A study of quasielastic neutrino interactions ν μ n → μ− p in the NOMAD experiment

In this note, we present preliminary results on the study of the quasielastic reaction ν _μ n → μ⁻ p using the full set of NOMAD neutrino data. We perform a measurement of the total cross section of this process, normalizing to deep-inelastic scattering events selected from the same data sample. The measured cross section is found to be about 20% smaller than the world average of previous bubble chamber experiments. The analysis is still in progress since it is important to estimate the systematic uncertainties. for the NOMAD Collaboration The text was submitted by the authors in English.     

Nuclear effects in neutral current quasi-elastic neutrino interactions

The interpretation of the charged (CCQE) and neutral (NCE) current quasi elastic events collected by the MiniBooNE Collaboration involves a number of unresolved issues. While it has been suggested that the data can be explained in terms of an effective nucleon axial mass, MA, the results of our theoretical calculations suggest that the CCQE and NCE samples cannot be described by the same value of MA. We argue that the disagreement between theory and data may arise from the uncertainties associated with the flux average procedure. We also analyze the role of the strange quark in NCE interactions and find that, due to a cancellation between proton and neutron contributions, it turns out to be negligible.     

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.     

Neutral strange particle production in neutrino and antineutrino charged current interactions on protons

The production of the neutral strange particlesK ⁰, and invp and charged current interactions is studied in an experiment with the Big European Bubble Chamber. Mean multiplicities are measured as a function of the event variablesE _v,W ² andQ ² and of the hadron variablesx _F,z andp _T ² .K ^*± (892) and ^*± (1385) signals are observed, whereas there is no evidence for ^*- (1385) production invp scattering. Forward, backward and total mean multiplicities are found to compare well with the predictions of an empirical model for deep-inelastic reactions in the case of the strange mesonsK ⁰ andK ^*± (892) but less so for the strange baryons , and ^*± (1385). The strange baryon multiplicities are used to obtain the decuplet to octet baryon production ratio and to assess the probabilities of auu orud system to break up.     

Charm dimuon production in neutrino-nucleon interactions in the NOMAD experiment

We present our new measurement of charm dimuon production in neutrino-iron interactions based upon the full statistics collected by the NOMAD experiment. After background subtraction we observe 15,340 charm dimuon events, providing the largest sample currently available. The analysis exploits the large inclusive charged current sample (about 9 million events after all analysis cuts) to constrain the total systematic uncertainty to ∼2%. The extraction of strange sea and charm production parameters is also discussed.     

Inclusive features of neutral strange particles in \overline p A interactions at 40 GeV/c

Mean inclusive features of neutral strange particles produced in antiproton interactions with D, Li, C, S, Cu, and Pb nuclei at an incident momentum of 40 GeV/c are found as functions of the target mass number.     

Observation of possible production and decay of short-living heavy neutral particles in the SKAT neutrino experiment

In the SKAT bubble chamber neutrino experiment production of a short-living neutral particle with mass (1.4?m?2.5) GeV/c² and lifetime τ≈6×10^?12 s has been detected. The event may be interpreted as production and decay of the heavy lepton M⁰→μ^?+e⁺+ν_e with mass (1.4?m_M⁰?2.1) GeV/c². It might also be the production of a charmed particle D⁰→e⁺+τ^?+ν_e (D⁰→e⁺+π^?+ν_e) with mass 1.4?m_D⁰?2.5) GeV/c² in a non-diagonal neutral current. The probability to interpret the event as other possible processes is very low.     

Measurement of the neutral to charged current cross section ratio in neutrino and antineutrino interactions

We report on the analysis of inclusive neutral current events produced in neutrino and antineutrino narrow band beams. We find for incident neutrino energies in the range 12–200 GeV and for hadron energies above 12 GeV a neutral to charged current cross-section ratio of R_v = 0.293 ± 0.010 for incident neutrinos, and $\text{R}{}_{\mathrm{<mtext>v</mtext>}}\text{= 0.35 ± 0.03}$ for antineutrinos. These ratios are consistent with the Weinberg-Salam model, with sin²θ_w = 0.24 ± 0.02.     

Experimental study of opposite-sign dimuons produced in neutrino and antineutrino interactions

A large sample of opposite-sign dimuons, produced by the interaction of neutrinos and antineutrinos in iron, is analysed. The data agree very well with the hypothesis that the extra muon is the product of charm decay. They yield information on the strength and space-time structure of the charmproducing weak current. The strange-sea structure functionxs(x) is determined. The difference between neutrino and antineutrino dimuon production is analysed to provide a value of the Kobayashi-Maskawa weak mixing angleθ ₂.     

Inclusive production of neutral strange particles in\bar pp interactions at 70 GeV/c

The inclusive production ofK _s ⁰ , Λ and \(\bar \Lambda \) particles is investigated in 70 GeV/c \(\bar pp\) interactions in an experiment performed at CERN using BEBC equipped with a TST. Differential cross-sections are studied and compared with corresponding data at surrounding energies. Differences withpp data obtained at the same energy allow an estimate of theK _s ⁰ , production cross-section in annihilation processes. Evidence is also given for central \(\Lambda \bar \Lambda \) production.     

Inclusive production of neutral strange particles in\bar pp interactions at 32 GeV/c

Multiplicities of charged particles produced in the forward and backward hemispheres are investigated for proton-nucleus and proton-nucleon collisions in the range from 20 to 400 GeV/c. Weak, but growing with incident beam momentum, forward-backward multiplicity correlations are observed which cannot be reduced to the inelastic diffraction. These correlations are more pronounced in proton-nucleus than proton-nucleon interactions. The experimental data are discussed in the frameworks of current cluster and multiple scattering models. It is shown that multiple scattering models describe well the forward-backward multiplicity correlations in nuclear production.     

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.     

Production characteristics of charmed particles in neutrino interactions

Using a hybrid emulsion spectrometer installed in the Fermilab wide-band neutrino beam, we located a total of 3855 neutrino interactions in the fiducial volume of our target. For 122 charmed-particle decays found in these interactions, we present distributions of x,y, charm-muon angular projection, Feynman-X, and the fragmentation Z. We find that the number of strange quarks in the nucleon sea is 4.2±2.1±2.6% of the number of down quarks.     

Search for correlated neutral strange particles and muon production in π−p interactions at 225 GeV

A measurement is made of the production correlation between neutral strange particles V and muons. The interactions originated in a streamer chamber containing a Lucite target bombarded by 225 GeV π^? mesons. The experiment has a sensitivity of 10 events per nanobarn and yields no evidence for new particles.     

Possible new interactions of neutrino and the KATRIN experiment

We analyse the possible role of new interactions of neutrino in the forthcoming tritium beta decay experiment KATRIN aimed at detecting the neutrino mass with the sensitivity of 0.3–0.2 eV. It is shown that under certain circumstances the standard procedure of data analysis would have to be modified by the introduction of an extra parameter describing the strength of the new interactions. Our model simulations show that the modified procedure may improve the quality of the fit compared with the standard case. Ignoring the possibility of new interactions may lead to a systematic error in the neutrino mass determination.     

Production of neutral strange particles in muon-nucleon scattering at 490 GeV

The production ofK ⁰, and particles is studied in the E665 muon-nucleon experiment at Fermilab. The average multiplicities and squared transverse momenta are measured as a function ofx _F andW ². Most features of the data can be well described by the Lund model. Within this model, the data on the K⁰/^± ratios and on the averageK ⁰ multiplicity in the forward region favor a strangeness suppression factors/u in the fragmentation process near 0.20. Clear evidence for QCD effects is seen in the average squared transverse momentum ofK ⁰ and particles.Deceased