Outlook
One of the most remarkable observations at RHIC [1] is the nearly complete quenching of away-side hadrons produced opposite a detected high p{sub T} hadron in central AuAu collisions at {radical}s{sub NN} = 200 GeV. This strong suppression implies a jet energy loss dE/dx {approx} 15 GeV/fm, some 30 times larger than the jet energy loss seen in pp, dA, and peripheral ion-ion collisions [2]. The observation of anomalous jet quenching at RHIC is perhaps the strongest evidence that a new phase of hot, dense hadronic matter has been produced in high energy ion-ion collisions. A possible dynamical mechanism for initiating this phenomenon in QCD is illustrated in transparency [2]: a soft gluon produced from an initial hard nucleon-nucleon collision can Compton back-scatter from the quark of another nucleon, efficiently converting its quark energy to gluonic energy in analogy to laser back-scattering on a high energy electron beam. The back scattering of soft gluons can occur repeatedly as the heavy nuclei approach, producing a gluon ''avalanche'' and a dense field of quark and gluon quanta which finally coalesce to a high multiplicity of hadrons. In this talk, I also discussed a number of other novel aspects of high p{sub T} hadron production at RHIC, including (1) the formation of hadrons and the suppression of quarkonium due to the coalescence of comoving partons; (2) the importance of higher twist and semi-exclusive hard scattering subprocesses in pp {yields} HX, such as uu {yields} p{bar d} and up {yields} up reactions; despite their relative suppression in inverse powers of p{sub T}, such subprocesses can nevertheless dominate over conventional quark and gluon scattering reactions. This is especially important for high p{sub T} baryon production--because of the more effective use of hadron energy by higher twist subprocesses; (3) the effects of color transparency in direct high p{sub T} hadron production; (4) the interesting effects of high x intrinsic charm quarks including s{bar c} {yields} W{sup -} production subprocesses; (5) the elimination of the renormalization scale ambiguities; (6); unusual aspects of diffraction, nuclear shadowing, and antishadowing; and (7) the use of single-spin high p{sub T} asymmetries as signals for initial and final state QCD interactions. The upcoming RHIC experimental program, including polarized pp collisions is extraordinarily interesting and diverse. The central challenge is to quantify the conditions and identify the specific signals of novel nuclear QCD matter and phenomena, such as anomalous direct photon and lepton pair production, anomalous heavy quark and quarkonium signals, and the anomalous production of anti-nuclei.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (US)
- DOE Contract Number:
- AC03-76SF00515
- OSTI ID:
- 826698
- Report Number(s):
- SLAC-WP-041; TRN: US0404124
- Resource Relation:
- Other Information: PBD: 15 Jan 2004
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
74 ATOMIC AND MOLECULAR PHYSICS
BARYONS
COALESCENCE
ELECTRON BEAMS
GLUONS
HADRONS
HEAVY NUCLEI
ION-ION COLLISIONS
LASERS
LEPTONS
MULTIPLICITY
PAIR PRODUCTION
PARTONS
PHOTONS
QUANTUM CHROMODYNAMICS
QUARKONIUM