Jean-Marc Gaillard

A simple phenomenological description of hadron production

The inclusive production distributions of the non-leading particles in pp collisions are fitted by a simple general formula. The contributions from the ϱ0, ω, φ, and Jψ decays to the direct lepton spectra are calculated. Possible contributions from the semi-leptonic decay of the conjectured charmed meson are discussed.

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.

The phase of ηoo and the invariances CPT and T

Abstract The decay amplitude ϵ o = 2 3 η +− + 1 3η oo is decomposed into a CPT-conserving, T-violating part ϵ, and a T-conserving, CPT-violating part δ. Using the measurement of the phase of ηoo together with other results on Ko decays we obtain: Reϵ = (1.68 ± 0.30) × 10−3, IM ϵ = (1.45 ± 0.30) × 10−3. Re δ = (0.07 ±) × 10 −3 , Im δ = (−0.30 ± 0.45) × 10 −3 .

Search for decays of the W± and Z bosons into quark-antiquark pairs

Abstract The invariant mass distribution of jet pairs observed in the UA2 central calorimeter is examined in the search for an excess of events in the region of the W ± and Z bosons, which would reveal their decays into quark-antiquark pairs. We give a detailed account of the methods of analysis used to optimize the mass resolution achieving ≅±10%. A structure is observed at the level of ≅ 3 standard deviations in the mass region of W ± and Z with shape and position consistent with expectation from their qqdecays. It contains 632 ± 190 events, 1.4 standard deviations above the standard model prediction of 340 ± 80 events.

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 .

Vector meson and ψ contributions to single lepton spectra

Abstract The data on the dilepton spectra in a forward cone are used to predict the ϱ 0 , ω 0 , and ψ production at θ cm ≈ 90° and their contributions to the single lepton spectra. The π, (ϱ 0 +ω 0 ), and ψ inclusive cross-sections are well fitted over the entire p T range by a simple expression. Combined contributions from ϱ 0 , ω 0 , and ψ are found to account for about 30% of the observed lepton spectra. The contribution from the dilepton continuum is also discussed.

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.

Observation of the interference between KLo and KSo in the πoπo decay mode

Data obtained with a copper regenerator on the interference between the decays KLo → 2πo and KSo → 2π o are presented. The analysis leads to the results: φoo = 510 ± 30o, |ηoo| = (1.23 ± 0.24) (|ƒ − ƒko) × 10−3 where (ƒ−ƒ)ko is the regeneration amplitude for copper at 2 GeV/c in fm2. Present experimental data suggest (ƒ−ƒ)ko = 2.7 ± 0.3.

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 .

Further results on the interference between the πoπo decay of KLo and KSo

The experiment of Chollet et al. has been continued with a similar set up. The analysis of these new data leads to 56 free decay events KLo→πoπo and 1481 interference events KS, Lo, → πoπo behind a 20 cm thick copper regenerator. The results are ϕoo = 38o ± 25o and |ηoo|/(|f−f|/k) = (1.13 ± 0.12) × 10−3 where |f−f|/k is the regeneration amplitude for copper at 2 GeV/c in fm2.