M. Tamada

Air-shower-triggered families: simulation calculation and its comparison with experimental data

Results of Monte Carlo simulations for a combined emulsion chamber and extensive air-shower array experiment are shown. Two totally distinct models are assumed for nuclear interactions, one based on the UA5 Monte Carlo algorithm (model A) and the other including exotic processes of Centauro and MiniCentauro (model B). Effects of different assumptions on the chemical composition of primary particles are also considered. Longitudinal and also lateral structures of gamma-families triggered by air-shower size, Ne, are studied and are compared with the data of the HADRON experiment at Tien-Shan and of the SYS experiment at Chacaltaya. The experimental data are found to disagree with the results of model A, even when we introduce the heavy-dominant assumption for primary cosmic rays. On the other hand, model B explains the general tendency of the experimental characteristics. It suggests that the nuclear interaction is changed drastically in the primary energy range over 1016 eV.

Attenuation mean free path of high energy hadrons in lead using a geometrical model for hadron-nucleus collisions

The attenuation mean free path, lambda att, of nucleons and pions in thick lead chambers is calculated assuming a simple geometrical model for hadron-nucleus interactions and also taking experimental procedure into consideration. The results are compared with experimental data of the Pamir and Chacaltaya collaboration experiment, where it is observed that lambda att of hadrons in high-energy families is much smaller than that of ordinary hadrons. lambda att of single-arrived hadrons, which are considered to be mostly protons, observed in the same experiment, agrees well with calculations for proton incidence. For hadrons in families, however, calculations give lambda att not smaller than that of single-arrived hadrons and fail to explain the experimental results even when we assume hadrons are mostly nucleons in high-energy families. Fluctuations in the estimation of lambda att are also discussed.

Empirical formulation of rapidity density distribution in multiple particle production in a wide energy range from fixed target to LHC

We formulate empirically the rapidity density distribution of produced particles in multiple particle production. We assume several emitting centers, distributed on the rapidity axis, from which the produced particles are emitted isotropically with energy distributed in the inverse-exponential form. The formula includes four parameters, the values of which are determined to reproduce the experimental data of the average value of the transverse momentum and the pseudo-rapidity density distributions at various incident energies. The formula describes well the pseudo-rapidity density distributions in a wide range of energy (, 53, 200, 546, 630, 900 and 1800 GeV), by adjusting the values of the parameters. The transverse momentum distributions, however, are not described well at large values of the transverse momentum. The multiplicity and the inelasticity of produced particles are discussed at high energies up to TeV (E0 = 1020 eV), based on the energy dependences of the parameters. The inelasticity becomes small at high energies, less than 0.1 at GeV, which is not consistent with the predictions of the existing models. The pseudo-rapidity density distribution of the produced particles at LHC energy ( TeV) is compared with those distributions obtained by other models.

Study of hadronic component in air showers at Mt. Chacaltaya

Abstract An experiment of an air shower array, a hadron calorimeter (8 m 2 ) and an emulsion chamber (8 m 2 , 15 cm Pb) is under way at Mt. Chacaltaya (5200 m above sea level, Bolivia), in order to study the hadron interactions and the primary cosmic rays in the energy region exceeding 10 15 eV. The number of particles in the hadronic component in the air shower, which is detected by the hadron calorimeter, is not compatible with that obtained by simulations, indicating that violation of the Feynman scaling law is stronger at 10 16 eV than the one assumed in the simulations. The average mass number of the primary cosmic rays, estimated from the distribution of the number of hadrons in the air shower, is A >= 2.8 ± 0.5 at 10 16 eV.

A halo event observed with an emulsion chamber and air shower array at Mt Chacaltaya

A hybrid experiment to operate simultaneously an air shower array, a hadron calorimeter and an emulsion chamber is under way at Mt Chacaltaya (5200 m, Bolivia). An event with a halo, a blackened area of ~1 cm on x-ray film of the emulsion chamber, was observed with the experiment. Information about the halo (Ehalo = 850 TeV) and on high energy particles of electromagnetic and hadronic components outside the halo (?E? = 632.5 TeV and ?E(?)h = 278.8 TeV with a detection threshold of 2 TeV) was obtained from emulsion chamber data. Details about low energy hadrons were determined from the hadron calorimeter data, and characteristics of the accompanying air shower (Ne = 7.0 ? 107, s = 0.59) were determined by the air shower array. We reconstruct the event, based on the observed data. The event is compared with simulated events, which supports the conclusion that nuclear interactions change their characteristics in the high energy region so as to result in stronger energy subdivision.

Emulsion chamber observations of Centauros, aligned events and the long-flying component

The cosmic ray emulsion chamber community has reported several unusual phenomena which are also relevant to experiments at the current high-energy accelerators, in particular the Fermilab Tevatron Collider and the CERN Large Hadron Collider (LHC). A summary of the ”Cosmic Rays at Mountain Altitude” workshop held at Plock (Poland, September 2010) is given.

The exotic characteristics of Centauro-I: a model to describe Centauro-I

In our previous paper on Centauro-I (Ohsawa et al 2004 Phys. Rev. D 70 074028), we showed that the shower cluster, found in the block I12 of the lower chamber, is produced in the target layer by a number of hadrons with appreciable lateral spread. These hadrons are accompanied by no (or one at most) γ-ray(s) with energy above detection threshold, and produce no shower in the upper chamber but 28 visible C-jets (with the visible energy more than 2 TeV) in the target layer. These characteristics are quite exotic and unable to be described by a fluctuation of ordinary atmospheric families. In the present paper, we propose a model of strange quark matter (SQM) among the primary cosmic rays to describe the exotic features of the event. A large SQM droplet enters the atmosphere and fragments into a bundle of small strangelets in the atmosphere without emission of γ-rays, and these small strangelets explode into nucleons in the upper chamber. The number of collisions in the upper chamber is estimated to be as small as 3–4 in contrast to 20–30 collisions in the target layer. We discuss the intensity of Centauro-I together with the exotic events observed by the balloon and satellite experiments, which were also ascribed to strange quark matter.

Neural net classification of proton- and heavy nucleus-induced cosmic ray families

A feed-forward neural network trained using backpropagation is applied to discriminate between proton-induced cosmic ray families and heavy nucleus-induced ones. Fifteen input variables which characterize three-dimensional behaviour of the families are chosen. The network successfully classify the events with classification efficiency ~ 85%. The trained neural network classifier is applied to the cosmic ray families observed in the Pamir chambers. The fraction of heavy nucleus-induced events is estimated, from the network-output distribution, to be at most ~ 3% of the observed families.

Baryon pair production with large decay Q‐value

Events of a new type have been observed by the chacaltaya Emulsion Chamber Experiment,1,2 which can consistently be interpreted as ’’baryon’’ pair decay of a heavy intermetiate state of rest mas 20–30 GeV/c2.

Experiment OMEGA —A proposal of cosmic ray experiment at Mt. Chacaltaya—

Physical idea of a proposal of new cosmic‐ray experiment at Mt. Chacaltaya is discussed.Physical idea of a proposal of new cosmic‐ray experiment at Mt. Chacaltaya is discussed.