M. R. Krishnaswamy

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.

Evidence for the production of a new particle in neutrino interactions

Abstract We present here evidence, based on 5 events recorded in cosmic ray experiments deep underground, for the production of new, massive (⪆ 2 GeV) and long lived (τ ∼ −9 sec) particles in neutrino with rock nuclei.

Evidence for the production of new particles in cosmic ray experiments deep underground

In the cosmic ray experiments deep underground in the Kolar Gold Mines, a special class of events has been observed, at present 6 in number, characterised by several, (in general 3), charged particles arising from a vertex, either in air or in the thin material of the detectors, with large opening angles; the vertex is at a distance of around 70–100 cms from the rock wall. The most plausible interpretation of these events is that they are due to the decay of new, massive and long-lived particles produced in neutrino collisions inside rock, or through hitherto unknown processes.

Neutrino backgrounds in the Kolar Gold Field nucleon decay experiment

The neutrino events recorded in the Kolar Gold Field Nucleon Decay detector are analysed here. It is shown that there is good agreement between the observations and the estimates based on the intensities of atmospheric neutrinos and interaction cross-sections of neutrinos available from accelerator experiments. In the context of the search for proton decay, we show that the low energy (<2 GeV) neutrino events, which would provide the main background, are suppressed at thekgf site since it is situated near geomagnetic equator, where the geomagnetic cut-off rigidities are high. A comparison of the predicted characteristics ofv-induced events with thekgf observations shows that, within the statistical accuracy of the present data, the signal due to nucleon decay stands out distinctly within thev-induced background.

Observations on the cosmic ray angular distribution underground at 1500 hg/cm2 (Kolar) and the question of muon production in the TeV energy region

Abstract Measurements on the angular distribution of cosmic ray muons at 1500 hgm2 (Kolar) are presented: these relate to muons with energies ⩾ 500 GeV. These observations are fully consistent with the picture that pions and kaons together are wholly responsible for the production of muons at these energies.

MEASUREMENT OF THE TOP QUARK PAIR PRODUCTION CROSS SECTION IN PP COLLISIONS

We present a measurement of the ttbar production cross section in ppbar collisions at root(s) = 1.8TeV by the D0 experiment at the Fermilab Tevatron. The measurement is based on data from an integrated luminosity of approximately 125 pb^-1 accumulated during the 1992-1996 collider run. We observe 39 ttbar candidate events in the dilepton and lepton+jets decay channels with an expected background of 13.7+-2.2 events. For a top quark mass of 173.3GeV/c^2, we measure the ttbar production cross section to be 5.5+-1.8 pb.

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.

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.