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Dielectrons with PHENIX: from p+p to Au+Au

Dielectrons with PHENIX: from p+p to Au+Au. - Torsten Dahms - Stony Brook University 2007 Annual Meeting of the Division of Nuclear Physics October 11, 2007. Dielectrons at RHIC. Possible modifications. Chiral symmetry restoration continuum enhancement

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Dielectrons with PHENIX: from p+p to Au+Au

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  1. Dielectrons with PHENIX:from p+p to Au+Au - Torsten Dahms - Stony Brook University 2007 Annual Meeting of the Division of Nuclear Physics October 11, 2007

  2. Dielectrons at RHIC Possible modifications Chiral symmetry restoration continuum enhancement modification of vector mesons thermal radiation charm modification exotic bound states suppression (enhancement) R. Rapp nucl-th/0204003 • Strong enhancement of low-mass pairs persists at RHIC • Open charm contribution becomes significant Why dielectrons • Don’t interact via strong force • Signal integrated over full evolution of the system Expected Sources: • Light hadron decays • Dalitz decays p0, h • Direct decays r/w and f • Hard processes • Charm (beauty) production • Important at high mass & high pT • Much larger at RHIC than at the SPS • Cocktail of known sources • Measure p0,h spectra & yields • Use known decay kinematics • Apply detector acceptance • Fold with expected resolution Torsten Dahms - Stony Brook University

  3. The PHENIX experiment EMC RICH • Charged particle tracking: • DC, PC1, PC2, PC3 • Electron ID: • Cherenkov light RICH • shower EMCal • Photon ID: • shower EMCal • Lead scintillator calorimeter (PbSc) • Lead glass calorimeter (PbGl) • charged particle veto • Remove π contamination with pair cut on parallel tracks in RICH • Remove conversions in detector material with cut on orientation in magnetic field p g e+ e- • ERT (EMC & RICH Trigger): • select events that were triggered by a track which fires RICH and showers in EMC (i.e. single electron trigger with pT threshold: 0.4GeV Torsten Dahms - Stony Brook University

  4. p+p Raw Spectra Combinatorial Background from mixed events: • normalize like sign above 600MeV (signal free region) • BG+- =2√N++N-- • Subtract conversions • Subtract cross pairs Unlike sign FG ERT BG MinBias Subtracted Like sign FG ERT BG MinBias cocktail Torsten Dahms - Stony Brook University

  5. p+p Cocktail Comparison • Data abs. normalized to J/ψ (acceptance correct our J/ψ yield and normalize to published yield) • Cocktail tuned for p+p • π0: Hagedorn parameterization of measured spectrum • η: mT scaling • φ and J/ψadjusted to measurement • Filtered in PHENIX acceptance • Very good agreement over all mass range • cc contribution from PYTHIA(567±57±193mb) • Known from single e analysis that PYTHIA is softer than the data Torsten Dahms - Stony Brook University

  6. ω & φ meson Measured cross section of ω & φ → e+ e- in p+p at √s = 200 GeV Goal: comparison to Au+Au measurement improving the hadronic cocktail components dσ/dy (mbarn) Extracted by integration ω: 3.50 +/- 0.18 (stat) +/- 0.88 (sys) φ: 0.37 +/- 0.02 (stat) +/- 0.09 (sys) Torsten Dahms - Stony Brook University

  7. Au+Au Cocktail Comparison submitted to Phys. Rev. Lett arXiv:0706.3034 • Data and cocktail absolutely normalized • Cocktail from hadronic sources • Charm from • PYTHIA • Single electron non photonic spectrum w/o angular correlations • Predictions are filtered in PHENIX acceptance & resolution • Low-MassContinuum:enhancement 150 < mee < 750 MeV • Intermediate-Mass Continuum: • Single e  pT suppression • PYTHIA softer than p+p but coincide with Au+Au • Angular correlations unknown • Room for thermal contribution? A prediction (Rapp, nucl-th/0204003) says direct thermal radiation is about the same as charm contribution in 1-2GeV/c2, and it will be dominant as we go to higher pT… Torsten Dahms - Stony Brook University

  8. Au+Au & p+p Comparison p+p normalized to mee<100 MeV p+p multiplied by Ncoll • p+p and Au+Au normalized to π0 region • Agreement at the resonances (ω, 2x φ) • Enhancement in 0.2-0.8 • Agreement in intermediate mass and J/ψ just for ‘coincidence’(J/ψ happens to scale as π0 due to scaling with Ncoll + suppression) Torsten Dahms - Stony Brook University

  9. Yield in Different Mass Ranges 0-100 MeV:π0 dominated; approximately scales with Npart 150-750 MeV: continuum 1.2-2.8 GeV: charm dominated;scales with Ncoll Study yield in these mass regions as a function of centrality Torsten Dahms - Stony Brook University

  10. Centrality Dependence LOW MASS INTERMEDIATE MASS submitted to Phys. Rev. Lett arXiv:0706.3034 π0 production scales with Npart Low Mass: • If in-medium enhancement from ππ or qq annihilation yield should increasefaster than proportional to Npart Intermediate Mass: • charm follows binary scaling yield should increaseproportional to Ncoll Torsten Dahms - Stony Brook University

  11. Conclusions • First dielectron continuum measurement at RHIC p+p • Very precise measurement: will fix cocktail components and charm Au+Au LOW MASS: • Enhancement above the cocktail expectations:3.4±0.2(stat.) ±1.3(syst.)±0.7(model) • Centrality dependency: increase faster than Npart INTERMEDIATE MASS: • Coincident agreement with PYTHIA • Room for thermal radiation? • Soon to come: study of pT shape of enhancement and comparison to p+p • HBD upgrade will reduce background great improvement of systematic and statistical uncertainty • Silicon Vertex detector will distinguish charm from prompt contribution Torsten Dahms - Stony Brook University

  12. Backup

  13. φ→e+e- in d+Au and Au+Au d+Au at √sNN=200 GeV Au+Au at √sNN=200 GeV Torsten Dahms - Stony Brook University

  14. Relation to previous analyses Torsten Dahms - Stony Brook University

  15. ω & φ meson: mT Spectra Torsten Dahms - Stony Brook University

  16. p+p Analysis • Used ERT triggered dataset to increase statistics: • Run5 ERT data set corresponds to ~50B MinBias events • 10B analyzed so far, more to come • select events that were triggered by a track which fires RICH and showers in EMC (i.e. single electron trigger with pT threshold: 0.4GeV) • Trigger bias on combinatorial background • Remove random benefit (only accept pairs in which at least one electron has fired the trigger) • Generate mixed events from MinBias dataset, with same requirement on the pair • Need to correct for trigger efficiency: • Hadron cocktail • Depends on trigger dead area • Determine trigger efficiency from MinBias (triggered electron/all electrons) • Simulate trigger efficiency for every EMC sector • Project into mass vs. pT Torsten Dahms - Stony Brook University

  17. The Raw Subtracted Spectrum submitted to Phys. Rev. Lett arXiv:0706.3034 • Same analysis on data sample with additional conversion material • Combinatorial background increased by 2.5 Good agreement within statistical error ssignal/signal = sBG/BG * BG/signal large!!! 0.25% 300,000 pairs 50,000 above p0 From the agreement converter/non-converter and the decreased S/B ratio scale error < 0.1%(well within the 0.25% error we assigned) Torsten Dahms - Stony Brook University

  18. Background Normalization • Background shape well reproduced • Four independent normalization factors: • like sign yield (no like sign signal):FG+-/BG+- = (FG++/BG++ + FG--/BG--)/2(needs to exclude low mass region, due to signal from double conversions) • pair production (geometrical mean):N+- = 2√N++N-- • number of mixed events: Nevt/Nmix • number of tracks: <N+-> = <N+><N-> • Very good agreement:within 0.5%  syst. uncertainty of ±0.25% Torsten Dahms - Stony Brook University

  19. Combinatorial Background • Normalization of unlike sign needs to be corrected for pair cuts bias between like and unlike sign pairs(i.e. pair cut on RICH ghosts) • Statistical uncertainty: 0.1% • + uncertainty on pair cut bias lead to total syst. uncertainty of ±0.25% like sign unlike sign --- Foreground: same evt --- Background: mixed evt BG fits to FG 0.1% --- Foreground: same evt --- Background: mixed evt Which belongs to which? γ e+ e-γ e+ e-γ e+ e-γ e+ e- π0  γ e+ e-π0  γ e+ e-π0  γ e+ e-π0  γ e+ e- PHENIX 2 arm spectrometer acceptance: dNlike/dm ≠ dNunlike/dm  different shape  need event mixing like/unlike differences preserved in event mixing  Same normalization for like and unlike sign pairs RATIO Torsten Dahms - Stony Brook University

  20. Dielectrons in p+p:Advantages and Challenges EMC RICH • Advantages: improved signal/background • Challenges:1. triggered data complications for the mixed-event technique • Used triggered dataset to increase statistics i.e. event triggered by track that hit RICH and EMC (pT threshold: 0.4GeV) • Trigger bias on combinatorialbackground • Remove random benefit (only acceptpairs in which at least one electronhas fired the trigger) • Generate mixed events from MinBiasdataset, with same requirement onthe pair Torsten Dahms - Stony Brook University

  21. Continuum in p+p: More Challenges 2. Need to correct for trigger efficiency • Hadron cocktail • Depends on triggered dead area • Determine trigger efficiency from MinBias (triggered electron/all electrons) • Simulate trigger efficiency EMC sector by sector • Project into mass vs. pT electrons from MB events + ERT triggered electrons from MB events + ERT triggered electrons from ERT triggered events Torsten Dahms - Stony Brook University

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