Au minbias, 0-20%, %, 40-80% EMC spectra measured in p+p, d+Au, Au+Au minbias, 0-5%, %, 40-80% Non-photonic electron spectra measured by TOF and EMC are consistent with each other Putting it together: current NPE measurements Current limitation in p T reach: coverage (half EMC, small patch TOF) and integrated luminosity (~50 ub -1 Au+Au on tape) QM05 Proceedings: J. Bielcik, nucl-ex/ H. Zhang, nucl-ex/

Heavy Quark Workshop, Dec PID Capabilities III: Direct Reconstruction Direct reconstruction using M inv –Uncertainty limitation is combinatoric background TOF: cleanly identify daughters HFT: identify displaced vertices PRL 94 (2005) p T range TPC PID TPC + TOF FOM All12M2.6M GeV/c 59M23M GeV/c 85M42M2.0 >6 GeV/c 115M 1.0 Number of Au+Au events required for 3  signal. FOM=reduction in N events from TOF N Events for 3  D0→K  Signal

Heavy Quark Workshop, Dec DAQ Limitations (and their removal) Current limit from TPC front-end electronics is 100 Hz –Limits size of datasets ~100M events/nominal RHIC run –Affects available luminosity Deadtime scales linearly with rate 50 Hz = 50% dead, i.e. 50% drop in luminosity available to rare triggers: usual compromise Proposal to replace TPC electronics with ALICE chips to increase maximum rate by order of magnitude –Rate of events to disk increased (though timely processing of events on disk is an issue) –Removes deadtime: effective doubling of RHIC luminosity

Heavy Quark Workshop, Dec Measurements with upgraded capability in RUN VIII Upgrades in place: DAQ1000, Half-barrel TOF –DAQ1000: untriggered AND triggered at same time 15 weeks: ~900 ub -1 sampled AND few x 100M minbias events –Significant capabilities brought by large-acceptance TOF Identified particle correlations in the intermediate p T regime Dileptons: Significant (~10 s) signal in  →e + e - Initial survey (statistical) measurement of D 0 →K +  to 4-5 GeV/c

Heavy Quark Workshop, Dec Event mixing technique Select K and  tracks from PID by energy loss in TPC Combine all pairs from same event  Signal+Background Combine pairs from different events  Background Signal = same event spectra – mixed event spectra More details about this technique can be found at PRC 71 (2005) and PRL 94 (2005) D Measurements: Brute Force and its Limitations Signal is tiny compared to background: loss in statistical power Residual background

Heavy Quark Workshop, Dec  Hadronic decay channels: D 0  K  D *  D 0  D +/-  K   Advantage: complete reconstruction of final state  Disadvantage: not triggerable (need high DAQ rate and cross-section)  Improvement: displaced vertex reco Cost/benefit of techniques Semileptonic channels: c  e + + anything (B.R.: 9.6%) D 0  e + + anything(B.R.: 6.87%) D   e  + anything(B.R.: 17.2%) Advantage: triggerable (full Luminosity) Disadvantages: Kinematics incomplete No measurements at low p T : flow? Mixture of B, D, and photonic decays

Heavy Quark Workshop, Dec Heavy flavor collectivity Charm quark kinetic equilibration Heavy flavor (c,b) energy loss Vector mesons → e + e - Two layers of Active Pixel Sensors (APS) around a new thin (0.5mm) small radius (14 mm) beam pipe 10 8 pixels, (30  m) 2 Crucial for low p T : thin 50  m thick 10  m point resolution Significant progress on: Simulations Mechanical design - integration and installation - support - alignment - calibration Sensor prototyping Readout design An enabling technology for event-by-event charm measurement in STAR: the Heavy Flavor Tracker

Heavy Quark Workshop, Dec D Measurements with the HFT: Run 9 From only 50M events, additional rejection power of HFT leads to extremely small uncertainties in both spectra and v 2 Charm quark flow can be fully addressed with this upgrade Also: Measure D s   +  D 0 → K  using HFT, 50M events

Heavy Quark Workshop, Dec γ conversion π 0 Dalitz decay η Dalitz decay Kaon decay vector meson decays Dominant source at low p T For each tagged e + (e - ), we select the partner e - (e + ) from TPC global tracks to make invariant mass.  Combinatorial background reconstructed by track rotating technique.  Invariant mass < 0.15 GeV/c 2 for photonic background: removal efficiency ~50-60% Photonic Background TOF EMC

Heavy Quark Workshop, Dec Future capabilities in photonic background Current methods –Photonic electrons dominate below ~1 GeV/c –Clear nonphotonic signals above   e + e - Future capabilities: Large suppression by HFT Enabling technology for low- mass dilepton measurements

Heavy Quark Workshop, Dec Central R AA Data Increasing density Strongly coupled probes: back to the Fragility of R AA Surface bias leads effectively to saturation of R AA with increasing density Challenge: Increase sensitivity to the density of the medium Method: decrease coupling of probe to the medium But: Non-photonic electron R AA ALSO in the saturation regime Not coincidental that electron R AA ~ light quark R AA, if both at ~lower bound Provocative question: Do we learn anything from charm R AA beyond the geometrical properties of Glauber overlap? K.J. Eskola, H. Honkanken, C.A. Salgado, U.A. Wiedemann, Nucl. Phys. A747 (2005) 511 A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38(2005) 461

Heavy Quark Workshop, Dec How to find a weakly coupled probe: B? Last hope for appreciable difference in R AA is in the B sector –Requirements for this to happen, given current measurements B energy loss significantly smaller than charm AND contribution to NPE not dominant at measured energies Requirement is to isolate potentially small signal

Heavy Quark Workshop, Dec b quark measurements B mesons accessible using semileptonic decay electrons Issue: nonphotonic electrons will be measured, but what is the real fraction of these from B? Highly model dependent Subtraction of direct D measurements one possibility Alternative: Using displaced vertex tag p T ~ 15 GeV/c:  (Au+Au) ~ 20  b/Gev  30 nb -1 yields 600K b-bar pairs Tagging in Au+Au (w/ HFT) The low end The high end

Heavy Quark Workshop, Dec Summary STAR has proven capabilities for heavy flavor measurements at RHIC –Electron identification using three detector systems (TPC, TOF, EMC) from 1 to >10 GeV/c –Photonic background rejection using topological methods –Triggering capabilities to utilize full luminosity for rare probes –Direct reconstruction of charmed mesons STAR has a clear path for improving its capabilities –Completion and extension of calorimetric coverage –Extension of TOF coverage to full azimuth for electrons and combinatoric background rejection in direct reconstruction –Upgrade of Data Acquisition to increase effective luminosity and untriggered data samples –Installation of the heavy flavor tracker for displaced vertices

Heavy Quark Workshop, Dec Backup: Comparison QM05 and proceedings Cuts on electron identification tightened post-QM: results consistent within errors Updated results are in proceedings: nucl-ex/ , nucl-ex/ , nucl-ex/ Please ask me for data points: happy to provide them (as for all STAR datapoints that are in proceedings) STAR Preliminary

Heavy Quark Workshop, Dec ● medium-induced radiation fills the dead-cone massive massless dead cone Armesto, Salgado, Wiedemann, PRD69 (2004) ● vacuum radiation suppressed in the dead-cone  < m/E Dokshitzer, Kharzeev, PLB 519 (2001) 199 ● total energy loss comparable but smaller than in the massless case Armesto, Salgado, Wiedemann, PRD69 (2004) B.W. Zhang, E. Wang, X.N. Wang, PRL93 (2004) Djordjevic, Gyulassy, NPA733 (2004) 265 Heavy Quark Energy Loss dI/d  2  Flavor dependence of coupling: Less radiation, and so less suppression, for massive objects

Heavy Quark Workshop, Dec The STAR DetectorMagnetCoilsCentralTriggerBarrel(CTB)ZCalTimeProjectionChamber(TPC) Year 2000 Barrel EM Cal (BEMC) Silicon Vertex Tracker (SVT) Silicon Strip Detector (SSD) FTPC Endcap EM Cal FPD TOFp, TOFr Year 2001+