Comprehensive Explanation of Cosmic-Ray "Anomalies": Quark Matter Formation by Heavy Nuclear Primaries

Abstract

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...

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