K.L. Wernhard

Multiplicities of Secondary Hadrons Produced in Neutrino

In an experiment with the hydrogen bubble chamber BEBC at CERN multiplicities of hadrons produced in νp and vp interactions have been investigated. Results are presented on the multiplicities of charged hadrons and neutral pions, forward and backward multiplicities of charged hadrons and correlations between forward and backward multiplicities. Comparisons are made with hadronic reactions and e+e− annihilation. In the framework of the quark-parton model the data imply similar charged multiplicities for the fragments of a u- and a d-quark, and a larger multiplicities for the fragments of a uu- than for a ud-diquark. The correlation data suggest independent fragmentation of the quark and diquark for hadronic masses above ∼ 7 GeV and local charge compensation within an event.

p

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.

and Anti-neutrino

Abstract Distributions of the Feynman x variable have been determined for positive and negative pions in charged current neutrino-proton and antineutrino-proton reactions with hadronic energy W > 3 GeV and Bjorken x B > 0.1. The distributions have been corrected for experimental effects such as measurement errors, uncertainties in estimating the neutrino energy and particle misidentification. In the framework of the quark-parton model, the distributions yield information about the fragmentation of forward going u and d quarks and backward going uu and ud diquarks. Approximate Feynman scaling is observed for the invariant Feynman x F distributions. They can be fitted by a power law of the form (1 − | x F |) n as suggested by the dimensional counting rules. Simple isospin relations predicted by the quark-parton model are fulfilled. The fragmentation of diquarks is compared with that of protons into π ± .

p

In a selected sample of 6770 charged current (CC) events of νp interactions with 〈Eν〉 = 43 GeV and 〈W〉 = 4.6 GeV, 359 K0, 180 Λ and 13 Λ have been observed, which corresponds to a corrected production rate at least one neutral strange particle in (17.4±0.8)% of the CC events. The ratio of the inclusive Λ to K0 production cross section is found to be 0.26±0.03. The number of CC events containing at least one K0 increases with increasing Eν and Q2, while the CC events containing at least one Λ remain practically constant. The fractions of the total hadronic energy carried by K0 and Λ are found to be approximately the same in νp as in ep and μp interactions. In the hadronic c.m.s., the K0 are produced mostly forwards, the Λ mostly backwards, with asymmetry parameters of +0.32±0.02 and −0.45±0.06, respectively. The total strange particle production cross section is estimated to be (25±4)% of the cross section for production of CC events with W>1.5 GeV and that for charm production (10±2)% of the CC cross section well above charm threshold (W>3 GeV). The production of the resonances K∗+ (890) and Σ+ (1385) has been observed. The production rate of K∗+ (890) is comparable to that of D∗+ (2009), above the corresponding thresholds.

Charged Current 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.

Multiplicity distributions in neutrino-hydrogen interactions

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 .

An investigation of quark and diquark fragmentation in νp and νp charged current interactions in BEBC

Abstract Inclusive ρ 0 production in neutrino-proton charged-current interactions is studied, using a sample of 7831 events obtained in BEBC filled with hydrogen and exposed to the CERN wideband neutrino beam. An average multiplicity of 0.14±0.02 ρ 0 per event is found, corresponding to a ratio 〈 ρ 0 〉/〈 π − 〉=0.13±0.02. The ρ 0 production characteristics are determined as functions of leptonic variables ( W , Q 2 , χ B ) and hadronic variables ( χ F , z , p t 2 ) and are found to be similar to those determined for hadron- and other lepton-induced reactions.

Inclusive neutral strange particle production in νp interactions

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.

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

AbstractNeutral kaon to negative pion production ratios fromvp andn