Bar Vp Research Articles

Neutral strange particle production in neutrino and antineutrino charged-current interactions on neon.

The production of the neutral strange particlesK0, Λ and\(\bar \Lambda \) invp and\(\bar vp\) charged current interactions is studied in an experiment with the Big European Bubble Chamber. Mean multiplicities are measured as a function of the event variablesEv,W2 andQ2 and of the hadron variablesxF,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 mesonsK0 andK*± (892) but less so for the strange baryons Λ,\(\bar \Lambda \) 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.

Stranger still: Kaon loops and strange quark matrix elements of the nucleon

Intrinsic strangeness contributions to lowenergy strange quark matrix elements of the nucleon are modelled using kaon loops and meson-nucleon vertex functions taken from nucleon-nucleon and nucleon-hyperon scattering. A comparison with pion loop contributions to the nucleon electromagnetic (EM) form factors indicates the presence of significantSU(3)-breaking in the mean-square charge radii. As a numerical consequence, the kaon loop contribution to the mean square Dirac strangeness radius is significantly smaller than could be observed with parity-violating elastic\(\vec e\) p experiments planned for CEBAF, while the contribution to the Sachs radius is large enough to be observed with PV electron scattering from (0+, 0) nuclei. Kaon loops generate a strange magnetic moment of the same scale as the isoscalar EM magnetic moment — a scale large enough to be observed at CEBAF — and a strange axial vector form factor having roughly one-third of the magnitude extracted from\(vp/\bar vp\) elastic scattering. In the chiral limit, the loop contribution to the fraction of the nucleon's scalar density arising from strange quarks has roughly the same magnitude as the value extracted from analyses of∑ πN . The importance of satisfying the Ward-Takahashi Identity, not obeyed by previous calculations, is also illustrated, and the sensitivity of results to input parameters is analyzed.

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

The production of the neutral strange particlesK 0, Λ and $$\bar \Lambda $$ invp and $$\bar vp$$ 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 Λ, $$\bar \Lambda $$ 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.

QCD corrections to charm quark production in deep-inelastic neutrino scattering

We evaluate theO(αs) corrections to weak, charged current production of charm quarks. For perturbative subtractions and parton densities in the deep inelastic scheme the residual corrections to νp and\(\bar vp\) charm production structure functionsF2,F3 andFL are presented. The consequences of these corrections with respect to they dependence of the cross section is discussed.

Multiplicity distributions of charged hadrons invp and charged current interactions

Using data onvp and $$\bar vp$$ 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 $$\bar v$$ . 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.

Inclusivef 2 (1270) meson production in ?p and $$\bar vp$$ charged current interactions

Using data obtained with the bubble chamber BEBC at CERN, the inclusivef2 (1270) meson production invp and\(\bar vp\) charged current reactions is studied. It is found thatf2 production occurs mainly in events with a hadronic invariant massW≳7 GeV. In these events, the averagef2 multiplicity is about half the average ρO multiplicity, and thexF andpT2 distributions of thef2 agree in shape with those of the ρO. The predictions of a semi-empirical model (Wells model) are in accord with the measured multiplicities atW>7 GeV, whereas at lowerW the model predicts too largef2 multiplicities.

Inclusive ρ0(770) meson production invp and $$\bar vp$$ charged current interactions

Using data obtained with the bubble chamber BEBC at CERN, the inclusive ρ0 (770) meson production in νp and $$\bar vp$$ charged current reactions is studied. The average ρ0 multiplicity is measured as a function of the event variablesE ν ,W 2,Q 2,x Bj , and the charged multiplicity. The differentialx F ,y *,z andp 2 distributions of the ρ0 are presented as well as the averagep 2 as a function ofW 2 andx F . The ρ0/π0 ratio and the fractions of the π± originating from ρ0 decays are given as functions ofx F . The results are compared to the predictions of fragmentation models. A particular version of the Lund model predicts ρ0 multiplicities which are generally too high, although it qualitatively reproduces many aspects of the data. The ρ0 multiplicities predicted by a semi-empirical model (Wells model) are in quantitative agreement with the measurements.

Quasielastic nucleon and hyperon production by neutrinos and antineutrinos with energies below 30 GeV

The cross sections of neutrino and antineutrino quasielastic reactions $$vn \to \mu ^ - p,\bar vp \to \mu ^ + n,\bar vp \to \mu ^ + \Lambda$$ were studied in the neutrino energy range between 3 and 30 GeV. In comparison withV-A theory axial mass parameters ofM A =(1.06±0.05±0.14) GeV/c2 from neutrino andM A =(0.71±0.10±0.20) GeV/c2 from antineutrino data were found. The total cross-section for the hyperon production process can be described byM A =1.0 GeV/c2.

W 2 andQ 2 dependence of charged hadron and pion multiplicities invp and $$\bar vp$$ charged current interactionscharged current interactions

Using data onvp and\(\bar vp\) charged current interactions from a bubble chamber experiment with BEBC at CERN, the average multiplicities of charged hadrons and pions are determined as functions ofW2 andQ2. The analysis is based on ∼20000 events with incidentv and ∼10000 events with incident\(\bar v\). In addition to the known dependence of the average multiplicity onW2 a weak dependence onQ2 for fixed intervals ofW is observed. ForW>2 GeV andQ2>0.1 GeV2 the average multiplicity of charged hadrons is well described by〈n〉=a1+a2ln(W2/GeV2)+a3ln(Q2/GeV2) witha1=0.465±0.053,a2=1.211±0.021,a3=0.103±0.014 for thevp anda1=−0.372±0.073,a2=1.245±0.028,a3=0.093±0.015 for the\(\bar vp\) reaction.

TheK 0/π- ratio and strangeness supression inv p and $$\bar vp$$ charged current interactions

Neutral kaon to negative pion production ratios fromvp and\(\bar vp\) charged current interactions in BEBC are presented and compared with LUND fragmentation model predictions. Good agreement is obtained with a strangeness suppression factor λ=0.203±0.014(stat)±0.010(sys). No evidence is seen for an energy dependence of λ in our kinematic region.

Similarities and differences between the inclusive reactions $$K^ - p \to \bar K^0 X_1 $$ and $$\bar vp \to \mu ^ + X_2 $$

We study in detail some aspects of “jet universality” in soft and hard processes interpreted by quark-parton diagrams. Using the framework of the Dual Topological Unitarization model for the soft process\(K^ - p \to \bar K^0 X_1 \) we compare hadron longitudinal momentum distributions and multiplicities in the “one-chain” part of this reaction to those in\(\bar vp \to \mu ^ + X_2 \). We observe not only close similarities (e.g. the same π+/π− ratio over the whole Feynman-x region) but also some significant differences in the jet systemsX1,X2, such as a lower cross-section in the central region and a smaller average multiplicity of the jets inX1.

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 1st order QCD (hard gluon emission) are negligible.

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,xF distributions for pions, fragmentation functions and theirQ2 andW2 dependence. The results are compared with the predictions of the Lund fragmentation model.

Charge distribution in a two-chain dual model

Charge distributions in the multiple production processes are analysed using the dual chain model. A parametrisation of charge distributions for single dual chains based on the νp and\(\bar vp\) data is proposed. The rapidity charge distributions are then calculated forpp and\(\bar pp\) collisions and compared with the previous calculations based on the recursive cascade model of single chains. The results differ at the SPS collider energies and in the energy dependence of the net forward charge supplying the useful tests of the dual chain model.

Jet cross sections in leptoproduction from QCD

We have calculated the longitudinal and other polarization dependent cross sections for jet production in deep inelasticep, vp, and\(\bar vp\) scattering up to order αs of the quark-gluon coupling constant. Fragmentation of final state partons into hadrons is taken into account. Distributions in thrust,p2T in andp2T out are predicted for all three reactions and various values ofW andQ.