Recent Progress in Open Heavy-Flavor Studies at RHIC and Future Prospects at RHIC and LHCStephen Baumgart RIKEN 1
Recent Progress in Open Heavy-Flavor Studies at RHIC and Future Prospects at RHIC and LHC
Stephen Baumgart RIKEN 1
Outline
A) Motivation B) Past Measurements of Heavy Flavor in RHIC Experiments 1) Hadronic measurements of charm 2) Semi-Leptonic measurement of heavy flavor 3) Angular charm/bottom separation analysis C) Future Upgrades and Analyses 1) STAR-HFT 2) PHENIX-VTX 3) ALICE 2
A) Motivation
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Charm as a Probe of the Medium
Gluon fusion predicted to be dominant process at collision energies of 200 GeV/nucleon. Sum of Feynman diagrams can be evaluated to find open charm cross-section. Is open charm produced during the initial stages of the collision or is some generated later? (Binary Scaling) Does the open charm cross-section measured at 200 GeV/nucleon match the predictions of QCD? 4
Prediction of Open Charm Cross-Section using Perturbative Quantum Chromodynamics (pQCD)
Charm Cross Section Predicted for 200 GeV Collisions: Ref: R. Vogt, arXiv:0709.2531v1 [hep-ph] Method 1: use dpt slices, then integrate final result treat charm as active flavor FONLL Calculation Charm Cross Section Predicted for 200 GeV Collisions: Method 2: calculate on full pt range in one step treat charm as NOT an active flavor (heavy quark considered massive) NLO Calculation 5 Experiment can help constrain these theoretical predictions.
Prediction from pQCD Low cross-section makes measurement difficult at RHIC energies
Prediction of Open Beauty Cross-Section 6
Nuclear Modification Factor
STAR light mesons Measures effect of nuclear medium on quarks. Light quark experience strong suppression at high pt due to medium induced gluon radiation Heavier quarks were expected to have less RAA suppression due to the dead-cone effect from their large mass, but this turned out not to be the case. 7
Collective Flow Effects
Quark scaling a signature of the QGP, as it shows quarks are deconfined If heavy quarks flow, they are interacting with the lighter quarks within the nuclear fireball (thermalized) From S. Shi, arXiv:0907.2265 8
Charm/Beauty Separation
Pythia and Hydro predictions for Charm/Beauty ratio contradict each other. Therefore, a measurement of this ratio would help define models. S. Batsouli et al., Phys. Lett. B 557 (2003) 26 9
Statistical Hadronization Model
Prediction of particle yields based on thermalized, deconfined plasma. Dinc/Ds ratio predicted to be ~2.8 at RHIC according to SHM. Compare with Pythia prediction of ~7.3 or e+e- collision data of ~4.8 Is the Dinc/Ds measured in 200 GeV/nucleon Au+Au collisions consistent with the predictions for a thermalized QGP? 10 RHIC
B) Past Measurements of Heavy Flavor in RHIC Experiments
STAR and PHENIX had made extensive heavy measurements at square-root-of-SNN = 200 GeV PHENIX had made semi-leptonic measurements of heavy flavor decays while STAR has undertaken both full reconstruction of open charm decays and semi-leptonic measurements. 11
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Semi-Leptonic Decay Hadronic Decay Example Decay Vertex Particle Type Mass (MeV) ct (mm) D0 1864.84 +/- 0.17 122.9 D+/- 1869.62 +/- 0.20 311.8 Ds 1968.49 +/- 0.34 149.9 B+/- 5279.17 +/- 0.29 491.1 B0 5279.50 +/- 0.30 457.2 Bs 5366.3 +/- 0.6 441 Primary Vertex Secondary Decay Vertex Primary Vertex Distance-of-Closest Approach (DCA) Electron D or B Meson Decay Vertex Geometry of Heavy Flavor Decays
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Hadronic Measurements of Open Charm in the STAR Experiment
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STAR Hadronic Reconstructions of Open Charm
D0s reconstructed through the Kp decay channel in d+Au, Cu+Cu, and Au+Au collisions at a CM beam energy of 200 GeV per nucleon. The STAR-SVT has been used to help geometrically reconstruct all three of the open charm mesons, D, D0, and Ds. Primary tracks are cut out using DCA and secondary vertex cuts. 14
Solenoidal Tracker at RHIC (STAR)
Full Azimuthal Coverage Primary detector is the TPC Coverage of |y| < 1.0 using TPC Magnetic Field of +/- 0.5 Tesla inside solenoidal magnet 15
The Time Projection Chamber (TPC)
Measures dE/dx and Momentum of particles Filled with P10 gas which is ionized by particles Electrons drift to read-outs at ends of detector. Length = 4.2 m, Inner diameter = 1 m, Outer diameter = 4 m. 16
STAR Particle Identification
dE/dx and momentum used with Bichsel Parameterization to do Particle Identification (PID). 17
Invariant Mass Spectra Before Background Subtraction
No signals are visible before background subtraction. 18 200 GeV Cu+Cu pK combinations 200 GeV Au+Au Fp combinations
Background Subtraction
Rotational background subtraction done every 5 degrees between 150 and 210 degrees. Event mixing done in D0 analysis. Offset Background Subtraction done in Ds analysis using K+K- pairs. Event Mixing (D0) Rotation (D0, Ds) Mass Offset Background (Ds) 19
Direct Reconstruction Of D0 mesons in STAR
Direct Invariant Mass Reconstruction From Kp track candidate pairs. Background subtraction necessary to find signal Residual shape appears udner signal. 200 GeV Cu+Cu 20 200 GeV Au+Au
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