Characterization of the astrophysical diffuse neutrino flux using starting track events in IceCube
R. Abbasi, M. Ackermann, J. Adams, Sanjib Kumar Agarwalla, J. A. Aguilar, M. Ahlers, Jean-Marco Alameddine, N. M. Amin, K. Andeen, G. Anton, C. Argüelles, Yosuke Ashida, S. Athanasiadou, L. Ausborm, Spencer Axani, X. Bai, Aswathi Balagopal, M. Baricevic, S. W. Barwick, Simeon Bash, Vedant Basu, R. Bay, J. J. Beatty, J. Becker Tjus, Jakob Beise, Chiara Bellenghi, Charlotte Benning, S. BenZvi, D. Berley, E. Bernardini, D. Besson, E. Blaufuss, Summer Blot, Federico Bontempo, Julia Book, Caterina Boscolo Meneguolo, S. Böser, O. Botner, J. Böttcher, J. Braun, Bennett Brinson, Jannes Brostean-Kaiser, Livia Brusa, Ryan T. Burley, Raffaela Busse, Delaney Butterfield, Michael Campana, I. Caracas, K. Carloni, J. Graciá‐Carpio, S. Chattopadhyay, Thien Nhan Chau, Z. Chen, D. Chirkin, S. Choi, Brian Clark, Alan Coleman, G. H. Collin, A. Connolly, J. M. Conrad, Paul Coppin, Rebecca Corley, Pablo Correa, D. F. Cowen, Pranav Dave, C. De Clercq, James DeLaunay, D. Delgado, S. Deng, Kunal Deoskar, Abhishek Desai, P. Desiati, K. D. de Vries, G. de Wasseige, T. DeYoung, Á. I. Díaz, J. C. Díaz–Vélez, Markus Dittmer, Alba Domi, Lincoln Draper, Hrvoje Dujmović, M. A. DuVernois, Thomas Ehrhardt, Leonhard Eidenschink, A. Eimer, P. Eller, E. Ellinger, Sharif El Mentawi, Dominik Elsässer, R. Engel, Hannah Erpenbeck, John Evans, P. A. Evenson, Kwok Lung Fan, Ke Fang, Kareem Ramadan Farrag, A. R. Fazely, Anatoli Fedynitch, Nora Feigl, Sebastian Fiedlschuster
Abstract
A measurement of the diffuse astrophysical neutrino spectrum is presented using IceCube data collected from 2011--2022 (10.3 years). We developed novel detection techniques to search for events with a contained vertex and exiting track induced by muon neutrinos undergoing a charged-current interaction. Searching for these starting track events allows us to not only more effectively reject atmospheric muons but also atmospheric neutrino backgrounds in the southern sky, opening a new window to the sub-100 TeV astrophysical neutrino sky. The event selection is constructed using a dynamic starting track veto and machine learning algorithms. We use this data to measure the astrophysical diffuse flux as a single power law flux (SPL) with a best-fit spectral index of $\ensuremath{\gamma}=2.5{8}_{\ensuremath{-}0.09}^{+0.10}$ and per-flavor normalization of ${\ensuremath{\phi}}_{\mathrm{per}\text{-flavor}}^{\text{Astro}}=1.6{8}_{\ensuremath{-}0.22}^{+0.19}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}\ifmmode\times\else\texttimes\fi{}{\mathrm{GeV}}^{\ensuremath{-}1}\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{sr}}^{\ensuremath{-}1}$ (at 100 TeV). The sensitive energy range for this dataset is 3--550 TeV under the SPL assumption. This data was also used to measure the flux under a broken power law, however we did not find any evidence of a low energy cutoff.