8554087
An episode of ultrahigh energy radiation from the gamma -ray source Geminga: GRAPES I observations at Ooty during 1984-1987.
A study of showers arriving from the direction of the γ-ray source Geminga (1E0630 + 178) has shown evidence for emission of ultrahigh energy radiation during the one week interval October 10-16, 1986. 83 showers were observed in the source bin as against an expected background of 44.1. The probability of observing this excess based on Monte Carlo simulations is less than 10 −4 . The flux observed during this period (1.00±0.24)×10 −11 cm −2 s −1 at energies ≥10 14 eV corresponds to a time-averaged luminosity of 6×10 32 erg s −1
67811342
GRAPES-3¿A high-density air shower array for studies on the structure in the cosmic-ray energy spectrum near the knee
Abstract The change in the spectral index from about - 2.7 to - 3.1 at ∼ 3 × 10 15  eV in the all-particle energy spectrum of primary cosmic rays is very significant for learning about the nature of cosmic sources of ultra-high energy particles and their acceleration and propagation in the galactic disk. Any observation of a fine structure in the spectrum would be important for improving our understanding of these physical processes. The GRAPES-3 air shower array has been designed to achieve higher precision in determination of various shower parameters to enable observation of any fine structure in the energy spectrum, if it exists. The details of the shower detectors, shower trigger and the data acquisition system are presented here along with estimates of trigger efficiencies from Monte Carlo simulations for primary photons ( γ -rays) and several nuclei.
121254838
Sporadic emission of ultra high energy gamma rays from Crab pulsar
In a further study of sporadic emission from pulsars we find evidence for short lived intense emission from the Crab pulsar.
55612742
Recent results from the GRAPES-3 experiment
The GRAPES-3 is a dense extensive air shower array operating with ~400 scintillator detectors and a 560 m 2 large tracking muon detector (E μ > 1 GeV), at Ooty in India. The muon detector has been used to observe acceleration of muons during thunderstorm conditions. The muon multiplicity distribution of the EAS is used to probe the composition of primary cosmic rays below 1 PeV, with an overlap with direct measurements. More recently we have explored the possibility of using the angular distribution of >1 GeV muons to identify the best from among several low- and high-energy hadronic interaction models. We have major expansion plans to enhance the sensitivity of the GRAPES-3 experiment in all of the areas listed above.
123618858
An experimental system for detection of high energy cosmic gamma ray bursts
Abstract While bursts of cosmic gamma rays of energies 0.1–10 MeV can be detected and studied only with satellite-borne detectors, bursts of gamma rays at GeV energies can be detected using sensitive ground-based detectors. An experimental system to detect these high energy gamma ray bursts is being operated at the mountain altitude laboratory at Ootacamund, India. The design features and the experimental details related to this system are described.
10726039
A micron resolution optical scanner for characterization of silicon detectors.
The emergence of high position resolution (∼10 μm) silicon detectors in recent times have highlighted the urgent need for the development of new automated optical scanners of micron level resolution suited for characterizing microscopic features of these detectors. More specifically, for the newly developed silicon photo-multipliers (SiPM) that are compact, possessing excellent photon detection efficiency with gain comparable to photo-multiplier tube. In a short time, since their invention the SiPMs are already being widely used in several high-energy physics and astrophysics experiments as the photon readout element. The SiPM is a high quantum efficiency, multi-pixel photon counting detector with fast timing and high gain. The presence of a wide variety of photo sensitive silicon detectors with high spatial resolution requires their performance evaluation to be carried out by photon beams of very compact spot size. We have designed a high resolution optical scanner that provides a monochromatic focused beam on a target plane. The transverse size of the beam was measured by the knife-edge method to be 1.7 μm at 1 - σ level. Since the beam size was an order of magnitude smaller than the typical feature size of silicon detectors, this optical scanner can be used for selective excitation of these detectors. The design and operational details of the optical scanner, high precision programmed movement of target plane (0.1 μm) integrated with general purpose data acquisition system developed for recording static and transient response photo sensitive silicon detector are reported in this paper. Entire functionality of scanner is validated by using it for selective excitation of individual pixels in a SiPM and identifying response of active and dead regions within SiPM. Results from these studies are presented in this paper.
7265145
Quark mixing and CP violation.
In view of the experimental indications that the top-quark mass may exceed the upper bound predicted by the Fritzsch ansatz for the quark mass matrices, we follow a phenomenological approach to find a modified form of the mass matrices to deal with quark mixing and {ital CP} violation in electroweak interactions. The essential feature of our mass matrices is that the diagonal elements corresponding to the light quarks {ital u}, {ital d}, and {ital s} are vanishingly small, while those corresponding to the heavy quarks {ital c}, {ital b}, and {ital t} are approximately equal to the observed values of their masses. By comparing our theoretical results for the Kobayashi-Maskawa mixing matrix elements with the experimental data, we obtain for the top-quark mass and the {ital CP}-violating phase the values {ital m}{sub {ital t}}{sup phys}{le}170 GeV and 91{degree}{le}{delta}{le}105{degree}.
31179622
Elastic scattering of alpha particles from 209Bi at 24.8, 28.5, 34.7, 38.8, and 69.5 MeV.
Differential cross sections for the elastic scattering of alpha particles from {sup 209}Bi have been measured over a wide angular range at a number of energies between 24 and 70 MeV. The present data along with existing data in this energy range have been analyzed using the optical model with both phenomenological and double-folded potentials. The application of the dispersion relation of Mahaux, Ng{cflx o}, and Satchler allows a reproduction of the observed energy dependence of the real part of the potential. A nearside-farside decomposition of the data clearly reveals large-angle Fraunhoefer oscillations. The inelastic cross sections at 69.5 MeV have also been measured and the deformation lengths obtained from a distorted-wave Born analysis are consistent with values reported in the literature.
17051703
Quantum-chromodynamic potential model for light-heavy quarkonia and the heavy quark effective theory.
We have investigated the spectra of light-heavy quarkonia with the use of a quantum-chromodynamic potential model, which is similar to that used earlier for heavy quarkonia. An essential feature of our treatment is the inclusion of the one-loop radiative corrections to the quark-antiquark potential, which contribute significantly to the spin splitting among the quarkonium energy levels. Unlike [ital c[bar c]] and [ital b[bar b]], the potential for a light-heavy system has a complicated dependence on the light and heavy quark masses [ital m] and [ital M], and it contains a spin-orbit mixing term. We have obtained excellent results for the observed energy levels of [ital D][sup 0], [ital D][sub [ital s]], [ital B][sup 0], and [ital B][sub [ital s]], and we are able to provide predicted results for many unobserved energy levels. Our potential parameters for different quarkonia satisfy the constraints of quantum chromodynamics. We have also used our investigation to test the accuracy of the heavy quark effective theory. We find that the heavy quark expansion yields generally good results for the [ital B][sup 0] and [ital B][sub [ital s]] energy levels provided that [ital M][sup [minus]1] and [ital M][sup [minus]1] ln [ital M] corrections are taken into account more » in the quark-antiquark interactions. It does not, however, provide equally good results for the energy levels of [ital D][sup 0] and [ital D][sub [ital s]], which indicates that the effective theory cannot be applied accurately to the [ital c] quark. « less
10011120
Bc spectroscopy in a quantum-chromodynamic potential model.
We have investigated {ital B}{sub {ital c}} spectroscopy with the use of a quantum-chromodynamic potential model which was recently used by us for the light-heavy quarkonia. We give our predictions for the energy levels and the {ital E}1 transition widths. We also find, rather surprisingly, that although {ital B}{sub {ital c}} is not a light-heavy system, the heavy quark effective theory with the inclusion of the {ital m}{sub {ital b}}{sup -}{sup 1} and {ital m}{sub {ital b}}{sup -}{sup 1}ln{ital m}{sub {ital b}} corrections is as successful for {ital B}{sub {ital c}} as it is for {ital B} and {ital B}{sub {ital s}}. {copyright} {ital 1995 The American Physical Society.}
33623649
Simple relationships in the eikonal model of the energy flow in ultrarelativistic heavy ion collisions.
The eikonal model has been formulated in terms of the participant and spectator probabilities. It has been used to relate the number of collisions, the numbers of participants from both the projectile and the target, and the energy in the zero degree detector. It is found by comparison with the recent data that the transverse energy or the charged particle multiplicity is directly proportional to the total number of participant nucleons rather than to the number of collisions.