The cosmic-ray plot continues to thicken. What’s more, the observed rigidity dependence is surprisingly different from that of the lighter primary helium, carbon and oxygen cosmic rays, which has been previously measured by AMS. The neon, magnesium and silicon fluxes display unexpectedly identical rigidity dependence above 86.5 GV, including an also unexpected deviation above 200 GV from the single-power-law dependence predicted by the conventional theory of cosmic-ray origin and propagation. These measurements are based on 1.8 million neon nuclei, 2.2 million magnesium nuclei and 1.6 million silicon nuclei, collected by AMS during its first 7 years of operation ( to ). In its latest paper, the AMS team describes flux measurements of these three cosmic nuclei in the rigidity range from 2.15 GV to 3.0 TV. Such measurements would help shed new light on the exact nature of primary cosmic rays and how they journey through space. But until now there have been no measurements of how the fluxes of the heavy nuclei of neon, magnesium and silicon change with rigidity. AMS and other experiments have previously measured the number, or more precisely the so-called flux, of several of these types of cosmic rays and how the flux varies with particle energy and rigidity – a measure of a charged particle’s momentum in a magnetic field. The most common are nuclei of hydrogen, that is, protons, but they can also take other forms, such as heavier nuclei and electrons or their antimatter counterparts. Primary cosmic rays are produced in supernovae explosions in our galaxy, the Milky Way, and beyond.
In a paper just published in Physical Review Letters, the AMS team reports measurements of heavy primary cosmic rays that, again, are unexpected.
It’s an impressive amount of data, which has provided a wealth of information about these cosmic particles, but remarkably, as the spokesperson of the AMS team Sam Ting has previously noted, none of the AMS results were predicted. Ever since astronauts attached the 7.5 tonne AMS detector to the International Space Station in May 2011, the space-based magnetic spectrometer, which was assembled at CERN, has collected data on more than 150 billion cosmic rays – charged particles that travel through space with energies up to trillions of electron volts.
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