J. Bourotte

ExperimentalJ/ψ hadronic production from 150 to 280 GeV/c

A detailed study ofJ/ψ hadronic production has been performed in a high statistics experiment (more than 1.5 106J/ψ observed in their dimuon decay mode). Data have been taken with incident π±,K±,p±, on hydrogen and platinum targets, at 150, 200 and 280 GeV/c. We find from the observed nuclear dependance of the cross sections, that about 18% of theJ/ψ are produced diffractively. Using known structure functions of the quarks in the nucleon and in the pion, we derive estimations for the gluon structure functions.

Heavy flavour production in Z decays

Abstract From an analysis of inclusive leptons in data collected by the ALEPH detector at LEP, we measure the fractions of b b and c c events in hadronic Z decays. The b b fraction times semileptonic branching ratio is measured to be Br ( b → e )·Γ b b /Γ had = 0.0224 ± 0.0016 ± 0.0010 . Assuming a b semileptonic branching ratio of 0.102 ± 0.010 gives Γ b b /Γ had = 0.220 ± 0.016 ± 0.024 , in good agreement with the standard model prediction of 0.217. The c c fraction times semileptonic branching ratio is measured to be Br ( c → e )·Γ c c /Γ had = 0.0133 ± 0.0040 −0.0031 +0.0038 . Assuming a c semileptonic branching ratio of 0.090 ± 0.013 gives Γ c c /Γ had = 0.148 ± 0.044 −0.038 +0.045 , in agreement with the standard model prediction of 0.171.

A precise measurement of the real part of the elastic scattering amplitude at the Sp̄pS

Abstract A precise measurement of pp elastic scattering in the Coulomb-strong interaction interference region was performed at the CERN SppS Collider at a centre-of-mass energy of 541 GeV. The ratio of the real to the imaginary part of the forward elastic scattering amplitude was found to be ρ = 0.135 ± 0.015. The slope of the exponential fall off of the strong interaction part was also measured to be b = 15.5 ± 0.1 GeV −2 .

Observation of an excess of νe, νe events in a beam dump experiment at 400 GeV

Abstract A beam dump experiment has been performed at CERN in Gargamelle using the neutrino facility to look for penetrating particles produced either directly in the beam interaction or by prompt decay of new particles. A total of 32 interactions with a visible energy greater than 10 GeV has been found, classified, aftercorrections, into 18 charged current ν μ or ν μ , 5.1 neutral current and 8.9 ν e or ν e charged current events. An excess of ν e events remains after all subtractions from any established sources. Results are presented in terms of the product of the cross section and the leptonic decay branching ratio of the possible source.

Observation of an Excess of electron-neutrino, anti-electron-neutrino Events in a Beam Dump Experiment at 400-GeV

Abstract A beam dump experiment has been performed at CERN in Gargamelle using the neutrino facility to look for penetrating particles produced either directly in the beam interaction or by prompt decay of new particles. A total of 32 interactions with a visible energy greater than 10 GeV has been found, classified, aftercorrections, into 18 charged current ν μ or ν μ , 5.1 neutral current and 8.9 ν e or ν e charged current events. An excess of ν e events remains after all subtractions from any established sources. Results are presented in terms of the product of the cross section and the leptonic decay branching ratio of the possible source.

Search for the neutral Higgs Boson from Z0 decay in the Higgs mass range between 11 and 24 GeV

Abstract A search for the neutral Higgs boson in the mass range above 11 GeV (above the H 0 →b b threshold), using the process Z0→H0e+e−, Z0→H0μ+μ− and Z 0 → H 0 v v , is performed on data collected by the ALEPH detector corresponding to about 25 000 events of Z0→ hadrons. Combining all these processes, the mass range excluded is 11 GeV at 95% CL. Together with a previously published result from ALEPH, the mass range excluded is 32 MeV to 24 GeV at 95% CL. This result also extends the excluded mass region for neutral Higgs bosons from supersymmetry.

Experimental Determination of the pi Meson Structure Functions by the Drell-Yan Mechanism

We have studied high statistics samples of dimuon events (∼35,000) produced from π± on platinum target in the mass interval 4.2≦Mμμ≦8.5 GeV at 150, 200 and 280 GeV/c. The π structure function is obtained by a fit ofd2σ/dx1dx2 to π+ and π− data. At 200 GeV, the simultaneous use of π+ and π− data allows a separate determination of the valence and sea structure functions of the π. Furthermore, the 150 and 280 GeV data allow an accurate determination of the shape of the valence structure function and give an estimate of its evolution betweenQ2=25 and 50 GeV2.

Evidence for ψψ production in π− interactions at 150 and 280 GeV/c

From the analysis of multimuon events produced by π− interactions at 150 and 280 GeV/c in the NA3 spectrometer, we present evidence for the production of two J/ψ mesons in the same interaction (13 events seen, for an expected background of about 0.2 events). Some possible production mechanisms are described and an estimation of the cross section is given.

Measurement of the K−π− structure function ratio using the Drell-Yan process

Abstract The first measurement of the kaon to pion structure function ratio has beenperformed in a high integrated luminosity experiment studying the production of massive muon pairs. The ratio u K u π clearly deviates from 1 for values of x1 > 0.7. A theoretical model comparison is also briefly discussed.

Observation and study of the νμe− → νμe− reaction in gargamelle at high energy

Abstract A search for the reaction ν μ + e − → ν μ + e − was made in the bubble chamber Gargamelle exposed to the wide-band neutrino beam of the CERN-SPS. Ten isolated e − were found above 2 GeV energy. All of them were emitted at an angle smaller than 1.5° with respect to the beam. The background is 0.2 ± 0.2 events. Results on cross section are given in terms of vector and axial vector coupling constants. A comparison is made with the standard SU(2) ⊗ U(1) model: no agreement is found with the currently accepted value of the mixing angle. Possible sources other than the above reaction are discussed.