W.G. Scott

Multiplicity distributions in neutrino-hydrogen interactions

Abstract Multiplicity distributions of charged hadrons produced in νp interactions are studied using a sample of 7850 charged current interactions in BEBC. Multiplicity moments are studied as functions of the invariant mass of the hadronic system, W , and a comparison is made with other lepton- and hadron-induced reactions. The mean charged multiplicity 〈 n ch 〉 is found to increase linearly with ln W 2 . The other multiplicity moments indicate a close similarity between the neutrino scattering and the class of annihilation processes. A study of the multiplicity distributions in the forward and backward directions in the hadronic c.m.s. gives results in qualitative agreement with the quark parton model.

Total cross sections νμ and ḡnμcharged-current interactions between 20 and 200 GeV

Abstract Exposures of the Ne/H 2 filled Big European Bubble Chamber (BEBC) to a dichromatic neutrino (antineutrino) beam produced by 400 GeV protons of the CERN SPS yielded ∼ 3100 events with a negative, and ∼ 1100 with a positive, muon. The neutrino flux is determined from the muon flux in the shielding. Assuming a linear energy dependence of the cross section, the values σ E between 20 and 200 GeV are found to be 0.657 ± 0.012 (stat.) ± 0.027 (syst.) and 0.309 ± 0.009 (stat.) ± 0.013 (syst.) cm 2 (GeV nucleon) −1 , for neutrinos and antineutrinos, respectively. The scaling variable q 2 E decreases significantly with increasing energy both for neutrinos and antineutrinos.

Observation of scaling deviations in the energy distribution of secondary hadrons in inelastic neutrino-proton interactions

Abstract An analysis is presented of the z distributions of secondary hadrons produced in 5600 charged current events from a BEBC neutrino-hydrogen experiment. Evidence is presented for scaling deviations in the z distributions and a breakdown of factorization in the single particle inclusive cross sections. The results are consistent with the leading order QCD predictions on the q 2 dependence of nonsinglet moments of quark fragmentation functions, yielding a value of Λ ≈ 0.6 GeV.

Transverse momentum distributions of hadrons in deep inelastic neutrino-proton scaterring

Abstract An analysis of the transverse momentum distributions of secondary hadrons produced in neutrino-proton charged current interactions is presented. It is found thatparticles going forward in the hadronic c.m.s. have a different behaviour from those going backward. A rise of the average transverse momentum squared as a function of both the invariant mass of the hadronic system and the fractional energy carried by the hadron in the c.m. frame, is observed. The result is not in good agreement with the predictions of a QCD based model if the non-perturbative parts are forward-backward symmetric. Using events with no missing neutral particles in the final state the average primordial transverse momentum squared of the quark inside the nucleon is estimated to be ∼0.3 GeV 2 / c 2 .

Measurement of the Ratio of Neutral to Charged Current Cross-sections of Neutrino Interactions in Hydrogen

Abstract The ratio R p of the neutral current to charged current cross sections has been measured in the BEBC bubble chamber filled with hydrogen and exposed to the CERN SPS wideband neutrino beam. It is found that an event selection in terms of the transverse momentum of the hadronic system is very effective in reducing backgrounds and enables R p to be determined with an error of less than 10%. Combining the results from hydrrogen and isoscalar targets, the individual values of the coupling constants u L 2 and d L 2 are determined separately to be u L 2 = 0.15 ± 0.06 and d L 2 = 0.17 ± 0.08. The results are compatible with the standard SU (2) × U(1) model. The value of sin 2 θ W determined from this experiment is 0.19 ± 0.04.

Transverse momentum of hadrons produced in ν and ν interactions on an isoscalar target in BEBC

The average transverse momentum squared, 〈p⊥2〉, of hadrons is studied as a function of W2 and of Q2 for ν and ν interactions on an isoscalar target. An increase of 〈p⊥2〉 with W2 is observed for the hadrons emitted forward in the hadronic c.m.s. The p⊥ dependence of the fragmentation function is found to factorise from the structure function at fixed W, but does not factorise at fixed Q2. Unlike the case of forward-going particles, the 〈p⊥2〉 of hadrons going backward in the c.m.s. shows no strong dependence on W2.

Single π+ production in charged current neutrino-hydrogen interactions

Abstract The reaction ν p→ μ − p π + (777 events) is studied at neutrino energies from 5 to 200 GeV. A total of 551 events fit the channel ν p→ μ − Δ ++ (1232) with χ 2 probability greater than 2%. Decay angular distributions of the Δ ++ are investigated and the density matrix elements are studied as functions of Q 2 , the square four-momentum transfer. The total Δ ++ production cross section and the differential cross section d σ /d Q 2 are determined. Using the Schreiner-von Hippel parametrization of the Adler model, the value of the axial mass determined by fitting the total cross sections above 20 GeV is M A = 0.85±0.10 GeV. The model describes the differential cross sections reasonably well above Q 2 ⋍0.2 GeV 2 . Disagreements, however, are found for some values of the density matrix elements of the Δ ++ decay angular distributions and their Q 2 dependence. The (p π + ) mass region above the Δ ++ (1232) contains evidence for the presence of higher mass Δ ++ resonances and, above 2 GeV, for the forward emission of fast π + .

Spherocity and thrust distributions in high energy neutrino interactions

Abstract The study of the hadronic system of charged current neutrino interactions in terms of the variables spherocity ( S ) and thrust ( T ) is presented. It is found that 〈 S 〉 and 〈1− T 〉 for fixed hadronic energy are similar for neutrino interactions, e + e − annihilations and φ − Ne interactions.

Production of charmed mesons in neutrino interactions in hydrogen

Abstract Production of charmed mesons has been observed in neutrino-hydrogen interactions in 285 000 photographs of BEBC exposed to the CERN wide-band neutrino beam. In ∼ 6000 charged current events, two events have been found each giving a three-constraint kinematical fit with production of only one strange particle, namely a K−, which is identified by its characteristic reaction K−p→Σ−π+. These events are thus examples of ΔS=−ΔQ reactions corresponding to charm production on a valence quark. For both events the effective mass of a (K− + pions) system is equal to the D0(1863) mass while the effective mass of this system plus a π+ is equal to the D∗+(2009) mass. The mass difference ΔM=M( D ∗+ )−M D 0 is 145.2 ± 0.6 MeV. The first event is interpreted as ν p →μ − pD ∗+ and the second as ν p →μ − pD ∗+ π + π − , both with D ∗+ → D 0 π + . The rate of inclusive D∗+ production has been estimated for all events by assuming that each negative track in turn is a K− and using the fact that the error on ΔM is small. It is found that the cross section σ(ν p →μ − D ∗+ + anything ) relative to σ(νp→μ− + anything), above the D∗ threshold, is (4.1 ± 2.4)%.

Determination of the quark density ratio d(x)u(x) in the proton

Abstract Data from an exposure of BEBC filled with hydrogen to a wideband neutrino beam are analysed to yield the structure function F v p 2 ( x ) for x > 0.2. Using our results in combination with data from electron-proton and muon-proton scattering, the quark density ratio d/u is determined as a function of x . The dominance u at large x is clearly seen. The results are compared with theoretical predictions.