Gluon bremsstrahlung production of heavy particles in neutrino and antineutrino scattering

Weak charged current production of charmed quark pairs is studied in the framework of the QCD inspired parton model. The magnitude of the cross section strongly depends on the charmed quark pair production threshold, above which the gluons are assumed to decay into either charmed particle pairs of hidden charmonium states. The normalized distributions are rather insensitive to the choice of this threshold value and the angular distribution of J/gy particles will show significant azimuthal asymmetry about the current-target axis. The sign of the asymmetry cannot be mimicked by the parton primordial transverse momentum effects and thus the process can serve a clean test of the gluon bremsstrahlung mechanism.     

A study of strange particles produced in neutrino neutral current interactions in the NOMAD experiment

Results of a detailed study of strange particle production in neutrino neutral current interactions are presented using the data from the NOMAD experiment. Integral yields of neutral strange particles (, Λ, ) have been measured. Decays of resonances and heavy hyperons with an identified or Λ in the final state have been analyzed. Clear signals corresponding to and Σ(1385)^± have been observed. First results on the measurements of the Λ polarization in neutral current interactions have been obtained.     

Investigation of the decay of charmed particles produced in neutrino interactions

The decay of charmed particles produced by high-energy neutrinos has been studied by an experiment using simultaneously emulsion, bubble chamber and counter techniques. Eight charmed particle candidates, 5 positively charged and 3 neutral, have been found in the emulsion, where their production and decay have been directly observed. One of these events is identified as a Λ_c⁺ baryon of mass 2.26±0.02 GeV/c² which undergoes the decay Λ_c⁺→pK^?π⁺ after a proper time of (7.3±0.1) · 10^?13 s.A statistical analysis of the other observed decays leads to the mean-life values τ⁺=(2.5_?1.1^+2.2) · 10^?13 s, τ⁰=(0.53_?0.25^+0.57) · 10^?13 s, for the sample of charged particles enriched by a similar event found in a previous experiment, and for the sample of 3 neutral particles, respectively. The former value is only slightly affected by including in the sample the Λ_c⁺ event or excluding that of the previous experiment.     

Asymmetries in heavy fermion production and decay

We calculate the forward-backward asymmetries of heavy fermions and of leptons from their semileptonic decay in e⁺e⁻ annihilation. In particular we study the corrections to the lowest-order prediction resulting from intial-state radiation, kinematic effects in heavy quark decay and the role of quark polarization.     

Prompt neutrino production in a proton beam-dump experiment

In the interactions of 400 GeV/c protons with copper nuclei, a flux of prompt neutrinos is observed. The reactions produced by these neutrinos in our apparatus appear consistent with those of electron- and muon-neutrinos. The prompt neutrino fluxes are interpreted as being due to associated production and subsequent semileptonic decay of charmed hadrons. The prompt flux ratio \(\bar v_\mu /v_\mu = 0.46_{ - 0.16}^{ + 0.21} \) suggests a sizeable production of charmed baryons near the forward direction. The ratio of prompte ^?+e ⁺ toµ ^?+µ ⁺ event rates is 0.64 _?0.15 ^+0.22 , where unity is expected frome-μ universality.     

HARP: a hadron production experiment for the neutrino factory and for the atmospheric neutrino flux

The HARP experiment will carry out, at the CERN PS, a large programme of measurements of secondary hadron production, over the full solid angle, produced on thin and thick nuclear targets by beams of protons and pions with momenta in the range 2 to 15 GeV/c. The first aim of the experiment is to acquire adequate knowledge of pion yields for an optimal design of the recently proposed neutrino factory. The second aim is to reduce substantially the existing 30% uncertainty in the calculation of absolute atmospheric neutrino fluxes and the 7% uncertainty in the ratio of neutrino flavours.     

On the possible production and detection of coherent low-energy neutrino beams

Seminal experiments are discussed to prove or disprove the possibility of producing and detecting collimated coherent beams of low-energy neutrinos with the assistance of lasers. Expressions are given for the relative probability that a laser-beam-aligned co- or counter-propagating neutrino-antineutrino pair is emitted instead of a laser photon, during stimulated de-excitations of lasable excited states inside a lasing medium. For a neodymium laser this probability is approximately 10^?7. To detect coherent beams of epithermal neutrinos and antineutrinos emitted from a pulsed high-power laser, it is anticipated that resonant non-absorptive stimulated de-excitations of lasing levels by neutrinos can be exploited to register their fly-through in a second near-threshold laser.     

On the possible presence of neutral antileptons of all generations in the solar neutrino flux

The hypothesis that part of solar electron neutrino flux transforms into antineutrinos of the second and third generations and related antiparticles is considered. Complete electroweak spectra of recoil electrons, including impurity components, are obtained and analyzed for the scattering of beryllium monoenergetic solar neutrinos with energies of 0.862 MeV on an electron target.     

Strange particle production and charmed particle search in the gargamelle neutrino experiment

Data is given for single and multiple strange particle production in neutrino reactions in both charged and neutral current channels. A total of 15000 neutrino and antineutrino events has been examined for possible evidence of semi-leptonic decay of a charmed particle. One candidate has been observed. Upper limits on charmed particle production cross-sections are given as a function of the neutrino energy and the invariant mass of the final state hadrons.     

Quark model and production of neutral strange secondaries in neutrino and antineutrino beams

Experimental data on K ⁰ and Λ roduction in ν and $\bar \nu $ beams are compared with the predictions of a quark model assuming that the direct production of secondaries dominates. Disagreement of these predictions with the data suggests that there exists a considerable resonance-decay contribution to the multiplicities of product particles.     

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.