Fragmentation in neutrino and antineutrino charged current interactions on proton and neutron

Some experimental properties of the charged hadronic fragments are compared for νp, νn, \(\bar vp\) and \(\bar vn\) interactions: multiplicities of forward and backward going particles,x _F distributions for pions, fragmentation functions and theirQ ² andW ² dependence. The results are compared with the predictions of the Lund fragmentation model.     

Cross-section measurements of single pion production in charged current neutrino and antineutrino interactions

All six exclusive single pion production processes from neutrino and antineutrino charged current interactions are studied in the energy range between 3 and 30 GeV. Using a quark model for single pion production from Rein and Sehgal we fitted the aximal mass parameter from total cross sections and compare the results with values from other experiments and the world-averages.     

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.     

Experimental test of the PCAC-hypothesis in charged current neutrino and antineutrino interactions on protons

Data obtained with the bubble chamber BEBC at CERN are used for the first significant test of Adler's prediction for the neutrino and antineutrino-proton scattering cross sections at vanishing four-momentum transfer squaredQ ². An Extended Vector Meson Dominance Model (EVDM) is applied to extrapolate Adler's prediction to experimentally accessible values ofQ ². The data show good agreement with Adler's prediction forQ ²→0 thus confirming the PCAC hypothesis in the kinematical region of high leptonic energy transfer ν>2 GeV. The good agreement of the data with the theoretical predictions also at higherQ ², where the EVDM terms are dominant, also supports this model. However, an EVDM calculation without PCAC is clearly ruled out by the data.     

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.     

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.     

Multiplicity distributions of charged hadrons invp and charged current interactions

Using data onvp and charged current interactions from a bubble chamber experiment with BEBC at CERN, the multiplicity distributions of charged hadrons are investigated. The analysis is based on 20000 events with incidentv and 10000 events with incident . The invariant massW of the total hadronic system ranges from 3 GeV to 14 GeV. The experimental multiplicity distributions are fitted by the binomial function (for different intervals ofW and in different intervals of the rapidityy), by the Levy function and the lognormal function. All three parametrizations give acceptable values forX ². For fixedW, forward and backward multiplicities are found to be uncorrelated. The normalized moments of the charged multiplicity distributions are measured as a function ofW. They show a violation of KNO scaling.     

Comparison of electron and muon charged current neutrino and antineutrino interactions in a neonH2 mixture

From an exposure of the Fermilab 15 ft Neon(64 atomic %)H₂ filled bubble chamber to a single-horn-focussed $\text{ν}$ beam, we have found 60 e^?X and 35 e⁺X events, which we compare with 227 μ^?X and 202 μ⁺X events. No statistically significant departures from μ-e universality are seen in the shapes of various differential cross sections.     

Neutral strange particle exclusive production in charged current high-energy antineutrino interactions

The cross section of the quasi-elastic reactions \(\bar v_\mu p \to \mu ^ + \Lambda (\Sigma ^0 )\) in the energy range 5–100 GeV is determined from Fermilab 15′ bubble chamber antineutrino data. TheQ ² analysis of quasi-elastic Λ events yieldsM _A=1.0±0.3 GeV/c² for the axial mass value. With zero µΛ K ⁰ events observed, the 90% confidence level upper limit \(\sigma (\bar v_\mu p \to \mu ^ + \Lambda {\rm K}^0 )< 2.0 \cdot 10^{ - 40} cm^2 \) is obtained. At the same time, we found that the cross section of reaction \(\bar v_\mu p \to \mu ^ + \Lambda {\rm K}^0 + m\pi ^0 \) is equal to \(\left( {3.9\begin{array}{*{20}c} { + 1.6} \\ { - 1.3} \\ \end{array} } \right) \cdot 10^{ - 40} cm^2 \) .     

On some effective mechanism for charmed particle production in neutrino and antineutrino beams

The paper describes an effective mechanism for charmed particle production in neutrino and antineutrino reactions, which consists in production of charmed virtual vector F1-meson in a weak vertex νF1μ (without suppression by the Cabibbo angle) with further strong rescattering of F1-meson on nucleon. This “quasidiffractive” mechanism should make the basic contribution to the production of charmed particles in neutrino experiments basic energies up to some hundreds of GeV. The charmed particles are mainly produced at limited momentum transfers $\text{|q}{}^2\text{| ≈ M}{}^2{}_{\mathrm{<mtext>F</mtext>}}\text{1}$ and with equal cross sections in the neutrino and antineutrino beams.     

Bose-Einstein correlations in neutrino and antineutrino interactions in deuterium

Bose-Einstein correlations between pions of equal charge have been observed in Charged Current and Neutral Current (anti)neutrino-deuterium interactions in the BEBC bubble chamber exposed to the SPS wide band beam. The pion emission region is found to be essentially spherical with a mean radius of (0.48±0.07) fm; the chaoticity parameter is 0.36±0.04.     

Coherent single pion production by antineutrino charged current interactions and test of PCAC

The cross section for coherent production of a single π^? meson in charged current antineutrino interactions on neon nuclei has been measured in BEBC to be (175±25) 10^?40 cm²/neon nucleus, averaged over the energy spectrum of the antineutrino wide band beam at the CERN SPS; this corresponds to (0.9±0.1) % of the total charged current \(\bar v_\mu \) cross section. The distributions of kinematical variables are in agreement with theoretical predictions based on the PCAC hypothesis and the meson dominance model; in particular, theQ ² dependence is well described by a propagator containing a massm=(1.35±0.18) GeV. The absolute value of the cross section is also in agreement with the model. This analysis thus provides a test of the PCAC hypothesis in the antineutrino energy range 5–150 GeV.     

Bose-Einstein correlations in neutrino and antineutrino interactions with nucleons

Four data sets of charged current neutrino and antineutrino interactions with neon, deuterium and hydrogen collected from BEBC and the 15 Foot Bubble Chamber are used to study the Bose-Einstein correlations between like-sign charged pions. Two forms of the parametrization for the effect are used. No substantial differences are found between the data sets obtained with neon, deuterium and hydrogen targets. The Lorentz invariant parametrization of Goldhaber gives for the radius of the pion emission region the valuer _G =0.80 ±0.04±0.16 fm and for the chaoticity parameter the value =0.61±0.04±0.15. Using the Kopylov-Podgoretskii parametrization yieldsr _K =1.27±0.06±0.12 fm, =0.58±0.03±0.12 and for the pion source lifetimec =0.52±0.05±0.12 fm. The Goldhaber parametrization was used to study the effect in further detail. The same emission radius and the same strength of the effect were found for particles produced in interactions on neutrons and protons. The data are compatible with a spherical shape of the pion emission region. No multiplicity or forward-backward dependences are found. No dependence of the effect on the event kinematical variables is seen.     

Observation of trimuon events produced in neutrino and antineutrino interactions

We report two trimuon events producedin v interactions. Of these, one is of the charge type ?++, not previously reported. In an antineutrino exposure, one candidate of the charge type +?? has been observed. This type of event has also not been reported previously. The combined π → μ and K → μ background for the three events are calculated to be ～ 0.7 events. The rate relative to charged current events corresponding to these three events is of the order of 4 × 10^?5.     

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.     

Physics of charmed hadrons

Basic experimental results on charmed-particle physics that have been obtained over the past few years are surveyed. Prospects for studying the properties of charmed particles in the near future are discussed.     

Study of transverse momenta of charged hadrons produced in νp and\bar vp charged current interactions

Data from a neutrino and antineutrino hydrogen experiment with BEBC are used to investigate transverse properties of the produced charged hadrons. Measurements are presented on average transverse momenta of charged pions as functions of Feynman-x and the hadronic mass, on the transverse momentum flow within an event and on jet-related quantities. The main features of the data are well described by the LUND model. The data favour a version of the model in which soft gluon effects are included and the primordial transverse momentum of the quarks in the proton is small. Effects from 1^st order QCD (hard gluon emission) are negligible.