Prof Subir Sarkar

Abstract:

We report here the first successful detection of highly relativistic cosmic ray iron group nuclei in the new type of solid state track detector, CR-39 (Allyl diglycol carbonate), in a stack composed of these plastics, nuclear emulsions and other types of plastic detectors, which was exposed in a balloon flight from Hyderabad, India, at 6 mb residual atmosphere for 8 h. The high value of the vertical geomagnetic cut-off rigidity of 16.7 GV ensured the relativistic nature of the particles and these were identified as Fe-group nuclei from the measurements in adjacent sheets of nuclear emulsion. Very well-defined etched cones were observed in the CR-39 plastics after 48 h etch in 6.25 N NaOH at 70 °C, at the locations corresponding to Fe-group nuclei tracks in the nuclear emulsions. The track etch rate (Vt) for relativistic (≥ GeV/nucleon) Fe-group nuclei was measured as 3.5 ± 1.3 μm/h and the bulk etch rate (Vg) as 1.5 ± 0.6 μm/h. The normalised track etch rate, (Vt/Vg) - 1, is compared with the data obtained at lower energies by other workers and the results are found to be consistent. The charge detection threshold for Cr-39 is obtained as Z≈20 for |β {reversed tilde equals} 1. © 1979.

Abstract:

During the first three flights of the Antarctic Impulsive Transient Antenna (ANITA) experiment, the collaboration detected several neutrino candidates. Two of these candidate events were consistent with an ultra-high-energy up-going air shower and compatible with a tau neutrino interpretation. A third neutrino candidate event was detected in a search for Askaryan radiation in the Antarctic ice, although it is also consistent with the background expectation. The inferred emergence angle of the first two events is in tension with IceCube and ANITA limits on isotropic cosmogenic neutrino fluxes. Here, we test the hypothesis that these events are astrophysical in origin, possibly caused by a point source in the reconstructed direction. Given that any ultra-high-energy tau neutrino flux traversing the Earth should be accompanied by a secondary flux in the TeV-PeV range, we search for these secondary counterparts in seven years of IceCube data using three complementary approaches. In the absence of any significant detection, we set upper limits on the neutrino flux from potential point sources. We compare these limits to ANITA's sensitivity in the same direction and show that an astrophysical explanation of these anomalous events under standard model assumptions is severely constrained regardless of source spectrum or time profile.

Abstract:

We report constraints on nonstandard neutrino interactions (NSI) from the observation of atmospheric neutrinos with IceCube, limiting all individual coupling strengths from a single dataset. Furthermore, IceCube is the first experiment to constrain flavor-violating and nonuniversal couplings simultaneously. Hypothetical NSI are generically expected to arise due to the exchange of a new heavy mediator particle. Neutrinos propagating in matter scatter off fermions in the forward direction with negligible momentum transfer. Hence the study of the matter effect on neutrinos propagating in the Earth is sensitive to NSI independently of the energy scale of new physics. We present constraints on NSI obtained with an all-flavor event sample of atmospheric neutrinos based on three years of IceCube DeepCore data. The analysis uses neutrinos arriving from all directions, with reconstructed energies between 5.6 GeV and 100 GeV. We report constraints on the individual NSI coupling strengths considered singly, allowing for complex phases in the case of flavor-violating couplings. This demonstrates that IceCube is sensitive to the full NSI flavor structure at a level competitive with limits from the global analysis of all other experiments. In addition, we investigate a generalized matter potential, whose overall scale and flavor structure are also constrained.