We examine uncertainties in the analysis of the reactor neutrino anomaly, wherein it is suggested that only about 94% of the emitted antineutrino flux was detected in short baseline experiments. We find that the form of the corrections that lead to the anomaly are very uncertain for the 30% of the flux that arises from forbidden decays. This uncertainty was estimated in four ways, is larger than the size of the anomaly, and is unlikely to be reduced without accurate direct measurements of the antineutrino flux. Given the present lack of detailed knowledge of the structure of the forbidden transitions, it is not possible to convert the measured aggregate fission beta spectra to antineutrino spectra to the accuracy needed to infer an anomaly. Neutrino physics conclusions based on the original anomaly need to be revisited, as do oscillation analyses that assumed that the antineutrino flux is known to better than approximately 4%.The term "reactor neutrino anomaly" first appeared in a publication by G. Mention et al. [1], where it generally referred to the 3σ deficit of neutrinos detected in short-baseline reactor neutrino experiments relative to the number predicted. The predicted number of detected neutrinos has evolved upward over time, largely as a consequence of a predicted increase in the energy of the neutrino flux and an increasedν e + p → n + e + cross section associated with smaller values for the neutron lifetime. This cross section is used to infer the neutrino flux in a presumably well-characterized detector. The changes in the predicted neutrino flux are mostly associated with improved knowledge of the beta decays of the isotopes created in fission reactors. Such an anomaly would potentially be extremely significant, if a shortfall in the detected neutrino flux could be ascribed toν e oscillation into a light sterile neutrino with a mass of about 1 eV.There is an extensive recent literature dealing with the reactor anomaly, starting with a seminal paper by Mueller et al. [2] that reexamined the reactor antineutrino flux. The latter publication sought to improve the earlier flux estimates based on the ILL on-line measurements [3][4][5] of the integral beta spectrum of the fission products. An antineutrino spectrum can be inferred from a beta spectrum provided one knows the linear combination of operators involved in the decay, the end-point energy, and the nuclear charge. The fission beta spectra involve about 6000 beta transitions, of which about 1500 are forbidden [6]. Clearly some assumptions are required in order to infer the fission antineutrino flux. The improvements [1, 2] on the earlier analyses of ILL integral measurements led to an increased energy of the antineutrino flux, which was subsequently verified in an independent analysis [7].The present contribution examines the consequences of the forbidden transitions known to be present (at the 30% level) in the beta decay of fission products. We analyze the antineutrino flux, using a first-principles derivation of the finite size (FS) and weak ...

We analyze within a nuclear database framework the shoulder observed in the antineutrino spectra in current reactor experiments. We find that the ENDF/B-VII.1 database predicts that the antineutrino shoulder arises from an analogous shoulder in the aggregate fission beta spectra. In contrast, the JEFF-3.1.1 database does not predict a shoulder for two out of three of the modern reactor neutrino experiments, and the shoulder that is predicted by JEFF-3.1.1 arises from 238 U. We consider several possible origins of the shoulder, and find possible explanations. For example, there could be a problem with the measured aggregate beta spectra, or the harder neutron spectrum at a light-water power reactor could affect the distribution of beta-decaying isotopes. In addition to the fissile actinides, we find that 238 U could also play a significant role in distorting the total antineutrino spectrum. Distinguishing these and quantifying whether there is an anomaly associated with measured reactor neutrino signals will require new short-baseline experiments, both at thermal reactors and at reactors with a sizable epithermal neutron component.Modern reactor neutrino experiments measuring θ 13 , such as Daya Bay [1], RENO [2], and Double Chooz [3], involve detectors both near and far from the reactors. The shape and magnitude of the antineutrino spectra emitted from the reactors have been measured to high accuracy in the near detectors of both Daya Bay and RENO. The Daya Bay near-detector has also provided an absolute determination of the reactor antineutrino flux, and this is consistent in magnitude with the previous world average short-baseline reactor neutrino experiments. As such, the measured magnitude is consistent with a deficit with respect to the most recent estimates [4,5] of the expected reactor antineutrino flux. The absolute magnitude of the RENO flux has yet to be published. However, in the near detector of both RENO and Daya Bay the shapes of the measured spectra are not consistent with the antineutrino spectrum predictions [4,5] that we refer to as the Huber-Mueller model. Most notably, the measured antineutrino spectra exhibit a significant shoulder relative to the model predictions at antineutrino energies ∼ 5 − 7 MeV. The spectra measured at Daya Bay, RENO, and Double Chooz all exhibit this shoulder. Thus, there are two puzzles associated with measured reactor antineutrino spectra: (1) the yield in all short-baseline experiments is lower than current models, and (2) the shape of the measured spectra deviate from these model predictions. However, these two issues are not necessarily related.In the Daya Bay, RENO and Double Chooz experiments the antineutrinos are measured by detecting the positrons produced in inverse beta decay on the protons (ν e + p → n + e + ) in the detector, and the positron energy is reconstructed from the scintillation light created by the kinetic energy of the positron and its annihilation. The antineutrino spectrum S(E ν ) emitted from a reactor is determined by [6] the reactor ther...

We present a review of the antineutrino spectra emitted from reactors. Knowledge of these and their associated uncertainties are crucial for neutrino oscillation studies. The spectra used to-date have been determined by either conversion of measured electron spectra to antineutrino spectra or by summing over all of the thousands of transitions that makeup the spectra using modern databases as input. The uncertainties in the subdominant corrections to beta-decay plague both methods, and we provide estimates of these uncertainties. Improving on current knowledge of the antineutrino spectra from reactors will require new experiments. Such experiments would also address the so-called reactor neutrino anomaly and the possible origin of the shoulder observed in the antineutrino spectra measured in recent high-statistics reactor neutrino experiments.Comment: Submitted for publication in the Annual Review of Nuclear and Particle Science, Vol.6

Neutrino reaction cross sections ( , Ϫ ), ( e ,e Ϫ ) and -capture and photoabsorption rates on 12 C are computed within a large-basis shell-model framework, which included excitations up to 4ប. When groundstate correlations are included with an open p shell the predictions of the calculations are in reasonable agreement with most of the experimental results for these reactions. Woods-Saxon radial wave functions are used, with their asymptotic forms matched to the experimental separation energies for bound states, and matched to a binding energy of 0.01 MeV for unbound states. We obtain, for the neutrino-absorption inclusive cross sections ͑but excluding the 12 N ground-state contribution͒ ϭ13.2ϫ10 Ϫ40 cm 2 for the ( , Ϫ ) decay-in-flight flux in agreement with the LSND datum of (11.7Ϯ1.8)ϫ10 Ϫ40 cm 2 and ϭ4.1 ϫ10 Ϫ42 cm 2 for the ( e ,e Ϫ ) decay-at-rest flux, less than the experimental result of (5.4Ϯ0.8)ϫ10 Ϫ42 cm 2 .

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We investigate cross sections for neutrino-12 C exclusive scattering and for muon capture on 12 C using wave functions obtained in the ab initio no-core shell model. In our parameter-free calculations with basis spaces up to the 6hΩ we show that realistic nucleon-nucleon interactions, like e.g. the CD-Bonn, under predict the experimental cross sections by more than a factor of two. By including a realistic three-body interaction, Tucson-Melbourne TM ′ (99), the cross sections are enhanced significantly and a much better agreement with experiment is achieved. At the same time, the TM ′ (99) interaction improves the calculated level ordering in 12 C. The comparison between the CD-Bonn and the three-body calculations provides strong confirmation for the need to include a realistic three-body interaction to account for the spin-orbit strength in p-shell nuclei. ) is a very sensitive test of nuclear structure models for mass 12 and, particularly, of the strength of the spin-orbit interaction. The two most common p-shell approximations for the structure of the ground state of 12 C ((a) the p-shell equivalent of a L=0 S=0 three alpha-cluster structure and (b) the closed p 3/2 shell structure) give very different (indeed opposite) predictions for the B(GT) strength to T=1 1 + triplet. In the p-shell alpha-cluster limit the ground state of carbon has good SU (4) (4) symmetry. This translates into an exact cancellation between the different p 1/2 and p 3/2 transition amplitudes. The observed transition strength requires the inclusion of higher SU(4) components in the wave functions and the breaking of the cancellation is quite sensitive to the assumed spin-orbit interaction. In the the jj-coupling limit, where one assumes that the ground state of 12 C is described by a closed p 3/2 shell, the transition to the T=1 1 + state is pure p 3/2 → p 1/2 . No cancellations between different transition amplitudes are allowed and the transition strength is over estimated by almost a factor of 6. When RPA correlations are included in the initial and final states the situation improves somewhat, but the transition remains over-estimated by about a factor of 4 [1,2]. The strong contrast between the predictions of the pure jj-coupling and the pure SU(4) limits makes this Gamow-Teller transition an ideal test case for the strength of the spin-orbit interaction and for model wave functions of mass 12.In this letter we present the predictions of no-core shell model (NCSM) [3] calculations of 12 C for the T=1 1 + transition in 12 C. We examine inelastic electron scattering to the 15.11 MeV state of 12 C, muon capture to the ground state of 12 B, and neutrino scattering to the ground state of 12 N. These different electroweak reactions probe different momentum transfers and comparisons between theory and experiment allow us to test the convergence of the no-core shell model with increasing basis size, up to 6hΩ. We also investigate the contributions of a three-nucleon force since it is now well established [4,5,6] that realistic nucleon-nucl...

We show that axions emitted by SN 1987A, with coupling strengths to nucleons in the range 9x \0~n If the luminosity of axions, L a , dominates that of neutrinos, L v , then the corresponding value of g a n is still excluded. As gaN is increased, however, r a also increases (since less material overburden is required for the same absorption probability) and the luminosity La-r^Ta decreases. Eventually, L a

We examine the time-reversal-violating nuclear "Schiff moment" that induces electric dipole moments in atoms. After presenting a self-contained derivation of the form of the Schiff operator, we show that the distribution of Schiff strength, an important ingredient in the ground-state Schiff moment, is very different from the electric-dipole-strength distribution, with the Schiff moment receiving no strength from the giant dipole resonance in the Goldhaber-Teller model. We then present shell-model calculations in light nuclei that confirm the negligible role of the dipole resonance and show the Schiff strength to be strongly correlated with low-lying octupole strength. Next, we turn to heavy nuclei, examining recent arguments for the strong enhancement of Schiff moments in octupole-deformed nuclei over that of 199 Hg, for example. We concur that there is a significant enhancement while pointing to effects neglected in previous work (both in the octupole-deformed nuclides and 199 Hg) that may reduce it somewhat, and emphasizing the need for microscopic calculations to resolve the issue. Finally, we show that static octupole deformation is not essential for the development of collective Schiff moments; nuclei with strong octupole vibrations have them as well, and some could be exploited by experiment.