V. Kopenkin

Cosmic-Ray Spectra and Composition in the Energy Range of 10-1000 TeV per Particle Obtained by the RUNJOB Experiment

This is a full report on the cosmic-ray spectra and composition obtained by the emulsion chambers on board 10 long-duration balloons, launched from Kamchatka between 1995 and 1999. The total exposure of these campaigns amounts to 575 m2 hr, with an average flight altitude of ~32 km. We present final results on the energy spectra of two light elements, protons and helium nuclei, and on those of three heavy-element groups, CNO, NeMgSi, and Fe, covering the very high energy region of 10-1000 TeV particle-1. We additionally present the secondary/primary ratio, the all-particle spectrum, and the average mass of the primary cosmic rays. We find that our proton spectrum is in good agreement with other results, but the intensity of the helium component is nearly half that obtained by JACEE and SOKOL. The slopes of the spectra of these two elements obtained from RUNJOB data are almost parallel, with values of 2.7-2.8 in the energy range of 10-500 TeV nucleon-1. RUNJOB heavy-component spectra are in agreement with the extrapolation from those at lower energies obtained by CRN (Chicago group), monotonically decreasing with energy. We have also observed secondary components, such as the LiBeB group and the sub-Fe group, and present the secondary/primary ratio in the TeV nucleon-1 region. We determine the all-particle spectrum and the average mass of the primary cosmic rays in the energy region of 20-1000 TeV particle-1. The intensity of the RUNJOB all-particle spectrum is 40%-50% less than those obtained by JACEE and SOKOL, and the RUNJOB average mass remains almost constant up to ~1 PeV.

Alignment in gamma -hadron families of cosmic rays.

Alignment of main fluxes of energy in a target plane is found in families of cosmic ray particles detected in deep lead X-ray chambers. The fraction of events with alignment is unexpectedly large for families with high energy and large number of hadrons. This can be considered as evidence for the existence of coplanar scattering of secondary particles in interaction of particles with superhigh energy,

Search for a simultaneous signal from small transient events in the Pierre Auger Observatory and the Tupi muon telescopes

E_0>10^{16}

Energy determination of the cascade shower by means of a new type of emulsion chamber with diffuser module

eV. Data analysis suggests that production of most aligned groups occurs low above the chamber and is characterized by a coplanar scattering and quasiscaling spectrum of secondaries in the fragmentation region. The most elaborated hypothesis for explanation of alignment is related to the quark-gluon string rupture. However, the problem of theoretical interpretation of our results still remains open.

First results obtained by RUNJOB campaign

We present results of a search for a possible signal from small scale solar transient events (such as flares and interplanetary shocks) as well as possible counterparts to Gamma-Ray Burst (GRB) observed simultaneously by the Tupi muon telescope Niteroi-Brazil, 22.90S, 43.20W, 3 m above sea level) and the Pierre Auger Observatory surface detectors (Malargue-Argentina, 69.30S, 35.30W, altitude 1400 m). Both cosmic ray experiments are located inside the South Atlantic Anomaly (SAA) region. Our analysis of several examples shows similarities in the behavior of the counting rate of low energy (above 100 MeV) particles in association with the solar activity (solar flares and interplanetary shocks). We also report an observation by the Tupi experiment of the enhancement of muons at ground level with a significance higher than 8 sigma in the 1-sec binning counting rate (raw data) in close time coincidence (T-184 sec) with the Swift-BAT GRB110928B (trigger=504307). The GRB 110928B coordinates are in the field of view of the vertical Tupi telescope, and the burst was close to the MAXI source J1836-194. The 5-min muon counting rate in the vertical Tupi telescope as well as publicly available data from Auger (15 minutes averages of the scaler rates) show small peaks above the background fluctuations at the time following the Swift-BAT GRB 110928B trigger. In accordance with the long duration trigger, this signal can possibly suggest a long GRB, with a precursor narrow peak at T-184 sec.

High-Energy Gamma Rays in the RUNJOB Experiment

Abstract An account is given of a new type of emulsion chambers which have been in our use since 1997 in our RUNJOB program (RUssia–Nippon JOint Balloon-program). Each chamber is equipped with an additional “diffuser module” placed under the usual set of modules. We have made the experiments using 4 cm thick diffuser modules composed of several photo-sensitive layers (X-ray films and/or nuclear emulsion plates) sandwiched with spacers. The result is as follows. Even in the case where the path length of only 6 radiation lengths is available within the calorimeter module placed above, the visible energy sum is determined with an accuracy better than σ∼0.2 for a group of electromagnetic cascade showers induced by a proton of energy up to several tens of TeV, or by an iron nucleus of energy up to one hundred TeV. If the available path length in the calorimeter module is 9 radiation lengths, we can estimate the energy sum up to ∼100 TeV within an accuracy of σ∼0.2 for a proton-induced cascade shower group. It means that the use of our new-type emulsion chamber can reduce the detector payload dramatically, which is essentially important for the high-energy cosmic-ray observations made on board the vehicles such as balloons, satellites and so on.

Hadron/gamma identification of showers observed by EC's

Abstract We report experimental results obtained by using a wide-gap type emulsion chamber flown in the first Japanese-Russo joint balloon project, called RUNJOB ( RU ssia- N ippon JO int B alloon-program). Two balloons were launched from Kamchatka in July 1995, and both were recovered successfully near the Volga River. The exposure time was 130 hours for the first flight and 168 hours for the second. The mean ceiling altitude, in both flights, was 32 km corresponding to 10 g/cm 2 . Total area of the emulsion chamber was 0.8 m 2 , and the thickness 0.385 and 2.28 collision m.f.p.s for vertically incident proton- and iron-primaries, respectively. We detected 381 showers using Fuji-#200-type X-ray film; of these 174 showers were due to atmospheric secondary γ-rays, and the rest 207 came from nuclear components. The energy range covers 20∼200 TeV for proton-primary, 3∼30 TeV/nucleon for helium-primary, and 0.7∼5 TeV/nucleon for iron-primary. We give the energy spectra for various elements (proton, helium, …, iron) as well as the all-particle spectrum and the average mass of the cosmic-ray primaries.

Inelasticity of hadron-lead collisions, estimated by thick lead emulsion chambers at the Pamirs

The latest results of studies of the gamma-ray spectra recorded together with charged particles in the Russian-Nippon Joint Balloon (RUNJOB) experiment are presented. A comparison of the experimental spectra with the results of the calculations based on assumptions of different intensities of the gamma-ray spectra demonstrates that the previously published intensities of primary cosmic rays measured in the RUNJOB experiments are underestimated.

Search for disoriented chiral condensate in cosmic gamma - hadron families

Abstract Fluctuations of hadron- and gamma-induced showers, which are observed by emulsion chambers, are studied making use of simulated showers. An algorithm is formulated to analyze gamma- and hadron-induced showers. The algorithm is applied to the showers observed by Pamir thick lead chambers, and its results are presented.

Proton and Helium spectra obtained by RUNJOB experiment

The inelasticity distribution of hadron-lead collisions in the energy region exceeding 1014 eV is estimated by 74 events of hadron interactions, observed by thick lead chambers at the Pamirs. The distribution is approximated as g(K)dK = 3.0 K2.0 dK (with 〈K〉 = 0.75) as a minimum estimate. The distribution is consistent with that by the simulation made under the assumptions of UA5 algorithm for hadron collisions and of geometrical model for intra-nuclear cascade. It is inferred that the average value of the inelasticity of hadron-nucleon collision is smaller than 0.5 in the energy region exceeding 1014 eV.