Neutrino production of M+ and E+ heavy leptons (II)

A theoretical analysis is made of possible experimental searches for the production of M⁺ heavy leptons in inclusive neutrino reactions by detection of their decay into μ⁺. Distributions of observable energy E_obs (sum of hadron and muon energies) and of the apparent y variable y_obs(y_obs=E_had/E_obs) are presented. These distributions are used to discuss the problem of distinguishing M⁺ production from effects of antineutrino admixtures in a neutrino beam.     

On the production of a lepton pair in the collision of ultrarelativistic neutral particle with nonzero magnetic moment with nuclei

Explicit formulas which describe muon pair production in reaction γν→μ⁺μ⁻ν through neutrino magnetic moment are obtained and used to derive in the leading approximation cross section of muon pair production in νN-scattering due to neutrino magnetic moment. This cross section appears to be proportional to log⁴E_ν. Comparison with experimental data on tridents production provides an upper bound μ_νμ<4×10⁻⁸μ_B, which is approximately two orders of magnitude weaker than that from ν_μe elastic scattering data.     

A search for decays of heavy neutrinos in the mass range 0.5–2.8 GeV

A search for decays of heavy neutrinos was conducted by the CHARM Collaboration in a prompt neutrino beam produced by dumping 400 GeV protons in a Cu target, and in the CERN wide-band neutrino beam produced by 400 GeV primary protons. No candidate event was found. In the beam-dump experiment heavy neutrinos have been assumed to be produced by mixing in charmed D meson decays. Neutrinos decaying into e⁺e⁻v_e, μ⁺e⁻v_μ, and μ⁺μ⁻v_μ were searched for. Limits of |U_ei|², |U_μi|² < 10⁻⁷ were obtained for neutrino masses around 1.5 GeV. In the wide-band experiment heavy neutrinos were assumed to be produced by neutral-current neutrino interactions in the CHARM calorimeter. Here a search was made for neutrinos decaying into a μ and hadrons. This experiment is sensitive to decays of neutrinos with mass in the range 0.5–2.8 GeV with limits of |U_μi|² < 3 × 10⁻⁴ for masses around 2.5 GeV. These measurements extend our previous results in the mass range 10–400 MeV.     

中微子振荡实验——超出标准模型的实验检验（Ⅰ）

文章总结了中微子振荡实验在历史和现状,介绍了几个太阳中微子丢失实验的结果和几个大气μ中微子丢失实验结果,这些结果表明存在中微子振荡,即中微子具有质量,它是超出标准模型的信号,文章还介绍了21世纪初研究中微子振荡和若干重要实验,噬基线中微子振荡实验以及建造μ子贮存环来产生高能电子中微子束进行中微子振荡的实验以及测量中微子振荡时的CP破坏的设想。     

Precision measurement of the muon momentum in pion decay at rest

A new series of precision measurements of the muon momentum p_μ⁺ in the decay π→μ⁺v_μ at rest have been made using a magnetic spectrometer. The result is p_μ⁺=(29.79139 ± 0.00083) MeV/c. The consequences of this value for the rest masses of the muon neutrino and of the charged pion are discussed.     

Are there “prompt” like-sign dimuons?

From exposures of the CDHS detector at the CERN SPS we have obtained 367μ ⁺ μ ^? events in neutrino beams and 73μ ⁺ μ ⁺ events in an antineutrino beam. The magnitude of a prompt like-sign signal has been controversial in the past and moreover could not be explained by known production mechanisms. A critical discussion of the experimental situation is given. We have tried to reduce the systematic uncertainties of previous experiments and to get more information on the dependence of the signal with energy and the muon momentum cut-off. This experiment yields a signal of 2.8σ (2.4σ) of prompt like-sign dimuon events in the case of neutrinos (antineutrinos). The rate to charged current events is of the order of 10^?4 forp _μ<9GeV andE>100 GeV. The prompt signal has all the properties expected from the production and decay of charm-anticharm events. The magnitude, however, is substantially higher then the prediction of perturbative QCD but lower than some other experiments.     

New determination of the upper limit for the muon neutrino mass

We have measured the muon momentum in pion decay at rest using a magnetic spectrometer. From the result, p_μ⁺ = (29.787±0.005) MeV/c, we deduce a squared muon neutrino mass of (0.23±0.54) MeV²/c⁴.     

Limits on neutrino oscillations derived from the ratio of neutral- to charged-current cross sections of neutrinos measured at the CERN SPS NBB

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 θ_w. 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 θ_w. Limits on ν_μ−ν_e, ν_μ−ν_τ, and ν_μ−ν_x 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 ν_μ−ν_x (x≠e, τ) they represent the best available results for large intervals in Δm².     

Lepton mixing under the lepton charge nonconservation, neutrino masses and oscillations and the “forbidden” decay µ− → e − + γ

The lepton-charge (L _e , L _μ , L _τ ) nonconserving interaction leads to the mixing of the electron, muon, and tau neutrinos, which manifests itself in spatial oscillations of a neutrino beam, and also to the mixing of the electron, negative muon, and tau lepton, which, in particular, may be the cause of the “forbidden” radiative decay of the negative muon into the electron and γ quantum. Under the assumption that the nondiagonal elements of the mass matrices for neutrinos and ordinary leptons, connected with the lepton charge nonconservation, are the same, and by performing the joint analysis of the experimental data on neutrino oscillations and experimental restriction for the probability of the decay µ^? → e ^? + γ per unit time, the following estimate for the lower bound of neutrino mass has been obtained: m ^(ν) > 1.5 eV/c ².     

中微子质量和中微子振荡实验

本介绍中微子质量测量的历史和现状。介绍太阳中微子丢失实验的结果和大气μ中微子丢失实验结果。这些结果表明存在中微子振荡,即中微子具有质量。它是超出标准模型的信号。本还介绍了21世纪初研究中微子振荡的若干重要实验,例如长基线中微子振荡实验以及建造μ子 贮存环来产生高能电子中微子束进行中微子振荡的实验以及测量中微子振荡时的CP破坏的设想。     

Precision measurement of neutrino oscillation parameters at INO-ICAL detector

A magnetized Iron CALorimeter (ICAL) detector at the India-based neutrino observatory (INO) is used to study neutrino oscillation sensitivity using atmospheric muon neutrino source. The ICAL detector will be able to detect muon tracks and hadron showers produced by neutrino interactions with the iron target. We have performed precision measurement analysis for the atmospheric neutrino oscillation parameters with the muon neutrino events, generated by Monte Carlo NUANCE event generator. A marginalized χ² analysis based on reconstructed neutrino energy and muon zenith angle binning scheme has been performed to determine the sensitivity for the atmospheric neutrino mixing parameters, \(\sin ^{2}\theta _{23}\) and \(| {\Delta } m^{2}_{23}|\).     

Seasonal and energy dependence of solar neutrino vacuum oscillations

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 ν_e 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.     

Present status of the opera experiment for the direct observation of neutrino oscillations in the νμ → ν τ channel

The OPERA experiment (Oscillation Project with an Emulsion-Tracking Apparatus) for the direct observation of neutrino oscillations in the ν_μ → ν _τ channel has been underway at the underground laboratory in Gran Sasso since 2007. In the course of data collection, more than 3000 ν_μ interactions have been registered in emulsion detectors. Twenty charmed neutrino interaction candidates have been found. Multidimensional criteria have been developed in order to select ν _τ interactions against νμ interactions accompanied by charmed hadron production. The first results from automated PAVIKOM emulsion scanning have been obtained. We discuss the measurements of the muon charge ratio of μ⁺ to μ^?.     

Lower limit for heavy muon mass obtained from the data of the CERN neutrino experiment

A lower limit for the heavy muon (heavy lepton omega′^? which can have the same lepton number as omega^? and ν_omega) mass M_μ′ > 1.8 GeV at 90% confidence level is obtained with the help of the bubble chamber “Gargamelle” data in the CERN neutrino experiment. This limit should not be confused with the known limit for an M⁺ (heavy lepton M⁺ which can have the same lepton number as μ^? and ν_μ).     

Neutrino mass spectrum with vμ → vs oscillations of atmospheric neutrinos

We consider the “standard” spectrum of the active neutrinos (characterized by strong mass hierarchy and small mixing) with additional sterile neutrino, v_s. The sterile neutrino mixes strongly with the muon neutrino, so that v_μ ↔ v_s oscillations solve the atmospheric neutrino problem. We show that the parametric enhancement of the v_μ ↔ v_s oscillations occurs for the high energy atmospheric neutrinos which cross the core of the Earth. This can be relevant for the anomaly observed by the MACRO experiment. Solar neutrinos are converted both to v_μand v_s. The heaviest neutrino (≈ v_τ) may compose the hot dark matter of the Universe. The phenomenology of this scenario is elaborated and crucial experimental signatures are identified. We also discuss properties of the underlying neutrino mass matrix. 1998 Published by Elsevier Science B.V.     

Search for the radiative capture reaction d+d → 4He+γ from the ddμ muonic molecule state

A search for the muon-catalyzed fusion (MCF) reaction d+d → ⁴He+γ in the ddμ muonic molecule was performed using the experimental MCF installation TRITON and NaI(Tl) detectors for γ quanta. A high-pressure target filled with deuterium was exposed to the negative muon beam of the JINR phasotron to detect γ quanta with an energy of 23.8 MeV. The first experimental estimation for the yield of radiative deuteron capture from the ddμ state J=1 was obtained at a level of η_γ≤2×10^?5 per one fusion.     

高能νN“弹性”反应的中间玻色子效应

利用中间玻色子理论和Cabibbo的弱相互作用SU₃模型,求得了中微子-核子“弹性”反应ν₁+N→l+B的微分截面和终态粒子纵极化的解析表式,并对若干过程进行了数值计算。结果表明:对给定的一组形状因子,当中微子能量足够高时,在适当的出射角附近,轻子和超子的纵极化的中间玻色子效应相当明显;如实验数据足够精确,将极化与微分截面相结合。可估计中间玻色子质量,并给出形状因子的一些知识。还估计了ν_μ[Z,A]→μ^-+[Z+1,A]过程的μ^-纵极化的核效应和中微子能谱的影响。     

Results from the T2K experiment

The T2K (Tokai-to-Kamioka) experiment is a long baseline neutrino oscillation experiment designed to probe the θ ₁₃ neutrino mixing parameter by looking for the appearance of ν _e in an almost pure ν _μ beam. The concurrent measurement of the ν _μ disappearance allows refined measurements of the atmospheric Δm ² and θ ₂₃ mixing parameters.     

Measurement of the average polarization of12B in the polarized-muon capture by12C: Magnitude of the induced pseudoscalar form factor

The average polarization of the nucleus¹²B (bound state) produced in the polarized-muon capture reaction¹²C(μ ^?,v _μ )¹²B was measured by the muon spin resonance method in a pulsed muon beam. The polarization of¹²B was maintained completely under a magnetic field of 3 kG in a Grafoil target. After the observed result was corrected for the contribution from the excited states of¹²B, P_av (ground state) was deduced to be 0.462±0.053. This result yieldsg _P /g _A =10.1 _?2.6 ^+2.4 , which is almost consistent with the PCAC prediction.