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Hard Scattering at RHIC

Hard Scattering at RHIC. John Lajoie Iowa State University lajoie@iastate.edu. A disjointed, random collection of general musings. 1. How did I get interested in this? 2. Hard Scattering at RHIC 4. Jet Quenching 5. Jet Flavor Tagging 6. A program of study for RHIC?

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Hard Scattering at RHIC

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  1. Hard Scattering at RHIC John Lajoie Iowa State University lajoie@iastate.edu A disjointed, random collection of general musings... 1. How did I get interested in this? 2. Hard Scattering at RHIC 4. Jet Quenching 5. Jet Flavor Tagging 6. A program of study for RHIC? 7. Where do I go from here?

  2. semi-leptonic D decays NA44 single particle distributions NA50 heavy flavor decay strangeness production Nch, dNch/dh, fluctuations spin program W+,W- WA80 E859 jet quenching ET, dET/dh, fluctuations

  3. strangeness charmonium temperature 1 10 1 150 MeV 5 QGP QGP QGP 0 0 0 radiation chiral symm. chiral cond. Chiral 1 QGP DCC 0 0 interferometry parton prop. jets ??? 1 mixed phase QGP 0 QGP Signatures

  4. “soft” interactions Log(dN/dpT2) “hard” parton scattering q1 q1’ g q2 q2’ g1 q pT ~1-2 GeV/c g q1 g2 q g q1’ Hard Scattering and Jets Low momentum particles arise from “soft” (large distance scale) interactions. High transverse momentum particles arise from parton (qq, qg and gg) scattering.

  5. PQCD at RHIC Relativistic Heavy Ion collisions have been extremely difficult to study due to the lack of a well-established, generally accepted theoretical framework for calculating experimental observables. However… Theoretical estimates predict that approximately half of the energy transfer from the projectile frame to midrapidity may be calculable using Perturbative Quantum Chromodynamics (PQCD). Input to Theoretical Models: Low Energy (AGS, SPS): flux and energy of nucleons High Energy (RHIC): flux and energy of quarks/gluons

  6. unbound proton - MRS(A) Bjorken xB Structure Functions Quark distributions determined in DIS experiments. Gluon distributions poorly determined experimentally - note the soft gluon distribution.

  7. Shadowing Parton distributions modified when nucleons bound in a nucleus - depletion at low x. Similar for gluons? Complicates things for RHIC... XN Wang an M. Guylassy, Phys. Rev. D 44 (1991) 3501

  8. Leading Particles in Jets Leading particles arise from the originally scattered partons and have a large fraction of the jet’s transverse momentum. Consider trying to sum the jet energy at RHIC: (Jet cone) Typical “pedestal” energy: Need to use high-pT leading particles at RHIC.

  9. parton prop. jets ??? 1 QGP 0 Jets and the QGP How does a QGP affect the evolution of jets? Energy loss and rescattering in the QGP: dE/dl increased (or reduced) in the plasma? pT~20GeV/c reduced by a factor of 10 Guylassy and Plümer, Phys Lett B243 (1990) 432 Dramatic effects at the phase transition? Energy imbalance in back-to-back jets? Jet acoplanarity? (Difficult?) Rammerstorfer and Heinz, Phys Rev D41 (1990) 306

  10. Jet Scattering in p+A FNAL E609: p+Pb at 400GeV/c E609 Collaboration, Phys. Lett. B259 (1991) 209

  11. HIJING Includes hard scattering and minijet production. Also includes a model for parton energy loss. XN Wang an M. Guylassy, Phys. Rev. Lett. 68 (1992) 1480 Jets, shadowing and quenching will all be important at RHIC!

  12. Jet Flavor Tagging q Select quark-quark and quark-gluon jets (average gluon at smaller xB). High-pT particles reflect scattered partons (string fragmentation). q g q In addition, the leading particle indicates the flavor of the scattered parton: • Leading p+ selects mainly u-quark jets • Leading p- selects mainly d-quark jets • Leading K- selects mainly gluon jets Use this to extract structure functions for A+A?

  13. K+ p + p - K- Selecting Jets by Leading Particles G. Bordes and A. Nicolaidis, Phys. Rev. D22 (1980) 2152 and Phys. Lett B114 (1982) 175

  14. Measure g(x) in pp at GeV from two body kinematics in • hard qg scattering (g + jet) • Repeat the above in p+Au to extract g(x) for a bound nucleon • Use the above to predict the high-pT spectra in Au+Au collisions • Compare with data: Jet Quenching? QGP? A program of study for RHIC? Observables: inclusive high-pT, dijets, g-jet coincidence Too naive! Requires systematic study - real results will take time!

  15. Where do I go from here? Lots more literature to read - study up on predictions as well as results from the ISR and Fermilab. Start to think about the first year - how far out in pT might we expect to look with a limited data sample. How do we trigger effectively on qq, qg and gg jets? What can we learn from looking at Au+Au data alone (without the benefit of g(x))? HIJING/PISA simulations of “jet triggered” events.

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