1 / 26

Heavy-Flavor Cross Sections at RHIC

Heavy-Flavor Cross Sections at RHIC. D mesons. vacuum. , Y ’, c. hadronic matter. QGP. Introduction. charm and bottom from hadronic collisions m c ~1.3 GeV, m b ~4.5 GeV hard process (m q >> L QCD ), even at low p T

samira
Download Presentation

Heavy-Flavor Cross Sections at RHIC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Heavy-Flavor Cross Sections at RHIC

  2. D mesons vacuum , Y’, c hadronicmatter QGP Introduction • charm and bottom from hadronic collisions • mc~1.3 GeV, mb~4.5 GeV • hard process (mq >> LQCD), even at low pT • open heavy flavor (D, Lc, B, Lb) • quarkonia (J/y, U) • heavy-ion collisions • heavy quarks are produced before the medium is formed • investigating QCD matter with hard probes • well calibrated in pp collisions • slightly affected and well understood in hadronic matter • strongly affected in a partonic medium • today's focus: calibration at RHIC

  3. K+ p- How to measure open heavy flavor • hadronic decay channels • D0 Kp (BR: ~4%) • D0  Kpp0 (BR: ~14%) • D±  Kpp (BR: ~10%) • Lc  pKp (BR: ~5%) • disadvantages • difficult to trigger • huge combinatorial background • improvement? • resolve decay vertices • charm: ct ~ 100-200 mm • bottom: ct ~ 400-500 mm •  silicon vertex detectors • advantage • unambiguous identification, i.e. a peak in invariant mass

  4. K+ p- How to measure open heavy flavor • semileptonic decay channels • D0 lX (BR: ~7%) • D±  lX (BR: ~17%) • Lc  lX (BR: ~5%) • B0,±  lX (BR: ~11%) • disadvantages • need to control/subtract background from other lepton sources • loss of kinematic information • continuum  can NOT disentangle c & b with single leptons only • advantages • 'straight forward' trigger • no combinatorial BG

  5. 2 central electron/photon/hadron spectrometer arms: |h|  0.35 p  0.2 GeV/c PHENIX optimized for leptons but can do hadrons STAR optimized for hadrons but can do leptons 2 forward muon spectrometers: 1.2 < |h| < 2.4 p  2 GeV/c PHENIX & STAR at RHIC • large acceptance (|h| < 1) tracking detector: TPC • hadrons: • TPC (dE/dx) • Time-of-Flight detector • electron ID: • EMC in addition • muons in forward arms • tracking • muon ID: • “absorber” • electrons in central arms • tracking • electron ID: • RICH + EMC

  6. PHOTONIC e± NON-PHOTONIC e± e± from heavy flavor: difficulties • electrons are rare: e±/p± ~ 10-2  need excellent PID! • MANY electrons sources • Dalitz decay of light neutral mesons • most important p0→ g e+e- • but also: h, w, h’, f • conversion of photons • main photon source: p0→ gg • in material: g → e+e- • weak kaon decays • Ke3, e.g.: K± → p0 e±ne • dielectron decays of vector mesons • r, w, f → e+e- • direct/thermal radiation • conversion of direct photons in material • virtual photons: g* → e+e- • heavy flavor decays  need excellent BG subtraction!

  7. Cocktail subtraction • ALL relevant background sources are measured • calculate e± BG • BG subtraction e± from heavy-flavor decays • performance limited by signal/background ratio • works well towards high pT • good for measurement of e± spectra • difficult towards low pT • limited use for measurement of total cross sections PRL 96(2006)032001 p+p @ √s = 200 GeV

  8. PRL 97, 252002 (2006) p+p @ √s = 200 GeV Converter subtraction • converter (known X/X0) added for part of the run • converter multiplies photonic BG by KNOWN factor  difference between converter in & out runs MEASURES photonic BG • performance limited by statistics in converter run • works well towards low pT • good for total cross section measurement • difficult towards high pT • excellent agreement between methods!

  9. PRL 97, 252002 (2006) • total cross section • scc= 567±57(stat)±224(sys) mb e± from heavy flavor in p+p (√s=200 GeV) • non-photonic e± from c  e± and b  e± • comparison with FONLL calculation • Fixed Order Next-to-Leading Log perturbative QCD (M. Cacciari, P. Nason, R. Vogt PRL95,122001 (2005)) • data ~ 2 x FONLL • seen also in charm yields at • DESY (photoproduction) • FNAL (hadroproduction) • consistent within large uncertainties • high pT: b is important!

  10. Background subtraction in STAR • photonic e± BG in STAR • dominant source • photon conversions • mainly in Si detectors near vertex • conv. / Dalitz ~ 5 • compare with PHENIX: conv. / Dalitz ~ 0.5 • subtraction • large acceptance TPC • reconstruction and subtraction of conversion and Dalitz pairs (efficiency: ~ 70-80% for pT > 4 GeV/c) • remaining BG: cocktail

  11. PHENIX vs. STAR vs. FONLL • ratio of heavy-flavor e± spectra to FONLL • PHENIX • spectral shape of e± agrees with FONLL • total cross section above FONLL by a factor ~2 • STAR • shape consistent with PHENIX and FONLL • total cross section above FONLL by a factor ~4 • systematic uncertainties in pQCD are large, i.e. a factor ~2 (or even ~4: R. Vogt hep-ph/0709.2531)

  12. PRL 98, 172301 (2007) PRL 98, 172301 (2007) Hot matter: Au+Au at √sNN=200 GeV • binary scaling of total e± yield from heavy-flavor decays  hard process production and no destruction (as expected) • high pT e± suppression increasing with centrality • footprint of medium effects; similar to p0 (a big surprise)

  13. Hot matter: Au+Au at √sNN=200 GeV • STAR & PHENIX: consistent in nucl. modification factor RAA • normalization discrepancy does NOT depend on system size! • high pT e± suppression - a challenge for models • what about bottom?  need additional observables to address these issues!

  14. A. Shabetai, QM'08 arXiv:0805.0364 PRL 94(2005)062301 D-meson reconstruction in STAR • D0 Kp invariant mass analysis • main problem: S/B ratio << 1/100  need huge stat. (yield uncertainty ~ 40-50%) • currently limited to pT ≤ ~3 GeV/c • reasonable for total cross section • insufficient to address high pT suppression

  15. Low pT muons in STAR • muon identification at low pT (~0.2 GeV/c) • Time-of-Flight and dE/dx in the TPC • subtraction of BG from p and K decay • distance of closest approach of tracks to primary vertex • low pT muon yield • sensitive to total charm cross section • insensitive to spectral shape

  16. Total charm cross section in STAR • combined fit to e±, m±, D0 • data are consistent • binary scaling of charm yield • total charm cross section ~ 1 mb • ~ 4x pQCD value (still within huge uncertainties) • ~ 2x PHENIX value

  17. charm: integration after cocktail subtraction • scc= 544 ± 39 (stat) ± 142 (sys) ± 200 (model) mb • from single e±: scc= 567±57(stat)±224(sys) mb simultaneous fit of charm and bottom: • scc= 518 ± 47 (stat) ± 135 (sys) ± 190 (model) mb • sbb= 3.9 ± 2.4 (stat) +3/-2 (sys) mb Charm and bottom from e+e- pairs • e+e- inv. mass after background subtraction compared to cocktail • absolutely normalized • excellent agreement • charm & bottom accessible after subtracting the cocktail arXiv: 0802.0050 • bottom irrelevant for total e± yield, but crucial at high pT!

  18. Separating ce from be (I) • the key: electron-hadron correlations • charm and bottom are different • electron – kaon charge correlation • D decay  unlike-sign eK pairs • B decay  mostly like sign eK pairs (with small (1/6) admixture of unlike-sign pairs) • approach • eh (for higher statistics) invariant mass • subtract like-sign pairs from unlike-sign pairs • disentangle charm and remaining bottom contribution via (PYTHIA) simulation of charm and bottom decay kinematics

  19. Separating ce from be (II) • the key: electron-hadron correlations • charm and bottom are different • electron-hadron azimuthal angle correlations • small angle (near side)  electron and hadron are from the same decay • width of near side correlation: largely due to decay kinematics • B decay has larger "Q value" than D decay • approach • eh azimuthal angle correlation for B and D decays from PYTHIA • fit measured correlation with B/(B+D) as parameter

  20. Separating ce from be (III) • the key: electron-hadron correlations • charm and bottom are different • electron-D0 correlations • trigger on e from heavy-flavor decay • use D meson (reconstructed in hadronic decay) as a probe • investigate eD correlation in azimuth

  21. B contribution to e± spectra • e from b / e from c ≥ 1 for pT ≥ 6 GeV/c • PHENIX & STAR: consistent with FONLL • not precise enough to extract b suppression • need vertex detectors to measure charm and bottom hadrons!

  22. Rapidity dependence of charm production • high pT muons in PHENIX: 1.2<|h|<2.2 • again, background subtraction is difficult

  23. Rapidity dependence of charm production • charm yield similar at mid and forward rapidity • large uncertainties everywhere • better data are needed  measurement of displaced vertices

  24. Summary • charm (& bottom) are crucial probes for the medium produced in HI collisions @ RHIC • even calibration measurements are difficult  large uncertainties • charm cross section / binary collision • binary scaling is observed in STAR & PHENIX • but the cross sections differ by a factor ~2 from e, m, D from e, e+e-

  25. Outlook: near future • complete systematics of existing observables • PHENIX • e± from d+Au & Cu+Cu • D reconstruction in p+p (D0 K+p-p0) • heavy flavor from e-m pairs X. Dong, Hard Probes '08 • STAR • improved e± data from running without inner silicon detectors photonic background reduced by factor ~10

  26. Outlook: longer term future • silicon vertex trackers for unambiguous resolution of displaced vertices  direct D- and B-meson measurements STAR PHENIX

More Related