N. Majumdar

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.

Simulation of three-dimensional electrostatic field configuration in wire chambers: A novel approach

Abstract Three-dimensional field configuration has been simulated for a simple wire chamber consisting of one anode wire stretched along the axis of a grounded square cathode tube by solving numerically the boundary integral equation of the first kind. A closed-form expression of potential due to charge distributed over flat rectangular surface has been invoked in the solver using Greens function formalism leading to a nearly exact computation of electrostatic field. The solver has been employed to study the effect of several geometrical attributes such as the aspect ratio ( λ = l / d , defined as the ratio of the length l of the tube to its width d ) and the wire modeling on the field configuration. Detailed calculation has revealed that the field values deviate from the analytic estimates significantly when the λ is reduced to 2 or below. The solver has demonstrated the effect of wire modeling on the accuracy of the estimated near-field values in the amplification region. The thin wire results can be reproduced by the polygon model incorporating a modest number of surfaces ( ⩾ 32 ) in the calculation with an accuracy of more than 99 % . The smoothness in the three-dimensional field calculation in comparison to fluctuations produced by other methods has been observed.

Simulation of 3D electrostatic configuration in gaseous detectors

A Boundary Element Method (BEM) solver based on the solution of boundary integral equations of potential and electric field has been developed to simulate 3D electrostatic configu- ration in gaseous detectors. Use of analytical solution of t he integral equations governing electric potential and field for estimating influence coefficients of t he BEM solver has empowered it to pro- vide extremely precise estimates of the potential and field f or a given geometry. The nearly exact BEM (neBEM) solver has been implemented in order to simulate physical and weighting poten- tial and field configurations in several gaseous detectors li ke MultiWire Proportional Counter and Time Projection Chamber. The efficacy of the solver for simul ating 3D electrostatic configuration in composite systems containing both conductors and layered dielectrics has been demonstrated for some of the MicroPattern Gas Detectors and Resistive Plate Chamber. It should be noted that the method treats the dielectric interfaces to be in a steady sta te with polarization charges only. The reasons why the neBEM can be a preferred tool for electrostatic simulation of gaseous detectors to other 2D or 3D numerical solvers are discussed on the basis of present results.

Experimental and numerical studies on the effect of SF6 in a glass RPC

The India based Neutrino Observatory (INO) collaboration is planning to build a 50 kton magnetized iron calorimeter (ICAL) detector to study neutrino oscillations and measure their associated parameters. ICAL will use 28,800 glass Resistive Plate Chambers (RPCs) of 2m × 2m size to be operated in the avalanche mode, as its active detector elements. As a part of detector R & D to develop the RPCs, we studied the effect of Sulfur hexaflouride (SF6) when it is added in small amount to the gas composition used for running the RPCs. In this paper, we present a comparative study of charge development on the RPC pick-up electrodes for different concentrations of SF6 in the RPC gas medium using simulation and experimental data.

Effect of finite dimensions on the electric field configuration of cylindrical proportional counters

Three dimensional electrostatic fields in cylindrical proportional counters have been computed to high accuracy using a zero-th order boundary element technique. The effects of finite bounds of the detector on the resulting field configuration have been studied in detail. It has been observed that electric field configurations at the mid-plane of cylindrical proportional counters can be considered to be identical (deviations less than 10%) to that of an infinitely long detector only if the aspect ratio [/spl lambda/=(l/b)] of the detector is greater than 2.0. Significant amount of deviation from the analytical solution (valid for infinitely long detectors) has been observed for a large percentage of the detector volume for the complete range of /spl lambda/ considered in the study (0.25</spl lambda/<10.0). The deviations have been found to be significant close to the anode wire and the cathode cylinder where the nature of the field configuration matters most. Attempts have been made to quantify the deviations as functions of /spl lambda/, and, for a given /spl lambda/, as functions of the distance from the mid-plane.

Measurement of complete fusion-fission and transfer-fission cross-sections and angular distributions for19F+232Th at sub-barrier energies by fission fragment folding-angle technique

SummaryFission fragment folding-angle technique has been used to separate the complete fusion-fission (CFF) and the transfer-induced fission (TF) components in the reaction of19F on232Th for the first time in sub-barrier energies. The fragment folding-angle distributions were measured using two position-sensitive Breskin-type detectors and were compared with simulations based on the kinematics for complete fusion-fission and transfer-fission events. The results on the excitation function and angular distributions for the CFF, TF and total fission events have been simultaneously measured over the bombarding energy range of 78.5 MeV to 106.5 MeV for the above system.

Simulation of efficiency and time resolution of resistive plate chambers and comparison with experimental data

The India based Neutrino Observatory (INO) collaboration is planning to build a 50 kton magnetized Iron Calorimeter (ICAL) detector to study neutrino oscillations and measure their associated parameters. ICAL will use 28,800 glass Resistive Plate Chambers (RPCs) of 2 m?2 m in size as its active detector elements. These RPCs will be operated in the avalanche mode. As a part of the detector R&D to develop the RPCs required for this detector, we made a comparative study of the effect of Sulphur Hexafluoride (SF6) in the gas mixture on the induced charge using simulation and experimental data in our earlier paper [1]. In this paper, we extend our studies to efficiency and time resolution of the RPC using simulation and experimental data. Several software tools have been used to carry out the simulation. We have calculated the primary interaction parameters using HEED and Geant4. The electron transport parameters have been computed using MAGBOLTZ. We have used nearly exact Boundary Element Method (neBEM) and COMSOL Multiphysics, a Finite Element Method package for calculating the weighting field and the electric field.

Numerical studies on electrostatic field configuration of Resistive Plate Chambers for the INO-ICAL experiment

As a part of detailed optimization studies on Resistive Plate Chambers (RPC) to be used in INO-ICAL experiment, the effect of geometrical artifacts like edge, corner, spacers on the device response should be investigated thoroughly. In this context, the electrostatic field within an RPC has been computed following Finite Element Method and Boundary Element Method to study the effect of these artifacts on the field map. The weighting field distribution for the given geometry has also been evaluated which is necessary for simulating the device signal. A unified model to calculate both physical and weighting field within RPC has been proposed and tested for its validity.

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.

Investigation of ion backflow in bulk micromegas detectors

The operation of gas detectors is often limited by secondary effects, originating from avalanche-induced photons and ions. Ion backflow is one of the effects limiting the operation of a gas detector at high flux, by giving rise to space charge which disturbs the electric field locally. For the Micromegas detector, a large fraction of the secondary positive ions created in the avalanche can be stopped at the micro-mesh. The present work involves measurements of the ion backflow fraction (using an experimental setup comprising of two drift planes) in bulk Micromegas detectors as a function of detector design parameters. 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, the effect of using a second micro-mesh on ion backflow and other parameters has been studied numerically.