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Charm Physics and Background Rejection – A Heavy-Flavor Tracker for STAR

Charm Physics and Background Rejection – A Heavy-Flavor Tracker for STAR. nucleus. Heat. Motivation. Quark Gluon Plasma: Deconfined and thermalized state of quarks and gluons Equilibration: - hadron yields Partonic Collectivity: - Spectra of multi-strange baryons

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Charm Physics and Background Rejection – A Heavy-Flavor Tracker for STAR

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  1. Charm Physics and Background Rejection – A Heavy-Flavor Tracker for STAR

  2. 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.

  3. Heavy-Flavor Quarks • Charm(Beauty) quarks dominantly produced in initial collisions • 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.

  4. Outline • Physics with the Heavy Flavor Tracker (HFT)- Heavy flavor collectivity- Charm quark kinetic equilibration - Heavy flavor (c,b) energy loss- Vector mesons • Mechanics • Tracking Simulations • Summary

  5. Charm Production • First direct measurement at RHIC • Reducing errors • Measure all charm hadrons • Cover large momentum range • What do we learn? • Test pQCD • Gluon pdf • Need direct open charm reconstruction to low pT!

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

  7. Charm Elliptic Flow • D  e +X • Sizeable elliptic flow • However, large photonic background:g e+e- 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), nucl-ex/0411007, (2004).

  8. 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 ! • Electrons completely lose memory of dynamics • Need direct open charm reconstruction to low pT! S. Batsouli et al., Phys. Lett. B 557 (2003) 26.

  9. 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).

  10. Heavy-Flavor Energy Loss • Suppression of pions and back-to-back correlations observed at RHIC • Consistent with partonic energy loss in the medium • Heavy(H) quarks suffer smaller energy loss than light(L) quarks • Dead cone effect • D/p ratio exponentially sensitive to color charge • Differential study of energy loss L = 5fm L = 5fm Yu.L. Dokshitzer and D.E. Kharzeev. Phys. Lett. B519 (2001) 199.

  11. 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 • Also: DD  e+e-

  12. A Heavy-Flavor Tracker for STAR • Two layers • 1.6 cm radius • 4.8 cm radius • 24 ladders • 2 cm by 20 cm • CMOS Sensors • Precise (<10 mm) , thin and low power • 50 mm thick chip + air cooling • 0.36% radiation length • Power budget 100 mW/cm2

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

  14. D0 Reconstruction Efficiency • 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 !

  15. Elliptic Flow Measurement • Au + Au, 50M central events • D0 K + p • Stat. uncertainties small • Probe charm quark flow ! • Also: Measure Ds f + p

  16. 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

  17. Summary • High-statisitcs spectra, elliptic flow and yields of D0, D, D+s, L+C Probe thermalization • Use Heavy-Flavor to probe medium • Measure Vector mesons Characterize medium ! • Need good momentum coverage to low pT ! • Need low mass detector !

  18. Mounting Support Figure 31: Detector support structure with kinematic mounts to insure repeatable detector positioning.

  19. Integration into STAR Figure 29: The HFT is shown integrated with the STAR inner detectors cone assembly.

  20. 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

  21. 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%)

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

  23. 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

  24. 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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