We propose a new method for the estimation of ultra-high energy cosmic ray (UHECR) mass composition from a distribution of their arrival directions. The method employs a test statistic (TS) based on a characteristic deflection of UHECR events with respect to the distribution of luminous matter in the local Universe modeled with a flux-weighed 2MRS catalog. Making realistic simulations of the mock UHECR sets, we show that this TS is robust to the presence of galactic and non-extreme extra-galactic magnetic fields and sensitive to the mass composition of events in a set. We apply the method to Telescope Array surface detector data for 11 years and derive new independent constraints on fraction of protons and iron in p-Fe mix at E > 10 EeV. At 10 < E < 100 EeV the data favors increase of allowed proton fraction and decrease of allowed iron fraction, while at E > 100 EeV — pure iron or even more massive composition. This result is in tension with Auger composition model inferred from spectrum–Xmax fit at 2.7σ (2.0σ) for PT’11 (JF’12) regular GMF model.
|Journal||Proceedings of Science|
|Publication status||Published - 2022 Mar 18|
|Event||37th International Cosmic Ray Conference, ICRC 2021 - Virtual, Berlin, Germany|
Duration: 2021 Jul 12 → 2021 Jul 23
Bibliographical noteFunding Information:
The State of Utah supported the project through its Economic Development Board, and the University of Utah through the Office of the Vice President for Research. The experimental site became available through the cooperation of the Utah School and Institutional Trust Lands Administration (SITLA), U.S. Bureau of Land Management (BLM), and the U.S. Air Force. We appreciate the assistance of the State of Utah and Fillmore offices of the BLM in crafting the Plan of Development for the site. Patrick A. Shea assisted the collaboration with valuable advice and supported the collaboration’s efforts. The people and the officials of Millard County, Utah have been a source of steadfast and warm support for our work which we greatly appreciate. We are indebted to the Millard County Road Department for their efforts to maintain and clear the roads which get us to our sites. We gratefully acknowledge the contribution from the technical staffs of our home institutions. An allocation of computer time from the Center for High Performance Computing at the University of Utah is gratefully acknowledged.
Acknowledgments: The Telescope Array experiment is supported by the Japan Society for the Promotion of Science(JSPS) through Grants-in-Aid for Priority Area 431, for Specially Promoted Research JP21000002, for Scientific Research (S) JP19104006, for Specially Promoted Research JP15H05693, for Scientific Research (S) JP15H05741, for Science Research (A) JP18H03705, for Young Scientists (A) JPH26707011, and for Fostering Joint International Research (B) JP19KK0074, by the joint research program of the Institute for Cosmic Ray Research (ICRR), The University of Tokyo; by the Pioneering Program of RIKEN for Matter in the Universe (r-EMU); by the U.S. National Science Foundation awards PHY-1404495, PHY-1404502, PHY-1607727, PHY-1712517, and PHY-1806797; by the National Research Foundation of Korea (2017K1A4A3015188, 2020R1A2C1008230, & 2020R1A2C2102800) ; IISN project No. 4.4501.18, and Belgian Science Policy under IUAP VII/37 (ULB). The application of the analysis method to data was supported by the Russian Science Foundation grant No. 17-72-20291 (INR). The foundations of Dr. Ezekiel R. and Edna Wattis Dumke, Willard L. Eccles, and George S. and Dolores Doré Eccles all helped with generous donations.
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