Angular distributions of neutrino and antineutrino scatterings by electrons and gauge models

Assuming a nonderivative point interaction, and Born approximation, the complete angular distributions for the scatterings of neutrinos and antineutrinos by electrons are obtained from only simple general considerations, without explicit calculation; the simple extension to parton targets is noted. Two pairs of simple constraints on the angular distributions can be violated only if the interaction has a helicity-flipping component; this can serve to disfavour the large class of models which are purely helicity-conserving. Comparison is made with some explicit calculations done for special cases of some of our results.     

Radiative corrections to semileptonic decays of charged hyperons

We have studied the radiative corrections to the lepton energy spectrum in semileptonic hyperon decays. The calculation is performed relativistically for the baryons as well as for the leptons, under the assumption of the effective current-current interaction of the V-?A type for the baryonic part. We obtain the explicit formula of radiative corrections to the lepton energy spectrum which we can exactly evaluate in case of charged hyperon decays. Numerical values of the radiative corrections to the decays rate and the shape of the lepton energy spectrum are also given for some decay modes. It is shown that the spectral shape is little affected by the radiative corrections.     

A symplectic context for level dynamics

We consider a mathematical context which was suggested by quantum mechanical considerations of level dynamics. Although the situation is a general one, we restrict our attention to certain examples of physical relevance where explicit calculations are possible. Cases where M is the cotangent space of some Lie group or Lie algebra Q of operators on a finite-dimensional vector space are of particular interest.     

On some tests of the basic properties of the neutral weak interaction. I. With massless neutrinos

We consider the Born approximation scattering, by electrons, of neutrinos (and antineutrinos) of the muon and of the electron types; the general Lagrangian respecting lepton locality is used. Throughout, we study only differential cross sections as the experimental observables. Some tests previously proposed for “neutrino identity” or Lorentz structure of the neutral weak interaction are reexamined. We find that, in general, these relations cannot uniquely answer the question of Lorentz structure. Similarly, in general, one cannot estblish whether the final neutral lepton is completely identical with, or “partly identical” with, or completely different from, the initial neutrino; identity allows a difference in helicity. In several experimental situations, one can exclude the possibility of a complete non-identity. In one experimental situation, assuming μe universality, one can establish that the final and the initial neutrinos are completely identical, even in their helicity. “Does an interference between neutral currents and the (V ? A) charged current exist in

e^- scattering?” Certain tests can answer this question completely if μe universality is assumed. Without μe universality, the answer is “destructive interference” if an observable (A_e) turns out to be less than 4; A_e = 4 would exclude a constructive interference. Assuming neutrino identity, time-reversal invariance for the helicity flipping types (S,P,T), and μe universality, certain simple combinations of observables were previously noted to determine the (V,A) neutral interaction couplings of the neutrino to the electron. With our general formalism, that determination is seen not to require the first two assumptions. Also, the couplings concerned are seen to be only the “diagonal” ones—which refer to that part of the final state in which the final neutrino is identical with the iniitial one. Keeping in view a recent experimental situation, the following question is answered: “When will the lack of enough events for $\text{ν}\text{e}{}^{\mathrm{?}}$ scattering (or, similarly, νe^? scattering) become a threat to lepton locality?” Some additional consequences of μe universality are noted.     

On neutrino and antineutrino scattering by electrons,and by partons

Assuming a non-derivative point interaction, and Born approximation, there are some simple relations between neutrino and antineutrino scattering on electrons or partons. They have been observed already, for some special cases, in the results of explicit calculations. Here they are obtained from simple general considerations.     

An example of intermittent behavior withn-dependence,from multiplicity distributions over the impact-parameter plane

We exhibit intermittent behavior in multiparticle production from explicit calculations within an idealized model in configuration space. The origin of intermittency with dependence uponn lies in the existence of a multitude of independent multiplicity distributions, of different form, over the impact-parameter plane. We also generalize these considerations to the longitudinal direction, along the collision line.     

Systematic analysis of lepton family number violating processes in the framework of local gauge theories

General unified electroweak gauge theories with neutral lepton mixing are reexamined with regard to processes that change lepton family numbers L_f. The most general allowed mass sectors of models based on SU(2) × U(1) and SU(2)_L × SU(2)_R × U(1) are studied and the consequences for L_f changing processes such as μ → eγ, ν_f′ → ν_f + γ are worked out. We discuss models that break individual lepton family numbers but still conserve total lepton number L, as well as models in which L is broken too.     

Theoretical study of lepton events in the atmospheric neutrino experiments at SuperK

Super-Kamiokande has reported the results for the lepton events in the atmospheric neutrino experiment. These results have been presented for a 22.5kT water fiducial mass on an exposure of 1489 days, and the events are divided into sub-GeV, multi-GeV and PC events. We present a study of nuclear medium effects in the sub-GeV energy region of atmospheric neutrino events for the quasielastic scattering, incoherent and coherent pion production processes, as they give the most dominant contribution to the lepton events in this energy region. We have used the atmospheric neutrino flux given by Honda et al. These calculations have been done in the local density approximation. We take into account the effects of Pauli blocking, Fermi motion, Coulomb effect, renormalization of weak transition strengths in the nuclear medium in the case of the quasielastic reactions. The inelastic reactions leading to production of leptons along with pions is calculated in a $ \Delta$ -dominance model by taking into account the renormalization of $ \Delta$ properties in the nuclear medium and the final-state interaction effects of the outgoing pions with the residual nucleus. We present the results for the lepton events obtained in our model with and without nuclear medium effects, and compare them with the Monte Carlo predictions used in the simulation and the experimentally observed events reported by the Super-Kamiokande Collaboration.     

Proton pick-up from nuclei in the middle of the 1p shell

The (d,³He) reaction has been used to excite proton hole states in⁸Li,⁹Be and¹⁰Be. Angular distributions have been measured and have been analyzed in terms of the DWBA to get spectroscopic factors for the considered transitions. Excitation energies and transition strengths are compared with the results of Cohen and Kurath's intermediate coupling shell model calculations, where the two models of the effective interaction produce different results especially for transitions to final states in mass 8 and 10 nuclei. The experimental results are clearly in favour of the (6–16) 2 BME interaction. A positive parity state in¹⁰Be predicted by the calculations has been looked for and found at 9.60 MeV.     

Massive particles as a probe of the early universe

The survival density of stable massive particles with general annihilation cross section is calculated in a cosmological model that expands anisotropically in its early stages (t<1 s). It is shown that the faster average expansion rate leaves a larger present density of surviving particles that in a model that expands isotropically. This allows particle survival calculations to be employed as a probe of the dynamics of the early universe prior to nucleosynthesis. Several examples of heavy lepton, nucleon and monopole survival are discussed.     

Lepton number violation in softly broken supersymmetry (II)

We study the implications of explicit lepton-number violating soft operators in a general low-energy effective theory with softly broken supersymmetry. Nonzero but relatively small VEVs of scalar neutrinos could exist. In the case where the VEVs of scalar neutrinos vanish, appreciable coefficients of the lepton-number violating soft operators are allowed. We also emphasize the role played by the mixing between the superpartners of the left- and right-handed leptons in the lepton family number violating process μ→eγ.     

Equation of State of Protoneutron Star Matter

We have calculated the equation of state of protoneutron star matter by using the lowest order constrained variational method. In our calculations, the modern Argonne potential (AV₁₈) together with its older model potential (AV₁₄) are used. It is found that the equation of state for high lepton fraction is stiffer than for low lepton fraction. It is seen that the increasing effect of pressure due to high lepton fraction and due to entropy are comparable. It is shown that the temperature and adiabatic index depend on the values of both entropy and lepton fraction.     

Approach to scaling in deep inelastic scattering and lepton pair production

The covariant parton model is used to investigate the approach to scalling in deep inelastic lepton scattering and in lepton pair production by hadron beams. The subasymptotic effects in these two reactions are controlled by rather different features. Of particular importance for lepton pair production is how far the partons are off shell before they annihilate, while for deep inelastic scattering what matters is rather the mass of the parton after it has absorbed the virtual photon. There are uncertainties because of problems with gauge invariance, but it seems that subasymptotic effects in lepton pair production may be large even at SPS/Fermilab energies.Transverse momentum and x distributions of partons in hadrons are discussed in a very simple model. In particular it is found that, while the model is constructed such that F₂(x) ～ (1 ? x)³ as x → 1, for values of x up to 0.85 F₂(x) is better approximated by (1 ? x)⁴.     

Exclusive semileptonic heavy meson decays including lepton mass effects

We discuss the exclusive semi-leptonic (s.l.) bottom meson decaysB→D(D ^*)+l+v where we include non-zero lepton mass effects in the kinematics and dynamics. We develop the general formalism for the non-zero lepton mass case. We then look at how rates, spectra and angular correlations are affected by non-zero lepton masses in the context of a specific spectator quark model. Numerical results are presented for s.l. decays involving thee-, μ- and τ-leptons. We also discuss the s.l. decaysB→π(ρ),D→K(K ^*) and the free quark decay model.     

On the hadron-parton reciprocity relation

The possibility of an equality between the distributions of partons inside hadrons and the distributions of hadrons in parton fragmentation is studied. It is consistent with existing electroproduction data when the momentum fractions involved are not too small. Implications for current-hadron interactions, large p_T hadronic cross sections and heavy lepton pair production in hadron-hadron collisons are discussed.     

Multiple exchanges in lepton pair production in high-energy heavy ion collisions

As an archetype reaction for pQCD multigluon hard processes in collisions of ultrarelativistic nuclei, we analyze generic features of lepton pair production via multiphoton processes in peripheral heavy ion scattering. We report explicit results for collisions of two photons from one nucleus with two photons from the other nucleus, 2γ + 2γ → l⁺l^?. The results suggest that the familiar eikonalization of Coulomb distortions breaks down for oppositely moving Coulomb centers. The breaking of eikonalization in QED suggests that multigluon pQCD processes cannot be described in terms of collective nuclear gluon distributions. We discuss a logarithmic enhancement of the contribution from the 2γ + 2γ → l⁺l^? process to production of lepton pairs with large transverse momentum; similar enhancement is absent for the nγ + mγ → l⁺l^? processes with m, n > 2. We comment on the general structure of multiphoton collisions and properties of higher-order terms that cannot be eikonalized.     

Charged lepton production from iron induced by atmospheric neutrinos

The charged current lepton production induced by neutrinos in ⁵⁶Fe nuclei has been studied. The calculations have been done for the quasielastic as well as the inelastic reactions assuming Δ-dominance and take into account the effect of Pauli blocking, Fermi motion and the renormalization of weak transition strengths in the nuclear medium. The quasielastic production cross-sections for lepton production are found to be strongly reduced due to nuclear effects, while there is about 10% reduction in the inelastic cross-sections in the absence of the final-state interactions of the pions. The numerical results for the momentum and angular distributions of the leptons averaged over the various atmospheric-neutrino spectra at the Soudan and Gran Sasso sites have been presented. The effect of nuclear-model dependence and the atmospheric-flux dependence on the relative yield of μ to e has been studied and discussed.     

A “4π-type” study of the reaction p(d,pp)n at Ed = 26.5 MeV

Experimental data on the three-nucleon reaction p(d, pp)n at E_d = 26.5 MeV obtained with the multidetector system BOL, covering most of the phase space, are presented. The data are compared with Faddeev calculations using a local S-wave potential for the nucleon-nucleon interaction. The calculated cross sections, which are in general not sensitive to the precise choice of the nucleon-nucleon potential, agree well with the data over the major part of phase space. We have, though, discovered a region in phase space with a strong discrepancy. In the same region, around a neutron c.m. angle of 140°, the calculations are sensitive to the N-N potential. Theoretical and experimental angular distributions in the p-n recoil c.m. subsystem for proton- neutron energies below 0.5 MeV agree in absolute magnitude, both being isotropic. For larger relative energies, a discrepancy develops, part of which might be related to missing higher par- tial wave components in the N-N interaction, rather than to Coulomb or S-wave scattering effects. The total breakup cross section has been deduced from the data as 169 ± 36 mb.     

Radiative effects in deep inelastic scattering of polarized leptons by polarized nucleons

Low-order electromagnetic corrections to deep inelastic scattering of polarized leptons by polarized nucleons are derived and investigated using a covariant method. Thorough numerical calculations of the corrections to cross sections and to the measured asymmetry are carried out for μp (ep) scattering in the range of lepton energy E = 200–500 GeV (10–16 GeV). The sensitivity of the corrections to the choice of the structure functions is investigated. The electromagnetic corrections to the asymmetry are found to be less than 10% within the greatest part of the kinematical region, but if x ～ 0, y ～ 1 they can reach a few tens of percent. The lowest order neutral current contribution to the asymmetry is obtained within the framework of standard electroweak interaction theory and the quark parton model. It is found this effect may be significant, especially in the kinematical range where electromagnetic corrections are negligible.     

l i → l jγ decays within a model involving a universal extra dimension

Flavor-changing radiative lepton decays of the l _i → l _jγ type are studied within a model involving a universal extra dimension. Loop amplitudes where intermediate fermions and scalar bosons have commensurate masses may be quite large since the quadratic suppression factor reduces to a linear one in this case. The situation where fermions and scalar bosons have commensurate masses in a loop is realized in a model featuring universal extra dimensions. The contribution of Kaluza—Klein towers to the l _i → l _jγ decay amplitude is explicitly calculated. However, the enhancement expected in the amplitude on the basis of general considerations disappears because of the maximal degeneracy of massive-neutrino tower modes associated with different generations.