A step forward in solving the reactor-neutrino flux problem

Date:
June 17, 2020
Source:
University of Jyva"skyla" - Jyva"skyla"n yliopisto
Summary:
A nuclear theory group experiment paves the way for solving the
reactor antineutrino flux problems. The experiment is designed to
measure the mass of the neutrino. As a by product of the calibration
efforts of the experiment the electron spectral shape of the beta
decay of Xe-137 could be measured.



FULL STORY ========================================================================== Joint effort of the nuclear theory group at the University of Jyvaskyla
and the international collaborative EXO-200 experiment paves the way for solving the reactor antineutrino flux problems. The EXO-200 collaboration consists of researchers from 26 laboratories and the experiment is
designed to measure the mass of the neutrino. As a by product of the calibration efforts of the experiment the electron spectral shape of
the beta decay of Xe-137 could be measured. This particular decay is
optimally well suited for testing a theoretical hypothesis to solve the long-standing and persistent reactor antineutrino anomaly. The results
of measurements of the spectral shape were published in Physical Review
Letters (June 2020)

========================================================================== Nuclear reactors are driven by fissioning uranium and plutonium
fuel. The neutron-rich fission products decay by beta decay towards the beta-stability line by emitting electrons and electron antineutrinos. Each
beta decay produces a continuous energy spectrum for the emitted electrons
and antineutrinos up to a maximum energy (beta end-point energy).

The number of emitted electrons for each electron energy constitutes
the electron spectral shape and the complement of it describes the
antineutrino spectral shape.

Nuclear reactors emit antineutrinos with an energy distribution that
is sum of the antineutrino spectral shapes of all the beta decays
in the reactor. This energy distribution has been measured by large neutrino-oscillation experiments. On the other hand, this energy
distribution of antineutrinos has been built by using the available
nuclear data on beta decays of the fission products.

The established reference for this construction is the Huber-Mueller
(HM) model. Comparison of the HM-predicted antineutrino energy spectrum
with that measured by the oscillation experiments revealed a deficit
in the number of measured antineutrinos and an additional "bump,"
an extra increase in the measured number of the antineutrinos between
4 and 7 MeV of antineutrino energy. The deficit was coined the reactor antineutrino anomaly or the flux anomaly and has been associated with the oscillation of the ordinary neutrinos to the so-called sterile neutrinos
which do not interact with ordinary matter, and thus disappear from
the antineutrino flux emitted by the reactors. Up to recently there has
not been a convincing explanation for the appearance of the bump in the measured antineutrino flux.

Only recently a potential explanation for the flux anomaly and bump
has been discussed quantitatively. The flux deficit and the bump could
be associated to omission of accurate spectral shapes of the so-called first-fobidden non-unique beta decays taken into account for the first
time in the so-called "HKSS" flux model (from the first letters of the
surnames of the authors, L. Hayen, J.

Kostensalo, N. Severijns, J. Suhonen, of the related article).

How to verify that the HKSS flux and bump predictions are reliable?
"One way is to measure the spectral shapes of the key transitions and
compare with the HKSS predictions. These measurements are extremely
hard but recently a perfect test case could be measured by the renowned
EXO-200 collaboration and comparison with our theory group's predictions
could be achieved in a joint publication [AlKharusi2020]. A perfect match
of the measured and theory- predicted spectral shape was obtained, thus supporting the HKSS calculations and its conclusions. Further measurements
of spectral shapes of other transitions could be anticipated in the
(near) future," says Professor Jouni Suhonen from the Department of
Physics at the University of Jyvaskyla.


========================================================================== Story Source: Materials provided by University_of_Jyva"skyla"_-_Jyva"skyla"n_yliopisto. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. S. Al Kharusi, G. Anton, I. Badhrees, P. S. Barbeau,
D. Beck, V.

Belov, T. Bhatta, M. Breidenbach, T. Brunner, G. F. Cao,
W. R. Cen, C. Chambers, B. Cleveland, M. Coon, A. Craycraft,
T.

Daniels, L. Darroch, S. J. Daugherty, J. Davis, S. Delaquis,
A.

Der Mesrobian-Kabakian, R. DeVoe, J. Dilling, A. Dolgolenko,
M. J.

Dolinski, J. Echevers, W. Fairbank, D. Fairbank, J. Farine, S.

Feyzbakhsh, P. Fierlinger, D. Fudenberg, P. Gautam, R. Gornea,
G. Gratta, C. Hall, E. V. Hansen, J. Hoessl, P. Hufschmidt,
M. Hughes, A.

Iverson, A. Jamil, C. Jessiman, M. J. Jewell, A. Johnson, A.

Karelin, L. J. Kaufman, T. Koffas, J. Kostensalo,
R. Kru"cken, A.

Kuchenkov, K. S. Kumar, Y. Lan, A. Larson,
B. G. Lenardo, D. S. Leonard, G. S. Li, S. Li,
Z. Li, C. Licciardi, Y. H. Lin, R. MacLellan, T. McElroy,
T. Michel, B. Mong, D. C. Moore, K. Murray, P. Nakarmi,
O. Njoya, O. Nusair, A. Odian, I. Ostrovskiy, A. Piepke, A. Pocar,
F. Retie`re, A. L. Robinson, P. C. Rowson, D. Ruddell,
J. Runge, S. Schmidt, D. Sinclair, K.

Skarpaas, A. K. Soma, V. Stekhanov, J. Suhonen, M. Tarka, S.

Thibado, J. Todd, T. Tolba, T. I. Totev, R. Tsang,
B. Veenstra, V.

Veeraraghavan, P. Vogel, J.-L. Vuilleumier, M. Wagenpfeil,
J. Watkins, M.

Weber, L. J. Wen, U. Wichoski, G. Wrede,
S. X. Wu, Q. Xia, D. R. Yahne, L. Yang, Y.-R. Yen,
O. Ya. Zeldovich, T.

Ziegler. Measurement of the Spectral Shape of the b-Decay of
Xe137 to the Ground State of Cs137 in EXO-200 and Comparison
with Theory. Physical Review Letters, 2020; 124 (23) DOI:
10.1103/PhysRevLett.124.232502 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200617150043.htm

--- up 21 weeks, 1 day, 2 hours, 34 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)