1 / 21

Measurement of the dielectron continuum in p+p & Au+Au collisions at √s NN = 200 GeV with PHENIX

Measurement of the dielectron continuum in p+p & Au+Au collisions at √s NN = 200 GeV with PHENIX. - Torsten Dahms - Stony Brook University 2 nd Berkeley School of Collective Dynamics in High-Energy Collisions May 24, 2007. Outline. Motivation: probe the medium Preliminary Au+Au result

carlyn
Download Presentation

Measurement of the dielectron continuum in p+p & Au+Au collisions at √s NN = 200 GeV with PHENIX

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Measurement of the dielectroncontinuum in p+p & Au+Au collisions at √sNN = 200 GeV with PHENIX - Torsten Dahms - Stony Brook University 2nd Berkeley School of Collective Dynamicsin High-Energy Collisions May 24, 2007

  2. Outline • Motivation: probe the medium • Preliminary Au+Au result • Status of the p+p measurement • Summary Torsten Dahms - Stony Brook University

  3. Motivation 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 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

  4. The PHENIX experiment • 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- Torsten Dahms - Stony Brook University

  5. 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

  6. Au+Au Result PHENIX Preliminary Systematic and Normalization Error 870 Million MinBias events Torsten Dahms - Stony Brook University

  7. Au+Au: MB comparison to Cocktail PHENIX Preliminary • Data have been corrected for single electron ID efficiency • Data and Cocktail absolutely normalized • Cocktail from hadronic sources (i.e. light mesons via mT scaling) • open charm from PYTHIA • Cocktail filtered into PHENIX acceptance • Indication of enhancement in region:150<mee<740MeV Torsten Dahms - Stony Brook University

  8. Au+Au Mass Ratios PHENIX Preliminary • Ratio of yield in various mass regions to the yield within the π0 mass range, 0-100 MeV • Yield in mass window 450-600 MeV increases faster with centrality than π0 mass range Torsten Dahms - Stony Brook University

  9. Intermediate Mass Region • IMR dominated by open charm • c-cbar produced in pairs • mee = p1p2(1- cos(θ12)) • Suppression of IMR in addition to observed high pT suppression of charm in single electron measurement • If decrease true, it could indicate modified dynamical correlation of c-cbar pair • But within errors constant with Npart Torsten Dahms - Stony Brook University

  10. p+p Status Au+Au • Important to provide reference beyond “cocktail” • Much smaller combinatorial background (S/B~1, compared to 1:100 in Au+Au collisions) • But also much smaller multiplicity triggered data p+p Torsten Dahms - Stony Brook University

  11. p+p Analysis • Used ERT triggered dataset to increase statistics: • 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

  12. First estimate of trigger effects • Inv. mass spectrum for e+e- pairs from hadronic cocktail: • for MinBias events • with trigger condition on at least one of the electrons • Small mass dependence (up to the φ) • Difference mainly due to dead area of trigger MinBias ERT Implementation Torsten Dahms - Stony Brook University

  13. p+p Combinatorial Background Signal due to double conversion Like Sign Pairs: FG ERT BG MinBias • To get shape of combinatorial background correct: • Mixed events from MinBias sample • Apply trigger condition as pair cut, i.e. at least one of the electrons has fired the ERT trigger • BG normalized to like sign above 700MeV Torsten Dahms - Stony Brook University

  14. p+p Raw Spectra Unlike Sign Pairs: FG ERT BG MinBias Subtracted • Resonances very well reproduced • Photon conversions in detector material removed after BG subtraction Torsten Dahms - Stony Brook University

  15. The ω and φ Torsten Dahms - Stony Brook University

  16. Summary • Background shape and normalization well understood • Au+Au: • Hint of low mass excess • Centrality dependent supression in charm region • Medium breaks opening angle correlation of c-cbar? • p+p: • Benefit of much smaller background: S/B~1 • Combinatorial BG from triggered data understood • Early stage of analysis • Could give answers to: • pT distribution of hadrons/input for cocktail • Baseline for charm • Identify thermal photons contribution to Au+Au • IMR: RCP  RAA Torsten Dahms - Stony Brook University

  17. Backup

  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. Trigger Efficiency all tracks (after eID cuts) from MB events + ERT triggered tracks from MB events + ERT triggered tracks from ERT triggered events E3 W3 W0 E0 • pT spectra for each sector • Good agreement of ERT triggered tracks from MinBias and ERT triggered events • Ratio of ERT triggered/MinBias trigger efficiency Torsten Dahms - Stony Brook University

  20. Trigger Efficiency Torsten Dahms - Stony Brook University

  21. “Wrong” Combinatorial BG • Mixed events from ERT triggered events • What if we apply a trigger condition on the mixed event • require every MinBias event that is used for mixed events to have at least one trigger particle • this should reproduce a ERT trigger sampleBG should have same trigger bias like sign:FG ERT BG ERT BG MinBias Torsten Dahms - Stony Brook University

More Related