Sudeb Bhattacharya

Invited review: Physics potential of the ICAL detector at the India-based Neutrino Observatory (INO)

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies and path lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial to address some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations. We describe the simulation framework, the neutrino interactions in the detector, and the expected response of the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Its charge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles.

Study of the characteristics of a clover detector

Abstract The resolution, efficiency and summing characteristics of a clover detector obtained from Eurisys Mesures, France, have been studied in the singles and the add-back mode. The results of the measurements using 152 Eu and 60 Co sources are presented in this paper.

Performances of linseed oil-free bakelite RPC prototypes with cosmic ray muons

Abstract A comparative study has been performed on Resistive Plate Chambers (RPC) made of two different grades of bakelite paper laminates, produced and commercially available in India. The chambers, operated in the streamer mode using argon, tetrafluroethane and isobutane in 34:59:7 mixing ratio, are tested for the efficiency and the stability with cosmic rays. A particular grade of bakelite (P-120, NEMA LI-1989 Grade XXX), used for high voltage insulation in humid conditions, was found to give satisfactory performance with stable efficiency of > 96 % continuously for more than 130 days. A thin coating of silicone fluid on the inner surfaces of the bakelite RPC is found to be necessary for the operation of the detector.

Neutron-gamma discrimination by pulse analysis with superheated drop detector

Abstract Superheated drop detector (SDD) consisting of drops of superheated liquid of halocarbon is irradiated to neutrons and gamma-rays from 252Cf fission neutron source and 137Cs gamma source, respectively, separately. Analysis of pulse height of signals at the neutron and gamma-ray sensitive temperature provides significant information on the identification of neutron and gamma-ray induced events.

Measurement of electrical properties of electrode materials for the bakelite Resistive Plate Chambers

Single gap (gas gap = 2 mm) bakelite Resistive Plate Chamber (RPC) modules of various sizes from 10 cm ? 10 cm to 1 m ? 1 m have been fabricated, characterized and optimized for efficiency and time resolution. Thin layers of different grades of silicone compound are applied to the inner electrode surfaces to make them smooth and also to reduce the surface resistivity. In the silicone coated RPCs an efficiency ~ 96% and time resolution ~ 2 ns (FWHM) have been obtained for both the streamer and the avalanche modes of operation. Before fabrication of detectors the electrical properties such as bulk resistivity and surface resistivity of the electrode materials are measured carefully. Effectiveness of different silicone coating in modifying the surface resistivity was evaluated by an instrument developed for monitoring the I-V curve of a high resistive surface. The results indicate definite correlation of the detector efficiency for the atmospheric muons and the RPC noise rates with the surface resistivity and its variation with the applied bias voltage. It was also found that the surface resistivity varies for different grades of silicone material applied as coating, and the results are found to be consistent with the detector efficiency and noise rate measurements done with these RPCs.

Study of timing properties of single gap high-resistive bakelite RPC

Abstract The time resolution for several single gap (2xa0mm) prototype Resistive Plate Chambers (RPC) made of high resistive ( ρ ~ 10 10 – 10 12 Ω cm ), 2xa0mm thick matt finished bakelite paper laminates with silicone coating on the inner surfaces, has been measured. The time resolution for all the modules has been found to be ~ 2 ns at the plateau region.

The nucleation parameter for heavy-ion induced bubble nucleation in superheated emulsion detector

The values of the nucleation parameter, k, for bubble nucleation induced by high energy heavy ions 12C (180 MeV/u), 20Ne (400 MeV/u) and 28Si (350 MeV/u) in superheated emulsion detector are determined by comparing the experimentally obtained normalized count rates with those obtained from simulations done using the GEANT3.21 simulation code. The results show that the nucleation parameter depends on the mass number of the incident heavy ions, and decreases with increasing mass number.

Development of linseed oil-free bakelite resistive plate chambers

In this paper we would like to present a few characteristics of the Resistive Plate Chambers (RPCs) made of a particular grade of bakelite paper laminates (P-120, NEMA LI-1989 Grade XXX), produced and commercially available in India. This particular grade is used for high voltage insulation in humid conditions. The chambers are tested with cosmic rays in the streamer mode using argon, tetrafluroethane and isobutane in 34:59:7 mixing ratio. In the first set of detectors made with such grade, a thin coating of silicone fluid on the inner surfaces of the bakelite was found to be necessary for operation of the detector. Those silicone coated RPCs were found to give satisfactory performance with stable efficiency of >90% continuously for a long period as reported earlier. Results of the crosstalk measurement of these silicone coated RPC will be presented in this paper. Very recently RPCs made with the same grade of bakelite but having better surface finish are found to give equivalent performance even without any coating inside. Preliminary results of this type of RPCs are also being presented.

Neutron detector array for measurement of neutron multiplicity

An array consisting of six neutron detectors has been constructed for measurement of neutron multiplicities in heavy ion reactions. The measurements are reported to demonstrate that, even with a modest array of six neutron detectors, it is possible to infer unambiguously the neutron multiplicity (upto M4) of the reaction channel from the neutron fold distribution obtained in coincidence with c-rays, if the array is calibrated with known reaction channels. The neutron multiplicity for the 991 keV c-ray produced in the two heavy ion reactions 133Cs(12,13C, xn) has been determined from this set-up-indicating that it deexcites levels in 142Pm. This is in agreement with the excitation function measurements for the same reactions. ( 2000 Elsevier Science B.V. All rights reserved.

Comparison of bulk Micromegas with different amplification gaps

Abstract The bulk Micromegas detector is considered to be a promising candidate for building TPCs for several future experiments including the projected linear collider. The standard bulk with a spacing of 128 μ m has already established itself as a good choice for its performances in terms of gas gain uniformity, energy and space point resolution, and its capability to efficiently pave large readout surfaces with minimum dead zone. The present work involves the comparison of this standard bulk with a relatively less used bulk Micromegas detector having a larger amplification gap of 192 μ m . Detector gain, energy resolution and electron transparency of these Micromegas have been measured under different conditions in various Argon-based gas mixtures to evaluate their performance. These measured characteristics have also been compared in detail to numerical simulations using the Garfield framework that combines packages such as neBEM, Magboltz and Heed. Further, we have carried out another numerical study to determine the effect of dielectric spacers on different detector features. A comprehensive comparison of the two detectors has been presented and analyzed in this work.