N. Ito

Candidate events for nucleon decay in the Kolar Gold Field experiment

Three candidate events for nucleon decay have been recorded so far in a 140 ton detector operating at a depth of 2300 m in the Kolar Gold Mines, India. It is shown that these events cannot be explained in terms of known backgrounds at such a great depth and that the observed features are consistent with those expected of nucleon decay.

Fully confined events indicative of proton decay in the Kolar Gold Fields detector

Abstract Three events have been recorded in the Kolar Gold Field experiment with tracks fully confined to the detector volume. It is shown that their characteristics are in conformity with the decay of bound nucleons and that the background due to neutrino interactions is extremely small. Based on these as well as the events reported earlier, we tentatively suggest a mean lifetime of about 7 × 10 30 yr for nucleons bound in iron nuclei.

Studies of the energy spectrum and composition of the primary cosmic rays at 100?1000 TeV from the GRAPES-3 experiment

The composition and energy spectrum of primary cosmic rays (PCRs) are the only observables at high energies to study the nature of sources accelerating PCRs to �1000 TeV. These observables have been directly measured up to ∼300 TeV with detectors aboard balloons and satellites. But measurements at >1000 TeV have to be obtained indirectly from ground-based observations of extensive air showers. However, their interpretation relies on an inadequate knowledge of hadronic interactions at �1000 TeV. The GRAPES-3 experiment is designed to operate at �30 TeV providing a sizable overlap in energy with direct measurements, enabling the selection of a suitable model of hadronic interactions at ∼1000 TeV. We present salient features of GRAPES-3 including details of muon multiplicity distributions observed with a 560 m 2 detector as a function of shower size from an analysis of data of 545 days. These distributions were compared with expectations from Monte Carlo simulations, using some of the hadronic interaction generators in CORSIKA, to deduce energy spectra of five nuclear groups in the 100–1000 TeV region. A comparison of GRAPES-3 results with direct measurements indicates that SIBYLL provides a good description of hadronic interactions for interpreting our data. These measurements extend energy spectra and composition of PCRs that is consistent with extrapolation of direct measurements. (Some figures may appear in colour only in the online journal)

Limits on the flux of monopoles from the Kolar gold mine experiments

Abstract A search was made for GUT monopoles in the data collected with the nucleon decay detector in the Kolar Gold Mines. The methods used are d E /d x , time of flight and catalysis of nucleon decay. A limit on the monopole flux of 2 × 10 −14 /cm 2 sec. st. for β > 10 −3 is set on the basis of this experiment.

Energy spectrum of TeV gamma rays from Mrk 501 obtained by stereoscopic analysis

Abstract We have observed flares of TeV-gamma rays from Mrk501 in 1997 using three telescopes of the Utah Seven Telescope Array at Dugway, Utah. Determination of the energy spectrum from such Active Galactic Nuclei (AGN) is very important, because the gamma-ray spectrum is expected to steepen around 10 TeV from objects like Mrk501 by the interaction of the infrared photons. We have developed the method to estimate energies of the gamma rays by stereoscopic analysis using multiple telescopes. The differential index of the energy spectrum obtained is well expressed by −2.5 between 700 GeV and 3 TeV. This spectrum seems to become steeper above several TeV.

A multi TeV muon bundle observed in the KGF underground detector

Abstract An unusually large multiplicity ( N μ = 20) muon bundle was observed in the KGF underground detector operating at a depth of 6045 hg/cm 2 . The mean energy of a muon to reach such a depth is ∼ 10 TeV. No other event has been recorded with N μ > 4 in this detector during the live time of ∼ 4 yr. In this paper, we estimate the energy of the primary cosmic rays which can give rise to such high multiplicity as well as the probability for such an occurrence.

A microcomputer based data acquisition system for the KGF nucleon decay experiment

We have adapted a microcomputer based data acquisition system using the concept of parallel processing. The active detector components consisting of 3800 proportional counters, are read out by a network of nine Z-80 based microprocessor modules. A look-up table concept for generating various trigger schemes has also been implemented.

The K.G.F. Nucleon Decay Experiment

A 140 ton nucleon decay detector is in operation in the Kolar Gold Mines in India at a depth of 2300 metres since November 1980. The experimental details, the method of analysis and the results obtained after different periods of observation are available in a series of earlier publications(1).

Proton decay experiment in the Kolar gold fields

In total 6 events of special type have been recorded as far in the Kolar Gold Fields experiment. Out of them, there events are fully confined to the detector volume. It is shown that their characteristics are in conformity with the decay of bound nucleons and the background due to neutrino interactions is extremely small. Based on these events, it is suggested that a mean lifetime of protons is about 8×1030 years.

Cosmic ray physics underground: Some puzzles

A series of experiments has been carried out since 1961 at depths of 750 to 8400 hg/cm2 in the Kolar Gold Mines and the general features of atmospheric muons and neutrinos have been studied. However, there are some prolems which are incompletely understood and some of the events observed suggest the existence of new phenomena caused by unknown particles or processes. We point out some problems observed at these great depths which are relevant to the prompt muons in hadronic collisions; the increase of average transverse momentum in the very high energy region, muon bundles, Kolar events, large electromagnetic cascades, and so on.