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Register a new userOn the search of sterile neutrinos by oscillometry measurements
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J.D. Vergados
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It is shown that the new neutrino with a high mass squared difference and a small mixing angle should reveal itself in the oscillometry measurements. For a judicious monochromatic neutrino source the new oscillation length $L_{42}$ is expected shorter than 1.5 m. Thus the needed measurements can be implemented with a gaseous spherical TPC of modest dimensions with a very good energy and position resolution. The best candidates for oscillometry are discussed and the sensitivity to the mixing angle $theta_{14}$ has been estimated: $sin^2{(2theta_{14})}$=0.05 (99{%}) for two months of data handling with $^{51}$Cr.
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The existence of sterile neutrino is an open question in neutrino physics up to now. The method of neutrino oscillometry provides a powerful tool to test the common 3+1 sterile neutrino hypothesis, i.e. three active flavors and one sterile falvor. There are several antineutrino sources can be used for this method. One of them is the well known isotope chain of $^{144}{rm Ce}-$$^{144}{rm Pr}$ with initial activity around 50-100 kCi. It has compact size and might be installed either outside or inside the detector. Another one is the short-lived isotope $rm^8Li$, which can be produced in nuclear reaction of a proton beam hitting beryllium target. The Lithium source has only the out-of-detector option due to its large size. The proposed Jinping water-based liquid scintillator detector will be used as a detection volume. Above experimental setups will allow us to cover the current best fit values of oscillation parameters with 90% C.L. At the same time, it is sensitive to the region of Neutrino-4 result.
The investigation of the oscillation pattern induced by the sterile neutrinos might determine the oscillation parameters, and at the same time, allow to probe CPT symmetry in the leptonic sector through neutrino-antineutrino mass inequality. We propose to use a large scintillation detector like JUNO or LENA to detect electron neutrinos and electron antineutrinos from MCi electron capture or beta decay sources. Our calculations indicate that such an experiment is realistic and could be performed in parallel to the current research plans for JUNO and RENO. Requiring at least 5$sigma$ confidence level and assuming the values of the oscillation parameters indicated by the current global fit, we would be able to detect neutrino-antineutrino mass inequality of the order of 0.5% or larger, which would imply a signal of CPT anomalies.
With the Deep Underground Neutrino Experiment (DUNE) as an example, we show that the presence of even one sterile neutrino of mass $sim$1 eV can significantly impact the measurements of CP violation in long baseline experiments. Using a probability level analysis and neutrino-antineutrino asymmetry calculations, we discuss the large magnitude of these effects, and show how they translate into significant event rate deviations at DUNE. Our results demonstrate that measurements which, when interpreted in the context of the standard three family paradigm, indicate CP conservation at long baselines, may, in fact hide large CP violation if there is a sterile state. Similarly, any data indicating the violation of CP cannot be properly interpreted within the standard paradigm unless the presence of sterile states of mass O(1 eV) can be conclusively ruled out. Our work underscores the need for a parallel and linked short baseline oscillation program and a highly capable near detector for DUNE, in order that its highly anticipated results on CP violation in the lepton sector may be correctly interpreted.
Neutrinos, being the only fermions in the Standard Model of Particle Physics that do not possess electromagnetic or color charges, have the unique opportunity to communicate with fermions outside the Standard Model through mass mixing. Such Standard Model-singlet fermions are generally referred to as sterile neutrinos. In this review article, we discuss the theoretical and experimental motivation for sterile neutrinos, as well as their phenomenological consequences. With the benefit of hindsight in 2020, we point out potentially viable and interesting ideas. We focus in particular on sterile neutrinos that are light enough to participate in neutrino oscillations, but we also comment on the benefits of introducing heavier sterile states. We discuss the phenomenology of eV-scale sterile neutrinos in terrestrial experiments and in cosmology, we survey the global data, and we highlight various intriguing anomalies. We also expose the severe tension that exists between different data sets and prevents a consistent interpretation of the global data in at least the simplest sterile neutrino models. We discuss non-minimal scenarios that may alleviate some of this tension. We briefly review the status of keV-scale sterile neutrinos as dark matter and the possibility of explaining the matter-antimatter asymmetry of the Universe through leptogenesis driven by yet heavier sterile neutrinos.
DANSS is a highly segmented 1~m${}^3$ plastic scintillator detector. Its 2500 one meter long scintillator strips have a Gd-loaded reflective cover. The DANSS detector is placed under an industrial 3.1~$mathrm{GW_{th}}$ reactor of the Kalinin Nuclear Power Plant 350~km NW from Moscow. The distance to the core is varied on-line from 10.7~m to 12.7~m. The reactor building provides about 50~m water-equivalent shielding against the cosmic background. DANSS detects almost 5000 $widetilde u_e$ per day at the closest position with the cosmic background less than 3$%$. The inverse beta decay process is used to detect $widetilde u_e$. Sterile neutrinos are searched for assuming the $4 u$ model (3 active and 1 sterile $ u$). The exclusion area in the $Delta m_{14}^2,sin^22theta_{14}$ plane is obtained using a ratio of positron energy spectra collected at different distances. Therefore results do not depend on the shape and normalization of the reactor $widetilde u_e$ spectrum, as well as on the detector efficiency. Results are based on 966 thousand antineutrino events collected at 3 distances from the reactor core. The excluded area covers a wide range of the sterile neutrino parameters up to $sin^22theta_{14}<0.01$ in the most sensitive region.
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