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Charmonium Production in p-A Collisions

This article discusses the physics of charmonium suppression in nuclei and presents results from various experiments. It examines nuclear modification of parton level structure and dynamics, as well as the production and suppression of heavy vector mesons. The article also explores the effects of color screening and nuclear absorption on charmonium production.

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Charmonium Production in p-A Collisions

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  1. Charmonium Production in p-A Collisions Mike Leitch - Los Alamos National Laboratory leitch@lanl.gov International Workshop on the Physics of the Quark-Gluon Plasma Ecole Polytechnique, Palaiseau, France September 4-7, 2001 E772 - 1991 • Introduction to Physics of Charmonium suppression in nuclei • E866/NuSea results for J/Y and Y’ • NA50 comparison & future at NA60 & HERA-B • Prospects at PHENIX • Summary Mike Leitch - LANL

  2. Nuclear modification of parton level structure & dynamics Drell-Yan Drell-Yan Process Ratio(W/Be) 1.0 0.9 0.8 E866 R(W/Be) NMC DIS E772 R(W/D) 0.7 • Modification of parton momentum distributions of nucleons embedded in nuclei • e.g. shadowing – depletion of low-momentum partons. Process dependent? • Nuclear effects on parton “dynamics” • energy loss of partons as they propagate through nuclei • and (associated) multiple scattering effects • Production of heavy vector mesons, e.g. J/Ψ, Ψ ',  • production: color singlet or octet ( ) and color neutralization timescale • hadronization time: • Coherence length for cc fluctuations: • absorption on nucleons or co-movers • feed-down from higher mass resonances, e.g. χc Mike Leitch - LANL

  3. DY  J/Y • J/Ψ suppression – an effective signature of Quark-gluon plasma (QGP) formation? • Color screening in a QGP would destroy pairs before they can hadronize into charmonium • But ordinary nuclear effects also absorb or modify J/Ψ’s • We need a comprehensive understanding of charmonium production in nuclei • Competing effects may be identified in p-A collisions by their strong kinematic dependencies, together with complementary studies of Drell-Yan scattering and open-charm production Mike Leitch - LANL

  4. FNAL E866/NuSea Collaboration Abilene Christian University Donald Isenhower, Mike Sadler, Rusty Towell, Josh Willis Argonne National Laboratory Don Geesaman, Sheldon Kaufman, Bryon Mueller Fermi National Accelerator Laboratory Chuck Brown, Bill Cooper Georgia State UniversityGus Petitt, Xiao-chun He, Bill LeeIllinois Institute of Technology Dan KaplanLos Alamos National LaboratoryTom Carey, Gerry Garvey, Mike Leitch, Pat McGaughey,Joel Moss, Jen-Chieh Peng, Paul Reimer, Walt Sondheim New Mexico State University Mike Beddo, Ting Chang, Vassili Papavassiliou, Jason WebbOak Ridge National Laboratory Paul Stankus, Glenn YoungTexas A & M UniversityCarl Gagliardi, Bob Tribble, Eric Hawker, Maxim VasilievValparaiso UniversityDon Koetke Mike Leitch - LANL

  5. FNAL E866/NuSea • Forward xF, high-mass spectrometer • Solid Be, Fe, W and empty targets • Thick absorber wall to filter out all but μ’s • Two acceptance defining magnets • Four tracking stations and one momentum analyzing magnet • Scale 60m long, 3m x 3m at back Mike Leitch - LANL

  6. DY Open Charm Randoms Mike Leitch - LANL

  7. Effect of experimental pT-acceptance on the measured J/Ψ suppression • Three E866/NuSea data sets • At lowest xF, pT-acceptance is considerablynarrowed • Shown in terms of α, where σA = σN * Aa (α = 1 corresponds to NO suppression) Mike Leitch - LANL

  8. Correction to Nuclear Dependence for pT Acceptance • Incomplete coverage in pT can distort J/Ψ suppression versus xF • E866/NuSea pT coverage is much better than previous experiment (e.g. E772) because of improved trigger • Most significant effects are at lowest xF where pT is cut off near 1 GeV/c • Use MC acceptance & dσ/dpT consistent with our data to correct for incomplete coverage Mike Leitch - LANL

  9. E866/NuSea 800 GeV p-A (Fermilab) PRL 84, 3256 (2000) • Three magnet settings in E866 match up well • Systematic errors shown at bottom of top panel • J/Ψ and Ψ’ similar at large xF where they both correspond to a cc traversing the nucleus • but Ψ’ absorbed more strongly than J/Ψ near mid-rapidity (xF ~ 0) where the resonances are beginning to be hadronized in nucleus. Mike Leitch - LANL

  10. Mike Leitch - LANL

  11. Scaling of J/ Suppression? • Comparison of 800 GeV (E866) and 200 GeV (NA3) • Appears to scale only with xF Mike Leitch - LANL

  12. Arleo,Gossiaux,Gousset,Aichelin Model (PRC 61, 054906 (2000) & hep-ph/0105047) E866 data J/Y pre-resonance Y’ • Absorption of color-octet or –singlet with color neutralizaton times • J/Y, Y’ & cc with feed-down • Fit to E866/NuSea data with no shadowing & no dE/dx. fully-formed resonances PHENIX Muon Arms xF J/Y • p-Au at RHIC: Predictions • J/Y & Y’ differences at negative rapidity • Effect of dE/dx, also at negative rapidity w/o dE/dx R(Au/p) Y’ 200 GeV p+Au (RHIC) J/Y +dE/dx yCM yCM Mike Leitch - LANL

  13. Parton Energy Loss in Nuclei – Kopeliovich Model Johnson, Kopeliovich et al., hep-ph/0105195 • Shadowing when coherence length, • is larger than nucleon separation • Three dE/dx mechanisms: • String breaking: dE/dz ~ Ks ~ 1 GeV/fm • Multiple bremstrahlung: • dE/dz ~ 3a /p <kT2> ~ .8 GeV/fm • Radiative gluon (BDMS): • DE ~ 3a /8 D<pT2><L> ~ .075 GeV/fm • (since <pT2> ~ 0.1 GeV2 from E772) • Total DE ~ 2 GeV/fm expected from above • From E866 DY data with separation of shadowing & dE/dx via Mass dependence, gives dE/dz ~ 3 ± .6 GeV/fm Shadowing dE/dx & Shadowing Drell-Yan data from E772 (PRL 64, 2479 (1990)) Mike Leitch - LANL

  14. Kopeliovich, Tarasov, Hufner hep-ph/0104256 E866 data • Model: • absorption • Dynamic calculation of shadowing and of energy loss • Also gluon anti-shadowing from Eskola Full calculation Mike Leitch - LANL

  15. Feeding of J/Ψ’s from Decay of Higher Mass Resonances E705 @ 300 GeV/c, PRL 70, 383 (1993) • Large fraction of J/Ψ’s are not produced directly • Nuclear dependence of parent resonance, e.g. χC is probably different than that of the J/Ψ • e.g. in proton production ~30% of J/Ψ’s will have effectively stronger absorption because they were actually more strongly absorbed (larger size) χC’s while in the nucleus Mike Leitch - LANL

  16. Open Charm Nuclear Dependence : xF Dependence? WA82 340 GeV - PRB 284,453 (1992) E769 250 GeV ± PRL 70,722 (1993) Vogt et al., NP 383,643 (1992) E769 250 GeV - WA78 320 GeV - (Beam dump) Mike Leitch - LANL

  17. NA50 Spectrometer • Muon spectrometer: air-gap toroidal magnet with B ~ 2.1 Tm • Covers 3 < yLAB < 4, mT >= 1.3 GeV/c2, |costCS| < 0.5 (-0.1 < xF < 0.1) • Good pT coverage with constant acceptance up to 4 GeV/c • Typically ~2e8 protons/(2.36s spill) • Targets for 450 GeV/c runs: Be, Al, Cu, Ag, W • NA50 (450 GeV/c); NA38 (200 GeV/c) Mike Leitch - LANL

  18. Comparison to NA50 J/Ψ Nuclear Dependence yCM : -0.4 1.0 p-p & p-d E866 800 GeV J/Y NA50/51 450 GeV Y’ Charmonia cross sections from NA50/51 for p-A collisions at 450 GeV/c • ay~0 dependence? • gluon shadowing? • change in production, e.g. octet vrs singlet balance? • (Both experiments have good pT coverage, so strong pT-dependence of α not the cause) * mid-rapidity part of E866 data Mike Leitch - LANL

  19. Ψ’ to J/Ψ ratio (in m+m- channel) • Independent of and rapidity? E789 – 800 GeV p-Au PRD52, 1307 (1995) NA50 – 200 & 450 GeV p-A PLB 444, 516 (1998) Mike Leitch - LANL

  20. J/Ψ Polarization • NRQCD based predictions [Braaten & Fleming, PRL 74, 3327 (1995)] necessary to explain CDF charm cross sections • E866 measurement not in agreement with NRQCD based predictions [Beneke & Rothstein, PRD 54, 2005 (1996)] which give 0.31 < λ < 0.63 • or with color-singlet models [PRD 51, 3332 (1995)] • Complicated by feedown (~40%) from higher mass states. • No clear information on production mechanism! CDF E866/NuSea Mike Leitch - LANL

  21. New Measurements of J/Ψ, Ψ' and χC planned at HERA-B J/Y’s & Y’’s from HERA-B 2000 test run Counts • 2002 run will measure charmonium nuclear dependence with 920 GeV protons on C, Ti, W targets • covering –0.3 < xF < 0.2, a region interestng in terms of formation time effects. • Also would be first measurement (along with NA60) of χC • Expect ~1.5M J/Y, 26k Y’ & 100k χC • Also will measure • via B -> J/Y + X Dimuon Mass (GeV) (Comparison to E866 data) Mike Leitch - LANL

  22. NA60 – (slide from Carlos Lourenço) Mike Leitch - LANL

  23. NA60 – (slide from Carlos Lourenço) Mike Leitch - LANL

  24. NA60 NA60 – (slide from Carlos Lourenço) Mike Leitch - LANL

  25. Charmonium at PHENIX - Coming soon! m+m- • PHENIX: South Muon & Electrons taking first data now • North Muon in 2003 (after shutdown) • Au-Au collisions now; but d-A collisions hopefully coming soon. e+e- * Min-bias/RHIC-year for a = .92 (Nagle & Brooks) ** E866 nuclear dependence data only *** Upsilons form E772 Mike Leitch - LANL

  26. J.C.Peng, LANL Eskola, Kolhinen, Vogt hep-ph/0104124 PHENIX μ+μ- E866/NuSea e+e- PHENIX μ PHENIX e E866 (mid-rapidity) NA50 Kopeliovich, Tarasov, & Hufner hep-ph/0104256 Gluon Shadowing for J/Ψ’s • In PHENIX μ acceptance for Au-Au collisions? • Eskola… : ~ 0.8 • Kopeliovich… : ~ 0.4 • Strikman…[hep-ph/9812322] : ~ 0.4 PHENIX μ+μ- (Au) Mike Leitch - LANL

  27. Gluon shadowing Gerland, Frankfurt, Strikman, Stocker & Greiner (hep-ph/9812322) 10 GeV Change due to shadowing for PHENIX μ relative to NA50 for different models to the W/H ratio (R) and the resulting effective α. 5 GeV Q = 2 GeV (Ratios due to gluon shadowing alone) Mike Leitch - LANL

  28. Summary: PRL 84, 3256 (2000) • Charmonium suppression involves a non-trivial interplay between different effects and involves several timescales including that for hadronizaton and for the coherence of a pair. • It has large variations with xF and pT that help reveal the underlying mechanisms Eskola, Kolhinen, Vogt hep-ph/0104124 • p-A (or d-A) measurements serve as a basis for understanding what is seen in nucleus-nucleus collisions and are a must at RHIC. • Shadowing is certainly very important at RHIC and must be measured in d-A collisions as soon as possible Mike Leitch - LANL

  29. Summary - continued: • Measurements of cc are also important both intrinsically and because they contribute through feed-down to the J/Y • as also are measurements of open charm which can reveal gluon structure function modifications and initial-state effects NA60 (from Carlos Lourenço) E789 D0 Measurement PRL 72, 2542 (1994) Mike Leitch - LANL

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