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PHENIX Single Non-Photonic Electron Spectra and v 2

PHENIX Single Non-Photonic Electron Spectra and v 2. Nathan Grau Journal Club April 12, 2006. Outline. What do single electrons tell us? Light quarks, heavy quarks, direct production Why is that interesting? Heavy quarks have a perturbative scale m Q Light vs. heavy quark differences

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PHENIX Single Non-Photonic Electron Spectra and v 2

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  1. PHENIX Single Non-Photonic Electron Spectra and v2 Nathan Grau Journal Club April 12, 2006 N. Grau, Journal Club

  2. Outline • What do single electrons tell us? • Light quarks, heavy quarks, direct production • Why is that interesting? • Heavy quarks have a perturbative scale mQ • Light vs. heavy quark differences • How do we measure them? • Need to remove large backgrounds • What do we conclude? N. Grau, Journal Club

  3. Physics sources of electrons Light quarks/hadrons fe+e-, w  e+e- Kpen, etc. Dalitz decay p0 ge+e-, etc. Heavy quarks/hadrons J/y e+e-, Y  e+e- D Ken, etc. Direct production Other sources of electrons Internal conversion of photons in material Note: almost everything here is true about muons as well. Sources of electrons N. Grau, Journal Club

  4. Two definitions • Inclusive electrons are all of these sources • Non-photonic electrons are those not from light hadron decay and from internal conversions and virtual direct photon production • Primarily from heavy flavor decays and Drell-Yan • Drell-Yan is small component down by a factor of 100 because of aEM • New sources of electrons in A+A? • Enhancement of low mass dileptions? • Thermal radiation? N. Grau, Journal Club

  5. Why not just measure heavy quarks directly? • Typically charm and bottom are measured from their quarkonia spectra • PHENIX does this at least for J/y • Open charm and bottom are also typically measured from displaced vertices • ct ~ 100 mm for D and ~200 mm for B • PHENIX can’t do this yet • Measure open charm in the hadronic decay channel • DKp, Dppp • After three years still don’t see it (but STAR does) • Measuring electrons maximizes usage of statistics • Catch more of the branching ratio N. Grau, Journal Club

  6. Interest in Heavy Flavors • In HIC we would like a probe that is • Strongly interacting with the medium • Heavy quarks have color charge • Survive the hadronization process of the plasma • See the next couple of slides • Heavy flavors compared to jets • Can be calculated perturbatively: aS(mQ) << LQCD • Auto-generated in the interaction in similar processes. N. Grau, Journal Club

  7. But this is a long and complicated story that Tatia will probably fill us in on in a couple of weeks! N. Grau, Journal Club

  8. Initial Expectations for Heavy Quark Energy Loss • Heavy quarks from hard scattering traverse the medium and lose energy • Survives QGP hadronization. • “Dead cone” effect • Can someone please explain the dead cone effect to me. I really couldn’t find a clear explanation in the literature. N. Grau, Journal Club

  9. Dokshitzer & Kharzeev PLB 519 199 (2001) RAAQ/RAAq quark pT Heavy-to-Light Comparison • Ratio of heavy quark RAA to light quark RAA. • 20% higher RAA predicted for heavy quarks at 5 GeV. N. Grau, Journal Club

  10. Anisotropy of Heavy Quarks (I) • Flow results from 2 sources • Pressure gradients in the overlap region of the nuclei • Low pT, hydrodynamics • Path length dependent energy loss • High pT • Question: Do heavy quarks couple as strongly to the medium as light quarks? • We should measure it! N. Grau, Journal Club

  11. Anisotropy of Heavy Quarks (II) • Another question: Less energy loss for heavy quarks, but does that necessarily reduce the anisotropy? if (Good to <10% from Dokshitzer and Kharzeev) ! We should measure it! N. Grau, Journal Club

  12. Electrons in PHENIX • Identification by • Charged track in DC/PC • Momentum, charge, position • Associated hit in RICH • Electrons only fire up to 3.5 GeV • Muons and pions then fire • Muons are rare • Associated EM cluster in calorimeter N. Grau, Journal Club

  13. Final Spectra • Inclusive Electrons • Need to determine the photonic contribution 10-20% 60-80% 0-10% N. Grau, Journal Club

  14. Cocktail Method • Parameterize the measured p0 spectrum as a function of centrality • Assume that all other light mesons mT scale, confirmed by h spectrum • Conversion photon spectrum determined from PISA simulation • Direct photons parameterized from NLO fit • Kaon spectrum parameterized from data • Run EXODUS which randomly picks from the given distribution and decays if necessary N. Grau, Journal Club

  15. Non-Photonic Spectrum (I) • Comparison of the minimum bias cocktail and converter spectra • Note that the cocktail is much more precise • Excellent agreement N. Grau, Journal Club

  16. Non-Photonic Spectrum (II) • Published spectrum • The line indicates a fit to the p+p spectra • Note no centrality above 60%? • Suppression observed at high-pT in all centrality N. Grau, Journal Club

  17. RAA • A dramatic suppression is seen at high pT. • Comparable to suppression of p0 • Is this misleading, shouldn’t we shift the electron spectrum to the left in order to compare heavy and light quark suppression? N. Grau, Journal Club

  18. What about >60% Centrality? • We have spectra that compares well to the converter method • But RAA looks terrible! Was PHENIX just sneaky? • The paper claims “More peripheral collisions have insufficient electron statistics to reach pT = 5 GeV/c.” • The p0 spectra do not reach to the same pT in all centrality bins… N. Grau, Journal Club

  19. What can we say about heavy quark Eloss? • Comparison of data to theory • 1a-1c BDMPS (next weeks talk) calculation of charm only for • a: no medium, only Cronin • b: • c: • 2a-2b GLV calculation with charm and bottom, bottom pulls up the RAA because of dead cone. • a: • b: • Very extreme range of densities and opacities! N. Grau, Journal Club

  20. Gluon Contribution to Spectrum? • A hard gluon from a hard process could split (fragment?) to Q-Qbar and create two hard mesons • If the formation time for such a splitting is longer than say the lifetime of the plasma, the gluon would lose the energy and this would be reflected in the resulting charm hadrons. • Because the gluon is fast, gamma is large and there will be a time dilation in it’s “decay” • No calculation of this I have found • p+p spectrum errors leave room for this production • Is it implemented in pythia? N. Grau, Journal Club

  21. Summary on Spectra • This is an open topic at the moment • No calculation can reproduce the observed spectra based on both charm and bottom contributions • On the face it seems that the charm and bottom loose as much energy as light quarks and gluons… • What about the coupling to the medium • i.e. do heavy quarks flow? N. Grau, Journal Club

  22. Extracting Inclusive Electron v2 • Measure the azimuthal angle wrt Y for both candidates and background • Subtract background from total to get signal and fit N. Grau, Journal Club

  23. Inclusive Electron v2 N. Grau, Journal Club

  24. Inclusive electron v2 is a weighted average of the components. True for any v2! Obtaining Non-photonic electron v2 N. Grau, Journal Club

  25. Obtaining Photonic v2 • Just use a cocktail similar to the singles spectra • EXODUS modified to produce a random RP and f distribution of the generated particles. • Study electron v2 given input v2 and spectra p+/- and p0 as input N. Grau, Journal Club

  26. Cocktail Sources • Cocktail sources (in order of importance) • p0 Dalitz(previous slide) and conversion (run through PISA) • Not suprisingly similar v2. • h Dalitz decay, assume v2 = kaon v2, spectrum mT scales • K decay, use measured v2 and spectra of K and STAR’s Ks0 • Nothing else without further assuming about heavier particle v2 (r, w, f, J/y, etc.) N. Grau, Journal Club

  27. Cocktail Results • The resulting v2 for the different components • Relative contribution to the total is also known from the cocktail e v2 from p0 Dalitz e v2 from K e v2 from h Dalitz N. Grau, Journal Club

  28. Non-photonic Electron v2 Results • The paper claims a 90% confidence level that non-photonic electron v2 !=0 • Why does that seem too low? • All points except on are >0 at 1.5s? N. Grau, Journal Club

  29. But I’m Missing the Point • Non-zero non-photonic electron v2! • And it is consistent with charm flow! • Is recombination believable? N. Grau, Journal Club

  30. The Summary • PHENIX has measured single non-photonic electron spectra and v2 and found that • High-pT electrons are suppressed wrt binary scaled p+p collisions to the level of p0 • There is a non-zero v2. • In RUN-4 these results have been extended to • Better the stats • Centrality binning • Other things that are necessary • Extending the pT reach of the electron spectra • Only reason stopping them at 5 GeV/c was pion turnon in RICH • Need to do this in p+p as well • Measure charmed hadrons and measure there v2 • J/y v2 ongoing analysis (but Tatia will let us know if we can distriminate between partonic flow + recombination, etc. with the J/y) N. Grau, Journal Club

  31. Backup Slides N. Grau, Journal Club

  32. Electron ID details • Exactly the same cuts for both analyses • High quality tracks • Excellent p resolution, S/B? • 2s matching to EMCal • Cluster association, multiple scattering • n0>=3, n3>=1 (number of pmts with good timing fired) • ? • -2s < E/p < 3s Overall S/B for 0.5-5 GeV/c is very good ~10/1 N. Grau, Journal Club

  33. Electron ID Background • Background is determined by the swap variables • z  -z of hits reassociate RICH and EMCal hits • Good for determining random association • Why is the background not the same shape as the tails? • Effect on the single particle spectrum and for the flow analysis • Just subtract off the background spectrum and dn/df shape from the measured spectrum and dn/df N. Grau, Journal Club

  34. Acceptance and Efficiency • Acceptance • Amount of dead area within the fiducial region • Study by PISA with detector response tuned to data • Efficiency • In active area probability for finding the electrons given the cuts in the analysis • Study by embedding single particles into real events 1/(Acc*Eff) pT N. Grau, Journal Club

  35. f=0 Qn Yn Measuring the RP • wi are weights, could be n for number of particles in the ith bin, pT for pT flow correlations N. Grau, Journal Club

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