Colliding high-energy heavy nuclei is the only known way to experimentally study the phase transition from nucleonic to quark matter. Observations are, however, frustrated by the fact that secondary rr mesons are formed in the later stages of the interaction and are therefore insensitive to the early stages when quark matter is formed. We speculate on two types of experimental signatures of phase transition to quark matter. (i) The structure in the rapidity distribution of the secondaries from a near central collision of two heavy nuclei. We estimate that the reduction in shear viscosity between the colored quark-gluon plasma and the peripheral spectator part of each nucleus leads to an observable separation in rapidity of the secondaries from each component. (ii) Abundant production of prompt photons with n , / n ,~3 0 % for central collisions with about 50 GeV energy per nucleon.
It is proposed that the 100-TeV threshold for the appearance of anomalies in cosmicray interactions is associated with the critical energy of about 60 GeV/nucleon centerof-mass energy for phase transition to quark matter in nucleus-nucleus interactions. This proposal implies that the high-energy primary spectrum contains a significant heavy nuclear component (e.g., Fe).PACS numbers: 94.40. Rc, 12.35.Ht, 13.85.Tp, 21.65.+f Whereas cosmic-ray-induced interactions below 100 TeV can be satisfactorily described in terms of standard ideas regarding hadronic interactions, "anomalies" appear above a threshold of about 100 TeV, 1 It is clear that these anomalies are not rare or exotic occurrences, but are features of a large subset of the interactions; i.e., they manifest themselves at the 10% level or above. It is also clear that these features are not observed in low-energy accelerator data. The highlights of the list 1 could be cast in the following form: (i) There is abundant deposition of energy in the electromagnetic (neutral) component. (ii) The final state contains a penetrating component indicating the presence of secondaries with large interaction length or small cross section. Occasional observation of a parallel bundle of penetrating particles (muons). (iii) Isolated events are observed with large multiplicity and anomalous charged-to-neutral composition of the secondaries (Centauro). Indications of both (i) and (ii) are observed in air-shower analysis, in emulsions, and in the observation of showers in the Tien-Shan Pb calorimeter.Mechanisms have been proposed for the various anomalies in the above list. We feel that they lack credibility in one important aspect: Every item has a corresponding explanation; L no uniform explanation for anomalies above 100 TeV exists. We propose that these observations reveal the presence of heavy nuclear primaries in the highenergy spectrum (e.g., Fe); when they interact with nuclei in the atmosphere or in a calorimeter, quark matter is formed. Its presence reveals itself in a multitude of ways which show an intriguing correlation with the list of anomalies previously itemized and also explains the 100-TeV value for its threshold of observation.The main point of this paper is not to explain all of high-energy cosmic-ray physics, but to point out that the very important question of composition could be settled in an unconventional way: One observes signatures 2 * 3 of quark-matter formation in isolated events or experiments, thus establishing the presence of nuclear primaries.Convincing arguments 2 have been made that in nucleus-nucleus collisions in the center-of-mass energy range of 60 GeV/nucleon the energy density of quarks and gluons is about 2 GeV/fm 3 , which is in excess of the energy density of quarks inside a nucleon (0.5 GeV/fm 3 ). Therefore, quarks and gluons cannot be identified any more with individual nucleons and we have a phase transition to quark matter. This large density results from heating of the projectile and target through individual nucleon-nucleon...
Time-reversal-odd asymmetry of hadrons produced in deep-inelastic lepton-photon scattering is calculated in perturbative quantum chromodynamics. The dependence of the asymmetry on the target, the differential variable, and some other factors is studied in a reasonably simplified model. Lepton-photon scattering provides some interesting features qualitatively different from those in lepton-nucleon scattering.
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