Analysis Result of the High-Energy Cosmic-Ray Proton Spectrum from the ISS-CREAM Experiment

The Cosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM) experiment successfully recorded data for about 539 days from August 2017 to February 2019. In this talk, we report the measurement of the cosmic-ray proton energy spectrum from the ISS-CREAM experiment in the energy range of 2.5 TeV - 655 TeV. For the analysis, we used the silicon charge detector (SCD) placed at the top of the ISS-CREAM payload to identify the incoming cosmic-ray charge. The SCD is finely segmented to minimize charge misidentification due to backscatter effects. The four-layer SCD consists of 10,752 silicon pixels, each of which is 1.37 × 1.57 × 0.05 cm ³ in size. The calorimeter (CAL) consists of 20 layers of tungsten/scintillating fibers preceded by carbon targets. It provided cosmic-ray tracking, energy determination, and the high-energy trigger. The Top and Bottom Counting detectors (T/BCD) are above and below the CAL respectively and provided the low energy trigger. Each T/BCD is composed of an array of 20 × 20 photodiodes on plastic scintillators. The measured proton spectral index of 2.67 ±0.02 between 2.5 and 12.5 TeV is consistent with prior CREAM measurements. The spectrum softening above ∼ 10 TeV is consistent with the bump-like structure as reported by CREAM-I+III, DAMPE, and NUCLEON, but ISS-CREAM extends measurements to higher energies than those prior measurements.