Ultrahigh energy cosmic rays provide the highest known energy source in the Universe to measure proton cross sections. Though conditions for collecting such data are less controlled than an accelerator environment, current generation cosmic ray observatories have large enough exposures to collect significant statistics for a reliable measurement for energies above what can be attained in the laboratory. Cosmic ray measurements of cross section use atmospheric calorimetry to measure depth of air shower maximum (Xmax), which is related to the primary particle's energy and mass. The tail of the Xmax distribution is assumed to be dominated by showers generated by protons, allowing measurement of the inelastic proton-air cross section. In this work, the proton-air inelastic cross section measurement, σp-airinel, using data observed by Telescope Array's Black Rock Mesa and Long Ridge fluorescence detectors and surface detector array in hybrid mode is presented. σp-airinel is observed to be 520.1±35.8[Stat]-42.9+25.3[Sys] mb at s=73 TeV. The total proton-proton cross section is subsequently inferred from Glauber formalism and is found to be σpptot=139.4-21.3+23.4[Stat]-25.4+15.7[Sys] mb.
Bibliographical noteFunding Information:
The Telescope Array experiment is supported by the Japan Society for the Promotion of Science 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, The University of Tokyo; by the U.S. National Science Foundation Awards No. PHY-0601915, No. PHY-1404495, No. PHY-1404502, and No. PHY-1607727; by the National Research Foundation of Korea (2016R1A2B4014967, 2016R1A5A1013277, 2017K1A4A3015188, 2017R1A2A1A05071429); by the Russian Academy of Sciences, RFBR Grant No. 20-02-00625a (INR), IISN Project No. 4.4502.13, and Belgian Science Policy under IUAP VII/37 (ULB). 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. 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, 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 Shea assisted the collaboration with valuable advice on a variety of topics. 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.
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All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics