Cosmic raysCosmos is the ultimate laboratory, where cosmic rays can be observed at energies higher than any accelerator. Charged cosmic rays have mass, and they are absorbed by the 100 km of Earth’s atmosphere (10 m of water). To study the intrinsic properties of charged cosmic rays requires a detector above the Earth’s atmosphere.

AMS, the magnetic spectrometer operating on the International Space Station (ISS), is the only way to provide long term (20 years) precision measurements of charged cosmic rays.

AMS uses the unique environment of space to advance the knowledge of the universe and to contribute to the understanding of its structure and origin by searching for the missing antimatter, by exploring the origin of dark matter and by measuring with the highest accuracy the composition of cosmic rays in the multi TeV region of energy.

Towards Understanding the Origin of Cosmic-Ray Positrons

Precision measurements of cosmic ray positrons are presented up to 1 TeV based on 1.9 million positrons collected by the Alpha Magnetic Spectrometer on the International Space Station. The positron flux exhibits complex energy dependence. Its distinctive properties are (a) a significant excess starting from $25.2 \pm 1.8$  GeV compared to the lower-energy, power-law trend, (b) a sharp dropoff above $284^{+91}_{−64} $ GeV, (c) in the entire energy range the positron flux is well described by the sum of a term associated with the positrons produced in the collision of cosmic rays, which dominates at low energies, and a new source term of positrons, which dominates at high energies, and (d) a finite energy cutoff of the source term of $E_{s}=810^{+310}_{−180} $ GeV is established with a significance of more than 4σ. These experimental data on cosmic ray positrons show that, at high energies, they predominantly originate either from dark matter annihilation or from other astrophysical sources.

Towards Understanding the Origin of Cosmic-Ray Electrons

Precision results on cosmic-ray electrons are presented in the energy range from 0.5 GeV to 1.4 TeV based on $28.1×10^{6}$ electrons collected by the Alpha Magnetic Spectrometer on the International Space Station. In the entire energy range the electron and positron spectra have distinctly different magnitudes and energy dependences. The electron flux exhibits a significant excess starting from $42.1^{+5.4}_{−5.2}$  GeV compared to the lower energy trends, but the nature of this excess is different from the positron flux excess above $25.2\pm1.8$  GeV. Contrary to the positron flux, which has an exponential energy cutoff of $810^{+310}_{−180}$  GeV, at the 5σ level the electron flux does not have an energy cutoff below 1.9 TeV. In the entire energy range the electron flux is well described by the sum of two power law components. The different behavior of the cosmic-ray electrons and positrons measured by the Alpha Magnetic Spectrometer is clear evidence that most high energy electrons originate from different sources than high energy positrons.

Precision Measurement of the Boron to Carbon Flux Ratio

Knowledge of the rigidity dependence of the boron to carbon flux ratio (B/C) is important in understanding the propagation of cosmic rays. The precise measurement of the B/C ratio from 1.9 GV to 2.6 TV, based on 2.3 million boron and 8.3 million carbon nuclei collected by AMS during the first 5 years of operation, is presented. The detailed variation with rigidity of the B/C spectral index is reported for the first time. The B/C ratio does not show any significant structures in contrast to many cosmic ray models that require such structures at high rigidities. Remarkably, above 65 GV, the B/C ratio is well described by a single power law $R^{Δ}$ with index $Δ=−0.333±0.014(fit)±0.005(syst)$, in good agreement with the Kolmogorov theory of turbulence which predicts $Δ=−1/3$ asymptotically.

Observation of identical rigidity dependence of He, C and O Cosmic Rays at High Rigidities

We report the observation of new properties of primary cosmic rays He, C, and O measured in the rigidity (momentum/charge) range 2 GV to 3 TV with $90 \times 10^{6}$ helium, $8.4 \times 10^{6}$ carbon, and $7.0 \times 10^{6}$ oxygen nuclei collected by the Alpha Magnetic Spectrometer (AMS) during the first five years of operation. Above 60 GV, these three spectra have identical rigidity dependence. They all deviate from a single power law above 200 GV and harden in an identical way.

Precision Measurement of Cosmic-Ray Nitrogen and its Primary and Secondary Components

A precision measurement of the nitrogen flux with rigidity (momentum per unit charge) from 2.2 GV to 3.3 TV based on $2.2 \times 10^{6}$ events is presented. The detailed rigidity dependence of the nitrogen flux spectral index is presented for the first time. The spectral index rapidly hardens at high rigidities and becomes identical to the spectral indices of primary He, C, and O cosmic rays above ∼700  GV. We observed that the nitrogen flux $Φ_{\rm N}$ can be presented as the sum of its primary component $Φ^{P}_{\rm N}$ and secondary component $Φ^{S}_{\rm N}$, $Φ_{\rm N}=Φ^{P}_{\rm N}+Φ^{S}_{\rm N}$, and we found $Φ_{\rm N}$ is well described by the weighted sum of the oxygen flux $Φ_{\rm O}$ (primary cosmic rays) and the boron flux $Φ_{\rm B}$ (secondary cosmic rays), with $Φ^{P}_{\rm N}=(0.090 \pm 0.002)×Φ_{\rm O}$ and $Φ^{S}_{\rm N}=(0.62 \pm 0.02) \times Φ_{\rm B}$ over the entire rigidity range. This corresponds to a change of the contribution of the secondary cosmic ray component in the nitrogen flux from 70% at a few GV to 

Observation of Fine Time Structures in the Cosmic Proton and Helium

We present the precision measurement from May 2011 to May 2017 (79 Bartels rotations) of the proton fluxes at rigidities from 1 to 60 GV and the helium fluxes from 1.9 to 60 GV based on a total of $1\times10^{9}$ events collected with the Alpha Magnetic Spectrometer aboard the International Space Station. This measurement is in solar cycle 24, which has the solar maximum in April 2014. We observed that, below 40 GV, the proton flux and the helium flux show nearly identical fine structures in both time and relative amplitude. The amplitudes of the flux structures decrease with increasing rigidity and vanish above 40 GV. The amplitudes of the structures are reduced during the time period, which started one year after solar maximum, when the proton and helium fluxes steadily increase. Above ∼3  GV the p/He flux ratio is time independent. We observed that below ∼3  GV the ratio has a long-term decrease coinciding with the period during which the fluxes start to rise.

Observation of Complex Time Structures in the Cosmic-Ray Electron and Positron Fluxes

We present high-statistics, precision measurements of the detailed time and energy dependence of the primary cosmic-ray electron flux and positron flux over 79 Bartels rotations from May 2011 to May 2017 in the energy range from 1 to 50 GeV. For the first time, the charge-sign dependent modulation during solar maximum has been investigated in detail by leptons alone. Based on $23.5 \times 10^{6}$ events, we report the observation of short-term structures on the timescale of months coincident in both the electron flux and the positron flux. These structures are not visible in the $e^{+}/e^{-}$ flux ratio. The precision measurements across the solar polarity reversal show that the ratio exhibits a smooth transition over $830 \pm 30$ days from one value to another. The midpoint of the transition shows an energy dependent delay relative to the reversal and changes by $260 \pm 30$ days from 1 to 6 GeV.

Observation of New Properties of Secondary Cosmic Rays Lithium, Beryllium and Boron

We report on the observation of new properties of secondary cosmic rays Li, Be, and B measured in the rigidity (momentum per unit charge) range 1.9 GV to 3.3 TV with a total of $5.4 \times 10^{6}$ nuclei collected by AMS during the first five years of operation aboard the International Space Station. The Li and B fluxes have an identical rigidity dependence above 7 GV and all three fluxes have an identical rigidity dependence above 30 GV with the Li/Be flux ratio of $2.0 \pm 0.1$. The three fluxes deviate from a single power law above 200 GV in an identical way. This behavior of secondary cosmic rays has also been observed in the AMS measurement of primary cosmic rays He, C, and O but the rigidity dependences of primary cosmic rays and of secondary cosmic rays are distinctly different. In particular, above 200 GV, the secondary cosmic rays harden more than the primary cosmic rays.