Experimental feature in the primary-proton flux at energies above 10 TeV according to the results of searches for primar
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EMENTARY PARTICLES AND FIELDS Experiment
Experimental Feature in the Primary-Proton Flux at Energies above 10 TeV according to the Results of Searches for Primary Particles in Nuclear Emulsions Exposed in the Stratosphere (RUNJOB Experiment) I. S. Zayarnaya Lebedev Institute of Physics, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 117924 Russia Received November 7, 2006; in final form, April 5, 2007
Abstract—In the RUNJOB experiment, a long-term exposure of x-ray emulsion chambers in the stratosphere from 1995 to 1999 with the aim of studying the composition and spectra of primary cosmic particles in the energy range 10–1000 TeV per nucleon revealed about 50% proton tracks. The remaining events of the proton group did not feature any candidate for a track of a singly charged particle within the search region determined from measurements of the coordinates of background nuclei going close to the sought track. Methodological factors that could explain this experimental observation are considered. A possible physical reason associated with the presence of a neutral component in the flux of primary protons in the energy region above 10 TeV is also analyzed. PACS numbers: 98.70.Sa DOI: 10.1134/S1063778808020075
INTRODUCTION Balloon-borne experiments involving a long-term exposure (about six to seven days) of x-ray emulsion chambers in the stratosphere were performed from 1995 to 1999 by the RUNJOB Collaboration, which includes Russian and Japanese researchers. Within ten successful long-term flights between Kamchatka and Wol’sk, two-sided nuclear emulsion films were exposed at an altitude of about 32 km. The total statistical sample underlying the ultimate results of the Russian–Japanese experiment in question contains 521 events, of which 360 are those of primary-proton interactions [1]. The measuring facility used, which included a strongly magnifying microscope that involved an automatically moving objective table and a CCD Scanning system, made it possible to perform high-precision searches for nucleons and nuclei of primary cosmic rays. For individual events, the accuracy in finding primary particles was as high as a few microns. According to data from processing the RUNJOB’95–99 chambers, the proton group contained about 50% events where no candidate for a track of a primary singly charged particle was found within the search region of radius about 3σ, where σ is the root-mean-square error of the method for determining the coordinates of the sought-particle track. In examining methodological factors that could explain this experimental observation, the proton tracks were continued over
several higher lying layers from the RUNJOB-6A and RUNJOB-5A chambers. The results obtained in this way and an analysis of methodological issues concerning searches for relativistic singly charged particles in the emulsion layers of x-ray emulsion chambers are reported in the present article. SEARCHES FOR PRIMARY PARTICLES IN THE RUNJOB EXPERIMENT Upon hitting an x-ray emulsion chamber (see Fig. 1), nucleons and nuclei of pri
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