Reactors (Anti)Neutrinos

Savannah River nuclear power plant 1960

Electron-antineutrinos are abundantly produced by the nuclear fission reactions inside the reactor cores (6 νe are produced in the uranium fission induced by neutrons [Way48]). A typical ~ 1 GW standard nuclear plant radiates about 5.1020 antineutrinos per second; their energy spectrum extends to 10 MeV and their mean energy is around 4 MeV. Thanks to these properties, they have been the first to be used by Reines and Cowan to observe the “neutrino” for the first time in 1956 [Cow56] and are still used to observe neutrino oscillation and infer neutrino properties.

Antineutrinos are observed via the inverse beta decay process: an electron-antineutrino interacts with a proton to give a positron and a neutron. The threshold of this reaction is 1.8 MeV (mass difference between the neutron and the proton). After a first try in 1953, which was using this principle [Rei53], Reines and Cowan, were more successful in 1956 [Cow56].
In 1955, Ray Davis had tried unsuccessfully to detect neutrinos at the Brookhaven nuclear reactor [Dav55]. But the detection principle proposed by Bruno Pontecorvo was sensitive to neutrinos, not to antineutrinos, and Davis showed that neutrinos and antineutrinos were different: [link].

From the end of the 70’s, a series of experiments close to reactors were used to look for neutrino oscillations. The first hint has been by Reines and his collaborators in 1980 [Rei80]. They reported a 2-3σ effect, described as “Evidence for neutrino instability” in the title, and more cautiously by “indications of neutrino instability” in the abstract. This effect has not been confirmed by an experiment at the Grenoble ILL reactor [Boe80]; the same team did an experiment at the Gösgen reactor and the result was also consistent with no neutrino oscillation [Vui82]. In 1984, a high statistics experiment at the Bugey reactor showed a difference in the counting rate at two different distances from the reactor’s core, difference interpreted in terms of oscillation [Cav84]. A re-analysis of the experiment two years later cancelled the previous result. It has been followed by more precise experiments always at Bugey at different distances (but smaller than 80 m), without indication of an oscillation.

In the mid 90’s, a new generation of bigger experiments was built at a larger distance (about 1 km), to test oscillation parameters in a lower Δmregion. The best result came from the Chooz experiment [Apo98,Apo99], confirmed later by Palo Verde [Boe00].

Daya Bay nuclear power plant 2012
Chooz nuclear power plant 2011

After the discovery of neutrino oscillation in the atmospheric sector (1998) and in the solar sector (2001), it became mandatory to measure the third mixing angle,θ13, to complete the PMNS mixing matrix. Chooz had already put a very constraining limit on this parameter (which was in any case much smaller than θ12 and θ23 , which values were close to the maximal). The idea to build two identical detectors (to reduce systematic errors), one close to the detector (~ 100 m), the other at a larger distance (~ km) and to compare the two measurements was developed by the Double Chooz collaboration [Ard04], followed by Daya Bay [Guo07] in China and RENO [Ahn10] in Korea (other projects in Russia or Brazil did not succeed [Goo05]). The comparison between the measurements of the two detectors could permit to observe small values of θ13. The results arrived end 2011-early 2012 [Abe11b] [An12] [Ahn12] and have been refined since this. See the review by Suekane and Bezerra for a detailed history of reactor θ13 experiments [Sue16].

The measurement of θ13 by reactor experiments has been completed by the result of the accelerator T2K experiment, which measured νe appearance in a νμ beam [Abe11a].

Further information

During the conference on the History of the Neutrino (Sept. 5-7, 2018 in Paris) the subject of Reactor Antineutrinos was reviewed by :


Abe11aK. Abe et al., T2K collaboration Indication of electron neutrino appearance from an accelerator-produced off-axis muon-neutrino beam Phys. Rev. Lett. 107 (2011) 041801; arXiv:1106.2822
Abe11bY. Abe et al., Double Chooz collaborationIndication for the disappearance of reactor electron antineutrinos in the Double Chooz experiment Phys. Rev. Lett. 108 (2012) 131801; arXiv:1112.6353
Ahn10J.K. Ahn et al., RENO Collaboration RENO : an experiment for neutrino oscillation parameter q13 using reactor neutrinos at Yonggwang arXiv:1003.1391
An12F.P. An et al., Daya Bay collaborationObservation of electron-antineutrino disappearance at Daya BayPhys. Rev. Lett. 108 (2012) 171803; arXiv:1203.1669
Apo98M. Apollonio et al., Chooz collaboration Initial results from the Chooz long baseline reactor neutrino oscillation experimentPhys. Lett. B420 (1998) 397
Apo99M. Apollonio et al. Limits on neutrino oscillations from the Chooz experiment Phys. Lett. B466 (1999) 415
Ard04F. Ardellier et al. Letter of intent for Double Chooz: a search for the mixing angle q13arXiv:hep-ex/0405032
Boe00F. Boehm et al., Palo Verde collaborationSearch for neutrino oscillations at the Palo Verde nuclear reactorsPhys. Rev. Lett. 84 (2000) 3764; arXiv:hep-ex/9912050
Boe80F. Boehm et al. Experimental study of neutrino oscillations at a fission reactor Phys. Lett. B97 (1980) 310
Cav84J.F. Cavaignac et al. Indication for neutrino oscillation from a high statistics experiment at the Bugey reactorPhys. Lett. B148 (1984) 387
Cow56C.L. Cowan, F. Reines, F.B. Harrison, H.W. Cruse and A.D. McGuire Detection of the free neutrino: a confirmationScience 124 (1956) 103, July 20, 1956 - Reprint in “Neutrino Physics”, ed. by K. Winter, Cambridge University Press, 1991
Goo05M. Goodman New reactor neutrino experiments besides Double Chooz arXiv:hep-ph/0501206
Guo07Xinheng Guo et al., Daya Bay CollaborationA precision measurement of the neutrino mixing angle q13 using reactor antineutrinos at Daya Bay arXiv:hep-ex/0701029
Rei53F. Reines and C.L. Cowan Detection of the free neutrino Phys. Rev. 92 (1953) 830
Rei56Frederick Reines and Clyde Cowan jr.The neutrinoNature 178 (1956) 446
Rei80F. Reines, H.W. Sobel, E. Pasierb Evidence for neutrino instability Phys. Rev. Lett. 45 (1980) 1307
Sue16Fumihiko Suekane and Thiago Junqueira de Castro Bezerra Double Chooz and a history of reactor q13 experimentsarXiv:1601.08041, Nucl. Phys. B908 (2016) 74
Vui82J.L. Vuilleumier et al. New limits on oscillation parameters for electron antineutrinos Phys. Lett. B114 (1982) 298 - Final results from Gösgen in G. Zacek et al. / Neutrino-oscillation experiments at the Gösgen nuclear power reactor / Phys. Rev. D34 (1986) 2621
Way48K. Way and E.P. WignerThe rate of decay of fission productsPhys. Rev. 73 (1948) 1318

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