The self-coupling of weak lepton currents in high energy neutrino and muon reactions

The transverse momentum distribution of the muons in the reaction $\text{ν + (z) → ν + μ +}\text{μ}\text{+ (z)}$ is discussed. The lower end of the energy spectrum of the muons in the previous study is also modified by using an improved interpolation formula.     

Neutral pion production by weak neutral currents in neutrino and antineutrino reactions

A study is presented of single π^o production in neutrino and antineutrino interactions in Gargamelle filled with freon CF₃Br. Limits on the neutral to charged current cross-section ratios $\text{R}{}_{\mathrm{v}}\text{=σ(v}\text{N}\text{→v}\text{N}\text{′π}{}^{\mathrm{o}}\text{)/2 σ(v}\text{N}\text{→ μ}{}^{\mathrm{-}}\text{N}\text{′π}{}^{\mathrm{o}}\text{)}$ and $\text{R}{}_{\mathrm{<mtext>\nu </mtext>}}\text{= σ(}\text{ν}\text{N}\text{→}\text{ν}\text{N}\text{′π}{}^{\mathrm{o}}\text{)/2 σ(}\text{ν}\text{N}\text{→ ω}{}^{\mathrm{+}}\text{N}\text{′π}{}^{\mathrm{o}}\text{)}$ are found to be $\text{0.10 < R}{}_{\mathrm{\nu }}\text{< 0.20}\text{and}\text{0.26 < R}{}_{\mathrm{<mtext>\nu </mtext>}}\text{< 0.44}$ at 68% confidence level.     

Right-handed weak currents in neutrino scattering

We investigate transition strengths of right-handed weak charged currents in deep inelastic neutrino scattering, exploiting the dominance of p, n valence quarks in the nucleon. The energy dependence of σ_t and the average quantities 〈y〉 and 〈Q²〉 are shown to provide sensitive measures of new quark production thresholds and right-handed currents in $\text{ν}\text{N}$ scattering. With our analysis, the present data give an upper bound on the right to left hand structure function ratio of $\text{F}{}_{\mathrm{<mtext>R</mtext>}}{}^{\mathrm{<mtext>\nu </mtext><mtext>N</mtext>}}\text{F}{}_{\mathrm{<mtext>L</mtext>}}{}^{\mathrm{<mtext>\nu </mtext><mtext>N</mtext>}}\text{≈}\text{1}\text{2}$, above a threshold of W≈7.5 GeV.     

Trimoun production in neutrino and muon interactions from structure at the lepton vertex

The direct production of three charged leptons by an incident high-energy neutrino can arise from approximately local structure effects at the lepton vertex, and be accompanied by limited energy-momentum transfer to the target nucleon. We estimate the relative rate in a simple model which illustrates this class of mechanisms, and then enumerate several unambiguous experimental tests, such as the absence of neutrinos in the final state, which distinguish this mechanism from those involving the production and weak decay of real new particles.     

Spin-dependent sum rule for high-energy neutrino reactions

We present a sum rule which related the inclusive cross section for high-energy neutrino scattering on polarized proton targets to the axial-vector coupling constant. The derivation of the sum rule rests on the equal-time algebra of the time-components of the weak currents. The sum rule also provides a discriminatory test of unified models of weak and electromagnetic interactions based on spontaneously-broken gauge symmetry.     

Charged lepton and neutrino oscillations

Problems long present in the conventional formalism employed for neutrino oscillations are discussed. We here develop a more satisfactory framework based on the Dirac equation and its propagators. When 4-momentum conservation is strictly enforced, there will be induced oscillations in space (but not between generations) for the charged leptons, e.g. and , produced in association with the neutrinos. The oscillations are computed explicitly for the pion decay . Leptonic decays of the are also briefly discussed. Received: 15 October 1996 / Revised version: 15 June 1997 / Published online: 20 February 1998     

Aspects of the two-component and four-component neutrino theories in connection with weak lepton and semilepton processes

A comparison is made of the results found in the application of two-component and four-component theories of the two neutrinos to weak lepton processes (muon decay) and semilepton processes. The predictions of the two theories clearly differ in the V-A version of the coupling of electron and muon currents and of muon and baryon currents. In contrast with the theory of two-component neutrinos (the V-A interaction), four-component theory predicts that a V + A interaction of electron and muon currents is responsible for muon decay.     

Vectorlike weak currents,massive neutrinos,and neutrino beam oscillations

If the weak currents are vectorlike, the neutrinos will not be massless, and there will exist weak mixing angles for leptons, analogous to the Cabibbo angle for hadrons. Neutrino beams will oscillate in a similar way as K_o-beams. The failure to observe a solar neutrino flux at the theoretically predicted rate can be interpreted as the consequence of these oscillations.     

Inclusive muon production reactions as a test of neutral currents

With right and left handed polarized muons scattering on an unpolarized target we discuss possible asymmetries of inclusive cross sections induced by neutral weak currents. Using general positivity arguments we derive rigorous upper bounds to the asymmetries. Numerical estimates of the bounds are already possible if use is made of the branching ratios NC/CC)_ν, $\text{v}$ observed in the CERN Gargamelle bubble chamber. Upper and lower bounds to the asymmetries, specific to the Weinberg-Salam model, are also discussed.     

Testing the structure of weak neutral currents by inelastic neutrino scattering from nuclei

By using selected nuclear transitions specific pieces of the weak neutral current may be greatly enhanced, leading to widely different results for different models of the weak neutral current. Predictions for low-energy inelastic neutrino scattering from ¹²C are examined within the framework of a variety of SU(2)_W × U(1) gauge theory models.     

The potential for neutrino physics at muon colliders and dedicated high current muon storage rings

Conceptual design studies are underway for muon colliders and other high-current muon storage rings that have the potential to become the first true “neutrino factories”. Muon decays in long straight sections of the storage rings would produce precisely characterized beams of electron and muon type neutrinos of unprecedented intensity. This article reviews the prospects for these facilities to greatly extend our capabilities for neutrino experiments, largely emphasizing the physics of neutrino interactions.     

On non-unitary lepton mixing and neutrino mass observables

There are three observables related to neutrino mass, namely the kinematic mass in direct searches, the effective mass in neutrino-less double beta decay, and the sum of neutrino masses in cosmology. In the limit of exactly degenerate neutrinos there are very simple relations between those observables, and we calculate corrections due to non-zero mass splitting. We discuss how the possible non-unitarity of the lepton mixing matrix may modify these relations and find in particular that corrections due to non-unitarity can exceed the corrections due to mass splitting. We furthermore investigate constraints from neutrino-less double beta decay on mass and mixing parameters of heavy neutrinos in the type I see-saw mechanism. There are constraints from assuming that heavy neutrinos are exchanged, and constraints from assuming light neutrino exchange, which arise from an exact see-saw relation. The latter has its origin in the unitarity violation arising in see-saw scenarios. We illustrate that the limits from the latter approach are much stronger. The drastic impact of the new limit on inverse neutrino-less double beta decay (e⁻e⁻→W⁻W⁻)$(e^{-}{e}^{-}\to W^{-}{W}^{-})$ is studied. We furthermore discuss neutrino mixing in case there is one or more light sterile neutrinos. Neutrino oscillation probabilities for long baseline neutrino oscillation experiments are considered, and the analogy to general non-unitarity phenomenology, such as zero-distance effects, is pointed out.     

Experimental limits on the strength of weak neutral currents in lepton pair production at PETRA energies

The processes e⁺e^? → e⁺e^? and μ⁺μ^? have been studied at PETRA using the JADE detector. The data, which were collected at s-values of up to 1300 GeV² have been analysed in terms of an electro-weak extension of QED to obtain values for the weak vector and axial vector couplings in the lepton sector. The values obtained agree with the predictions of the standard Salam-Weinberg model and the data are further analysed in terms of this model to obtain the limits 0.10 < sin²?_w < 0.40 (68% CL). The mass of the neutral weak gauge boson is deduced to be greater than 51 GeV/c².     

Theoretical aspects of neutrino mass and lepton flavour violation

We consider lepton flavour violation (LFV) in the charged lepton sector both from the bottom-up effective Lagrangian approach and from the top-down approach via various case studies that have been analysed. The implications for LFV studies at the LHC is briefly discussed. Finally the nature of LFV in the neutrino sector is considered, paying particular regard to the implications of the recent measurements of ?? ₁₃.     

Running of neutrino parameters and the Higgs self-coupling in a six-dimensional UED model

We investigate a six-dimensional universal extra-dimensional model in the extension of an effective neutrino mass operator. We derive the β  -functions and renormalization group equations for the Yukawa couplings, the Higgs self-coupling, and the effective neutrino mass operator in this model. Especially, we focus on the renormalization group running of physical parameters such as the Higgs self-coupling and the leptonic mixing angles. The recent measurements of the Higgs boson mass by the ATLAS and CMS Collaborations at the LHC as well as the current three-flavor global fits of neutrino oscillation data have been taken into account. We set a bound on the six-dimensional model, using the vacuum stability criterion, that allows five Kaluza–Klein modes only, which leads to a strong limit on the cutoff scale. Furthermore, we find that the leptonic mixing angle _θ12${\theta }_{12}$ shows the most sizeable running, and that the running of the angles _θ13${\theta }_{13}$ and _θ23${\theta }_{23}$ are negligible. Finally, it turns out that the findings in this six-dimensional model are comparable with what is achieved in the corresponding five-dimensional model, but the cutoff scale is significantly smaller, which means that it could be detectable in a closer future.     

Nonconservation of muon number in a model of lepton structure

We speculate on a possible primary structure for leptons similar to the quark structure for hadrons, and thus propose a new possible approach to the study of these particles. A suppression mechanism is provided for the effects of the new interaction upon the muon anomalous magnetic moment and in the decay amplitude for μ → eγ.     

The extraterrestrial neutrino flux sensitivity of underground and undersea muon detectors

Summary The sensitivity of underground and undersea muon detectors to point sources of extraterrestrial neutrinos with power law spectra is calculated from very general considerations. It is shown that this sensitivity depends critically on the spectral slope, but is essentially independent of the muon energy threshold of the instrument out to 100 GeV. Sources with a neutrino flux comparable to the γ-ray flux from Cygnus X-3 would not be detectable underground, and are only marginally detectable by the proposed large undersea experiment, DUMAND. However, fluxes perhaps 100 times higher are possible and these would be marginally detectable underground with MACRO or in the proposed DUMAND Stage II detector, the TRIAD.

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Riassunto Si calcola la sensibilità dei rivelatori muonici sotto terra e sott'acqua a sorgenti puntiformi di neutrini extraterrestri con spettri a legge di potenza partendo da considerazioni molto generali. Si mostra che questa sensibilità dipende in modo critico dalla pendenza dello spettro ma è sostanzialmente indipendente dalla soglia d'energia muonica dello strumento fino a 100 GeV. Sorgenti con un flusso di neutrini confrontabili con il flusso di raggi γ da Cygnus X-3 non sarebbero individuabili sottoterra e sono solo marginalmente rilevabili con il grande esperimento sott'acqua DUMAND proposto. Comunque flussi forse 100 volte maggiori sono possibili e questi sarebbero marginalmente rilevabili sottoterra con MACRO o nel rivelatore proposto DUMAND del secondo stadio, il TRIAD.

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Резюме Из очень общих рассуждений вычисляется чувствительность подземных и подводных мюонных детекторов к точечным источникам внеземных нейтрино со степенными спектрами. Показываэтся, что эта чувствительность очень сильно зависит от наклода спектра, но по существу не зависит от мюонного энергетического порога прибора вне 100 ГэВ. Источники с нейтринным потоком, сравнимым с потоком ч-лучей от Лебедь X-3, не могут быть зарегистрированы подземными детекторами и не являются маргинально детектируемыми с помощью предложенного крупного подводного эксперимента ДОМАНД. Однако потоки, в 100 раз большие, оказываются возможными и могли бы быть маргинально зарегистрированы подземными детекторами, тогда как в эксперименте ДОМАНД они производят слишком большпй сигнал.

     

Diquark breakup in high-energy neutrino interactions

We examine the experimental tests and theoretical predictions for diquark breakup in high-energy neutrino interactions. Most tests of diquark breakup are found to be inconclusive and the only compelling evidence comes from lambda production in νp interactions.