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Antiproton Production In p+A Collisions

Antiproton Production In p+A Collisions. J. Lajoie and B. Fadem Iowa State University for the E941 Collaboration: UCLA - Penn. State - U.C. Riverside - Yale - Wayne State - Purdue - ISU - Vanderbilt - MIT - U. Mass. - Columbia. Introduction and Motivation

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Antiproton Production In p+A Collisions

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  1. Antiproton Production In p+A Collisions J. Lajoie and B. Fadem Iowa State University for the E941 Collaboration: UCLA - Penn. State - U.C. Riverside - Yale - Wayne State - Purdue - ISU - Vanderbilt - MIT - U. Mass. - Columbia • Introduction and Motivation • Measurements for p+Be, p+Pb at 12 and 18 GeV/c • Implications E864/E878 AA Data • Future Prospects LBNL pA Workshop - J. Lajoie and B. Fadem

  2. E941 Apparatus LBNL pA Workshop - J. Lajoie and B. Fadem

  3. E941 Late Energy Trigger Energy ACCEPT REJECT Time E941 data taken with flat energy cut at 300MeV. LBNL pA Workshop - J. Lajoie and B. Fadem

  4. Why Antiprotons? • Enhanced Production: • Resonance-nucleon and resonance-resonance collisions • can enhance production by making more energy • available • P. Koch and C. Dover, Phys. Rev. C40 (1989) 145 • QGP models predict enhanced antimatter production • P. Koch et al., Mod. Phys. Lett. A8 (1988) 737 • Mean field effects could reduce the antiproton mass • in the medium, enhancing production and changing the • distribution of antimatter • V. Koch et al., Phys. Lett. B265 (1991) 29 • Annihilation: • Large annihilation cross section makes the antiproton • sensitive to the density created in the collision • P. Koch and C. Dover, Phys. Rev. C40 (1989) 145 • Annihilation cross section could be modified or screened • in the nuclear medium • S. Kahana et al., Phys. Rev. C47 (1993) 1356 P. Koch and C. Dover, PRC 40 (1989) 145 LBNL pA Workshop - J. Lajoie and B. Fadem

  5. p+Be pbar +X @ 18 GeV/c E941PRELIMINARY Pi-minus K-minus Antiprotons (~1700) Mass (GeV/c2) E941 Data Sampled Events: Target 18GeV/c 12GeV/c Be 39.8M175.4M Pb 113.8M134.7M Corrections: • Delta ray triggered events • Empty target contributions • Elastic scattering off M1 collimator LBNL pA Workshop - J. Lajoie and B. Fadem

  6. Antiproton Production Spectra relatively flat over (limited) pT range. Greater production in p+Be. yNN=1.8 yNN=1.8 (errors shown are statistical only) Systematic errors ~5-10%. LBNL pA Workshop - J. Lajoie and B. Fadem

  7. Production at pT=0 (statistical errors only) yNN=1.8 LBNL pA Workshop - J. Lajoie and B. Fadem

  8. Annihilation? Data consistent with annihilation in p+Pb system. Enhanced production winning at low pT? (errors shown are statistical only) LBNL pA Workshop - J. Lajoie and B. Fadem

  9. Using the pA Data The pA data may be able to shed light on the amount of annihilation in ordinary nuclear matter. A comparison between AA production at 12 GeV/c and first-collisions scaled p+Be antiproton production can shed light on the competition between enhanced production and annihilation. LBNL pA Workshop - J. Lajoie and B. Fadem

  10. Antiprotons in E864/E878 Pbar production versus collision centrality (first collisions): E864/E878 difference interpreted as evidence for antihyperon production (also E859 and E917) LBNL pA Workshop - J. Lajoie and B. Fadem

  11. Antihyperons in Au+Au(Pb) PRC 59, 2699 (1999) Suggests large antihyperon production in central collisions. LBNL pA Workshop - J. Lajoie and B. Fadem

  12. <Nf>=19.5 <Nf>=10.0 yNN=1.6 <Nf>=37.6 <Nf>=50.0 Scaling p+Be to AA at 11.5 GeV/c p+Be overestimates at large impact parameter by ~2x E864 data matches p+Be scaling well - competing annihilation and antihyperon production? LBNL pA Workshop - J. Lajoie and B. Fadem

  13. Future Prospects • Complete analysis of p+Cu, p+Al data at 18 GeV/c • Possibly p+Pb at 12 GeV/c • Analysis of annihilation in pA - lessons for AA collisions at the AGS? This data will provide useful input to models of antiproton production in pA and AA collisions at AGS energies. LBNL pA Workshop - J. Lajoie and B. Fadem

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