Experimental tests of sub-surface reflectors as an explanation for the ANITA anomalous events. (arXiv:2009.13010v3 [astro-ph.HE] UPDATED)

Experimental tests of sub-surface reflectors as an explanation for the ANITA anomalous events. (arXiv:2009.13010v3 [astro-ph.HE] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Smith_D/0/1/0/all/0/1">D. Smith</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Besson_D/0/1/0/all/0/1">D. Z. Besson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Deaconu_C/0/1/0/all/0/1">C. Deaconu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Prohira_S/0/1/0/all/0/1">S. Prohira</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Allison_P/0/1/0/all/0/1">P. Allison</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Batten_L/0/1/0/all/0/1">L. Batten</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Beatty_J/0/1/0/all/0/1">J. J. Beatty</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Binns_W/0/1/0/all/0/1">W. R. Binns</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bugaev_V/0/1/0/all/0/1">V. Bugaev</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cao_P/0/1/0/all/0/1">P. Cao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chen_C/0/1/0/all/0/1">C. Chen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chen_P/0/1/0/all/0/1">P. Chen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Clem_J/0/1/0/all/0/1">J. M. Clem</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Connolly_A/0/1/0/all/0/1">A. Connolly</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cremonesi_L/0/1/0/all/0/1">L. Cremonesi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dasgupta_P/0/1/0/all/0/1">P. Dasgupta</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gorham_P/0/1/0/all/0/1">P. W. Gorham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Israel_M/0/1/0/all/0/1">M. H. Israel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_T/0/1/0/all/0/1">T. C. Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ludwig_A/0/1/0/all/0/1">A. Ludwig</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matsuno_S/0/1/0/all/0/1">S. Matsuno</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Miki_C/0/1/0/all/0/1">C. Miki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nam_J/0/1/0/all/0/1">J. Nam</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Novikov_A/0/1/0/all/0/1">A. Novikov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nichol_R/0/1/0/all/0/1">R. J. Nichol</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Oberla_E/0/1/0/all/0/1">E. Oberla</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Prechelt_R/0/1/0/all/0/1">R. Prechelt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rauch_B/0/1/0/all/0/1">B. F. Rauch</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Russell_J/0/1/0/all/0/1">J. Russell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Saltzberg_D/0/1/0/all/0/1">D. Saltzberg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Seckel_D/0/1/0/all/0/1">D. Seckel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Varner_G/0/1/0/all/0/1">G. S. Varner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vieregg_A/0/1/0/all/0/1">A. G. Vieregg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wissel_S/0/1/0/all/0/1">S. A. Wissel</a>

The balloon-borne ANITA experiment is designed to detect ultra-high energy
neutrinos via radio emissions produced by an in-ice shower. Although initially
purposed for interactions within the Antarctic ice sheet, ANITA also
demonstrated the ability to self-trigger on radio emissions from ultra-high
energy charged cosmic rays interacting in the Earth’s atmosphere. For showers
produced above the Antarctic ice sheet, reflection of the down-coming radio
signals at the Antarctic surface should result in a polarity inversion prior to
subsequent observation at the $sim$35-40 km altitude ANITA gondola. ANITA has
published two anomalous instances of upcoming cosmic-rays with measured
polarity opposite the remaining sample of $sim$50 UHECR signals. The steep
observed upwards incidence angles (25–30 degrees relative to the horizontal)
require non-Standard Model physics if these events are due to in-ice neutrino
interactions, as the Standard Model cross-section would otherwise prohibit
neutrinos from penetrating the long required chord of Earth. Shoemaker et al.
posit that glaciological effects may explain the steep observed anomalous
events. We herein consider the scenarios offered by Shoemaker et al. and find
them to be disfavored by extant ANITA and HiCal experimental data. We note that
the recent report of four additional near-horizon anomalous ANITA-4 events, at
$>3sigma$ significance, are incompatible with their model, which requires
significant signal transmission into the ice.

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