Second-order interference of pion pairs of equal charge is observed in good statistics samples of 16 GeV/c π+p and K−p interactions (2 × 106 and 106 pion pair combinations, respectively) and in a smaller sample of pp annihilations at rest. The effective radius R of the pion source is found to be approximately 1.4 fm for all three types of interaction. The interference does not appear to be “total”, about 60–80% of the like pairs interfering. It is shown that the numerical results for the radius R, for the depth cτ of the source “photosphere” and for the fraction λ of the interfering pairs are sensitive to any dynamical correlation in the background, and hence depend on the background chosen. It is argued that further refinements in the theoretical formulation of the phenomenon and in the experimental approach are needed for truly quantitative results.

Inclusive ρ0 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 ρ0 per event is found, corresponding to a ratio 〈ρ0〉/〈π−〉=0.13±0.02. The ρ0 production characteristics are determined as functions of leptonic variables (W, Q2, χB) and hadronic variables (χF, z, pt2) and are found to be similar to those determined for hadron- and other lepton-induced reactions.

Charge properties of the hadronic systems from νp and νp scattering in BEBC are studied in the framework of the quark-parto model (QPM). The average charges 〈Qjet〈ν and 〈Qjet〈ν of a quark jet and a d-qua jet, respectively, are determined according to two different methods. The difference 〈Qjet〈ν− 〈Qjet〈ν is in agreement with e QPM value of 1. Scaling of charge and energy flow in the angular variable λ is demonstrated. The ratios ΔQν/ΔQν of charge flows in νp a νp scattering are in accord with the QPM in both hemispheres.

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.

A study is presented of the reactions K+p→(K+ω)p at 8.25 and 16 GeV/c and K−p→(K−ω)p at 10 and 16 GeV/c and comparison is made with K+ results at 10 GeV/c and K− at 7.3 GeV/c. The (K+ω) and (K−ω) mass spectra both present a strong enhancement very near threshold, while a second peak at ∼1.7 GeV is evident only with incident K− at the lower energies. The threshold peak has very weak energy dependence and is mostly due to the 1+S state which is produced conserving s-channel helicity. It is suggested that this is another decay mode of the resonance Q1(1290) known to decay mainly into Kϱ. The ratio of the Q1 coupling constants to the Kω and Kϱ decay channels, Rω = gKω2/gKϱ2 is determined to be 0.21±0.04. The enhancement at 1.7 GeV is predominantly, but not exclusively, due to the 2− state. While the K+ and K− induced reactions give basically similar results, small differences are observed that can be qualitatively explained in the framework of the Deck model.

Data from an exposure of BEBC filled with hydrogen to a wideband neutrino beam are analysed to yield the structure function Fvp2(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.

Two examples of charmed baryon production by neutrinos have been observed in BEBC filled with hydrogen. Both events fit uniquely the reaction νp → μ−pK−π+π+ and thus apparently violate the ΔS = ΔQ rule. None of the appropriate mass combinations is consistent with the mass values of the D0 and D+ mesons. However, for the mass combinations of the pK−π+ systems, values of (2.285 ± 0.005) GeV and (2.280 ± 0.003) GeV are found for event 1 and 2, respectively. These values agree with the mass of (2.285 ± 0.006) GeV for the Λc+ charmed baryon determined recently in e+e− collisions at SLAC.

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 〈nch〉 is found to increase linearly with ln W2. 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.

The reaction νp→μ−pπ+ (777 events) is studied at neutrino energies from 5 to 200 GeV. A total of 551 events fit the channel νp→μ−Δ++ (1232) with χ2 probability greater than 2%. Decay angular distributions of the Δ++ are investigated and the density matrix elements are studied as functions of Q2, the square four-momentum transfer. The total Δ++ production cross section and the differential cross section dσ/dQ2 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 MA = 0.85±0.10 GeV. The model describes the differential cross sections reasonably well above Q2⋍0.2 GeV2. Disagreements, however, are found for some values of the density matrix elements of the Δ++ decay angular distributions and their Q2 dependence. The (pπ+) 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+.

Cross-section values or upper limits are presented for twenty-five two-body hypercharge-exchange reactions in K−p and π+p interactions at 10 and 16 GeV/c. The 16 GeV/c results are compared with some predictions of line-reversal plus exchange-degenerate Regge poles, of SU(3) and of the additive quark model. Agreement is found in all cases.

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∗+)−MD0 is 145.2 ± 0.6 MeV. The first event is interpreted as νp→μ−pD∗+ and the second as νp→μ−pD∗+π+π−, both with D∗+→D0π+. 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(νp→μ−D∗++anything) relative to σ(νp→μ− + anything), above the D∗ threshold, is (4.1 ± 2.4)%.

A total of 101 ω− decays have been found in K−p interactions at 10 and 16 GeVc. The decay angular distribution has been fitted under the assumptions that the ω− has spin either 12or32. It has been found that the probability of isotropy (spin12) is less than one in a thousand, whereas the probability for spin 32 is about 70%. Thus, we exclude the spin 12 assignment. The lifetime of the ω− is found to be (1.41−0.24+0.15) × 10−10 s, in agreement with our earlier result based on about 15 of the present sample.

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, τ's, and as yet undiscovered particles. Limits are given on axion production.

The sources of negative pions are analysed in π+p interactions at 16 GeV/c. It is shown that the kinematics of resonance decay is crucial in determining the pions′ longitudinal and transverse momentum spectra. The identifiable meson resonances, of which η, ω, ϱ0 and f are the dominant ones, account for about 50% of all π−'s produced. The “direct” pions, i.e. those that are primary products of the π+p interactions, appear to constitute 10 to 30% of the total π− yield.

The inclusive production of Σ+(1385) and Σ−(1385) has been studied in K−p interactions at 10 and 10 and 16 GeV/c. It is found that the cross sections for the reactions K−p →Σ±(1385) + anything are approximately constant in the energy range form 10 to 32 GeV/c, being ≈ 350 μb for Σ+ (1385) and ≈ 250 μb for Σ− (1385). The dσdp⊥2 distributions for Σ±(1385) fall off exponentially with increasing p⊥2, with sloped of about 3 (GeV/c)−2. The dσ/dx distributions for Σ+(1385) and Σ−(1385) are markedly different: the production of Σ−(1385) is symmetrical forwards and backwards in the c.m.s.; for Σ+(1385), the distribution is the same as for Σ−(1385) in the forward direction, but presents a large excess of events in the backward direction. This indicates that for the production of both Σ+(1385) and Σ−(1385) the fragmentation of the incoming kaon is negligible. The fragmentation of the target proton is negligible for Σ−(1385), but it is important for Σ+(1385) and is responsible for the excess (∼100μb) of its cross section over that for Σ−(1385).