Cosmic ray studies at high altitude:

The quark structure of hadrons suggest the existence of Strange Quark Matter (SQM), containing a large amount of strangeness as postulated by various authors quite a few years ago. In a seminal work in 1984, Witten proposed that SQM with roughly equal numbers of up, down and strange quarks could be the true ground state of Quantum Chromodynamics (QCD), the accepted theory of strong interactions. The occurrence of stable (or metastable) lumps of SQM, would lead to many rich consequences; for example, the SQM, which may exist as relics of the cosmic quark-hadron phase transition during the microsecond epoch of the early universe, could provide a natural and viable explanation for the dark matter as well as the large amount of dark energy found by WMAP observation.

The final proof of SQM will be its experimental detection. Especially, the existence of smaller lumps of SQM would make the task of detection a lot easier, as these would then be detectable in cosmic ray flux.

Passive Detectors:

The primary objective of the programme is to set up a large array of passive solid-state nuclear track detectors (SSNTD) and expose them to cosmic rays for a long period (2-3 years). Parts of the detector array are replaced with fresh detectors at regular intervals. The exposed ones are chemically and examined under microscope to look for cosmic ray events.  This way, data collection and analysis proceed simultaneously. The analysis requires a number of optical microscopes with automatic stage movement and a sophisticated image analyzing software.

Active Detectors:

In addition to the passive detectors (SSNTD), we are also setting up an active detector array. This  consists of 1m² plastic scintillators coupled with 2 inch photomultiplier tubes. To increase the efficiency of light collection, we are using wavelength shifting fibers on the surface of the scintillators. This setup are used for the study of the strangelets, having energy above the breakup threshold. These strangelets, if enters the atmosphere, disintegrate due to the collision with atmospheric nuclei, which will result in the formation of smaller strangelets as well as unusually large showers. In the first phase we are setting up the array with 7 detectors in a hexagonal pattern, with one at the center. Later on we will increase the number to 61.

Important Results:

Selected Publication:

1.   “Calibration of a solid state nuclear track detector (SSNTD) with high detection threshold to search for rare events in cosmic rays”, S. Dey, D. Gupta, A. Maulik, S. Raha, S. K. Saha, D. Syam, J. Pakarinen, D. Voulot and F. Wenander,  Astropart. Phys. 34 (2011) 805.

2.   “Observation of rare cosmic ray event at mountain altitude”, B. Basu, S. Raha, S. K. Saha, S. Biswas, S. Dey, A. Maulik, A. Mazumdar, S. Saha and D. Syam, Astropart. Phys. 61 (2015) 88.

3.   “Determination of the detection threshold for Polyethylene Terepthalate (PET) Nuclear track Detector”, R. Bhattarcharyya, S. Dey, S. K. Ghosh, A. Maulik, S. Raha and D. Syam, Nucl. Instrum. Meth. B370 (2016) 63.

Studies on Changing Airspace Environment in Eastern Himalayas:

Various long-term changes of chemical species in the atmosphere are determined by emissions from anthropogenic and natural sources as well as by atmospheric transport, physical and chemical processes, and deposition. On the other hand, the impact of increasing atmospheric concentrations of gaseous species and aerosols on climate has become one of the most widely discussed issues in atmospheric science. It is known that the current tropospheric chemical composition is quite different from the one in the pre-industrial era as a result of changed emissions of CH₄, CO, Nox, SO₂ and other species. However, prediction of future changes of both atmospheric composition and climate requires the understanding of interactions among emissions, chemistry and climate and is a major challenge at the present time.

The Himalaya braces the northern periphery of the Indo-Gangetic plains region. This region acts as the main source of all kinds of atmospheric pollutants and also vulnerable from changing environment. This complex two-way interactive mechanism needs to be understood to get qualitative as well as quantitative information useful for proper policy formulations to mitigate emissions of pollutants as well to reduce vulnerability. In this regard, the Himalayas offer a unique place to monitor airspace environment as it is not only subject to emissions coming out from IGP Region but also to the pollutants transported from long distances from other source regions.

Objectives:

• Characterization of aerosol chemical components including elemental and organic carbonaceous species in size segregated aerosols for exact identification of sources and better understanding of the formation mechanism of aerosols.
• Physical characterization of nano-scale aerosols to understand the formation of nucleating particles and their role in cloud formation and their effect on net changes in radiative properties.
• Studies on aerosol scattering coefficient to estimate the single scattering albedo of aerosol and correlate with the scattering and absorbing type of aerosol chemical components.
• Characterization of Valatile Organic Compounds (VOC), carbonyls and ozone to establish the photochemical cycles between them.
• Characterization of methane to investigate its role in the formation of surface ozone and most reactive hydroxyl radical.
• Effect of aerosol chemistry on the aerosol radiative properties through radiative transfer model.
• Long-term characterization of wet and dry precipitated aerosols and role of cloud towards aerosol scavenging.
• Experimental estimate of relative phases of water inside cloud, drop size distribution, aerosol profiles, correlation between observed parameters
• Understandings of role of aerosols on formation of Cloud Condensation Nuclei  (CCN) along with the understanding the growth of Cloud Condensation Nuclei (CCN)
• Studies on Thundercloud formation – cloud charging, atmospheric electric field and electric structure of cloud
• Cosmic ray induced ionization
• Studies of cloud electricity in relation to microwave earth-space communication
• Experimental measurement of lightning & electric field
• Understanding Cosmic ray - cloud connection: cosmic ray contribution to CCN formation