New light on ‘dark matter’

R. Ramachandran
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An international experiment aboard the International Space Station (ISS) today reported the observation of an excess of positrons in the cosmic ray flux, the source of which could be the elusive dark matter.

This forms the most important part of the first results from the experiment, called the Alpha Magnetic Spectrometer (AMS), which were reported by the experiment’s spokesperson, Nobel Laureate Samuel Ting of the Massachusetts Institute of Technology (MIT) at the meeting of the American Association for Advancement of Science (AAAS) at Boston, Massachusetts.

The mysterious dark matter, which is believed to account for a quarter of the universe’s mass-energy balance and is distributed isotropically — invariant with respect to direction — in the space, can be observed indirectly through its gravitational interaction with visible matter but is yet to be directly detected.

The search for dark matter is one of the objectives of this space-borne AMS even as it is being actively searched for in ground-based experiments such as the Large Hadron Collider (LHC) and other experiments in deep underground experiments.

The instrument is basically a giant magnet and an antimatter detector attached to the outside of the ISS. It is the most powerful and sensitive particle spectrometer ever deployed in space. It is designed to study the cosmic ray particles, which are charged high-energy particles that permeate space, before they have a chance to interact with the Earth’s atmosphere.

The first AMS results are based on the analysis of about 25 billion recorded primary cosmic ray events.

The events were recorded between May 19, 2011 and December 10, 2012. Of these, an unprecedented 6.8 million were unambiguously identified as electrons and their antimatter counterparts, positrons, observed in the energy range 0.5 Giga electron-Volt (GeV) to 350 GeV. Of these 6.8 million particles, more than 400,000 were positrons.

This is the largest number of energetic…

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