Prospects for improved understanding of isotopic reactor antineutrino fluxes

Abstract

Predictions of antineutrino fluxes produced by fission isotopes in a nuclear reactor have recently received increased scrutiny due to observed differences in predicted and measured inverse beta decay (IBD) yields, referred to as the "reactor antineutrino flux anomaly." In this paper, global fits are applied to existing IBD yield measurements to produce constraints on antineutrino production by individual plutonium and uranium fission isotopes. We find that fits including measurements from highly 235 U-enriched cores and fits including Daya Bay's new fuel evolution result produce discrepant bestfit IBD yields for 235 U and 239Pu. This discrepancy can be alleviated in a global analysis of all data sets through simultaneous fitting of 239 Pu, 235 U, and 238 U yields. The measured IBD yield of 238 U in this analysis is ð7.02 AE 1.65Þ × 10 −43 cm 2 =fission, nearly two standard deviations below existing predictions. Future hypothetical IBD yield measurements by short-baseline reactor experiments are examined to determine their possible impact on the global understanding of isotopic IBD yields. It is found that future improved short-baseline IBD yield measurements at both high-enriched and low-enriched cores can significantly improve constraints for 235 U, 238 U, and 239 Pu, providing comparable or superior precision to existing conversion-and summation-based antineutrino flux predictions. Systematic and experimental requirements for these future measurements are also investigated.

Improved measurement of the reactor antineutrino flux at Daya Bay

“…[15][16][17] that the allowed parameter space is compatible with earlier anomalies from LSND [18,19], MiniBooNE [20], GALLEX [21], and SAGE [22]. On the other hand, a number of authors [23][24][25][26] have argued that the RAA may be due to the theoretical uncertainties in the flux calculations. Recent antineutrino flux evolution results from Daya Bay are in tension with the sterile-neutrino-only explanation of RAA [27].…”

Diagnosing the reactor antineutrino anomaly with global antineutrino flux data

“…Allowed regions for isotopic IBD yields of 235 U, 239 Pu, and 238 U provided by a fit of all IBD yield datasets to the 235+239+238 hypothesis described in the text. The blue solid, dashed and dotted contours show the previous 235+239+238 regions obtained in Ref [19]. at 1σ, 2σ, and 3σ, respectively.…”

“…The ∆χ 2 min between 235 and OSC increased to from 5.7 for Daya Bay to 7.3 in the combined fit. Using a frequentist Monte Carlo statistical analysis [19,28], this corresponds to a change in the preference of the 235 model against the OSC model from 2.6σ for Daya Bay to 2.9σ in the combined fit of RENO and Daya Bay.…”

First Search for Short-Baseline Neutrino Oscillations at HFIR with PROSPECT

“…Of these, the sterile neutrino hypothesis has received particular attention due to its broad potential impact and to existing supporting experimental indications from accelerator and radioactive source neutrino experiments [14][15][16][17][18]. A range of experimental [19][20][21][22][23], theoretical [24][25][26][27][28], and global analysis [29][30][31][32] efforts have sought to understand the origin of these discrepancies.…”