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October 2, 2014
The Alpha Magnetic Spectrometer (AMS) collaboration has today presented its latest results. These are based on the analysis of 41 billion particles detected with the space-based AMS detector aboard the International Space Station. The results, presented during a seminar at CERN, provide new insights into the nature of the mysterious excess of positrons (antielectrons) observed in the flux of cosmic rays. The findings are published today in the journal Physical Review Letters.
The AMS experiment is able to map the flux of cosmic rays with unprecedented precision and in the results published today, the collaboration presents new data at energies never before recorded. The AMS collaboration has analysed 41 billion primary cosmic-ray events among which 10 million have been identified as electrons and positrons. The distribution of these events in the energy range of 0.5 to 500 GeV shows a well-measured increase of positrons from 8 GeV with no preferred incoming direction in space. The energy at which the positron fraction ceases to increase has been measured to be 275±32 GeV.
Image above: View of the AMS detector on the International Space Station (Image credit: NASA).
This rate of decrease after the “cut-off energy” is very important to physicists as it could be an indicator that the excess of positrons is the signature of dark-matter particles annihilating into pairs of electrons and positrons. Although the current measurements could be explained by objects such as pulsars, they are also tantalizingly consistent with dark matter particles with mass of the order of 1 TeV. Different models on the nature of dark matter predict different behaviour of the positron excess above the positron fraction expected from ordinary cosmic ray collisions. Therefore, results at higher energies will be of crucial importance in the near future to evaluate if the signal is from dark matter or from a cosmic source.
Editor notes:
The AMS detector is operated by a large international collaboration led by Nobel laureate Samuel Ting. AMS involves about 600 researchers from China, Denmark, Finland, France, Germany, Italy, Korea, Mexico, the Netherlands, Portugal, Spain, Switzerland, Taiwan, and the United-States. The AMS detector was assembled at CERN, tested at ESA’s ESTEC centre in the Netherlands and launched on 16 May 2011 onboard NASA’s Space Shuttle Endeavour. It is installed on the International Space Station where it tracks incoming charged particles such as protons, electrons and antimatter particles such as positrons, mapping the flux of cosmic rays with unprecedented precision.
CERN, the European Organization for Nuclear Research, is the world's leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Israel, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. Romania is a Candidate for Accession. Serbia is an Associate Member in the pre-stage to Membership. India, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer Status.
Related links:
Physical Review Letters “High Statistics Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5-500 GeV with the Alpha Magnetic Spectrometer on the International Space Station”: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.121101
Physical Review Letters “Electron and Positron Fluxes in Primary Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the International Space Station”: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.121102
Alpha Magnetic Spectrometer (AMS): http://www.ams02.org/
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CERN’s ALPHA experiment measures charge of antihydrogen: http://orbiterchspacenews.blogspot.ch/2014/06/cerns-alpha-experiment-measures-charge.html
Antimatter experiment produces first beam of antihydrogen: http://home.web.cern.ch/about/updates/2014/01/antimatter-experiment-produces-first-beam-antihydrogen
For more information about CERN, visit: http://home.web.cern.ch
Image (mentioned), Text, Credits: CERN / Corinne Pralavorio.
Cheers, Orbiter.ch