J.J. Aubert

Shadowing in deep inelastic muon scattering from nuclear targets

Abstract Results are presented on the ratio of the inelastic muon-nucleus cross section per nucleon for carbon and calcium relative to that for deuterium. The measurements were made in the kinematic range of low x (0.003–0.1) and low Q 2 (0.3–3.2 GeV 2 ) at an incident muon energy of 280 GeV. The calcium to deuterium ratio shows a significant x dependence which is interpreted as a shadowing effect. No strong Q 2 dependence is observed. This suggests that the effect is due at least partially to parton interactions within the nucleus.

Measurement of Hadron Azimuthal Distributions In Deep Inelastic Muon Proton-scattering

A study of the distribution of the azimuthal angle ϕ of charged hadrons in deep inelastic μ−p scattering is presented. The dependence of the moments of this distribution on the Feynmanx variable and the momentum transverse to the virtual photon indicates that non-zero moments arise mainly from the effects of the intrinsicKT of the struck quark with >≳(0.44 GeV)2, and to a lesser extent from QCD processes. No significant variation withQ2 orW2 is observed.

Measurements of the u valence quark distribution function in the proton and u quark fragmentation functions

Abstract A new determination of the u valence quark distribution function in the proton is obtained from the analysis of identified charged pions, kaons, protons and antiprotons produced in muon-proton and muon-deuteron scattering. The comparison with results obtained in inclusive deep inelastic lepton-nucleon scattering provides a further test of the quark-parton model. The u quark fragmentation functions into positive and negative pions, kaons, protons and antiprotons are also measured.

Large aperture Čerenkov counter

Abstract Design and performance of a large, multi-cell treshold Cerenkov counter is described. Electrons from K 0 → e πν decays are detected with an efficiency of better than 0.99 over an angular range of ±50° in one plane and of ±15° in the other.

Strangeness production in deep inelastic muon nucleon scattering at 280 GeV

The production of strange particles has been studied in a 280 GeV muon nucleon scattering experiment with acceptance and particle identification over a large kinematical range. The data show that at large values ofxBj the interactions take place mostly on au valence quark in agreement with the basic quarkparton model predictions. This feature results in a strong forward-backward asymmetry in the distribution of strangeness along the rapidity axis. The data are compatible with a strange to non-strange quark suppression factor of ≈0.3 and with a strong suppression of strange diquarks. The distributions ofK+K− pairs show that the two kaons are preferentially produced at neighbouring values of rapidity.

Experimental study of the ΔSΔQ rule in the time-dependent rate of Ko → πeν

Abstract The time-dependence of the decay rate of initially pure Ko into the final states ( π - e + ν) and (π + e - ν ) has been studied to investigate the validity of the ΔS ΔQ rule. In a sample of 4724 events no evidence for weak hadronic current with ΔS = − ΔQ is found. The ratio of the ΔS = ΔQmplitude and the ΔS = ΔQ amplitude is x = (0.04 ± 0.03) − i(0.06 ± 0.05).

Experimental study of the time-dependent rate of K0 → π+π−π0

Abstract The time-dependence of the decay rate of initially pure K 0 into the final state ( π + π − π 0 ) has been studied in search for the decay k S 0 → π + π − π 0 . No evidence is found in a sample of 384 observed events. The ratio of the CP -violating K S 0 amplitude and the K L 0 amplitude is η +−0 = (0.13 −0.20 +0.17 ) + i(0.17 −0.26 +0.27 ); the ratio of the CP -conserving K S 0 amplitude and the K L 0 amplitude is ∣ ϱ ∣ 0 → π + π − π 0 matrix element is found to be a +−0 = −0.31 ± 0.03.

Large-area wire spark chambers with two-coordinate read-out and ferrite core memory

Spark chambers with crossed wire planes and sensitive areas up to 240 x 130 cm 2 have been constructed for use in an electronics experiment at the CERN Proton Synchrotron. A two-coordinate read-out, which has the advantage of lower mass/cm 2 and compactness in space, has been achieved by special design of the high-voltage coupling, the ferrite core modules, and the read-out system. The spatial resolution for 1.5 mm wire spacing is ±0.5 mm and ±0.65 mm for the Iow- and for the high-voltage planes, respectively.

Production of an initially pure K0 beam of known momentum

Abstract Apparatus is described which selects electronically K + interactions in liquid hydrogen which produce K 0 in the reaction K + p→K 0 p π + . The directions of all 3 particles of the final state are measured in wire chambers. These measurements determine the K 0 production vertex and decay vertex and the K 0 momentum to a precision of ± 3 × 10 −2 , and thus the eigentime of K 0 . Calibration measurements using K 0 → π + π − decays are described. The apparatus has been designed for a study of the time dependent K 0 → π e v and K 0 → π + π − π 0 decay rates.

A study of the reaction K+p → K0 Δ++ (1236) at 2.25 GeV/c

Abstract The reaction K + p → K 0 Δ ++ (1236) has been studied at 2.25 GeV /c incident momentum. Results based on 15 800 events are discussed. The differential cross-section is observed to be strongly suppressed at t ′ = 0. Spin density matrix elements show a dominance of helicity flip at | t ′| ≠ 0.