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A Heavy-Flavor Tracker for STAR at RHIC

A Heavy-Flavor Tracker for STAR at RHIC. Kai Schweda* Lawrence Berkeley National Laboratory for the STAR Collaboration. * Now at University of Heidelberg. Outline. Motivation Mechanical Setup & Active Pixel Sensor Tracking Simulations Summary. Time Scale. deconfinement.

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A Heavy-Flavor Tracker for STAR at RHIC

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  1. A Heavy-Flavor Tracker for STAR at RHIC Kai Schweda* Lawrence Berkeley National Laboratory for the STAR Collaboration * Now at University of Heidelberg

  2. Outline • Motivation • Mechanical Setup & Active Pixel Sensor • Tracking Simulations • Summary

  3. Time Scale deconfinement u-, d-quarks and ‘bound-states’ gain mass Phase and Chiral transitions Coalescence processes occur during (phase) transition and hadronization; u-,d-quarks and ‘bound-states’ gain mass accompanied by expansion; Early thermalization with partons and its duration need to be checked.

  4. Heavy-Flavor Quarks • Symmetry is broken: QCD dynamical mass EW Higgs mass • Even in a QGP, charm and beauty quark-mass heavy ! • Charm(Beauty) good probe for medium created at RHIC • If heavy quarks flow:  frequent interactions among all quarks light quarks (u,d,s) likely to be thermalized 106 105 104 103 102 10 1 Mass (MeV/c2) Plot: B. Mueller, nucl-th/0404015. Plot: B. Mueller, nucl-th/0404015.

  5. Anisotropy Parameter v2 coordinate-space-anisotropy  momentum-space-anisotropy y py px x Initial/final conditions, EoS, degrees of freedom

  6. Charm Elliptic Flow • D  e +X • Sizeable elliptic flow • But: large background:g e+e-p0  e+e-g ... large stat. and syst. uncertainties •  Need direct open charm reconstruction ! M. Kaneta (PHENIX), J. Phys. G: Nucl. Part. Phys. 30, S1217 (2004). F. Laue et al. (STAR), J. Phys. G: Nucl. Part. Phys. 31, S27 (2005).

  7. Open Charm Flow • Two extreme scenarios: • (a) No charm quark flow (PYTHIA) • (b) Charm quark flow (Hydro) •  Differences in D-meson spectra ~30% at pT < 2.0 GeV/c • D  e + X: electron spectra undistinguishable ! • Electron spectrum contains no information on dynamics • Need direct open charm reconstruction to low pT! S. Batsouli et al., Phys. Lett. B 557 (2003) 26.

  8. Counts AuAu 200 GeV min.bias S/B = 1 : 1000 D0 - Spectra • D0 K + p • d+Au : no flow • Au+Au: charm-quark flow, b = 0.4c ? • Differences in spectra: 50% • Need precise (direct) measurement • TPC (+TOF): - large combinatorial backgrd.- large syst. uncertainties (30%) • Use decay topology Data: STAR, Phys. Rev. Lett. 94, 062301.Also: H. van Hees and R. Rapp, Phys. Rev C71, 034907.

  9. Silicon Vertex            Tracker Magnet Coils E-M Calorimeter Time Projection Chamber Trigger Barrel Electronics Platforms Forward Time Projection Chamber The STAR Detector

  10. A Heavy-Flavor Tracker for STAR • D0 K + p, ct = 123 mm need precise tracking device • Two layers: r = 1.5, 5.0 cm • 24 ladders • 2 cm by 20 cm • CMOS Sensors (monolithic) • 100M pixels total , 100 k/cm2 • Precise (<10 mm) , thin and low power • 50 mm thick chip + air cooling • 0.36% radiation length • Low power budget 100 mW/cm2

  11. MIMOSA* Active Pixel Sensor • CMOS technology • Charge generated in non-depleted region collected through thermal diffusion • 100% fill factor in active volume • active sensor thinned to 50mm • total thickness 0.36% X0 (ALICE: 1.0 – 1.5%) *M. Winter et al., IReS/LEPSI, Strasbourg; http://ireswww.in2p3.fr/ires/recherche/capteurs/index.html.

  12. Active Sensors Figure 22: Wafer of reticle size sensors (left) and zoomed-in view of individual chips (right).

  13. Ladder Assembly Figure 40: A prototype readout cable for the HFT. Figure 41: Mechanical Prototype with 4 MIMOSA-5 detectors glued to the Kapton cable assembly

  14. Mounting Support • Single-sided support • Reproducible alignment s < 10mm Figure 31: Detector support structure with kinematic mounts to insure repeatable detector positioning.

  15. Mechanical Stability • Air cooling of 1m/s @ 150mW/cm2 • Position location due to vibration: s = 1.6mm • Stiffness and bending characteristics meet expectations

  16. Monte Carlo Simulations • D0 K + p • Efficiency small at low momentum: Decay length cut > 200mm • Increases with pT and then saturates • ALICE-type pixel layers: Efficiency drops by factor 8! •  Need low mass detector !

  17. Flow Measurements • Au + Au, 50M central events • D0 K + p • Expected statistical uncertainties small • Probe charm quark flow ! • Also: Measure Ds f + p D0 v2-predictions: D. Molnar, J. Phys. G31, S421.

  18. Summary • High-statisitcs spectra, elliptic flow and yields of D0, D, D+s, L+C Probe thermalization • Use heavy-flavor to probe medium • Possibly measure vector mesons Characterize medium ! • Need good momentum coverage to low pT ! • Need low mass detector !

  19. nucleus Heat Motivation • Quark Gluon Plasma: Deconfined and thermalized state of quarks and gluons • Equilibration:- hadron yields • Partonic Collectivity:- Spectra of multi-strange baryons • Thermalization:- heavy-quark (c,b) flow- (thermal photons, di-leptons) Compress Q G P nucleon boundary irrelevant J.C. Collins and M.J. Perry, Phys. Rev. Lett. 34 (1975) 1353.

  20. B-Mesons at High-pT* • Measure B  e + X • Background around 0mm • Select displaced decay vertex at > 250mm • Enhance Signal / Backgrd by factor 100! •  Disentangle c,b  e + X •  Measure heavy quark energy loss *Simulations: F. Retiere

  21. g e+e- Measure Vector Mesons • w, f  e+e- probe the medium at the early stage • Background: g  e+e- • HFT discriminates background ! • Need low mass detector

  22. Open Charm Yields* • No thermal creation of c or b quarks; m(c) = 1.1GeV >> T • c and b quarks interact with lighter quarks  kinetic equilibration ? statistical recombination ? • Ds+ / D0 ratio very sensitive ! • J/y: suppression vs recombination ? D0 = cu Ds+ = cs *A. Andronic et al., Phys. Lett. B571, 36 (2003).

  23. Open Charm Yields* • No thermal creation of c or b quarks; m(c) = 1.1GeV >> T • c and b quarks interact with lighter quarks  kinetic equilibration ? statistical recombination ? • Ds+ / D0 ratio very sensitive ! • J/y: suppression vs recombination ? *A. Andronic et al., Phys. Lett. B571, 36 (2003).

  24. Ghost Tracks GEANT Monte Carlo + ITTF Analytic Calculations • 120 Au+Au collisions pile up in HFT • Ghost Track: pick up the wrong HFT hit on a track • Ghost tracks 10(4)% at 0.5(2.0) GeV/c • Both calculation agree fairly well Analytic calcs.: E. Yamamoto

  25. Beam Pipe Strucutre

  26. Read-Out / Data Acquisition • two concepts: • (a) RDO chip mounted on sensor • (b) Analog signal lines to end of ladder • Decision spring 2006 • continuous readout / no triggering

  27. Accumulated Cost Estimate • Non-contributed: $ 7.1 M • Contributed: $ 2.2 M • Total: $ 9.3 M • Installation completed before next long Au+Au run • Complements TOF

  28. Complementary Detectors Heavy Flavor Tracker PHENIX upgrade plan* MIMOSTAR ALICE-type 0.36% X0 1.0 – 1.5% X0 D,B  e(m) + X inclusive e (non-photonic) inclusive e (non-photonic) pT > 0.5 GeV/c pT = 0.5 – 2.5 GeV/c D p + K pT = 0 – 20 GeV/c pT > 2 GeV/c *PHENIX decadal plan

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