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SUMMARY:First-forbidden transitions in the reactor antineutrino  ux and sp
 ectral anomalies
DTSTART;VALUE=DATE-TIME:20200226T070000Z
DTEND;VALUE=DATE-TIME:20200226T073000Z
DTSTAMP;VALUE=DATE-TIME:20260411T024604Z
UID:indico-contribution-1507@indico.tlabs.ac.za
DESCRIPTION:Speakers: Leendert Hayen (North Carolina State University & Tr
 iangle Universities Nuclear Laboratory)\nIt has been almost a decade since
  the reactor antineutrino anomaly entered the stage\, where the number of 
 experimentally detected antineutrinos emerging from a nuclear power reacto
 r interior was signicantly less than theoretically predicted from nuclear 
  decay. This has\, in turn\, motivated the search for an eV-scale sterile 
 neutrino in several very short baseline experiments\, none of which have s
 o far confirmed its existence. From the theory point of view\, initial ana
 lyses introduced a signicant number of approximations\, in particular for 
 the treatment of so-called forbidden transitions. We report on the first l
 arge-scale calculation of the influence of first-forbidden transitions usi
 ng state-of-the-art nuclear shell model calculations for a select number o
 f highly-contributing  branches. We use these results to propose a probabi
 lity distribution for first-forbidden spectral shapes and employ Monte Car
 lo techniques to translate this into a detailed construction of theoretica
 l uncertainties for the remaining forbidden transitions. We observed signi
 cant changes in both the integrated \nux and spectral shape of the cumulat
 ive antineutrino spectra spectra for all ssion actinides [1\, 2]\, and dis
 cuss both a mitigation of the so-called reactor shoulder and changes in th
 e reactor antineutrino anomaly. Finally\, we will comment how an improved 
 treatment of allowed  transitions [2\, 3] can further signicantly change b
 oth ux and spectral shape.\n[1] L. Hayen\, J. Kostensalo\, N. Severijns\, 
 and J. Suhonen\, Physical Review C 99\, 031301(R) (2019).\n[2] L. Hayen\, 
 J. Kostensalo\, N. Severijns\, and J. Suhonen\, Physical Review C 100\, 05
 4323 (2019)\, arXiv:1805.12259.\n[3] L. Hayen\, N. Severijns\, K. Bodek\, 
 D. Rozpedzik\, and X. Mougeot\, Reviews of Modern Physics 90\, 015008 (201
 8)\,\narXiv:1709.07530.\n\nhttps://indico.tlabs.ac.za/event/85/contributio
 ns/1507/
LOCATION:Main Venue
URL:https://indico.tlabs.ac.za/event/85/contributions/1507/
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