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Evidence of a Hardening in the Cosmic Ray Proton Spectrum at around 166 TeV Observed by the GRAPES-3 Experiment
Journal
Physical Review Letters
ISSN
00319007
Date Issued
2024-02-02
Author(s)
Varsi, F.
Chakraborty, M.
Chandra, A.
Dugad, S. R.
Goswami, U. D.
Gupta, S. K.
Hariharan, B.
Hayashi, Y.
Jagadeesan, P.
Kawakami, S.
Kojima, H.
Lipari, P.
Mahapatra, S.
Mohanty, P. K.
Muraki, Y.
Nayak, P. K.
Nonaka, T.
Oshima, A.
Pant, B. P.
Pattanaik, D.
Pradhan, G. S.
Rameez, M.
Reddy, L. V.
Saha, S.
Sahoo, R.
Scaria, R.
Shibata, S.
Zuberi, M.
Abstract
We present the measurement of the cosmic ray proton spectrum from 50 TeV to 1.3 PeV using 7.81×106 extensive air shower events recorded by the ground-based GRAPES-3 experiment between 1 January 2014 and 26 October 2015 with a live time of 460 day. Our measurements provide an overlap with direct observations by satellite and balloon-based experiments. The electromagnetic and muon components in the shower were measured by a dense array of plastic scintillator detectors and a tracking muon telescope, respectively. The relative composition of the proton primary from the air shower data containing all primary particles was extracted using the multiplicity distribution of muons which is a sensitive observable for mass composition. The observed proton spectrum suggests a spectral hardening at ∼166 TeV and disfavors a single power law description of the spectrum up to the Knee energy (∼3 PeV).