R. Hartmann

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.

ϱ0 and f production in π+p interactions

Abstract Inclusive ϱ 0 and f(1270) production are analysed in π + p collisions at 8, 16 and 23 GeV/ c . The ϱ 0 cross section increases with energy such that the ϱ 0 /π − ratio remains constant. Emphasis is laid on cross sections as a function of the transverse momentum and of the Feynman x variable. The ϱ 0 s can be attributed to two sources: some ϱ 0 s are centrally produced, but there is a pronounced forward peak. The distribution of leptons coming from ϱ 0 decay is discussed.

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).

Determination of the fire-ball dimensions from second-order interference between two pions

Abstract Positive correlations are observed for pion pairs of equal charge and similar momentum vectors, produced in the reactions π p→p+5 π and π p→p + 7 π at 4 to 25 GeV/ c . The results are consistent with being due to the second-order interference effects expected for pairs of identical bosons and lead to the determination of the average dimension of the “fire-ball’ from which the pions are emitted (〈 R 〉 = 1.0 ± −0.2 +0.4 fm). Attempts are made to study the fire-ball shape by selecting pions pair emitted in various polar and azimuthal directions.

A comparison of πππ, Kππ, πKKKK system produced in the reactions meson +p→3 mesons + p

Abstract A comparison is made of the low-mass three-meson systems (πππ), (Kππ), (π K K ) and ( K K K ) diffractively produced in the reaction meson + proton → three mesons + proton. Several striking similarities and a few important differences are observed: (i) the reactions are consistent with the assumption that the three mesons decay entirely into a 0− meson and a 0+, 1− or 2+ resonance; (ii) the three-meson mass spectra have a peak ≈ 250 MeV above the effective threshold Meff of the dominant decay mode and then fall off approximately as (mass)−3;(iii) the average spin 〈J〉 = 0.55 + 1.1 Qeff, where Qeff = M - Meff; (iv) the average orbital angular momentum 〈l〉 increases according to 〈l〉 = 0.75 Qeff; (v) the three-meson states are produced dominantly in unnatural spin-parity states and no evidence for their being resonant is found; (vi) the only natural spin-parity states found are the well-established 2+ resonances A2 and K∗ (1420); they have similar properties to the non-resonant unnatural parity states except for a dip at t = 0 in the dσ/dt distributions; (vii) both the unnatural and natural spin-parity states are produced mostly by an exchange of natural parity; (viii) there is evidence for two types of production mechanism with different polarization properties, one approximately conserving helicity in the t-channel and the other in the s-channel.

Simplicity of “transverse energy” spectra of hadrons

Abstract Using data from a 16 GeV/c π+p bubble chamber experiment, we have studied the production of pions and meson resonances in the central region. Transverse spectra have been analysed in terms of the transverse energy variable Et=√pt2+M2. We find that the Et spectra of “stable” particles, of resonances like ϱ, ω and f, and of corresponding non-resonant two- and three-pion systems all follow one simple exponential in Et over several orders of magnitude in cross section. All spectra are consistent with one common slope parameter of approximately (120 MeV)−1.

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.

The structure of the weak neutral current: An analysis of the hadronic energy distribution from neutrino and antineutrino interactions

Abstract An analysis is presented of the distribution of hadronic energy in neutrino and antineutrino neutral current interactions occurring in BEBC, filled with a neon-hydrogen mixture and exposed to the CERN-SPS narrow-band neutrino beam. This shows that the contributions by scalar or pseudo-scalar forms of the interaction are consistent with zero and pure V, A and V + A are excluded; there is good agreement with the Weinberg-Salam model.

Inclusive Δ++ production and a test of the triple regge limit

Abstract Results on the inclusive reaction π+ p→Δ++ X0 at 8, 16 and 23GeV/c are used for quantitative tests of the triple Regge formula. As predicted, the slopes ofthe missing mass (M) spectra at fixed t are independent of s. Furthermore the trajectory α(t) obtained from the s-iependence at fixed M appears consistent with that obtained from the M-dependence at fixed s. However, the pomeron intercept α (0) is found to depend on t, suggesting that no single triple Regge diagram dominates at the M and s values studied in this reaction. Provided such a t-dependence is allowed, a single term triple Regge formula gives a very satisfactory parametrisation of our data.

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.