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New data from PAMELA provides better measure of positrons

Posted August 27, 2013

PAMELA is launched onboard a Resurs-DK1 Russian satellite by a Soyuz rocket in June 2006.

A large team made up of researchers from several European countries (Italy, Russia, Sweden and Germany) has published, in the journal Physical Review Letters, the latest findings from the Payload for Antimatter/Matter Exploration and Light-nuclei Astrophysics—PAMELA—satellite project. In addition to publishing raw data, the team offers an interpretation of findings as they relate to the excess of positrons (electron antiparticles) observed at high energies.

Experiments conducted over the past several years have shown that under certain conditions there are more positrons striking the Earth than theories have predicted. That has led to new theories to explain the seeming anomaly, such as suggestions that they come from pulsars, or more exotically, from collisions between dark matter particles. More specifically, researchers have found a continuous rise in the number of positrons relative to electrons at energies of 10 GeV and above. According to everything astrophysicists know, that just shouldn’t be happening. The new data from PAMELA doesn’t offer any hard evidence of why the number of positrons increase or where they are coming from, rather it provides a more detailed, clear picture of what is occurring.

Up until now, measurements of positrons—taken from research balloons, planes and even from PAMELA—have used a method to count positrons called the positron-electron fraction, which is a ratio obtained by comparing the number of positrons observed over a period of time relative to the number of electrons. All have confirmed the rise in positrons at high energies. The new data from PAMELA (collected over the period 2006-2009) offers a more detailed assessment of the number of positrons, called absolute numbers—which are the actual number of positrons observed over a given length of time. The new numbers have been made possible by using new technology that not only measures positrons observed, but accurately measures the ones that are missed due to less than perfect measuring instruments. The researchers report that 24,500 positrons were observed by PAMELA over the course of the experimental run.


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