Center for Astroparticle Physics and Space Science (CAPSS)

Cosmic Rays at High Altitude

Search for strangelets using passive detectors:

At Bose Institute one of our main goals is the search for strangelets at mountain altitude. Strangelets are nuggets of Strange Quark Matter containing up, down and strange quarks in almost equal measure. The signature for strangelets is their highly unusual charge to mass ratio (Z/A << ½) which gets even more skewed as they travel through the earth’s atmosphere. The detectors found suitable for our purpose is a kind of polymer called polyethylene terephthalate. When charged particles pass through such polymers they break the molecular bonds leaving behind narrow damage trails. When the polymers containing those latent tracks are chemically etched the material is gouged out preferentially along the damaged regions forming etch pits which can then be studied under optical microscopes. As the track etch rate (VT) is higher than bulk etch rate (VB), we can determine the VT / VB ratio by studying the geometry of etch pit openings which enables us to identify the ions causing the damage, as this ratio is related to the specific energy loss which in turn is related to the charge and energy of the ions. The main advantage of the detector material we have chosen is its high detection threshold because of which it does record proton or Alpha articles, eliminating the low Z background.

We are also in the process of setting up a large area (400 sq.m) passive etector array at Sandakphu at an altitude of 3600 m above sea level. Given the predicted flux of strangelets we are expecting 20 – 40 events of interest per year over the given area at that altitude.

Cosmic rays and γ-rays air shower array using active detectors:

We are in the process of setting up an active detector array system at Darjeeling in collaboration with TIFR, Mumbai for Air Shower studies. The objective is to find the nature of cosmic ray primaries i.e., the composition and energy spectrum of the particles coming from outer space in the PeV (10¹⁵ eV) energy range, to shed light on the origin of this very-high energy cosmic radiation and to search for point sources of UHE γ-rays (> 10¹⁴ eV) from periodic sources during γ-ray bursts. We plan to use this detector system in coincidence with the GRAPES-3 shower array of TIFR at Ooty in Tamil Nadu to detect extended showers. Initially we will set up an array of seven detectors each consisting of 1m² plastic scintillator attached with a photomultiplier tube, which will later be extended to 50 detectors. We have acquired the necessary associated electronics. All equipments were tested and assembled. We have also gained experience in setting up the electronics for measuring coincident events at GRAPES array at Ooty.

More about cosmic rays:

• Cosmic Rays Primer
• Cosmic Ray in Wiki
• Article on Cosmic Ray by Richard Mewaldt
• Article on Cosmic Ray by James Schombert

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