R. M. Brown

Measurements of hyperon semileptonic decays at the CERN Super Proton Synchrotron

Results on five different hyperon semileptonic decays from the WA2 experiment, performed in the CERN SPS charged hyperon beam, have been analysed within the framework of the Cabibbo model. For the first time, the inconsistencies, which inevitably occur when the results from different experiments are combined, have been avoided in these comprehensive fits to high statistics data from a single hyperon decay experiment. Excellent agreement with the basic Cabibbo model has been obtained using the WA2 data either alone or together with neutron lifetime measurements. These results contrast strongly with other recent Cabibbo analyses which have indicated the presence ofSU(3) breaking effects. Including radiative corrections we have obtained the results,F=0.477±0.012,D=0.756±0.011 and sinθc=0.231±0.003. The ratio (D/D+F) is 0.613±0.009, which is close to theSU(6) prediction of 3/5. Using additional information onft values for superallowed nuclear Fermi transitions, an upper limit on the mixing parameter sinθ3 in the Kobayashi-Maskawa six quark scheme has been obtained: |sinθ3|<0.20.

Particle and antiparticle production by 200 GeV/c protons in the charged hyperon beam at the CERN SPS

Abstract A charge hyperon beam has been brought into operation at the CERN SPS. Particles are identified by a DISC Cerenkov counter, and decay products are analysed by a magnetic spectrometer. Cross sections for the inclusive production of π + , K + , p , Σ + , Σ − , ζ − , d, and π − , K − , p , Σ + , Σ − , ζ − , ω − , d in the forward direction have been measured at laboratory momenta between 70 and 130 GeV/ c . This range of momenta corresponds to 0.35 ⩽ x ⩽ 0.66 for an incident proton momentum of 200 GeV/ c . Antihyperon ( Σ − , ζ − , Σ + ) and Σ + and ω − fluxes have been measured for the first time in a hyperon beam. Scaling behaviour is observed when the data are compared with the results from other experiments. The inclusive particle production cross sections have a (1 − x ) n dependence, where n is characteristics of the particle. A search has been made for new particles in the mass range 2–10 GeV/ c 2 . No evidence is found for such particles.

First measurement of the Ω− decay branching ratios

Abstract In an experiment in the CERN-SPS charged-hyperon beam, the main Ω − decay branching ratios have been measured to be Γ(Ω − →Λ K − /Γ( all )=0.686±0.013 , Γ(Ω −1 →Ξ 0 π − )/Γ( all )=0.234±0.013 , Γ(Ω − →Ξ − π 0 )/Γ( all )=0.080±0.008 . The relative branching ratio of the two Ξπ modes provides a test of the ΔI= 1 2 rule in decuplet-octet transitions. A search has also been made for the rare decay modes Ω − →Λπ − , Ω − →Ξ − γ, Ω − →Ξ − π + π − and Ω − →Ξ 0 e − ν .

Measurement of Ω− decay properties in the CERN SPS hyperon beam

In an experiment in the CERN SPS charged hyperon beam, a sample of 16 000Ω− decays was collected at an Ω− momentum of 131 GeV/c the Ω− lifetime, the branching ratios and decay asymmetry parameters for the main decay modes were measured, giving: τΩ−=(0.823±0.015)×10−10s , Γ(Ω−→ΛK−)Γ(Ω−-→all)=0.675±0.008 , α(Ω−→ΛK−)= −0.025±0.028, Γ(Ω−→Ξ0π−)Γ(Ω−→all) = 0.236±0.008 , α(Ω−→Ξ0π−)=0.09±0.14, Γ(Ω−→Ξ−π0)Γ(Ω−→all)=0.089±0.005 , α(Ω−→Ξ−π0)=0.05±0.21. For the rare decay modes, the following results for the branching ratios were obtained: if Γ(Ω−→Ξ0e−ν)Γ(Ω−→all)=(0.56±0.28)×10−2 , if Γ(Ω−→Ξ−π+π−)(Γ(Ω→all)=(3.7−1.1+3.6)×10−4 , Γ(Ω−→Ξ−γ)(Γ(ω−→all)<2.2×10−3 at the 90% confidence level, Γ(Ω−→Λπ−)(Γ(Ω−→all)<1.9×10−4 at the 90% confidence level . A sample of 32 000 Ξ− decays collected under the same experimental conditions gave a new measurement of the Ξ− lifetime: τΞ−=(1.652±0.051)×10−10 s . Combining the measurements of the present experiment with those obtained in a previous experiment in the SPS hyperon beam gives: if τΩ−=(0.823±0.013)×10−10 s , Γ(Ω−→ΛK−)Γ(Ω−→all=0.678±0.007 , Γ(Ω−→Ξ0π−)Γ(Ω−→all)=0.236±0.007 , Γ(Ω−→Ξ−π0)Γ(Ω−→all=0.086±0.004 , Γ(Ω−→Ξ−π+π−)Γ(Ω−→all=(4.3−1.3+3.4)×10−4 . The experimental results are compared with theoretical calculations.

A measurement of the Ω− lifetime

Abstract In an experiment at the CERN-SPS charged-hyperon beam, a sample of 2500 Ω − → ΛK − decays has been collected at Ω− momenta of 98.5 and 115 GeV/c. The Ω− lifetime is found to be τ Ω = (0.822 ± 0.028) × 10 −10 s .

Measurement of {Mathematical expression} using impact parameters and leptons

AbstractA measurement of