Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Suppression of Non-photonic Electrons at High Pt John W. Harris Yale University for the Collaboration

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) High p T Suppression - Energy Loss of Partons Parton energy loss due to gluon radiation Depends on properties of medium (gluon density and volume) Depends on properties of the “probe” (color charge and mass) –dE/dx (gluons) > dE/dx (quarks) (due to stronger color coupling with medium) –dE/dx (heavy quarks (c,b)) < dE/dx (light quarks) mass dep. suppression of small angle radiation – (“dead cone”) ref – Dokshitzer, Kharzeev PLB 519(2001)199 –dE/dx due to heavy quark elastic scattering? ref - M.G.Mustafa Phys. Rev C 72 (2005) Must consider dynamics! ref – Wicks, Gyulassy et al, nucl-th/ hadrons qgqg production parton energy loss in medium fragmentation light M.Djordjevic PRL 94 (2004) E-loss

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Suppression of Light Quarks High p T suppression / quenching of away-side jet for light quark hadrons Pedestal&flow subtracted

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Why Investigate Non-photonic Electrons? Non-photonic electrons come from semi-leptonic decays of heavy quarks –c  e + + anything (B.R. = 9.6%) D o  e + + anything(B.R. = 6.87%) D ±  e ± + anything(B.R. = 17.2%) –b  e + + anything (B.R. = 10.9%) B ±  e ± + anything(B.R. = 10.2%) –plus small contribution from Drell-Yan for p T < 10 GeV/c Hadronic decays channels are –D o  K  –D *  D o  –D ±  K  Must understand background from photonic electrons –  conversions (  o  ,  e + e - ) – Dalitz decays of  o, ,  ’ – Decays of ,  small  – K e3 decays (small)

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Predictions for Heavy Quark  Electron Non-photonic electron suppression Single e - R AA Large electron suppression ~ 5 for c Modest suppression ~ 2.5 for c+b Single e - from NLO/FONLL M. Cacciari et al., PRL 95: (2005) Above which p T does beauty dominate? Single e - from NLO/FONLL

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Directly Reconstructed Open Charm Decays Measure D o (D o )  K  i n d + Au and Au + Au for p T < 3 GeV/c Investigating DD ±  K  Non-photonic electrons push heavy quark studies to higher pp T (~ 10 GeV/c) D0D0 STAR, Phys. Rev. Lett. 94 (2005) H.Zhang (STAR) QM2005 STAR STAR

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) First Must Understand Production of Heavy Quarks Heavy quarks produced via gg fusion in initial scattering –Predicted by pQCD (should follow binary scaling) Total charm cross section per NN interaction 200 GeV minimum bias AuAu 1.11  0.08(stat.)  0.42(sys.) mb dAu 1.4  0.2(stat.)  0.4(sys.) mb Binary scaling dAu to AuAu  Charm produced in initial collisions! STAR Preliminary NLO pQCD from R. Vogt H. Zhang, X. Dong (STAR) QM05

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Experimental Setup Detectors used for electron ID:  TPC tracking, dE/dx |  |<1.3,  =2   EMC towers, Shower Max 0 <  < 1,  =2   ToF patch STAR EMC Barrel High Tower Trigger:  Events with E T > 3 GeV in an EMC tower  Enhanced high p T particles

hadrons electrons Electron ID Using TPC and EMC TPC: dE/dx for p > 1.5 GeV/c Tracks from primary vertex only (intent – eliminate conversions, i.e. reduce effective radiation length) Electrons discriminated from hadrons for p T ≤ 8 GeV/c EMC: a)Tower E  p/E b)Shower Max Detector (SMD) Hadron/electron showers develop different shapes Use cuts on # hits Hadron Discrimination ~ electrons  Kp d hadronselectrons Jaro Bielcik (STAR) QM05 STAR

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Determining the Electron Background Inclusive Electron Spectra Signal –Heavy quark semi-leptonic decays Background –  conversion –Dalitz decays (primarily  0,  ) Background rejection efficiency for central Au+Au M e+e- <0.14 GeV/c 2 Red - like-sign Black/gray - unlike-sign Strategy for Photonic Electron Rejection Combine all TPC electron candidates –M e+e- < 0.14 GeV  photonic e’s Subtract all non-primary vertex electrons Correct for background rejection efficiency STAR

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) High p T Electron ID and Background Subtraction STAR

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Inclusive Electron Spectra for  s NN = 200 GeV AuAu 3 centrality bins 0-5%, 10-40%, 40-80% High tower trigger extends e spectra to p T ~ 10 GeV Hadron contamination correction (inc.) ~ 10 – 15 % Remaining issue under study charge exchange in EMC (at high p T )  ±   0  STAR

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Non-photonic electron spectra for pp, dAu and AuAu Photonic electrons subtracted Excess of non-photonic electrons observed Consistent with STAR ToF spectra Beauty contribution expected above ~ 5 GeV/c ToF data - H.Zhang (STAR) QM05 STAR

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Non-photonic Electron R AA Suppression observed ~ in 40-80% centrality ~ in 10-40% ~ 0.2 in 0-5% Max suppression at p T ~ 5-6 GeV STAR Theories currently cannot describe the data! Only c contribution describes R AA but not p+p spectra

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Emphasis – Closer Look at Present Theory Djordjevic et al, nucl-th/ Observed suppression of heavy quarks is not understood! Requires excessive gluon densities or dE/dx - incompatible with light quark R AA !

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Contributions to Charm vs Beauty E-loss and Yields Radiative and collisional dE/dx differs for charm and beauty S. Wicks, M. Gyulassy et al, nucl-th/

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Further Considerations for Suppression of Heavy Flavor Significant charm suppression due to 3-body elastic scattering (cqq  cqq) in a QGP! Charm quark drag-coefficient 3-body ~ 2-body elastic and radiative scatterings. Large charm suppression at high p T described when both 2- & 3-body scatterings included. Only charm included here – beauty expected to increase R AA ! W. Liu and C.M. Ko, nucl-th/ (March 2006)

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Present Uncertainties in Non-photonic Electrons R. Vogt uncertainty analysis  when does beauty overtake charm? The low end of c-b overlap The high end of c-b overlap

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Summary and Conclusions Non-photonic electrons measured in pp, dAu, Au up to p T ~ 10 GeV/c –Can be used to determine charm + beauty spectra (R AA ) at RHIC Strong suppression of non-photonic electrons (heavy flavors) in AuAu –Suppression similar to light quark suppression in AuAu –Large energy loss for heavy quarks also (similar to light quarks)? Observed suppression not explained by present theory –Unless little to no beauty contribution –However, this is incompatible with p + p spectrum Need further consideration of production/propagation of charm & beauty –Theory – collisional (3-body) & radiative E-loss, dynamical evolution,… –Experiment – measure displaced vertices directly measure and separate charm/beauty secondary vertices

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Special thanks for contributions to presentation Jaro Bielcik Alex Suaide Zhangbu Xu Thomas Ullrich