Science Facts Forum: October 2019

India based Neutrino Observatory (INO) is a particle physics research project under construction to primarily study atmospheric neutrinos in a 1,200 meters (3900 ft) deep cave under INO Peak near Theni in Tamil Nadu, India. This project is notable in that it is anticipated to provide a precise measurement of neutrino mixing parameters. The project is a multi-institute collaboration and one of the biggest experimental particle physics project undertaken in India.

The project was originally to be completed in 2015 at an estimated cost of Rs 1500 crores (US $ 209.7 million), has been cleared by the ministry of environment for construction in the Bodi West Hills Reserved Forest in the Theni District in Tamil Nadu. Although delayed, the project is underway as of 2015.

When completed, the magnetised iron calorimeter (ICAL) experiment will include the world’s largest magnet, four times larger than the 12,500-tonne magnet in the Compact Muon Solenoid detector at CERN in Geneva, Switzerland.

IRON CALORIMETER (ICAL) DETECTOR:

The main experiment proposed at the INO is the Iron-Calorimeter Detector which aims to probe the earth matter effects on the propagation of atmospheric neutrinos and to determine neutrino oscillation parameters in the 2-3 oscillation sectors. ICAL will be a 50000 tonne magnetised detector with iron as the passive detector element and the resistive plate chambers (RPCs) as the active detector elements. That is, the neutrinos will interact with iron to produce final state particles which have charge and will record the signals and these signals which have position and timing information will help us reconstruct the tracks and/or showers and thus the energy and directions of the final state particles and also the incident neutrinos.

The ICAL design is mostly based on the Monolith detector. ICAL detector will have three modules, each module will have 151 layers of iron and 150 layers of RPCs stacked one over the other. The dimension of the entire detector will be 48m x 16m x 14.5m. The detector, owing to its huge size, will require around 30000 glass RPCs for the purpose of charged particle detection. ICAL being a neutrino detector will be situated underground to reduce the cosmic ray muon signal.

The location of INO has attracted a lot of attention from the neutrino physics community as the distance between INO and CERN is very close to “magic baseline” - a distance at which the effect of the CP phase on the measurement is minimal. But the major physics advantage of INO ICAL is its ability to measure neutrino mass hierarchy via studying atmospheric neutrinos. Currently ICAL is the only proposed magnetised detector which can resolve mass hierarchy via studying the survival of muon neutrinos and anti-neutrinos.

NEUTRINO:

A neutrino is a fermion that interacts only via the weak subatomic force and gravity. The neutrino is so named because its rest mass is so small. The weak force has a very short range, the gravitational interaction is extremely weak, and neutrinos, as leptons, do not participate in the strong interaction. Thus, neutrinos typically pass through normal matter unimpeded and undetected.

Weak interactions create neutrinos in one of the three leptonic flavors; electron neutrinos, muon neutrinos and tau neutrinos, in association with the corresponding charged lepton. Although neutrinos were long believed to be massless, it is now known that there are three discrete neutrino masses with different tiny values, but they do not correspond uniquely to the three flavours. A neutrino created with a specific flavour has an associated specific quantum superposition of all three mass states.

For each neutrino, there also exists a corresponding antiparticle, called an anti neutrino, which also has half-integer spin and no electric charge. They are distinguished from the neutrinos by having opposite signs of leptons number and chirality. To conserve total lepton number, in nuclear beta decay, electron neutrinos appear together with only positrons (anti electrons) or electron – antineutrinos, and electron antineutrinos with electrons or electron neutrinos.

Neutrinos are created by various radioactive decays, including the following:

1. In beta decay of atomic nuclei or hadrons.

2. During a supernova.

3. In the spin-down of neutron star.

4. When accelerated particle beams or cosmic rays strike atoms.

The majority of neutrinos detected in the vicinity of the earth are from nuclear reaction in the sun.

In the vicinity of the Earth, about 65 billion solar neutrinos per second pass through every square centimetre perpendicular to the direction of the sun.

HISTORY

The possibility of a neutrino observatory located in India was discussed as early as 1989 during several meetings held at that year. The issue was raised again in the first meeting of the neutrino physics and the cosmology working group during the workshop on High Energy Physics Phenomenology (WHEPP-6) held at Chennai in January 2000 and it was decided then to collates concrete ideas for a neutrino detector.

Further discussions took place in August 2000 during a meeting on Neutrino Physics at the Saha Institute of Nuclear Physics, Kolkata, when a small group of neutrino physics enthusiasts started discussing the possibilities. The neutrino 2001 meeting was held in the Institute of Mathematical Sciences, Chennai, during February 2001 with the explicit objective of bringing the experimentalists and theorists in this field together. The INO collaboration was formed during this meeting. The first formal meeting of this collaboration of this meeting was held in Tata Institute of Fundamental Research, Mumbai, during 6^thand 7^th September 2001 at which various subgroups were formed to study the detector options and electronics, physics goals and simulations, and site survey.

On 18^th October 2010, the Ministry of Environment and Forests approved both environment and forest clearance for setting up the observatory in the Bodi West Hills Reserved Forest in the Theni district of Tamil Nadu.

On 5^th January 2015, union cabinet headed by Prime Minister Narendra Modi approved to set up the India Based Neutrino Observatory (INO).