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1.
Our collaboration has installed a long baseline neutrino oscillation experiment at the Palo Verde Nuclear Generating Station in Arizona. 12 tons of Gd loaded liquid scintillator, in a segmented detector, are used to search for oscillations at 740 m distance to three reactors. The anti-neutrino capture on the proton serves as detection reaction. The experiment is expected to reach a sensitivity of Δm2 > 1.3 · 10−3 eV2 and sin22Θ > 0.1. Our range of sensitivity is tuned to test the νμ ↔ νe solution of the atmospheric neutrino anomaly.  相似文献   

2.
The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS which provides νμ's, νe's and from the π+−μ+-decay at rest. The oscillation channels νμ → νe and are investigated with a 56 t liquid scintillation calorimeter. No evidence for oscillations could be found with KARMEN, resulting in 90% CL exclusion limits of sin2(2Θ) < 8.5 · 10−3 ( ) and sin2(2Θ) < 4.0 · 10−2μ → νe) for Δm2 > 100 eV2. In 1996, the experiment has been upgraded by an additional veto counting system with a total coverage of 300 m2. The new system allows the identification of cosmic muons in the vicinity of the detector. Vetoing these muons suppresses energetic neutrons from deep inelastic scattering of muons as well as from μ-capture by a factor of 40. Up to 1996, these neutrons represented the main background for oscillation search. The experimental sensitivity for will be significantly enhanced towards sin2(2Θ) 1.0 · 10−3 after a further measuring period of 2–3 years.  相似文献   

3.
Models of neutrino masses are discussed capable of explaining in a natural way the maximal mixing between νμ and ντ observed by the Super-Kamiokande Collaboration. For three generations of leptons two classes of such models are found implying: a) Δm232Δm122≈Δm132 and a small mixing between νe and the other two neutrinos, b) Δm122Δm132≈Δm232 and a nearly maximal mixing for solar neutrino oscillations in vacuum.  相似文献   

4.
The results of the search for ν μ ν e oscillations in the NOMAD experiment at CERN are presented. The experiment looked for the appearance of ν e in a predominantly ν μ wideband neutrino beam at the CERN SPS. No evidence for oscillations was found. The 90% confidence limits obtained are Δm 2<0.4 eV2 for maximal mixing and sin2(2θ)<1.4×10−3 for large Δm 2. This result excludes the LSND allowed region of oscillation parameters with Δm 2≳10 eV2. From Yadernaya Fizika, Vol. 67, No. 11, 2004, pp. 1967–1972. Original English Text Copyright ? 2004 by Popov. This article was submitted by the author in English. The author represents the NOMAD Collaboration  相似文献   

5.
Motivated by recent experimental data, we study solar neutrino oscillations in the range δm2/E ε [10−10, 10−7] eV2/MeV. In this range vacuum oscillations become increasingly affected by (solar and terrestrial) matter effects for increasing δm2, smoothly reaching the MSW regime. A numerical study of matter effects in such “quasi-vacuum” regime is performed. The results are applied to the analysis of the recent solar neutrino phenomenology.  相似文献   

6.
We make a global vacuum neutrino oscillation analysis of solar neutrino data, including the seasonal and energy dependence of the recent Super-Kamiokande 708-day results. The best fit parameters for νe oscillations to an active neutrino are δm2=4.42×10−10 eV2, sin22θ=0.93. The allowed mixing angle region is consistent with bi-maximal mixing of three neutrinos. Oscillations to a sterile neutrino are disfavored. Allowing an enhanced hep neutrino flux does not significantly alter the oscillation parameters.  相似文献   

7.
In the SKAT neutrino bubble chamber experiment at the Serpukhov accelerator we observe 83 events with electrons and no further lepton in the final state. Comparing the ratio of electron to muon charged current events at energies 3<E v <30 GeV with that expected fromv e -beam background assuming lepton universality we find \(R = (N_{e^ - } /N_{\mu ^ - } )_{\exp } /(N_{e^ - } /N_{\mu ^ - } )_{calc} = 0.98 \pm 0.15\) . Furthermore we compare experimental observations and theoretical expectations for some differential distributions of the electron-neutrino charged current reaction. No significant deviation from lepton universality is found. Looking in the charged current reaction for oscillations of muon to electron type neutrinos we find no effect down to the 90% confidence limits Δm 2 =1.3 eV2 at sin22θ=1 and sin22θ=2.5·10?3 at Δm 2=60 eV2.  相似文献   

8.
An updated analysis of the full NOMAD data corresponding to 1.35 × 106 charged current interactions has been performed to search for neutrino oscillations through ντ appearance. This document updates the recently published results on the νμ → ντ and νμ → νe oscillations search in NOMAD [1] with a unified analysis of the hadronic channels.  相似文献   

9.
We present here the final results of experiments searching for neutrino oscillations, carried out by the CHARM Collaboration. The data — taking took place in 1983. The first experiment was performed by exposing two detectors simultaneously to the CERN PS low energyv µ beam. In the second experiment the full CHARM detector was exposed to the wide-band horn-focusedv µ beam of the CERN SPS. Complete details of the experiments and data reduction are presented. No statistically significant signals for neutrino oscillations were observed. Our 90% CL limits in the appearance experiment (v µv e ) exclude Δm 2≧0.19 eV2 for complete mixing (sin22θ=1), and sin22θ≧0.008 for the region Δm 2≧30 eV2. These results, and the limits observed for (v µv x ) (disappearance of (v µ), are in agreement with those of most other experiments but exclude part of the region previously reported as a possible indication ofv µv e oscillations.  相似文献   

10.
Possible solar neutrino oscillations are reviewed in the two-neutrino case taking into account the effect of coherent forward scattering when neutrinos travel through the sun and earth. As recently pointed out by Mikheyev and Smirnov this effect can induce a large suppression of the solar νe flux for values of Δm 2 around 10?4–10?8 eV2 even for small values of the mixing angle. It also may cause substantial modifications of the solar neutrino spectrum shape. All this may be used for determining Δm 2 and sin2 2θ in a large domain from the experimental results of the chlorine, gallium, indium and heavy water detectors.  相似文献   

11.
We consider the status of the Kr2Det project aimed at sensitive searches for neutrino oscillations in the atmospheric neutrino mass parameter region around Δm2 ~ 3×10?3 eV2 and at obtaining new information on the electron neutrino mass structure (Ue3).  相似文献   

12.
The project of a large underground experiment, NOE (Neutrino Oscillation Experiment), composed by modules of scintillating fiber calorimeter interleaved with TRD modules, total weight 6.7 ktons, is presented. This apparatus has been optimized for long baseline neutrino oscillation studies, in particular to be sensitive in the region of sin2 2θ and Δm2 suggested by the atmospheric neutrino anomaly (fig. 3).  相似文献   

13.
The NOMAD experiment has sought νμ ? ντ oscillations by looking for the emergence of τ? in events from the CERN SPS neutrino beam. With some improvements in the techniques of analysis in relation to the results published previously and with the inclusion of data from the 1998 run, no evidence for the oscillations has been found, which results in an updated limit on the oscillation probability [Pμ → ντ) < 0.5 × 10?3 at a 90% C.L.]. The corresponding limit on the oscillation mixing angle is given by sin2μτ < 1.0 × 10?3 for large Δm 2. By using a 1% contamination of νe in the neutrino beam, we can also rule out ν e ? ντ oscillations and constrain the probability of the relevant transition as P e → ντ) < 3 × 10?2 at a 90% C.L. (sin2 eτ < 6 × 10?2 at large Δm 2).  相似文献   

14.
Expected sensitivity of future atmospheric neutrino data from Super-Kamiokande on neutrino oscillation physics is discussed. We expect that the accuracy of the sin 2θ23 measurement will be improved with (exposure time) . By analyzing high energy fully contained events, it could be possible to statistically demonstrate the existence of charged current ντ interactions at the 3 standard deviation level with a few more years of data. Subdominant νμ → νe oscillations could be observed if θ13 is near the present limit. However, significantly more data will be required to observe a 3 standard deviation effect.  相似文献   

15.
《Physics letters. [Part B]》1988,206(4):711-714
We present an analysis, in terms of neutrino oscillations, of the recent measurements of the ratio R of neutral-current to charged-current neutrino cross sections performed by the CDHS and CHARM Collaborations at the CERN Super Proton Synchroton narrow-band beam. The measurementswere aimed at the determination of sin2 θw. Our analysis is based on the observation that muon-neutrino oscillations would decrease the number of interactions with a muon in the final state. The effect of oscillations on R can be studied, comparing the actual measurements with the value of R predicted by an independent measurement of sin2 θw. Limits on νμνe, νμντ, and νμνx oscillations are presented. They refer to a region of high mass squared difference of the two oscillating neutrinos (Δm2 > 3 eV2). For high Δm2 the limits on the mixing angle θ are very restrictive. In particular, for the transition νμνx (x≠e, τ) they represent the best available results for large intervals in Δm2.  相似文献   

16.
A search for νμ → νe oscillations has been conducted at the Los Alamos Meson Physics Facility (LAMPF) using νμ from π+ decay in flight. An excess in the number of beam-related events from the νe Ce X inclusive reaction is observed. The excess is too large to be explained by normal νe contamination in the beam at a confidence level greater than 99%. If interpreted as an oscillation signal, the observed oscillation probability of (2.6 ± 1.3 ± 0.5) × 10−3 is consistent with the previously reported oscillation evidence from LSND.  相似文献   

17.
If neutrinos have non-vanishing mass and non-vanishing magnetic moments, then electron neutrinos emitted in nuclear reactions in the solar interior may undergo flavour oscillations, spin precession or resonant spin-flavour precession. Assuming equal values for the magnetic moments of all neutrino flavours and using the data from Homestake and SuperKamiokande we obtain an upper limit on the neutrino magnetic moment and find μνe ≤ (2.2 − 2.3) × 10−10μB, within four standard solar models. We also point out that this limit may be further reduced if the detector threshold energy for the νee scattering is decreased.  相似文献   

18.
The CHORUS experiment is designed to search for νμ → ντ oscillation with a hybrid detector system containing 800 kg nuclear emulsions as target and vertex detector. Run I (320 000 recorded νμCC in 1994/5) and more than half of the run II (460 000 νμCC in 1996/7) data taking have been successfully completed. Approximately 80 000 events have been analyzed so far, searching for and τh (nπ0) ντ decays. No candidate has been found, leading to a limit sin2μτ ≤ 4.5 10−3 for large Δm2.  相似文献   

19.
We calculate with Monte Carlo the goodness of fit and the confidence level of the standard allowed regions for the neutrino oscillation parameters obtained from the fit of the total rates measured in solar neutrino experiments. We show that they are significantly overestimated in the standard method. We also calculate exact allowed regions with correct frequentist coverage. We show that the exact VO, LMA and LOW regions are much larger than the standard ones and merge together giving an allowed band at large mixing angles for all Δm2 10−10 eV2.  相似文献   

20.
For the purpose of deriving the observed nearly tribimaximal neutrino mixing, a possible yukawaon model in the quark sector is investigated. Five observable quantities (2 up-quark mass ratios and 3 neutrino mixing parameters sin22θatm, tan2θsolar and |U13|) are excellently fitted by two parameters (one in the up-quark sector and another one in the right-handed Majorana neutrino sector).  相似文献   

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