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Event Generator: Electron and electron-pair simulations for PHENIX using EXODUS and PYTHIA

Event Generator: Electron and electron-pair simulations for PHENIX using EXODUS and PYTHIA. Ralf Averbeck, State University of New York at Stony Brook, PHENIX Upgrade Workshop, Montauk 3/21 - 3/23 2001. Outline. Motivation The heart of the simulation package: EXODUS event generator

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Event Generator: Electron and electron-pair simulations for PHENIX using EXODUS and PYTHIA

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  1. Event Generator:Electron and electron-pair simulations for PHENIX using EXODUS and PYTHIA Ralf Averbeck, State University of New York at Stony Brook, PHENIX Upgrade Workshop, Montauk 3/21 - 3/23 2001

  2. Outline • Motivation • The heart of the simulation package: EXODUS • event generator • decay machine • acceptance filter • Proof of principle: CERES cocktail • Electrons in PHENIX (Au+Au @ 130 GeV): part I • Electrons from open charm • Can PYTHIA describe existing open-charm data? • PYTHIA extrapolated to RHIC • Electrons in PHENIX (Au+Au @ 130 GeV): part II • Summary R. Averbeck, SUNY SB

  3. Motivation • Simulation of • phase-space distributions of “all relevant” sources of electrons & electron pairs (or whatever particle species you prefer) • decays • acceptance • resolution • Valuable for: • acceptance studies (e.g. detector upgrades) • development of analysis strategies • “reference” for data (“cocktail” plots) • THE example: ”GENESIS” generator (CERES) G. Agakichiev at al.: Eur.Phys.Jour. C4(98)231 R. Averbeck, SUNY SB

  4. EXODUS: a “new” cocktail generator • standalone C++ package using ROOT classes • complete separation of particle generator, decay machine, acceptance filter, detector resolution => extremely flexible! cc bb DY p0, h, r, w, f p,K,p PYTHIA Particle generator Event Builder Events Ntuples ASCII Decay Machine Ntuples ASCII Experiment Filter Ntuples ASCII R. Averbeck, SUNY SB

  5. EXODUS: particle generator • particle: PID, (E;p), weight • standalone phenomenological generator: • p0, h, h’, r, w, f, J/y (p, K, p) • needed as input: • weight factor (relative to p0): measurement (or model) • phase space distributions (pt, y): measurement (or model) • mass distributions (r, w, f) • input distributions provided using “standard” parameterizations (ROOT histograms) R. Averbeck, SUNY SB

  6. G.J. Gounaris, J.J. Sakurai: (Phys.Rev.Lett. 21(1968)244 With: Resonance mass distributions (r, w, f) R. Averbeck, SUNY SB

  7. Phase space distributions and relative particle weights (Au+Au @ 130 GeV) Transverse momentum: Rapidity: • relative particle weights from thermal model (J.Stachel QM99): • p: 1 • h: 0.097 • h’: 0.0086 • r: 0.10 • w: 0.08 • f: 0.02 UA1 parametrization + mt-scaling • Alternative pt distributions: flat, exponential • Alternative y distribution: R. Averbeck, SUNY SB

  8. Decay machine • Task: first generation => full history (for each event) • Generic decay algorithms: Dalitz, 2- and 3-body decays • Individual decay channels can be activated/deactivated • Propagation of weight factors! • Only non-trivial decay: Dalitz R. Averbeck, SUNY SB

  9. with Dalitz Decays • Parent -> X + l+l- (masses: M, mx, ml) • Lepton pair mass: (N. Kroll, W.Wada: Phys. Rev. 98(1955)1355) • Electromagnetic form factors from exp. data: Lepton-G • (L.G. Landsberg et al. Phys. Rep. 128(85)301) • Angular distr. of leptons in the virtual photon’s restframe: R. Averbeck, SUNY SB

  10. Proof of principle: p+Be @ 450 GeV/c (CERES) • Take resolution into account: • Take acceptance into account: • Generation and decay of 10M primary particles/species: • Reasonable description of data (as did GENESIS) • EXODUS technically OK! R. Averbeck, SUNY SB

  11. PHENIX: resolution and acceptance • momentum resolution: (nominal: ) • PHENIX acceptance filter (available from J.Jia) R. Averbeck, SUNY SB

  12. Electrons in PHENIX (Au+Au @ 130 GeV): part I • Relative weights from thermal model (except J/Y) • transverse momentum distribution from data (+ mt scaling) • flat rapidity distributions • Run1 momentum resolution + full PHENIX acceptance • But what about the contribution from open charm? R. Averbeck, SUNY SB

  13. Open charm production in PYTHIA • Goal: tune PYTHIA to describe existing open-charm data (following P. Braun-Munzinger et al. Eur.Phys.J. C 1(98)123)and extrapolate to RHIC • the surprising truth: data exist only from SPS and FNAL fixed target experiments (srqt(s) < 40 GeV) • parameters available in PYTHIA: • parton-distribution function (pdf): MRS(G) • mass of charm quark: mc = 1.35 GeV/c2 • average intrinsic transverse momentum of partons: <kt2> = 1.0 (GeV/c)2 • K (“fudge” cross section scaling factor): K = 5.2 R. Averbeck, SUNY SB

  14. PYTHIA tuning: total D cross sections • PYTHIA describes sqrt(s) dependence • different K factors for charged and neutral Ds! • different PDFs do equally well • different <kt2>work too R. Averbeck, SUNY SB

  15. PYTHIA tuning: D kinematics • Data: D+, D-, D0, D0, Ds+, Ds+ (E769 PRL 77(96)2392) • Common K factor: 5.2 Different PDFs: different <kt2>: R. Averbeck, SUNY SB

  16. PYTHIA tuning: D-meson correlations • Data: D+, D-, D0, D0, Ds+, Ds+(WA92 CERN PPE/36-180) R. Averbeck, SUNY SB

  17. PYTHIA extrapolation to RHIC • extrapolation to RHIC: • reasonably small uncertainty • cc cross sections (pp): • 380 mb (130 GeV) • 730 mb (200 GeV) R. Averbeck, SUNY SB

  18. Electrons in PHENIX (Au+Au @ 130 GeV): part II • Add semi-leptonic decay contributions from open charm to cocktail from light-meson decays: R. Averbeck, SUNY SB

  19. Electrons in PHENIX (Au+Au @ 130 GeV): part II • Expected pair spectrum with nominal resolution: R. Averbeck, SUNY SB

  20. Summary • (Simple) simulation tools are available • phenomenological event generator • decay machine • detector resolution parameterization • acceptance filter • and can easily be extended! • PYTHIA: • describes existing open-charm data • has been extrapolated to RHIC energies • has been coupled with EXODUS • In case you want to use the package: GO AHEAD! R. Averbeck, SUNY SB

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