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Measurement of Single Electron from Semileptonic Decay of Charm/Bottom Quarks in RHIC-PHENIX

Measurement of Single Electron from Semileptonic Decay of Charm/Bottom Quarks in RHIC-PHENIX. Fukutaro Kajihara (CNS, Univ. of Tokyo). Introduction. RHIC で行われた二つの代表的な測定 楕円型フロー ジェット・クェンチング Next Step は？ これまでの成果は Soft probe ( p , K, p 等 ) による結果 反応初期状態を直接的に probe する観測量が必要

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Measurement of Single Electron from Semileptonic Decay of Charm/Bottom Quarks in RHIC-PHENIX

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  1. Measurement of Single Electronfrom Semileptonic Decay of Charm/Bottom Quarksin RHIC-PHENIX Fukutaro Kajihara (CNS, Univ. of Tokyo)

  2. Introduction • RHICで行われた二つの代表的な測定 • 楕円型フロー • ジェット・クェンチング • Next Step は？ • これまでの成果は Soft probe (p, K, p 等) による結果 • 反応初期状態を直接的に probe する観測量が必要 • 「閉じ込めの破れ」の検証 • Soft probe から Hard probe へ • Heavy quark の測定 完全流体性 高密度状態 熱的電磁輻射、Heavy quarks (charm/bottom) J/y, Y, Heavy quark v2

  3. hA g c _ (a) c g (c) (b) hB Heavy Quark Production • Production • gg->QQ “gluon fusion” • Sensitive to the initial gluon density • Mass is largeas(mC2) ~ 0.3  can use pQCD • Cold nuclear matter effect • Cronin effect • (Anti-) shadowing • Absorption • Hot/dense matter effect • Energy loss Need systematic study for entanglement. p-p, d-Au Au-Au

  4. p+ How do We Measure Heavy Quarks? 間接測定: Semileptonic decayからのレプトンを測定 Single Electron/Prompt muon 直接測定: DKp, DKpp 比較的大きな branching ratio

  5. History of Single Electron Measurement • Single electronは1970年代の初期にCERN-ISRにおいて測定された. • 当時は charm quarkがまだ発見されていなかった. • F. W. Busser et al, PLB53, 212 • F. W. Busser et al, NPB113, 189 • 後にcharm quarkのsemileptonic decayから生成された電子であると判明 • I. Hunchlife and C. H. Llewellyn Smith, PLB61,472 • M. Bourquin and J.-M. Gaillard, NPB114,334

  6. PHENIX Single electron measurements in p+p, d+Au, Au+Au sNN = 130,200,62.4 GeV STAR Direct D mesons hadronic decay channels in p+p/d+Au D0Kp D±Kpp D*±D0p Single electron measurements in p+p, d+Au Phys. Rev. Lett. 88, 192303 (2002) Heavy Quark Measurement at RHIC

  7. 実験とデータ解析

  8. The PHENIX detector • A composite detector to measure leptons, photons and hadrons. Beam Beam

  9. The PHENIX detector • Event trigger is defined by beam-beam counters. Beam-beam counters

  10. The PHENIX detector • Central arms Tracking chambers RICH counters Central arm EM calorimeters TOF counters

  11. Cross-section of PHENIX • PHENIX central arm: • |h| < 0.35 • Df = 2 x p/2 • p > 0.2 GeV/c • vertex: |zvtx| < 20 cm • Charged particle tracking analysis using DC and PC → p • Electron identification • Ring Imaging Cherenkov detector (RICH) • Electro- Magnetic Calorimeter (EMC) → energy E

  12. Cerenkov photons from e+ or e- are detected by array of PMTs Most hadrons do not emit Cerenkov light mirror ＲＩＣＨ Au-Au data PMT array PMT array All charged tracks Electrons emit Cerenkov photons in RICH. Central Magnet Apply RICH cut r [cm] Real Net signal Accidental background z [cm] RICH ring shape (signal accumulated) Energy-Momentum [GeV] Electron ID • Electrons are identified by RICH and EMCal E/p matching, position matching, shower shape cut.

  13. Background for Inclusive Electron • Main source • Random combinations of EMC cluster and RICH ring • pT independent • Minor source • d-electrons knocked by the hadron in RICH active volume • d/h<10-6

  14. E/p in Au+Au collisions • Purity of e± sample excellent after • subtraction of “random association” background • E/p cut

  15. Singnal and Background Photonic Electron • Photon Conversion Main photon source: p0 → gg In material: g → e+e- (Major contribution of photonic electron) • Dalitz decay of light neutral mesons p0 → g e+e- (Large contribution of photonic) • The other Dalitz decays are small contributions • Direct Photon (is estimated as very small contribution) • Heavy flavor electrons (the most of all non-photonic) • Weak Kaon decays Ke3: K± → p0 e±e (< 3% of non-photonic in pT > 1.0 GeV/c) • Vector Meson Decays w, , fJ → e+e-(< 2-3% of non-photonic in all pT.) Non-photonic Electron

  16. Background Subtraction: Cocktail Method Most sources of background have been measured in PHENIX Decay kinematics and photon conversions can be reconstructed by detector simulation Then, subtract “cocktail” of all background electrons from the inclusive spectrum Advantage is small statistical error.

  17. Ne Electron yield converter 0.8% 0.4% 1.7% With converter Photonic W/O converter Dalitz : 0.8% X0 equivalent radiation length Non-photonic 0 Material amounts: 0 Background Subtraction: Converter Method We know precise radiation length (X0) of each detector material The photonic electron yield can be measured by increase of additional material (photon converter was installed) Advantage is small systematic error in low pT region Background in non-photonic is subtracted by cocktail method Photon Converter (Brass: 1.7% X0)

  18. Consistency Check of Two Methods Both methods were checked each other Left top figure shows Converter/Cocktail ratio of photonic electrons Left bottom figure shows non-photon/photonic ratio

  19. Results and Discussion

  20. D0 ~factor 2 Result of p+p at s = 200 GeV PRL, 97, 252002 (2006) Heavy flavor electron compared to FONLL Data/FONLL = 1.71 +/- 0.019 (stat)+/- 0.18 (sys) Tevatronの実験結果 CDF, PRL 91, 241804 (2003) Upper limit of FONLL

  21. Drell-Yan process FONLL: electron spectrum may be ~50% c + ~50% b for 3 < pT < 8 GeV Drell-Yan component investigated as well: < 10% up to 10 GeV FONLL calculation: Cacciari, Nason, Vogt, PRL95 (2005) 122001 Drell-Yan from: Gavin et al., hep-ph/9502372 Comparison: Armesto, Cacciari, Dainese, Salgado, Wiedemann, hep-ph/0511257

  22. Result of d+Au at sNN=200 GeV • No strong modification compared to p+p PHENIX PRELIMINARY

  23. Result of Au+Au at sNN = 200 GeV Submitted to PRL (nucl-ex/0611018) Heavy flavor electron compared to binary scaled p+p data (FONLL*1.71) Clear high pT suppression in central collisions S/B > 1 for pT > 2 GeV/c (according to inside figure) MB p+p

  24. Gluonsstrahlung probability Q Energy Loss of Heavy Quark • In vacuum, q < mQ/EQ ではGluonの制動放射が抑制される “dead cone” effect • Heavy quarkのenergy lossは小さい(Dokshitzer-Kharzeev, 2001): • 放射されたgluonのエネルギー分布 wdI/dwは放出角依存性があり、抑制される Dokshitzer, Khoze, Troyan, JPG 17 (1991) 1602. Dokshitzer and Kharzeev, PLB 519 (2001) 199.

  25. Nuclear Modification Factor: RAA p+p reference: Data (converter) for pT<1.6 [GeV/c] 1.71*FONLL for pT>1.6 [GeV/c] Suppression level is the almost same as p0 and h in high pT region

  26. RAA vs. Npart 横運動量で積分し、Npartの関数として計算した Binary scaling works well for pT>0.3 GeV/c integration Clear suppression is seen for pT>3.0 GeV/c integration Total error from p+p

  27. schematic dilepton mass distribution Dielectron Continuum Measurements in √sNN = 200GeV Au+Au

  28. Radiative Energy Loss • Radiative Energy Loss with reasonable gluon densities do not explain the observed suppression Djordjevic, Phys. Lett. B632 81 (2006) Armesto, Phys. Lett. B637 362 (2006) DGLV Radiative Energy Loss Model dNg/dy = 1000

  29. Collisional Energy Loss • Collisional energy loss may be significant for heavy quarks Wicks, nucl-th/0512076 van Hess, Phys. Rev. C73 034913 (2006) DGLV Radiative + Elastic Scattering dNg/dy = 1000 van Hee & Rapp Elastic Scattering

  30. Other models • Charm alone seems to describe better the suppression at high-pT • Dead cone is more significant for bottom quark  Larger collisional (relative) Energy loss DGLV Radiative + Elastic Scattering For Only Charm Larger Dead Cone and Larger Collisional E-loss For Bottom Quark

  31. Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. MNR: Mangano, Nason, Ridolfi, NPB 373 (1992) 295. Heavy Flavor RAA at LHC • >100 cc pairs and >5 bb pairs per central Pb-Pb collision • Baseline: PYTHIA to reproduce c and b pT distributions from NLO pQCD Eskola, Kajantie, Ruuskanen, Tuominen, NPB 570 (2000) 379.

  32. Summary • sNN=200 GeV における Au+Au 衝突実験において、 • mid rapidity • 0.3 < pT < 9.0 GeV/c Heavy quarkからの寄与と考えられる電子を測定した • Integrated yield (pT > 0.3 GeV/c) がBinary scaling している • RAAが high pT領域において強い抑制効果を示した • 理論計算との比較 • 典型的なRadiative Energy Loss のModelが成り立たない • 更なる発展には、D/Bの識別測定が必要不可欠 • Outlook D meson measurement in p+p by electron （ Kp measurement ） High statistic Cu+Cu analysis Single m measurementin forward rapidity D/B direct measurement by Silicon Vertex Tracker

  33. Backup slides

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