Search for sterile neutrinos in the neutrino-4 experiment

An experimental search for sterile neutrinos has been carried out at a neutrino facility based on the SM-3 nuclear reactor in Dimitrovgrad, Russia. The movable detector with passive shielding against the external radiation may be positioned at a distance varying between 6 and 12 m from the center of the reactor. The antineutrino flux has for the first time been measured using a movable detector placed close to the antineutrino source. The accuracy of the measurements is largely restricted by the cosmic background. The results of the measurements performed at small and large distances are analyzed in terms of the sterile-neutrino model parameters Δm ₁₄ ² and sin²2θ₁₄.     

Indication of reactor ν(e) disappearance in the Double Chooz experiment

The Double Chooz experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. An observed-to-predicted ratio of events of 0.944±0.016(stat)±0.040(syst) was obtained in 101 days of running at the Chooz nuclear power plant in France, with two 4.25 GW(th) reactors. The results were obtained from a single 10 m(3) fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 flux measurement after correction for differences in core composition. The deficit can be interpreted as an indication of a nonzero value of the still unmeasured neutrino mixing parameter sin(2)2θ(13). Analyzing both the rate of the prompt positrons and their energy spectrum, we find sin(2)2θ(13)=0.086±0.041(stat)±0.030(syst), or, at 90% C.L., 0.017相似文献   

First result for the neutrino magnetic moment from measurements with the GEMMA spectrometer

The first result obtained in the measurements of the neutrino magnetic moment at the Kalinin nuclear power plant with the GEMMA spectrometer is presented. A high-purity germanium detector of mass 1.5 kg placed at a distance of 13.9 m from the reactor core is used in the spectrometer. The antineutrino flux at the detector position is 2.73 × 10¹³ $ \bar \nu The first result obtained in the measurements of the neutrino magnetic moment at the Kalinin nuclear power plant with the GEMMA spectrometer is presented. A high-purity germanium detector of mass 1.5 kg placed at a distance of 13.9 m from the reactor core is used in the spectrometer. The antineutrino flux at the detector position is 2.73 × 10¹³ /(cm² s). The differential method is used to select events of electromagnetic antineutrino-electron scattering. The spectra taken in the reactor-on and reactor-off modes over 6200 and 2064 h, respectively, are compared. On the basis of a data analysis, an upper limit of 5.8 × 10⁻¹¹ μB was set on the neutrino magnetic moment μ _ν at a 90% C.L. Original Russian Text ? A.G. Beda, V.B. Brudanin, E.V. Demidova, C.Vylov, M.G. Gavrilov, V.G. Egorov, A.S. Starostin, M.V. Shirchenko, 2007, published in Yadernaya Fizika, 2007, Vol. 70, No. 11, pp. 1925–1935.     

Experiment for search for sterile neutrino at SM-3 reactor

In connection with the question of possible existence of sterile neutrino the laboratory on the basis of SM-3 reactor was created to search for oscillations of reactor antineutrino. A prototype of a neutrino detector with scintillator volume of 400 l can be moved at the distance of 6–11 m from the reactor core. The measurements of background conditions have been made. It is shown that the main experimental problem is associated with cosmic radiation background. Test measurements of dependence of a reactor antineutrino flux on the distance from a reactor core have been made. The prospects of search for oscillations of reactor antineutrino at short distances are discussed.     

TEXONO反应堆中微子能谱的计算

在低能反应堆中微子物理实验中,无论是研究中微子振荡、中微子反应还是测量中微子反常磁矩,都必须准确地知道反应堆中微子的通量和能谱.本文详细讨论了反应堆中微子能谱的计算方法,依据TEXONO实验所用的NP2反应堆的实际情况及探测器的安排,计算并得到中微子的通量和能谱.     

Employing low-power reactors in studying the mixing parameter sin<Superscript>2</Superscript>(2<Emphasis Type="Italic">θ</Emphasis><Subscript>13</Subscript>)

Measurement of the mixing parameter sin²(2θ₁₃) is one of the pressing problems in neutrino physics. Projects of reactor experiments characterized by a sensitivity of sin²(2θ₁₃)≈0.01 are being presently discussed. Almost all of them are based on the one reactor-two detectors scheme. Within this methodological approach, one employs an NPP reactor of power about a few GW for an antineutrino source and two detectors of identical configurations that are arranged at different distances from the reactor. In such experiments, the systematic error may be about 1%, which ensures a precision of about 0.01. In the present study, it is proposed to use, in a measurement of sin²(2θ₁₃), the existing SuperKamiokande (SK) detector combined with its own antineutrino source, a nuclear reactor of low thermal power, about 300 MW (low-power reactor, or LPR). Such an experiment can be performed within a rather short time. An analysis that studied various detection mechanisms revealed that the LPR-SK combination would make it possible to attain a sensitivity of sin²(2θ₁₃)≈0.002.     

Neutrino geophysics at Baksan I: Possible detection of georeactor antineutrinos

J.M. Herndon in the 1990s proposed a natural nuclear fission georeactor at the center of the Earth with a power output of 3–10 TW as an energy source to sustain the Earth magnetic field. R. S. Raghavan in 2002 pointed out that, under certain conditions, antineutrinos generated in such a georeactor can be detected using massive scintillation detectors. We consider the underground Baksan Neutrino Observatory (4800 m.w.e.) as a possible site for developments in geoneutrino physics. Here, the intrinsic background level of less than 1 event/yr in a liquid scintillation ～1000-t target detector can be achieved and the main source of background is the antineutrino flux from power reactors. We find that this flux is ～10 times lower than at the KamLAND detector site and two times lower than at the Gran Sasso laboratory and thus at Baksan the georeactor hypothesis can be conclusively tested. We also discuss possible searches for the composition of georeactor burning nuclear fuel by analysis of the antineutrino energy spectrum.     

Gemma experiment: Three years of the search for the neutrino magnetic moment

The result of the 3-year neutrino magnetic moment measurement at the Kalinin Nuclear Power Plant (KNPP) with the GEMMA spectrometer is presented. Antineutrino-electron scattering is investigated. A high-purity germanium detector of 1.5 kg placed at a distance of 13.9 m from the 3 GW_th reactor core is exposed to the antineutrino flux of 2.7 × 10¹³ cm⁻² s⁻¹. The scattered electron spectra taken in (5184 + 6798) and (1853 + 1021) h for the reactor ON and OFF periods are compared. The upper limit for the neutrino magnetic moment μ_v < 3.2 × 10⁻¹¹μ _B at 90% CL is derived from the data processing.     

The concept of a powerful antineutrino source

A powerful antineutrino source with a hard [(n)\tilde] _e\tilde \nu _e spectrum obtained upon the (n, γ) activation of the ⁷Li isotope and the subsequent β⁻ decay (T _1/2 = 0.84 s) of the ⁸Li isotope with the emission of high-energy [(n)\tilde] _e\tilde \nu _e with E _v of up to 13 MeV was discussed. The source can be constructed both in the static regime (by covering the active reactor zone with highly purified ⁷Li) and in the dynamic regime of operation. In the dynamic regime, lithium is pumped over in a closed cycle through a converter (i.e., a volumetric reservoir) close to the active reactor zone and further to a remote detector. The source can be constructed on the basis of both highly purified ⁷Li isotope in the metal state and chemical compounds of the ⁷Li isotope. The setup can be developed on the basis of an intensive neutron source or an accelerator with a neutron-producing target. In the dynamic regime, the proposed lithium antineutrino source enables us to increase the cross-section of the ([(n)\tilde] _e\tilde \nu _e , d) reaction by two orders of magnitude over a purely reactor spectrum.     

Are there sterile neutrinos at the eV scale?

New predictions for the antineutrino flux from nuclear reactors suggest that reactor experiments may have measured a deficit in this flux, which can be interpreted in terms of oscillations between the known active neutrinos and new sterile states. We perform a reanalysis of global short-baseline neutrino oscillation data in a framework with one or two sterile neutrinos. While one sterile neutrino is still not sufficient to reconcile the signals suggested by reactor experiments and by the LSND and MiniBooNE experiments with null results from other searches, we find that, with the new reactor flux prediction, the global fit improves considerably when two sterile neutrinos are introduced.     

Antineutrino energy spectrum unfolding based on the Daya Bay measurement and its applications

The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era.The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by the Day a Bay experiment,in combination with the fission rates of fissile isotopes in the reactor,is used to extract the positron energy spectra resulting from the fission of specific isotopes.This information can be used to produce a precise,data-based prediction of the antineutrino energy spectrum in other reactor antineutrino experiments with different fission fractions than Day a Bay.The positron energy spectra are unfolded to obtain the antineutrino energy spectra by removing the contribution from detector response with the Wiener-SVD unfolding method.Consistent results are obtained with other unfolding methods.A technique to construct a data-based prediction of the reactor antineutrino energy spectrum is proposed and investigated.Given the reactor fission fractions,the technique can predict the energy spectrum to a 2% precision.In addition,we illustrate how to perform a rigorous comparison between the unfolded antineutrino spectrum and a theoretical model prediction that avoids the input model bias of the unfolding method.     

Gemma experiment: The results of neutrino magnetic moment search

The result of the neutrino magnetic moment (NMM) measurement at the Kalinin Nuclear Power Plant (KNPP) with GEMMA spectrometer is presented. The antineutrino-electron scattering is investigated. A high-purity germanium (HPGe) detector with a mass of 1.5 kg placed at a distance of 13.9 m from the 3 GW_th reactor core is exposed to the antineutrino flux of 2.7 × 10¹³ cm^?2s^?1. The recoil electron spectra taken in 18134 and 4487 h for the reactor ON and OFF periods are compared. The upper limit for the NMM μ_ν < 2.9 × 10^?11 μ_B at 90% C.L. is derived from the data processing.     

A minimal Beta Beam with high-<Emphasis Type="Italic">Q</Emphasis> ions to address CP violation in the leptonic sector

In this paper we consider a Beta Beam setup that tries to leverage at most existing European facilities: i.e. a setup that takes advantage of facilities at CERN to boost high-Q ions (⁸Li and ⁸B) aiming at a far detector located at L=732 km in the Gran Sasso Underground Laboratory. The average neutrino energy for ⁸Li and ⁸B ions boosted at γ∼100 is in the range E _ν ∈[1,2] GeV, high enough to use a large iron detector of the MINOS type at the far site. We perform, then, a study of the neutrino and antineutrino fluxes needed to measure a CP-violating phase δ in a significant part of the parameter space. In particular, for θ ₁₃≥3°, if an antineutrino flux of 3×10¹⁹ useful ⁸Li decays per year is achievable, we find that δ can be measured in 60% of the parameter space with 3×10¹⁸ useful ⁸B decays per year.     

Measuring of fissile isotope partial antineutrino spectra in direct experiment at nuclear reactor

The direct measuring method is considered to get nuclear reactor antineutrino spectrum. We suppose to isolate partial spectra of the fissile isotopes by using the method of antineutrino spectrum extraction from the inverse beta-decay reaction positron spectrum applied at Rovno experiment. This admits to increase the accuracy of partial antineutrino spectra forming the total nuclear reactor spectrum. It is important for the analysis of the reactor core fuel composition and could be applied for non-proliferation purposes.     

DANSS Neutrino Spectrometer: Detector Calibration,Response Stability,and Light Yield

Apart from monitoring nuclear reactor parameters, the DANSS neutrino experiment is aimed at searching for sterile neutrinos through a detailed analysis of the ratio of reactor antineutrino spectra measured at different distances from the reactor core. The light collection system of the detector is dual, comprising both the vacuum photomultiplier tubes (PMTs) and silicon photomultipliers (SiPMs). In this paper, the techniques developed to calibrate the responses of these photodetectors are discussed in detail. The long-term stability of the key parameters of the detector and their dependences on the ambient temperature are investigated. The results of detector light yield measurements, performed independently with PMTs and SiPMs are reported.     

Status of the MUNU experiment

We built a low background detector based on a 1 m³ time projection chamber surrounded by an active anti-Compton shielding. The detector has been installed near a nuclear reactor in Bugey for the experimental study of the scattering. A low threshold, around 500 keV, can be set on the electron recoil energy, giving the experiment a sensitivity to the magnetic moment down to 3·10⁻¹¹ Bohr magnetons.     

Upper limit on the solar antineutrino flux according to LSD data

The experimental data obtained on the liquid scintillation detector LSD are analyzed for the purpose of searching for the solar electron antineutrino flux predicted in the model of spin-flavor precession of the neutrino. The currently most accurate upper limit on the solar v̄_e/v _e flux ratio is established: Φ_v̄/Φ_v⩽1.7% (90% confidence range). Pis’ma Zh. éksp. Teor. Fiz. 63, No. 10, 753–757 (25 May 1996) The spelling of the authors names are presented here in English as requested by the Russian Editorial office.     

Inverse-square law violation and reactor antineutrino anomaly

We discuss a possibility that the so-called reactor antineutrino anomaly can be, at least in part, explained by applying a quantum field-theoretical approach to neutrino oscillations, which in particular predicts a small deviation from the classical inverse-square law at short but macroscopic distances between the neutrino source and detector. An extensive statistical analysis of the reactor data is performed to examine this speculation.     

Possibility of hgh Z material detection by a setup for natural cosmic-ray muon flux measurement

A design is proposed and a resolving power is calculated for a detector that monitors the unauthorized transportation of high Z materials (nuclear materials with Z > 90) using the natural cosmic-ray muon flux. The identification of nuclear materials is based on the strong dependence of the multiple scattering angle on the matter charge upon traversing the matter by cosmic muons. It is proposed that chambers assembled from drift aluminum tubes similar to chambers used in the muon system of the ATLAS detector be used as the coordinate detector for the setup. The calculations show that the proposed variant of the setup makes it possible to detect the presence of nuclear materials with a weight of about 0.5–1 kg and higher in the inspected volume in a measurement time of several minutes.     

Monte Carlo simulation of the Neutrino-4 experiment

Monte Carlo simulation of the two-section reactor antineutrino detector of the Neutrino-4 experiment is carried out. The scintillation-type detector is based on the inverse beta-decay reaction. The antineutrino is recorded by two successive signals from the positron and the neutron. The simulation of the detector sections and the active shielding is performed. As a result of the simulation, the distributions of photomultiplier signals from the positron and the neutron are obtained. The efficiency of the detector depending on the signal recording thresholds is calculated.