In this work we are reporting on the measurement of the proton-air inelastic cross section ${\sigma }_{p-\text{air}}^{\text{inel}}$ using the Telescope Array detector. Based on the measurement of the ${\sigma }_{p-\text{air}}^{\text{inel}}$, the proton-proton cross section ${\sigma }_{p-p}$ value is also determined at $\sqrt{s}=95_{-8}^{+5}\mathrm{TeV}$. Detecting cosmic ray events at ultrahigh energies with the Telescope Array enables us to study this fundamental parameter that we are otherwise unable to access with particle accelerators. The data used in this report are the hybrid events observed by the Middle Drum fluorescence detector together with the surface array detector collected over five years. The value of the ${\sigma }_{p-\text{air}}^{\text{inel}}$ is found to be equal to $567.0\pm 70.5[\text{Stat}{]}_{-25}^{+29}[\text{Sys}]\mathrm{mb}$. The total proton-proton cross section is subsequently inferred from Glauber formalism and the Block, Halzen and Stanev QCD inspired fit and is found to be equal to $170_{-44}^{+48}[\text{Stat}{]}_{-17}^{+19}[\text{Sys}]\mathrm{mb}$.

• Received 7 May 2015
• Corrected 14 September 2015

DOI:https://doi.org/10.1103/PhysRevD.92.032007