55962889
Solar diurnal anisotropy measured using muons in GRAPES-3 experiment in 2006
The GRAPES-3 experiment at Ooty contains a large-area (560 m2) tracking muon detector. This detector consists of 16 modules, each 35 m2 in area, that are grouped into four supermodules of 140 m2 each. The threshold energy of muons is sec(θ) GeV along a direction with zenith angle θ and the angular resolution of the muon detector is 6°. Typically, it records ~4×109 muons every day. The muon detector has been operating uninterruptedly since 2001, thus providing a high statistics record of the cosmic ray flux as a function of time over one decade. However, prior to using these data, the muon rate has to be corrected for two important atmospheric effects, namely, variations in atmospheric pressure and temperature. Because of the near equatorial location of Ooty (11.4°N), the seasonal variations in the atmospheric temperature are relatively small and shall be ignored here. Due to proximity to the equator, the pressure changes at Ooty display a dominant 12 h periodic behaviour in addition to other seasonal changes. Here, we discuss various aspects of a novel method for accurate pressure measurement and subsequent corrections applied to the GRAPES-3 muon data to correct these pressure-induced variations. The pressure-corrected muon data are used to measure the profile of the solar diurnal anisotropy during 2006. The data, when divided into four segments, display significant variation both in the amplitude (~45%) and phase (~42 m) of the solar diurnal anisotropy during 2006, which was a period of relatively low solar activity.
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.
67815721
The angular resolution of the GRAPES-3 array from the shadows of the Moon and the Sun
Abstract The absence of a well established point source of very high energy ( ≳ 10 TeV ) γ-rays in the sky, makes the measurement of the angular resolution and the absolute pointing accuracy of an extensive air shower (EAS) array a challenging task. In the past, several groups have utilized the reduction in the isotropic flux of cosmic rays due to the shadows of the Moon and the Sun, to measure the angular resolution and the absolute pointing accuracy of their arrays. The data collected from the GRAPES-3 EAS array, over the period of 4 years from 2000 to 2003, has been used to observe the shadow of the Moon at a level of ∼ 5 σ and that of the Sun at a lower level of significance. The high density of the detectors in GRAPES-3 enabled an angular resolution of 0.7° to be obtained at energies as low as 30 TeV. The angular resolution studies were further extended by using two other techniques, namely, the even–odd and the left–right methods. All three techniques have yielded nearly identical results on the energy dependent angular resolution.
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
119032709
Emission of Radiation at Energies > 1014 eV: Binary X-Ray Sources SCO X-1, CYG X-1, HER X-1 and Others
118245922
Cygnus experiment at Los Alamos
The Cygnus experiment at Los Alamos National Laboratory has been designed to study, with high angular accuracy, point sources of gamma rays of energy above 1014 eV. The experimental detector consists of an air shower array to observe gamma-ray showers and a shielded, large-area track detector to study the muon content of the showers. In this paper we present preliminary data from the array and describe its performance.
123004962
Flavour degrees of freedom and the transition temperature in QCD
We study the finite temperature transition in QCD with four flavours of dynamical quarks. Our simulation is performed on an 8×16 3 lattice for quarks of mass ma=0.01. At the coupling β c =5.15, we find long-lived metastable states, as well as an abrupt change in the entropy density, suggesting a first order phase transition. Using presently available results from corresponding calculations of the hadron masses and the chiral condensate, this gives us a transition temperature T c ≅100 MeV, which is a factor two lower than the transition temperature found in quenched QCD.
120287039
Physics beyond instantons. Measuring the physical correlation length
In broken-symmetry phases of models with discrete global symmetry, the physical correlation length can be measured using time-slice correlators projected to non-zero momenta. A transfer matrix based argument is used to construct the finite-size scaling for this quantity. We extract the correlation length for the two-dimensional ten-state Potts model by this means, and the surface tension from the zero-momentum correlator.
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.
118548387
On criticality and the equation of state of QCD at finite chemical potential
We obtain the baryon number density, n, and the excess contribution to the pressure, Delta P, at finite chemical potential, mu_B, and temperature, T, by resumming the Taylor series expansion in a lattice computation with lattice spacing of 1/(4T) and two flavours of quarks at three different quark masses. The method proceeds by giving a critical mu_B and limits on the critical exponent, and permits reliable estimations of the errors in resummed quantities. We find that n and Delta P are insensitive to the quark mass. We also report the bulk isothermal compressibility, kappa, over a range of T and mu_B.