Piet Van Dam

Bose-Einstein correlations in αα, pp and pp interactions

Abstract Bose-Einstein correlations between pions produced in the central region of rapidity in αα, pp and p p interactions have been studied at the ISR. The parameters r and τ c -often interpreted as the radius and depth of the π-emitting region - are found to be independent of incident particle type but to depend on the mean charged multiplicity. In high multiplicity events, the pions appear to originate from a larger space-time region.

Experimental Study of the Reaction Neutrino p --> mu- p pi+. GARGAMELLE Neutrino Propane Experiment

Abstract A sample of 357 events fitting the reaction ν + p → μ − + p + π + on free proton is obtained from the Gargamelle neutrino propane experiment at the CERN-PS. The average value of the cross section above 1 GeV is found to be (0.60 ± 0.07) 10 −38 cm 2 . The reaction is dominated by the production of the Δ ++ (1232) resonance. Results on the Δ ++ spin density matrix are given.

The transverse energy distribution in hadron-lead collisions

The transverse energy cross-sectiondσ/dET has been measured in the pseudorapidity region 0.6<η<2.4 for hadron-lead collisions at 200 GeV/c incident hadron momentum. TheET distribution extends to 40 GeV, which is twice the kinematic limit forp-p collisions at the same incident beam momentum. The distribution ofET is found to shift towards low pseudorapidities with increasing total transverse energy.

Bose-Einstein correlations between kaons

Abstract Bose-Einstein correlations between identical charged kaons are observed in αα, pp, and p p collisions at the CERN Intersecting Storage Rings. The average radial extension of the K-enitting region is found to be (2.4±0.9) fm.

The transverse energy distribution in proton-lead collisions

Abstract The distribution in transverse energy, E T , has been measured in p-Pb collisions at 200 GeV/c incident proton momentum. The data cover the pseudorapidity (η) range 0.6 to 2.4 in the laboratory frame. The E T distribution extends to 50 GeV, which is nearly 2.5 times the kinematic limit for the pp centre of mass. Furthermore, the distribution of E T in η is found to shift towards low rapidities with increasing total E T .

Performance of the Forward RICH detector system at DELPHI

One quarter of the Forward Ring Imaging Cherenkov (Forward RICH) detector has been installed and operated in the DELPHI experiment. The detector covers the forward-backward regions (15 degrees >

Fragmentation Functions in High-energy Neutrino and Anti-neutrino Deuterium Interactions

Quark fragmentation functions are studied in charged current ν and ν interactions in deuterium. The W2, Q2 and y dependences are compared with the predictions of first order QCD and with those of higher twists. The W2 dependence is a small effect in our kinematical range and our data are well linked to the higher W2 muon scattering experiment. The Q2 dependence of non singlet fragmentation functions is well reproduced by first order QCD but part of this dependence could be due to some low W kinematical effect. The y-z factorization breaking seems to be a low W effect but a small higher twist term, as predicted by Berger cannot be excluded.

FRAGMENTATION INTO STRANGE PARTICLES IN HIGH-ENERGY NEUTRINO P, neutrino N, ANTI-NEUTRINO P AND ANTI-NEUTRINO N INTERACTIONS

Abstract The fragmentation of the hadronic system into Λ, Σ(1385), K ) and K ∗ (892) in deep-inelastic charged-current interactions of high energy neutrinos and antineutrinos with proton and neutron is analyzed. The results obtained for the production of these particles from the various initial states are compared with each other and with the predictions of the Lund fragmentation model. This comparison shows that a spectator diquark does not fragment as a whole in a fraction of the interactions. The role of the sea quarks in the baryon formation process is underlined. Strange vector and pseudoscalar mesons are likely to be produced at similar rates.

Measurement of the Ratios of

Abstract From the analysis of 5630 v υ and of 1372 v π charged current interactions, obtained in the BEBC bubble chamber filled with deuterium and exposed to the CERN wide band antineutrino beam, the ratios of cross section on neutron and photon targets have been measured and found to be R  σ ν)/σ v p = 0.51 ± 0.01 (±0.03) , and R  σ( ν n )/σ( v p ) = 22.2 ± 0.12 (±0.25) The dependence of these ratios on the x scaling variable shows, in a direct way, that the momentum distribution of the majority quark, up(x) = dn(x), is broader than that of the minority quark, un(x) = dp(x).