4/12/2006 N. Grau, Journal Club1 PHENIX Single Non-Photonic Electron Spectra and v 2 Nathan Grau Journal Club April 12, 2006

4/12/2006 N. Grau, Journal Club2 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 How do we measure them? –Need to remove large backgrounds What do we conclude?

4/12/2006 N. Grau, Journal Club3 Sources of electrons Physics sources of electrons –Light quarks/hadrons   e + e -,   e + e - K   e, etc. Dalitz decay  0   e + e -, etc. –Heavy quarks/hadrons J/   e + e -, Y  e + e - D  Ke, etc. –Direct production Other sources of electrons –Internal conversion of photons in material Note: almost everything here is true about muons as well.

4/12/2006 N. Grau, Journal Club4 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  EM –New sources of electrons in A+A? Enhancement of low mass dileptions? Thermal radiation?

4/12/2006 N. Grau, Journal Club5 Why not just measure heavy quarks directly? Typically charm and bottom are measured from their quarkonia spectra –PHENIX does this at least for J/  Open charm and bottom are also typically measured from displaced vertices –c  ~ 100 mm for D and ~200 mm for B –PHENIX can’t do this yet Measure open charm in the hadronic decay channel –D  K , D   –After three years still don’t see it (but STAR does) Measuring electrons maximizes usage of statistics –Catch more of the branching ratio

4/12/2006 N. Grau, Journal Club6 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:  S (m Q ) <<  QCD –Auto-generated in the interaction in similar processes.

4/12/2006 N. Grau, Journal Club7 But this is a long and complicated story that Tatia will probably fill us in on in a couple of weeks!

4/12/2006 N. Grau, Journal Club8 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.

4/12/2006 N. Grau, Journal Club9 Heavy-to-Light Comparison Ratio of heavy quark R AA to light quark R AA. 20% higher R AA predicted for heavy quarks at 5 GeV. R AA Q /R AA q Dokshitzer & Kharzeev PLB (2001) quark p T

4/12/2006 N. Grau, Journal Club10 Anisotropy of Heavy Quarks (I) Flow results from 2 sources –Pressure gradients in the overlap region of the nuclei Low p T, hydrodynamics –Path length dependent energy loss High p T Question: Do heavy quarks couple as strongly to the medium as light quarks? –We should measure it!

4/12/2006 N. Grau, Journal Club11 Anisotropy of Heavy Quarks (II) Another question: Less energy loss for heavy quarks, but does that necessarily reduce the anisotropy? if ! We should measure it! (Good to <10% from Dokshitzer and Kharzeev)

4/12/2006 N. Grau, Journal Club12 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

4/12/2006 N. Grau, Journal Club13 Final Spectra Inclusive Electrons Need to determine the photonic contribution 0-10% 10-20%60-80%

4/12/2006 N. Grau, Journal Club14 Cocktail Method Parameterize the measured  0 spectrum as a function of centrality Assume that all other light mesons m T scale, confirmed by  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

4/12/2006 N. Grau, Journal Club15 Non-Photonic Spectrum (I) Comparison of the minimum bias cocktail and converter spectra –Note that the cocktail is much more precise Excellent agreement

4/12/2006 N. Grau, Journal Club16 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- p T in all centrality

4/12/2006 N. Grau, Journal Club17 R AA A dramatic suppression is seen at high pT. –Comparable to suppression of  0 Is this misleading, shouldn’t we shift the electron spectrum to the left in order to compare heavy and light quark suppression?

4/12/2006 N. Grau, Journal Club18 What about >60% Centrality? We have spectra that compares well to the converter method But R AA looks terrible! Was PHENIX just sneaky? The paper claims “More peripheral collisions have insufficient electron statistics to reach p T = 5 GeV/c.” The  0 spectra do not reach to the same p T in all centrality bins…

4/12/2006 N. Grau, Journal Club19 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!

4/12/2006 N. Grau, Journal Club20 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?

4/12/2006 N. Grau, Journal Club21 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?

4/12/2006 N. Grau, Journal Club22 Extracting Inclusive Electron v 2 Measure the azimuthal angle wrt  for both candidates and background Subtract background from total to get signal and fit

4/12/2006 N. Grau, Journal Club23 Inclusive Electron v 2

4/12/2006 N. Grau, Journal Club24 Obtaining Non-photonic electron v 2 Inclusive electron v 2 is a weighted average of the components. True for any v 2 !

4/12/2006 N. Grau, Journal Club25 Obtaining Photonic v 2 Just use a cocktail similar to the singles spectra EXODUS modified to produce a random RP and  distribution of the generated particles. Study electron v 2 given input v 2 and spectra  +/- and  0 as input

4/12/2006 N. Grau, Journal Club26 Cocktail Sources Cocktail sources (in order of importance) –  0 Dalitz(previous slide) and conversion (run through PISA) Not suprisingly similar v 2. –  Dalitz decay, assume v 2 = kaon v 2, spectrum m T scales –K decay, use measured v 2 and spectra of K and STAR’s K s 0 Nothing else without further assuming about heavier particle v 2 (  J , etc.)

4/12/2006 N. Grau, Journal Club27 Cocktail Results The resulting v 2 for the different components Relative contribution to the total is also known from the cocktail e v 2 from  0 Dalitz e v 2 from K e v 2 from  Dalitz

4/12/2006 N. Grau, Journal Club28 Non-photonic Electron v 2 Results The paper claims a 90% confidence level that non-photonic electron v 2 !=0 –Why does that seem too low? –All points except on are >0 at 1.5  ?

4/12/2006 N. Grau, Journal Club29 But I’m Missing the Point Non-zero non- photonic electron v2! And it is consistent with charm flow! Is recombination believable?

4/12/2006 N. Grau, Journal Club30 The Summary PHENIX has measured single non-photonic electron spectra and v 2 and found that –High-p T electrons are suppressed wrt binary scaled p+p collisions to the level of  0 –There is a non-zero v 2. In RUN-4 these results have been extended to –Better the stats –Centrality binning Other things that are necessary –Extending the p T 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 v 2 J/  v 2 ongoing analysis (but Tatia will let us know if we can distriminate between partonic flow + recombination, etc. with the J/  )

4/12/2006 N. Grau, Journal Club31 Backup Slides

4/12/2006 N. Grau, Journal Club32 Electron ID details Exactly the same cuts for both analyses –High quality tracks Excellent p resolution, S/B? –2  matching to EMCal Cluster association, multiple scattering –n0>=3, n3>=1 (number of pmts with good timing fired) ? –-2  < E/p < 3  Overall S/B for GeV/c is very good ~10/1

4/12/2006 N. Grau, Journal Club33 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/d  shape from the measured spectrum and dn/d 

4/12/2006 N. Grau, Journal Club34 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) pTpT

4/12/2006 N. Grau, Journal Club35 Measuring the RP w i are weights, could be n for number of particles in the i th bin, p T for p T flow correlations QnQn nn  =0