Today marks the unveiling of new findings regarding energetic cosmic ray electrons and positrons, drawn from the analysis of the first 41 billion events observed by the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station (ISS). These results offer unprecedented insights into the behavior of high-energy cosmic rays and provide valuable clues regarding the existence of dark matter.
AMS has meticulously scrutinized 41 billion primary cosmic ray events, pinpointing 10 million as electrons and positrons. In the energy range of 0.5 to 500 GeV, AMS has scrutinized the positron fraction, revealing a notable onset of increase at 8 GeV, indicative of new sources of positrons. This increase, showcased in Figure 1, unveils a significant milestone after decades of cosmic ray exploration. Moreover, AMS has precisely determined the energy at which the positron fraction peaks, measuring it to be 275±32 GeV, as illustrated in Figure 2. This milestone represents the first experimental observation of the positron fraction’s maximum, demonstrating isotropy within 3% and suggesting that energetic positrons are not preferentially sourced from specific spatial directions.
The precise measurement of the positron fraction holds profound implications for understanding dark matter origins. Various models predicting distinct behaviors of the positron fraction excess are being scrutinized, with the latest AMS results showcasing unambiguous observations, as outlined in items (1)-(4). These findings align with expectations from a neutralino dark matter particle with a mass on the order of 1 TeV. To further discern the observed phenomena’s origin, AMS is underway in measuring the rate of decrease beyond the turning point, as well as the anti-proton fraction, for future analyses.
Additionally, AMS has reported precise measurements of the electron and positron fluxes, revealing distinct differences between them in magnitude and energy dependence. Notably, the positron flux exhibits a unique pattern, first rising, then leveling out, before increasing again, and subsequently displaying a tendency to decrease above 200 GeV, as depicted in Figure 3. These observations underscore the fundamental disparity between matter (electrons) and antimatter (positrons), as highlighted by Dr. Michael S. Turner.
Over the last 50 years, non-magnetic detectors on Earth and in space have probed the combined flux of electrons and positrons in cosmic rays, hinting at potential structures in the 300-800 GeV range. AMS, equipped as a particle physics detector, offers independent measurements of electrons, positrons, and their combined flux, unveiling new insights. Remarkably, AMS’s measurement of the combined flux reveals a smooth distribution at high energies, as illustrated in Figure 4.
These precision measurements, collectively, enhance our understanding of high-energy cosmic rays’ origins and offer vital clues about dark matter’s existence. The AMS Collaboration’s groundbreaking contributions, showcased at ICRC 2013, underscore the ongoing quest to unravel the mysteries of the cosmos and redefine our understanding of fundamental physics.