M. G. K. Menon

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.

The Kolar Gold Fields neutrino experiment II. Atmospheric muons at a depth of 7000 hg cm-2 (Kolar)

An experiment has been performed in the Kolar Gold Fields in Southern India to search for the interaction products of cosmic ray neutrinos. In the course of four years operation of the detectors at a depth of 2316 m of rock, some 165 particles were recorded which were attributed to muons of atmospheric (as distinct from neutrino-) origin and the present paper describes the results of measurements on these particles. The measured vertical intensity at the depth in question (2316 m of Kolar rock corresponding to 7.6 x 105 g cm-2 of standard rock) is (1.1 ± 0.2) 10-6 m-2 s-1 sr-1. Including measurements at shallower depths by other workers, from sites elsewhere in the same Gold Fields, a best fit to the data gives the relation I(h) = 7.73 x 10-3 exp (–h/790) m-2 sr-1 s-1 for depth range 4000 < h < 9500 hg cm-2 Kolar rock (1 hg cm-2 = 102 g cm-2). An approximate estimate has been made of the mean energy of the atmospheric muons at the depth of operation; its value, ca. 330 GeV, is not inconsistent with the expected value.

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.

The Kolar Gold Fields neutrino experiment I. The interactions of cosmic ray neutrinos

Final results are presented of an experiment to study the interactions of cosmic ray neutrinos deep underground, at a depth of 7.6 x 105 g cm-2 (standard rock). Clear examples have been recorded of neutrino-induced muons, including cases of upward moving particles and neutrino interactions within the detector assembly itself. The observed rate of events is compared with expectation and conclusions are made about the variation of the inelastic cross-section with energy and the lower limit to the mass of the intermediate boson. An examination has also been made of the celestial coordinates of the detected neutrinos and details are presented.

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.

Muon intensities and angular distributions deep underground

Recent measurements of the intensity of muons below 3000 m.w.e. (metres water equivalent) underground have been combined to give an estimate of the depth-intensity relation and the angular distribution for atmospheric muons down to a maximum depth of approximately 9000 m.w.e. It is found that the vertical intensity can be represented by the expression I(0, h) = 9.8 × 10-7 exp(-h/λ)cm-2sec-1sterad-1 where h is the depth in m.w.e. and λ = 810 ± 50 m.w.e. The corresponding angular distribution at vertical depth h is given by I(θ, h) = I(0, h) secθ exp{-(h/λ)(secθ - 1)} where θ is the zenith angle. The implication of the above angular distribution for the estimate of neutrino fluxes in deep underground cosmic-ray experiments is discussed.

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.