An extremely energetic cosmic ray observed by a surface detector array

• Published in: Science (American Association for the Advancement of Science) Vol. 382; no. 6673; pp. 903 - 907
• Main Authors: Abbasi, R. U., Allen, M. G., Arimura, R., Belz, J. W., Bergman, D. R., Blake, S. A., Shin, B. K., Buckland, I. J., Cheon, B. G., Fujii, T., Fujisue, K., Fujita, K., Fukushima, M., Furlich, G. D., Gerber, Z. R., Globus, N., Hibino, K., Higuchi, R., Honda, K., Ikeda, D., Ito, H., Iwasaki, A., Jeong, S., Jeong, H. M., Jui, C. H., Kadota, K., Kakimoto, F., Kalashev, O. E., Kasahara, K., Kawata, K., Kharuk, I., Kido, E., Kim, S. W., Kim, H. B., Kim, J. H., Komae, I., Kubota, Y., Kuznetsov, M. Y., Lee, K. H., Lubsandorzhiev, B. K., Lundquist, J. P., Matthews, J. N., Nagataki, S., Nakamura, T., Nakazawa, A., Nonaka, T., Ogio, S., Ono, M., Oshima, H., Park, I. H., Potts, M., Pshirkov, S., Remington, J. R., Rodriguez, D. C., Rott, C., Rubtsov, G. I., Ryu, D., Sagawa, H., Sakaki, N., Sako, T., Sakurai, N., Shin, H., Smith, J. D., Sokolsky, P., Stokes, B. T., Stroman, T. S., Takahashi, K., Takeda, M., Taketa, A., Tameda, Y., Thomas, S., Thomson, G. B., Tinyakov, P. G., Tkachev, I., Tomida, T., Troitsky, S. V., Tsunesada, Y., Udo, S., Urban, F. R., Wong, T., Yamazaki, K., Yuma, Y., Zhezher, Y. V., Zundel, Z.
• Format: Journal Article
• Language: English
• Published: Washington The American Association for the Advancement of Science 24.11.2023
• Subjects: Active galaxies; Arrays; Charged particles; Cosmic radiation; Cosmic rays; Magnetic fields; Particle accelerators; Particle physics; Surface detectors
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.abo5095

Cosmic rays are energetic charged particles from extraterrestrial sources, with the highest-energy events thought to come from extragalactic sources. Their arrival is infrequent, so detection requires instruments with large collecting areas. In this work, we report the detection of an extremely energetic particle recorded by the surface detector array of the Telescope Array experiment. We calculate the particle’s energy as 244 ± 29   stat .   − 76 + 51 syst .  exa–electron volts (~40 joules). Its arrival direction points back to a void in the large-scale structure of the Universe. Possible explanations include a large deflection by the foreground magnetic field, an unidentified source in the local extragalactic neighborhood, or an incomplete knowledge of particle physics. Editor’s summary Cosmic rays are charged particles from space. At low energies, they mostly originate from the Sun, whereas at high energies, they are expected to be emitted by nearby active galaxies. The Telescope Array Collaboration now reports the detection of a cosmic ray event with an energy of about 240 exa–electron volts, more than a million times higher than that achieved by artificial particle accelerators. Such high-energy particles should experience only small deflections by foreground magnetic fields, but tracing back the arrival direction shows no obvious source galaxy. The authors suggest that the foreground magnetic fields might be stronger than expected, or there could be unknown particle physics at high energies. —Keith T. Smith Detection of a highly energetic cosmic ray is traced back to its arrival direction, but no source galaxy is evident.