Characteristics of the diffuse astrophysical electron and tau neutrino flux with six years of IceCube high energy cascade data. (arXiv:2001.09520v2 [astro-ph.HE] UPDATED)

Characteristics of the diffuse astrophysical electron and tau neutrino flux with six years of IceCube high energy cascade data. (arXiv:2001.09520v2 [astro-ph.HE] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Collaboration_IceCube/0/1/0/all/0/1">IceCube Collaboration</a>: <a href="http://arxiv.org/find/astro-ph/1/au:+Aartsen_M/0/1/0/all/0/1">M. G. Aartsen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ackermann_M/0/1/0/all/0/1">M. Ackermann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Adams_J/0/1/0/all/0/1">J. Adams</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aguilar_J/0/1/0/all/0/1">J. A. Aguilar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ahlers_M/0/1/0/all/0/1">M. Ahlers</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ahrens_M/0/1/0/all/0/1">M. Ahrens</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alispach_C/0/1/0/all/0/1">C. Alispach</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Andeen_K/0/1/0/all/0/1">K. Andeen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Anderson_T/0/1/0/all/0/1">T. Anderson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ansseau_I/0/1/0/all/0/1">I. Ansseau</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Anton_G/0/1/0/all/0/1">G. Anton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Arguelles_C/0/1/0/all/0/1">C. Argüelles</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Auffenberg_J/0/1/0/all/0/1">J. Auffenberg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Axani_S/0/1/0/all/0/1">S. Axani</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Backes_P/0/1/0/all/0/1">P. Backes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bagherpour_H/0/1/0/all/0/1">H. Bagherpour</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bai_X/0/1/0/all/0/1">X. Bai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+V%2E_A/0/1/0/all/0/1">A. Balagopal V.</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barbano_A/0/1/0/all/0/1">A. Barbano</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barwick_S/0/1/0/all/0/1">S. W. Barwick</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bastian_B/0/1/0/all/0/1">B. Bastian</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Baum_V/0/1/0/all/0/1">V. Baum</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Baur_S/0/1/0/all/0/1">S. Baur</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bay_R/0/1/0/all/0/1">R. Bay</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:+Becker_K/0/1/0/all/0/1">K.-H. Becker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tjus_J/0/1/0/all/0/1">J. Becker Tjus</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+BenZvi_S/0/1/0/all/0/1">S. BenZvi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Berley_D/0/1/0/all/0/1">D. Berley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bernardini_E/0/1/0/all/0/1">E. Bernardini</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:+Binder_G/0/1/0/all/0/1">G. Binder</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bindig_D/0/1/0/all/0/1">D. Bindig</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blaufuss_E/0/1/0/all/0/1">E. Blaufuss</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blot_S/0/1/0/all/0/1">S. Blot</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bohm_C/0/1/0/all/0/1">C. Bohm</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Boser_S/0/1/0/all/0/1">S. Böser</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Botner_O/0/1/0/all/0/1">O. Botner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bottcher_J/0/1/0/all/0/1">J. Böttcher</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bourbeau_E/0/1/0/all/0/1">E. Bourbeau</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bourbeau_J/0/1/0/all/0/1">J. Bourbeau</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bradascio_F/0/1/0/all/0/1">F. Bradascio</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Braun_J/0/1/0/all/0/1">J. Braun</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bron_S/0/1/0/all/0/1">S. Bron</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brostean_Kaiser_J/0/1/0/all/0/1">J. Brostean-Kaiser</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Burgman_A/0/1/0/all/0/1">A. Burgman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Buscher_J/0/1/0/all/0/1">J. Buscher</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Busse_R/0/1/0/all/0/1">R. S. Busse</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Carver_T/0/1/0/all/0/1">T. Carver</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:+Cheung_E/0/1/0/all/0/1">E. Cheung</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chirkin_D/0/1/0/all/0/1">D. Chirkin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Choi_S/0/1/0/all/0/1">S. Choi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Clark_K/0/1/0/all/0/1">K. Clark</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Classen_L/0/1/0/all/0/1">L. Classen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Coleman_A/0/1/0/all/0/1">A. Coleman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Collin_G/0/1/0/all/0/1">G. H. Collin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Conrad_J/0/1/0/all/0/1">J. M. Conrad</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Coppin_P/0/1/0/all/0/1">P. Coppin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Correa_P/0/1/0/all/0/1">P. Correa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cowen_D/0/1/0/all/0/1">D. F. Cowen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cross_R/0/1/0/all/0/1">R. Cross</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dave_P/0/1/0/all/0/1">P. Dave</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Clercq_C/0/1/0/all/0/1">C. De Clercq</a>, et al. (297 additional authors not shown)

We report on the first measurement of the astrophysical neutrino flux using
particle showers (cascades) in IceCube data from 2010 — 2015. Assuming
standard oscillations, the astrophysical neutrinos in this dedicated cascade
sample are dominated ($sim 90 %$) by electron and tau flavors. The flux,
observed in the sensitive energy range from $16,mathrm{TeV}$ to
$2.6,mathrm{PeV}$, is consistent with a single power-law model as expected
from Fermi-type acceleration of high energy particles at astrophysical sources.
We find the flux spectral index to be $gamma=2.53pm0.07$ and a flux
normalization for each neutrino flavor of $phi_{astro} = 1.66^{+0.25}_{-0.27}$
at $E_{0} = 100, mathrm{TeV}$, in agreement with IceCube’s complementary muon
neutrino results and with all-neutrino flavor fit results. In the measured
energy range we reject spectral indices $gammaleq2.28$ at $ge3sigma$
significance level. Due to high neutrino energy resolution and low atmospheric
neutrino backgrounds, this analysis provides the most detailed characterization
of the neutrino flux at energies below $sim100,{rm{TeV}}$ compared to
previous IceCube results. Results from fits assuming more complex neutrino flux
models suggest a flux softening at high energies and a flux hardening at low
energies (p-value $ge 0.06$). The sizable and smooth flux measured below $sim
100,{rm{TeV}}$ remains a puzzle. In order to not violate the isotropic
diffuse gamma-ray background as measured by the Fermi-LAT, it suggests the
existence of astrophysical neutrino sources characterized by dense environments
which are opaque to gamma-rays.

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