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.
119032709
Emission of Radiation at Energies > 1014 eV: Binary X-Ray Sources SCO X-1, CYG X-1, HER X-1 and Others
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.
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.
55926788
A large area muon tracking detector for ultra-high energy cosmic ray astrophysics — the GRAPES-3 experiment
Certain aspects of ultra-high energy (UHE) cosmic ray astrophysics require correlated studies on the electron and muon components of air showers, namely, the search for cosmic ray sources through g-ray astronomy and studies on the variation of the nuclear composition of primary cosmic rays with energy. While studies on the electron component provide basic information about the arrival direction and energy, it is the muon component that plays a crucial role in distinguishing primary g-rays from charged cosmic ray particles and in determining the composition. A large area (560m), tracking muon detector of the GRAPES-3 experiment, operating at Ooty in southern India, has been designed for detailed studies on both of these aspects of UHE cosmic ray astrophysics. We present here the details of the muon detector, associated electronics and the data acquisition system. A brief discussion of the potential of the muon detector is presented through simulation studies. r 2005 Elsevier B.V. All rights reserved. PACS: 98.70.Sa; 96.40.Pq; 96.40.De; 98.70.Rz; 95.55.Vj; 13.85.Tp
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.
16059029
Coalescence, percolation and nuclear multifragmentation
Abstract We show that the coalescence model for fragment formation leads to an approximate site percolation model. Features characteristic of a percolation model also appear in microscopic models of disassembly.
120000887
Angular resolution of the Ooty EAS array based on UHE gamma rays from Her X-1
The angular resolution of an extensive air shower array for studies on cosmic sources of ultra-high-energy gamma rays has been determined by most of the experimental groups generally by inter-comparison between sub-arrays, in the absence of the knowledge of any steady and strong discrete source. The sub-arrays have been obtained mostly by dividing the main array into two arrays, one containing the even-numbered detectors and another having the odd-numbered detectors. Using this method the angular resolution of the 24-detector array operated at Ooty during 1984-7 was estimated to be about 1.5 degrees . Recently the Ooty group has reported the detection of four episodes of pulsed emission of ultra-high-energy photons from Her X-1 which have been shown to be phase locked with a period of 1.2357701 s. The authors have made a study of the angular resolution for the Ooty array using this signal from Her X-1 which had a relatively low background. The angular resolution of the array has been determined to be 1.6 degrees +or-0.4 degrees . This is the first direct measurement of angular resolution of an air shower array using a point source of ultra-high-energy photons.
118614091
Study of Cosmic Ray Short Term Variations Using GRAPES-3 Muon Telescopes
120395006
ONE-GRAVITON EXCHANGE INTERACTION OF ELEMENTARY PARTICLES
The interaction of elementary particles of several different spins due to the exchange of a graviton is investigated. The exact one-graviton exchange potentials are obtained, and then simplified by making various approximations. The gravitational interaction is found to be independent of the spins of the particles, provided that the distance between them is large compared with their Compton wavelengths. I t is pointed out that the spin-dependent interaction terms, whose range is of the order of the Compton wavelength, may be of interest in the theory of gravitational collapse. I t is also shown that the gravitational particle-antiparticle interaction differs from the corresponding particle-particle interaction only by contact interaction terms.
128078572
A preshower photon multiplicity detector for the WA93 experiment
Abstract A fine granularity preshower detector has been designed, fabricated and installed in the WA93 experiment for the first ever measurement of photon multiplicity in ultra-relativistic heavy ion collisions. Photons are counted by detecting the preshower signal in plastic scintillator pads placed behind a lead converter and applying a threshold on the scintillator signal to reject the minimum ionizing particles. The photon detection efficiency estimated using Monte-Carlo and beam test results is found to be ∼65–75% depending on centrality. Simulation and performance results of the detector for counting of photons and rejection of hadrons in the large multiplicity environment of ultra-relativistic heavy ion collisions are described.