K. Hinotani

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.

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.

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.

V. Studies of cosmic ray neutrino interactions in the Kolar Gold Field experiment

Results are presented of an experiment to study the penetrating particles in the cosmic radiation deep underground, at a depth of 7500 m. w. e. (standard rock). The events recorded are attributable, in the main, to muons produced either in the atmosphere or by the interactions of neutrinos in the surrounding rock. The muons have been studied in some detail and it appears that the mean energy of the neutrino induced muons (probably less than about 30 GeV) is low compared with that of the muons of atmospheric origin. The significance of the celestial coordinates of the muons and the measured rate of neutrino- induced muons is discussed and the future experimental programme is indicated.

Multiple muon events observed underground

Observations are reported on events involving multiple penetrating particles recorded in a scintillator-neon flash tube telescope, at a depth of 1500 hg/cm2 in the Kolar Gold Mines. From these, it is shown that: (1) the cross-section for nuclear interaction of muons of average energy ∼200 GeV is ∼ 6 × 10−30 cm2/nucleon; (2) the decoherence curve for events involving two parallel muons is uniform over the range of distances from 0 to 2 metres; and (3) the angular distribution of double-parallel muons closely resembles that of single muons, implying that these two types of events are probably produced in the atmosphere in a similar manner.