P.O. Hulth

Analysis of nucleon structure functions in CERN bubble chamber neutrino experiments

Abstract We present results for the differential cross sections of neutrinos and antineutrinos on nucleons in the energy range E = 2−200 GeV, from the BEBC and Gargamelle experiments. The structure functions F2, 2χF1 and χF3 have been evaluated as a function of χ and q2. Deviations are observed from Bjorken scaling, which are very similar to those found in electron and muon inelastic scattering. For the Callan-Gross ratio, we find 2χF 1 F 2 = 0.80 ± 0.12 and the corresponding value for 〈R〉 = 〈 σ S σ T 〉 = 0.15 ± 0.10 . Our results are consistent with the Gross-Llewellyn-Smith sum rule; we measure ⩾2.5 ± 0.5 valence quarks per nucleon. Quark and antiquark distributions are given. The Nachtmann moments of F2 and χF3 are quantitatively consistent with the predictions from QCD. The value of the strong interaction parameter is λ = 0.74 ± 0.05 GeV without corrections, and 0.66 ± 0.05 GeV including αS2 corrections. The moments of the gluon distribution are found to be positive and indicate an χ distribution of gluons which is comparable with that of the valence quarks.

Observation of Prompt Neutrinos from 400-GeV Proton Nucleus Collisions

Abstract In 70 000 photos taken in BEBC during an experiment in which the 400 GeV proton beam of the CERN SPS was dumped into a massive Cu target 820 m upstream of BEBC, 70 interactions induced by neutral primaries above 10 GeV were observed. In 11 events the secondary charged lepton is an e − , in four events an e + . This number of electron events cannot be due to electron neutrinos from conventional sources (K, Λ, Σ − decays). The flux of the additional (prompt) neutrinos is evaluated. Possible origins are discussed in terms of charmed particles, τs, and as yet undiscovered particles. Limits are given on axion production.

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.

Hadron production in charged current neutrino and antineutrino interactions at high energy

The general features of hadrons produced in charged current interaction of high-energy neutrinos on nucleons are shown to be basically consistent with the idea of quark fragmentation within the framework of the quark parton model. However, many of the effects observed are shown also to follow from longitudinal phase space. Evidence is presented for a rise in 〈pT2〉 with Q2 in qualitative agreement with the predictions of quantum chromodynamics (QCD).

Total cross sections for charged-current neutrino and antineutrino interactions in BEBC in the energy range 20–200 GeV

Abstract The charged-current cross sections for neutrinos and antineutrinos on nucleons in the energy range 20–200 GeV are given. Taken in conjunction with the previous Gargamelle results, they show that σ E is almost constant with energy for antineutrinos, and falls with energy for neutrinos. The value of 〈q 2 〉 E decreases with energy for both neutrinos and antineutrinos, and these deviations from exact Bjorken scaling are consistent with those observed in electron and muon inelastic scattering. We find no evidence for new heavy quark states with right-handed coupling.

Further study of the prompt neutrino flux from 400 GeV proton-nucleus collisions using BEBC

Abstract In a second beam-dump experiment using BEBC the prompt neutrino flux has been measured and its characteristics studied. The use of targets of variable effective density allowed a determination of the conventional decay neutrino flux and a direct demonstration of a prompt neutrino signal. Assuming that the prompt neutrinos originate in the decay of charmed D mesons then a production cross section is estimated. An upper limit of 10% can be set to the proportion of interactions induced by τ neutrinos.

Inclusive neutral strange particle production in νp interactions

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.

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.

Di-Lepton events in the BEBC narrow-band beam neutrino experiment

Abstract In film taken with BEBC filled with a Ne(74%mol)/H 2 mixture and exposed to the CERN narrow-band neutrino beam (200 GeV), tenμ − μ + , one μ − μ + μ − and five μ − e + events were found in the ν exposure and two μ + μ − events and one μ + e − event in the ν exposure. Assuming the same production mechanism for μμ and μe events, the relative rates, corrected for identification inefficiency and background, can be combined and are (1.3 ± 0.4)% for (μ − e + + μ − μ + )/μ − in neutrino interactions, and (1.2 ± 0.5)% for (μ + e − + μ + μ − )/μ + antineutrino interactions. Eight out of the sixteen μ − l + events have a V 0 , leading to a corrected K 0 -multiplicity of 1.7 ± 0.7. No evidence is found for heavy-lepton production.