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  1. The Heavy Flavor Tracker for STAR Xin Dong Lawrence Berkeley National Laboratory HFT SSD IST PXL

  2. Phase Transition in Quantum ChromoDynamics Today t = 51017 sec T=1 MeV H Higgs boson Universe evolution QCD Phase Diagram Quark-hadron t = 10-6 sec T = 1 GeV Quark Gluon Plasma Temperature Hadrons Nuclei Neutron Star The Planck epoch Baryon Density

  3. wikipedia arXiv:1111.5475 Water phase diagram (QED) Quarks/gluons phase diagram (QCD)

  4. High Energy Nucleus-Nucleus Collisions Time Hadronic stage Initial hard scatterings Partonic stage Freeze-out Observables Nuclear modification factor (RAA) Elliptic flow (v2) = 2nd Fourier coefficient Sensitive to the early stage properties Characterize the medium effect

  5. Heavy Ion Experiments Currently under operation: PHENIX, STAR @ RHIC (BNL) ALICE, ATLAS, CMS @ LHC (CERN) RHIC since 2000 LHC since 2010 ALICE ATLAS CMS

  6. Evidences of the Formation of sQGP PRL 91 (2003) 072304 “Jet Quenching” - Significant suppression in particle yield at high pT in central heavy ion collisions PRL 99 (2007) 112301 “Partonic Collectivity” - Strong collective flow, even for multi-strange hadrons (f, W) - Flow driven by Number-of-Constituent-Quark (NCQ) in hadrons v2 RHIC discoveries reaffirmed by LHC experiments Strongly-coupled Quark-Gluon Plasma (sQGP)

  7. Heavy Ion Frontiers

  8. Heavy Quarks – Ideal Probes to Study QCD mu, md ms LQCD mc mb MeV Tc TQGP 10 102 103 104 1 mc,b >> LQCD amenable to perturbative QCD mc,b >> TQGP predominately created from initial hard scatterings B. Mueller, nucl-th/0404015 Heavy quark masses not easily modified in QCD medium

  9. Heavy Quarks to Probe Medium Thermalization • Heavy quarks created at early stage of HIC, and sensitive to the partonic re-scatterings. • Heavy quark collectivity/flow to experimentally quantify medium thermalization. charm quarks G. Moore & D. Teaney, PRC 71 (2005) 064904 HQ propagation in QCD medium – Brownian Motion, described by Langevin Equation hD / x - drag/diffusion coefficients related to the medium transport properties

  10. Charm Quark Hadronization Direct (hard) fragmentation in elementary collisions. However, in heavy ion collisions … v2 Hadronization through coalescence V. Greco et al., PLB 595(2004)202 Charm baryon enhancement ? - coalescence of c and di-quark Lee, et. al, PRL 100 (2008) 222301

  11. Charm Cross Section STAR, PRL 94 (2005) 062301, PHENIX, PRL 96 (2006) 032001 Yifei Zhang, QM11 • Sizable experimental (statistical & systematical) uncertainties • Crucial to interpret both open charm and charmonia data in heavy ion collisions • Need precision measurements on various charm hadrons via displaced vertices

  12. Heavy Quark Energy Loss in Hot QCD Medium STAR PRL 98 (2007) 192301, Yifei Zhang QM11 • Heavy quark decay electrons - mixture of charm and bottom decays • RAA(e) ~ RAA(h) • Contradict to the naïve radiative energy loss mechanism • Re-visit the energy loss mechanisms • Require precision measurements of direct topological reconstruction of charm or bottom hadrons for clear understanding

  13. Electrons - Incomplete Kinematics New micro-vertex detector is needed for precision measurements on charmed hadrons production in heavy ion collisions

  14. Requirements to Micro-Vertex Detector for STAR • Ultimate position resolution and solid mechanical support • Thin detector material to allow precision measurement at low pT • Full azimuthal angle coverage at mid-rapidity • Fast DAQ readout to be able to handle RHIC-II luminosity • Sufficient radiation tolerance to be operated in RHIC collider environment

  15. Solenoidal Tracker At RHIC (STAR)

  16. Heavy Flavor Tracker HFT SSD IST PXL Inner Field Cage Magnet Return Iron FGT Outer Field Cage TPC Volume Solenoid EAST WEST

  17. Heavy Flavor Tracker • SSD existing single layer detector, double side strips (electronic upgrade) • IST one layer of silicon strips along beam direction, guiding tracks from the SSD through PIXEL detector - proven strip technology • PIXEL double layers, 20.7x20.7 mm pixel pitch, 2 cm x 20 cm each ladder, 10 ladders, delivering ultimate pointing resolution. - new active pixel technology ~1mm ~300µm ~250µm < 30µm vertex TPC SSD IST PXL HFT consists of 3 sub-detector systems inside the STAR Inner Field Cage

  18. Pixel Geometry End view 8 cm radius 2.6 cm radius 20 cm Inner layer Outer layer total 40 ladders  coverage +-1 One of two half cylinders

  19. Monolithic Active Pixel Sensors (MAPS) MAPS pixel cross-section (not to scale)‏ Properties: • Standard commercial CMOS technology • Sensor and signal processing are integrated in the same silicon wafer • Signal is created in the low-doped epitaxial layer (typically ~10-15 μm) → MIP signal is limited to <1000 electrons • Charge collection is mainly through thermal diffusion (~100 ns), reflective boundaries at p-well and substrate

  20. Prototype Detector Performance Meets PIXEL requirements • Test beam results for Mimosa 16 prototype - sensor • Integration time of 640 µs • Continuous binary readout of all pixels

  21. Some pixel features and specifications critical and difficult 0.52% Cu-cable more than a factor of 3 better than other vertex detectors (ATLAS, ALICE and PHENIX)

  22. Pointing Resolution Performance Mean pT 30 m 2 2 GEANT: Realistic detector geometry + Standard STAR tracking including the pixel pileup hits at RHIC-II luminosity Hand Calculation: Multiple Coulomb Scattering + Detector hit resolution PXL telescope limit: Two PIXEL layers only, hit resolution only

  23. Intermediate Silicon Tracker (IST) 24 ladders, liquid cooling. S:N > 20:1, >99.9% live and functioning channels

  24. Silicon Strip Detector (SSD) “Old” SSD 44 cm 20 Ladders ~ 1 Meter New/Faster Readout “Old” Ladders, refurbished New, direct mounting on support Ladder Cards

  25. Reconstruction of Displaced Vertices D0 decays Direct topological reconstruction of charm and bottom decays

  26. Golden Physics Outcome Assuming D0 v2 distribution from quark coalescence. 1 billion Au+Au m.b. events at 200 GeV. - Charm v2 Thermalization of light-quarks! Drag/diffusion coefficients! • Assuming D0 RAA as charged hadron • 1 billion Au+Au m.b. events at 200 GeV + 8pb-1 sampled L in p+p 200 GeV • Charm RAA • Energy loss mechanism! • Interaction with QCD matter!

  27. Uniqueness Uniqueness of HFT: Fine pixel granularity provides ultimate hit resolution Thin detector design allows precision measurements down to low pT State-of-art mechanical design retains detector stability Full azimuthal acceptance allows high statistics correlation measurements HF measurements at RHIC – not just complementary to those at LHC Uniqueness of HF measurements at RHIC Heavy quarks are calibrated probes at RHIC - predominately created via initial gluon-gluon hard scatterings. Heavy quarks are mostly created through the leading order 2->2 process at RHIC – clean physics interpretation of results, particularly correlation measurements.

  28. Test PXL system (3/10 sectors) in beam conditions before deployment of full system Integrate it with the STAR DAQ and Trigger system. Explore many configurations/settings to optimize response and identify problems Environment not optimal (p-p 500 GeV collisions at high luminosity) but still good for: Offline/reconstruction chain development/testing Calibration/Alignment code/procedures development/testing Estimates of efficiency, pointing resolutions limited physics results expected from this sample ? Most commissioning data are taken with the low-luminosity at STAR. De-steer beam to ~1-2% of full luminosity to reduce pile-up in TPC and PXL Specific Engineering Goals for 2013 Run Run finished early June

  29. Engineering Run: Installation May 8, 2013 – PXL detector installed within 12 hours - 3 (out of 10) sectors in the prototype - Data seen from DAQ on the next day Successful commissioning run for the PXL! • Integration with the STAR TRG/DAQ system • Sensor threshold scan to optimize the performance • Test robustness of electronics/firmware • - a few issues and solutions identified • Detector performance in collider environment • Online/offline software for the PXL • Offline alignment calibration

  30. Detector Performance One snap-shot of sensor status TPC-PXL association! Dedicated low luminosity runs taken for tracking / alignment calibration

  31. Survey / Alignment Calibration Pixel positions within the (half-)PXL detector - Survey via high precision CMM machine - similar survey measurements for IST/SSD Global position w.r.t. the TPC CS – use tracks (cosmic/beam collisions) seen in the TPC before After

  32. Detector single hit resolution Single hit resolution < 20/2 ~ 14 mm – close to the designed goal – 12 mm - slight offset likely due to residual misalignment

  33. Pointing resolution

  34. Physics Run Plan • 2014 - First run with HFT: Au+Au 200 GeV • v2 and Rcp of D-mesons with 1B minimum bias collisions • v2 and Rcp of charm/bottom decay (separated) electrons/muons • 2015 - Second run with HFT: p+p 200 GeV • RAA of D-mesons/electrons/muons • 2016 - Third run with HFT: Au+Au 200 GeV high statistics • Systematic studies of v2 and RAA • c baryon with sufficient statistics • Charm correlation / Electron pair • 2017+ - p+p / p+Au 200 GeV …

  35. Muon Telescope Detector for STAR • Characteristics • Long MRPC gas detector • Magnet iron yoke as the absorber • Acceptance: 45% in azimuth, |h|<0.5 • Physics goals • Mid-rapidity quarkonia production • Separated Upsilon states • e-m correlation – heavy flavor correlation • Schedule • 2012 10% coverage • 2013 63% coverage • 2014 100% coverage HFT+TPC+TOF+EMC+MTD Precision measurements of open heavy flavor and quakonia production and correlations at RHIC

  36. STAR Physics Focus in Future (HFT’) Precision measurements on HF and dileptons: Quantify the sQGP properties (hot QCD) Precision measurements on focused energies Map out the QCD phase structure Precision measurements on pA and eA Study QCD in cold matter

  37. Summary Quantifying the QGP medium properties is one of the main goals of the heavy ion program in the next decade. STAR HFT – a state-of-art silicon pixel detector will enable precision measurements of heavy quark production at RHIC. HFT project has been processing very well. HFT is now under installation, and will become operational next year. Go Heavy or Go Home !

  38. HFT/MTD Workshop at USTC September 9-11, 2013, USTC Chair of local organizer: Prof. Ming Shao