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Single and di-leptons from Open charm at RHIC

Single and di-leptons from Open charm at RHIC. Y. Akiba (RIKEN) June 8, 2005 Electromangetic Probes of Hot and Dense Matter. Outline. Introduction Experimental method PHENIX detector Electron measurement Muon measurerement Results p+p  e + X at 200 GeV p+p  m + X at 200 GeV

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Single and di-leptons from Open charm at RHIC

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  1. Single and di-leptons from Open charm at RHIC Y. Akiba (RIKEN) June 8, 2005 Electromangetic Probes of Hot and Dense Matter

  2. Outline • Introduction • Experimental method • PHENIX detector • Electron measurement • Muon measurerement • Results • p+p  e + X at 200 GeV • p+p  m + X at 200 GeV • d+Au  e + X at 200 GeV • Au+Au  e +X at 63, 130, and 200 GeV • Electron v2 • Summary and Outlook

  3. Physics of heavy quark production at RHIC • Heavy quarks (charm/beauty) are important probes of dense matter created at RHIC. • Most of charm/beauty is produced at the early stage of collision • Sensitive to gluon density of the early stage of collision • Test of NLO pQCD calculation of HQ production • Binary scaling of the production yield can be tested • Interaction with the dense medium can be different from that of light quark/gluons • Smaller energy loss than light quarks? • Does charm/beauty flows like light quarks or gluons? • Base line for J/y measurement • Yield ratio J/y/cc is a direct measure of J/y suppression or enhancement • Background for thermal di-leptons

  4. gluons in Pb / gluons in p X Heavy quark as probe Heavy/Light difference of jet quenching Initial gluon density Baseline for J/y B.G. for thermal di-lepton

  5. Open Heavy Quark measurement at RHIC • Semi-leptonic methods • Measurement of single lepton from heavy quark decay (ce, be, cm, bm) • PHENIX uses this method in p+p, d+Au, Au+Au • STAR also use this method in p+p and d+Au • Measurement of double leptonic decay of c+cbar or b+bbar pairs • Small cross section • Clean signal in em channel • Direct method • Reconstruct DKp, Kpp in invariant mass spectrum • STAR uses this method in d+Au • S/B is mall (1/600 in d+Au) • In this talk, I mainly discuss on open heavy quark measurement by PHENIX using the single lepton method • The measurements by STAR will be discussed by the next speaker

  6. Open heavy quark measurement through leptons • open heavy quarks are measured by the semi-leptonic (electron) decay channel. • Lepton yield  total charm yield • Lepton pT specta  charm/beauty specta  Semi-leptonic decay channel g c e, medium s,d g

  7. electrons: central arms • electron measurement in range:|h|  0.35 p  0.2 GeV/c • muons: forward arms • muon measurement in range: 1.2 < |h| < 2.4 p  2 GeV/c two central electron/photon/hadron spectrometers two forward muon spectrometers The PHENIX experiment at RHIC • optimized for lepton measurements, so e± from heavy flavor should be easy??

  8. Kinematical coverage

  9. PC3 PC2 RICH PC1 DC Mirror e+ X EMCalorimeter Cherenkov light in RICH Electron measurement at PHENIX • Electrons are measured by • DC→PC1→RICH→EMCal • Electron Identification : • Cherenkov light in RICH • Number of Hit PMT • Ring shape • Energy – Momentum matching e±candidates. Net e± BG E/p

  10. Photon conversions : • Dalitz decays of p0,h,h’,w,f (p0eeg, heeg, etc) • Kaon decays • Conversion of direct photons • Di-electron decays of r,w,f • Thermal di-leptons Most background isPHOTONIC • Charm decays • Beauty decays Non-PHOTONIC Signal p0  g g e+e- Background Sources of electrons The backgrounds are subtracted by (1) cocktail method or (2) converter methods

  11. Cockail subtraction method • From all knows souces, a cocktail of the background electron is constructed. • The input to the cocktail is measured yield of pi0. The other contributions are from Mt scaling and measured eta/pi0 ratio. • Good S/B at high pT (pT>1.5 GeV/c) thanks to small amount of material in PHENIX acceptance. • This method is useful to determine pT distribution of electrons at high pT

  12. Ne 1.7% 1.1% Photon Converter 0.8% With converter Conversion in converter e+ W/O converter Conversion from pipe and MVD Dalitz : 0.8% X0 equivalent γ Non-photonic e- Converter 0 0 Reality e+ e- Au Au Converter subtraction • Introduce additional converter in PHENIX acceptance for a limited time • comparison of spectra with and without converter installed allows to separate electrons from photonic and non-photonic sources 0.3% in Run4 This method has higher accuracy than the cocktail method at low pT.  GOOD to determine total charm yield

  13. pp  e at 200 GeV • Heavy flavor (charm+beauty) signal is extracted by the cocktail method • Material: beam pipe (0.3% + Air) (the cocktail method works better) • The observed signal level is checked by the cocktail method and (e-g) coinsidense The data shown here is from short p+p run in RUN2 We have higher statistics data in RUN3p+p and RUN4p+p A much larger data set is being recorded in RUN5 p+p

  14. Converter vs. cocktail (pp) • In the RUN2 p+p analysis, the cocktail method is to extract non-photonics (= charm+beauty) signal • The converter method and (e+g) tagging method is also used to check the results. All three methods gives consistent results. Signal/backgroud ratio

  15. p+p  (c,b)  e at 200 GeV • Cocktail subtracted electrons compared to PYTHIA expectations • Spectrum is “harder” then PYTHIA prediction • Bottom enhancement? • Higher twist contributions to charm crossection? • Fragmentation function? • The reference for nuclear modification studies is obtained • Charm cross section from the data: ds/dy = 0.20±0.03±0.11 mb scc = 0.92±0.15±0.54 mb PHENIX

  16. Comparison with FONLL Predictions From thesis of S. Busyk (StonyBrook) • Mateo Cacciari provided us with the theoretical prediction using the Fixed Order Next Leading Logarithm pQCD approach (hep-ph/0502203) • FONLL total charm/beauty cross section charm: 254+400-146 mb beauty: 1.87+0.99-0.67 mb • The FONLL prediction is somewhat lower than the data, but it is consistent within large theoretical and experimental uncertainties.

  17. pp  m at 200 GeV • This is a recent result from RUN2 p+p • Background from hadron decay and punch throughs are experimentally determined and subtracted from the raw muon spectrum to obtain heavy quark component. • The details of the analysis will be explained in the next few slides. • The obtained spectrum is consistent with the electron data

  18. Muon track + muon identifier South Muon arm : -1.2 > h > -2.0 North Muon arm : 2.4 > h > 1.2

  19. 2 1 3 4 5 Major Sources of Inclusive Tracks Tracker Absorber Identifier Collision Collision range GAP 5 4 3 2 1 Symbols Hadron Detector Absorber Muon Items 2 and 4 are small fraction of the original hadrons, but are more than prompt muon signal 5. 1 : Hadrons, interacting and absorbed (98%) 2 : Charged /K's,"decaying" before absorber (≤1%) 3 : Hadrons, penetrating and interacting ("stopped") 4 : Hadrons, "punch-through" 5 : Prompt muons, desired signal

  20. Start of hadron absorber +1 l Decay in free space Decay muons Punch-through hadrons Prompt muons Vertex analysis to extract decay muons • Decay muon yield increases linearly with the distance from the absorber. Thus the decay component is a linear function of the vertex position. • The punch-through component and HQ decay component is independent to the vertex position. • Decay component can be separated from the vertex dependence • The decay component ends at about 1 l into the absorber. Normalized muon yield Event vertex position

  21. Absorber GAP1, GAP2 GAP3, GAP4 log(Ihard) Last absorber Hadron Decay  Tracking Volume Front Absorber Prompt  Measured (PT) 690 660 0 600 40 120 z(cm) 670 Flux of hard tracks at various detector layers Reasonably deduced Simple absorption model yields for each pt bin, Hadrons Stopped at Gap 4 = I0 exp(-140/) - I0 exp(-160/ ) (1) Hadrons reach Gap 5 = I0 exp(-160/ ) (2)---> 2 equations, 2 unknowns The yield of interacting hadron in GAP4 is used to determine the punch-through background at Gap5 (Last Gap)

  22. Signal vsestimatedbackground Inclusive negative tracks Requesting PRELIMINARY Background Uncertainty pT distribution of p/K is used to constraint the pT dependence of the decay background.

  23. Production cross section for prompt m-for p+p collisions at s1/2 = 200 GeV PHENIX PRELIMINARY

  24. Invariant cross section of electrons and muons in p+p at s1/2 = 200 GeV Once the decay muon spectra and the hadron punch-though spectra are properly constructed, then the prompt muon spectra can be assembled, yielding a cross section. PHENIX PRELIMINARY 2002 Data Set Cross sections of e and m are consistent

  25. Comparison to STAR electron results (p+p)

  26. d+Au  e at 200 GeV • From RHIC RUN3 (2003) (preliminary data) • The converter method is used to extract the non-photonic components • MB trigger + ERT electron trigger is used • Converter data ~10% of total data set. • Material in the detector: beam pipe(~0.3%)+MVD(~1%)+He bag(~0.1%)

  27. Cross check: Photonic electron (good agreement with the cocktail) • Photonic component of single electron is also extracted from the converter method • Black: MB data • Red: ERT electron trigger data • The photonic component is compared with the cocktail calculation. The agreement of the data and the cocktail is very good. red curve: Dalitz only. black curve: total cocktail pT(GeV/c)

  28. PHENIX Preliminary Non-photonic electron invariant crossection for d+Au • d+Au PHENIX result was divided by the average number of binary collisions • d+Au data agrees with scaled p+p

  29. PHENIX Preliminary PHENIX Preliminary PHENIX Preliminary PHENIX Preliminary Centrality dependance of non-photonic crossection for d+Au Charm production scaled with the binary collisions

  30. AuAu • PHENIX has many data sets of Au+Au  e • RUN1 130 GeV (published in PRL) 1M events • RUN2 200 GeV, converter data (published in PRL) 2M evts • RUN2 200 GeV, cocktail analysis (preliminary) 20M evts • RUN4 63 GeV (preliminary) 30M (2M conv) evts • RUN4 200 GeV (to appear in QM05) 100M + 1.4 B evts • RUN2 converter results shows Ncoll scaling of the total charm yield • RUN2 cocktail analysis data suggests there is a significant energy loss for high pT charm • RUN4 63 GeV data are consistent with Ncoll scaling of old ISR single electron data

  31. gconversion p0 gee h gee, 3p0 w ee, p0ee f ee, hee r ee h’  gee page1 RUN1 (130 GeV) • The first measurement of charm at RHIC • Background from photon conversions and Dalitz decay of p,h,etc are subtracted from the inclusive electron spectrum by a cocktail method. • Observed an excess over hadronic background in pT>0.6 GeV/c PRL 88(2002)192303

  32. c b direct g (J. Alam et al. PRC 63(2001)021901) RUN1 (130 GeV) The shape of the observed single electron spectra is consistent with that are expected from charm decay calculated by PYTHIA. The signal is consistent with the binary scaling (with large uncertainty) The charm cross section extracted from the single electron data is 380±200 mb per binary NN collisions. PYTHIA PRL 88(2002)192303

  33. RUN2 Au+Au converter analsysis • The inclusive electron yield with and without the converter is compared. • The ratio is smaller than the expectation of all photonic source: a non-photonic source exisits. • The signal level is about 10% of the photonic sources at low pT. It increase to 50-80% at high pT. • The measurement is statistically limited at high pT PHENIX PRL94 082301 (2005)

  34. Au+Au heavy flavor Electrons • “Converter subtraction” method used • The remaining background (Ke3, etc) are subtracted by using MC. • Limiting factor - statistics of Converter run period • Statistics is too low to make a definitive statement about spectral shapeor centrality dependence PHENIX PRL94 082301 (2005)

  35. Binary Scaling of Electron Yield • dN/dy of “Non-photonic” electrons for pT > 0.8 GeV/c indicates scaling with Ncoll • dN/dy ~ Ncolla where 0.906 < a < 1.042 within 90% C.L. • scc = Ncc/TAA= 622 ±57 (stat) ± 160 (sys) mb PHENIX PRL94 082301 (2005)

  36. RUN2 Au+Au e (cocktail analysis) Curves: scaled p+p cross section ~20 times of effective statistics of the converter analysis data

  37. PHENIX Preliminary RAA (2.5<pT<5.0 GeV/c) RAA of Au+Au  e at sqrt(sNN) = 200 GeV/c • Significant suppression of single electron at high pT (pT>2.5 GeV/c) is seen! • Systemtatic error is still large (mainly from the p+p data) • A much higher statistics data from RUN4 Au+Au will be shown in QM05

  38. Au+Aue at 62.4 GeV • RHIC has short low energy run (63 GeV) in RUN4 • Heavy flavor component is obtained by the converter subtraction method • Spectra agree with the ISR p-p data scaled by TAB with uncertainty.  Confirms the binary scaling of charm yield at 63 GeV Au+Au  e Historical notes: “prompt” electron is discovered at CERN ISR in early 1970’s before the discovery of charm. The signal level is e/p ~ 2 x 10-4 in pT > 1 GeV/c PHENIX PRELIMINARY

  39. Single electron v2 in RUN2 Au+Au • If charm has v2, single electron from charm decay should also has v2. • Charm v2 is sensitive to thermalization of charm quark in the high density medium • V2 of the non-photonic (= charm) electron is extracted from the data. • This results is now published nucl-ex/0502009 (accepted in Phys. Rev. C)

  40. Y X pY pX Single electron v2 component • The elliptic flow comes from pressure. High pressure (Like ellipticity) Low pressure The R is the angle between reaction plane and y=0. Z Reaction plane: Z-X plane If heavy quarks are thermalized  Elliptic flow (or v2) of D meson  Single electron v2. Flow

  41. dNe/df nucl-ex/0502009 • dN/df is obtained for each pT bins • V2 from the background (~10%) is subtracted

  42. Inclusive e v2 vs photonic v2 nucl-ex/0502009 • Using the known S/B of single electron (measured by the converter analysis) and the v2 of pi0, the v2 of the photonics contribution is subtracted

  43. How about heavy quarks? do they flow? • PHENIX measures v2 of non-photonic e± • electron ID in Au+Au via RICH + EMCAL • measure and subtract photonic sources using converter nucl-ex/0502009 YES v2≠ 0 at 90% confidence level data consistent with heavy q thermalization also “predicted” by Teaney *but large errors; run4 will tell Greco,Ko,Rapp. PLB595, 202 (2004)

  44. What Can we expect @ Run4 ? Total event number @ Run4 -> 1200 M (Run2 : 16 M) Minimum bias - most central - mid central - peripheral - More data points @ high pT - Extend pT region (~5 GeV/c) S/B ratio of charm signal in Run4 is higher than Run2 (MVD removed 1.1% -> 0.3% X0 of material) nucl-ex/0502009 More data points @ high pT Extend pT region (~5 GeV/c) page7

  45. Summary • Now we have variety of data of heavy flavor production through semi-leptonic method at RHIC eneregies • p+p, d+Au, and Au+Au (soon in Cu+Cu) • 63, 130, and 200 GeV • Electrons (y~0) and muons (y~1.7) • In p+p, electron and muon measurements consisitent • The cross sections are somewhat higher than FONLL pQCD • No significant cold matter effect is seen in d-Au data • The total yield of charm in Au+Au scaled with the binary • The high pT charm is suppressed relative to the binary scaling --- charm energy loss? • V2 of electrons from charm is measured

  46. ~50% of total data from RUN4 Au+Au J/y Outlook • The upcoming RUN4 Au+Au 200 GeV data will give definite measurements of • Charm V2 • Energy loss of charm • In Future (~2008), a much better charm/beauty measurement become possible with proposed VTX detector

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