STUDY AND DETECTION OF MUONS USING RPC DETECTORS READ-OUT WITH NINO ASIC CHIP BASED BOARD

Abstract

Important developments have occurred newly in neutrino physics and neutrino astronomy. Oscillations of neutrinos, and the inferred evidence that neutrinos have mass, are likely to have far-reaching consequences. This discovery has come from the study of neutrinos from the Sun and those produced in interactions of cosmic rays with the earth’s atmosphere. The groundbreaking Home stake Mine Neutrino Experiment in the USA, the gigantic Super-Kamiokande detector and the KamLAND detector in Japan, the Heavy-water detector at the Sudbury Neutrino Observatory in Canada, and a few other laboratories, together, have contributed in a very basic way to our information of neutrino properties and interactions. Encouraged by these discoveries and their implications for the future of particle physics, plans have been made world-wide, for new neutrino detectors, neutrino factories and long base-line neutrino experiments. Indian scientists started initiating in atmospheric neutrino experiments. In fact, neutrinos produced by cosmic ray interactions in the earth’s atmosphere were first detected in the deep mines of the Kolar Gold Fields (KGF) in south India in 1965. In order to revive underground neutrino experiments in India, a multi-institutional collaboration has been formed with the objective of creating an India-based Neutrino Observatory (INO). Considering the physics possibilities and given the past experience at KGF, the INO collaboration has decided to build a magnetised Iron CALorimeter (ICAL) detector with Resistive Plate Chambers (RPCs) as the active detector elements. In the first phase of its operation, ICAL will be used for atmospheric neutrino physics with the aim of making precision measurements of the parameters related to neutrino oscillations. The detector will be magnetised to a field of about 1.3 T, enabling it to distinguish the positive and negative muons and thus identifying muon-type neutrino and anti-neutrino produced events separately. This will be useful for ICAL to provide an exciting possibility to determine the ordering of the neutrino mass levels. Finally, this detector can also be used as the far-detector of a futuristic long-base-line neutrino experiment ix using the neutrino beam from a neutrino factory. Good tracking, energy and time resolutions as well as charge identification of the detecting particles are the essential capabilities of this detector. The ICAL experiment will need about 27,600 RPCs each of about 200 cm × 200 cm in area. RPCs are fast, planar, rugged and low-cost gas detectors which are being, and will be, used extensively in a number of high energy and astro-particle physics experiments. They find applications for charged particle detection, time of flight, tracking and digital calorimetry due to their large signal amplitudes as well as excellent position and time resolutions. A dedicated R&D programme is currently underway to design, develop and characterise large area RPCs, ultimately leading to their large scale and low-cost production required for the ICAL detector. In essence, this thesis outlines the successful completion of designing, building and characterising large size RPCs, for the first time in India. To begin with, we developed a large number of single gap glass RPCs of 30 cm × 30 cm in area, using the glass procured from local market, and studied their operation in the streamer mode (using a gas mixture of R134a : Isobutane : Argon in the ratio of 62 : 8 : 30). The results fined from the characterisation study of these chambers were reliable with those reported in the literature. However, we were faced with a grave problem as far as stability of their operation is concerned. They died of sudden aging when operated continuously. In order to understand this problem, we studied widely the glass, gas and other mechanism of the RPC detector using a number of different method. We then fabricated a large number of RPCs of 100 cm × 100 cm in area and operated them in the avalanche mode (using a gas mixture of R134a: Isobutane: SF6 in the ratio of 95.15: 4.51: 0.34), without facing any aging problems. These chambers show typical efficiencies of over 98% and timing resolutions of about 1 ns. For the full utilization of the outstanding timing properties of the Resistive Plate Chamber (RPC), front-end electronics with unique characteristics are required. These are (1) Differential input, to profit from the differential signal from the RPC (2) A fast amplifier with less than 1 Nano-second peaking time and (3) Input charge measurement by Time- Over-Threshold (TOT) for slewing correction. An 8-channel amplifier and discriminator chip has been developed to match these necessities. This is the NINO ASIC, fabricated with 0:25 mm CMOS technology. The power requirement at 27 mW/channel is low. Results on the performance of the RPCs using the NINO ASIC are presented. Typical time resolutions of the RPC system are in the 50 Pico-second range, with an efficiency of 99:9%. The time over threshold method is used in the NINO amplifier chip in time of flight measurements in the MPD detector. For the TOF measurements MRPC detectors are used. Using a signal and noise generator the effects of the noise on the time resolution in the time over threshold method is experimentally studied.