E. A. De Wolf

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.

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 + .

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)%.

Study of the exchange mechanism in K+p → K+π-N*++ at 5 GeV/c incoming K+ momentum

We present results on the analysis of the quasi three-body reaction K+p → K+π-N*++ obtained from bubble chamber exposures at 5 GeV/c incident K+ momentum. We have applied a method of analysis based on the study of the longitudinal phase space plot recently proposed by Van Hove. Evidence for the existence of π- mesons with a four-momentum transfer peaked at small values is shown. (Events contributing to this peak correspond to the cross section of about 80 μb.) The difficulties in explaining this result in terms of the double-particle exchange model are discussed.

Six- and seven-body final states in K+p interactions at 5 GeV/c

We present a study of six- and seven-body final states among the K+p interactions at 5 GeV/c incident K+ momentum. Results on cross sections, resonance and single-particle productions are given. Charge dependent angular correlations for pairs of pions occur as in pp and π+p interactions (the so called GGLP effect). In contrast, no dependence on the charge is observed in the angular correlations between kaons and pions. The influence of the production of K∗ and N∗ resonances on these angular correlations is investigated. The predictions of a multi-Regge Model (CŁA) are compared to the experimental results.

Resonance production in five-body final states from K+p interactions at 5 GeV/c

The final states corresponding to the reaction K+p → KNπππ are studied at 5.0 GeV/c incident momentum. The general characteristics of these reactions are given. A more detailed study is made of resonance production. The more abundantly produced resonances are K∗(892), Δ(1236), ϱ, ω, η, K∗(1420), N∗(1520) and N∗(1700). Fits to the multidimensional space of effective masses show that for the final state Kopπ+π−π−, more than 30% of the reaction proceeds through quasi two-body intermediate states, and that more than 88% proceeds through the production of at least one resonance. Some evidence is found for the production of other resonances such as K∗(1660) → K3π, Δ(1920) → → pπ+π+π− and N∗(2064) → pπ+π−πo. Several example of cascade decays are found, but no direct decay into more than three bodies is observed

An LPS analysis of the reactions K+p→K+π+π−p and K+p→Koπ+πop

Abstract Results are presented on the reactions K + p→K + π − π + p and K + p→K 0 π 0 π + p studied with the method of the longitudinal phase space. The analysis is based on data at 7 incoming K + momenta, ranging from 5 to 12.7 GeV/ c . The energy dependence of partial cross sections in various regions of the LPS is discussed. Evidence is presented for the dominance of diffractive processes in particular regions of the phase space and for the hypothesis of factorization.

Anti-lambda production in K+p interactions at 8.25 GeV/c

We present the data on the Λ(Σ) events produced in final states of K+p interactions at 8.25 GeV/c. Cross sections for Yo production are given for most final states obtained in this experiment, and the results at other energies are listed for comparison. No significant enhancement is seen in the Yo N mass distributions while there is some indication of the production of Y∗ (1385) and N∗ (1236) in the Λπ and Nπ systems respectively. An attempt at the description of the reaction K+p→Λpp in terms of a five-point Veneziano amplitude is also included.

Double-peripheral model and the four-momentum-transfer distributions in the reaction K+p → K+π-N*++ at 5 GeV/c incoming momentum

Abstract We have analyzed the reaction K + p → K + π − N ∗++ at 5 GeV/ c K + primary momentum, from the point of view of the double-peripheral model. The distributions of four-momentum transfers t′ pN ∗ and t′ KK (t′=t t t min ) have been studied as functions of the masses of the N ∗++ π − and K + π − systems. We have found that the observed correlations cannot be explained adequately by the present version of the Chan-oskiewicz-Allison model. The disagreement is particularly striking for the low N ∗++ π − mass region, where the data show peripheral production of the N ∗++ , contrary to the prediction of the model. The implications of the results for the double peripheral model are discussed.

QCD effects in hadronic final states

Progress in the study of hadronic final states in deep inelastic scattering as well as pp, photoproduction and e+e− annihilation, as presented at the DIS97 workshop, is reviewed.