S. Almehed

Double parton scattering inpp collisions at\(\sqrt s = 63\) GeV

AbstractIn a study ofpp collisions at

The axial field spectrometer at the CERN ISR

\sqrt s = 63

Direct evidence for the emergence of jets in events triggered on large transverse energy in pp collisions at s = 63 GeV

GeV with more than 29 GeV total transverse energy emitted into 1.8 units of rapidity in the central region, we have extracted a sample of 4-jet events and compared it with models of the two sources of 4-jet production: double bremsstrahlung and double parton scattering. The data cannot be described by bremsstrahlung alone, and we extract the fraction of 4-jet events attributed to double parton scattering for various definitions of the 4-jet sample. We determine the double parton scattering/2-jet yield ratio, and this leads to a determination of the proton radius. We discuss the implications of our observations for the general understanding of high-ΣET events.

Bose-Einstein correlations in αα, pp and pp interactions

We present results from a study of centrally produced mesons in 3 × 106 events with two small-angle protons at the CERN Intersecting Storage Rings. A high-statistics sample of exclusive pp → ppπ+π− events at √s = 63 GeV has been obtained, where the reaction mechanism is dominated by double pomeron exchange. Scalar or tensor glueballs may be produced by this process. The π+π− mass spectrum has a distinctive structure, and analysis shows that the data are dominantly S-wave up to 1600 MeV. The behaviour of the D-wave provides evidence for a 2++ resonance (M = 1480 ± 50 MeV, Γ = 150 ± 50 MeV) in addition to the f(1270). We also show data on exclusive K+K−, pp, and π+π−π+π− production, and on the analogous reaction αα → ααπ+π− at √s = 126 GeV. Flavour independence is suggested by the observation of approximately equal numbers of K+K− and π+π− pairs for mass above 1 GeV. The mass spectra are also apparently independent of √s (45, 63, 126 GeV) and incident particle type (p, α).

A search for heavy stable and long-lived squarks and sleptons in

Abstract The axial field spectrometer is being exploited in a wide-ranging programme to study pp and p p -collisions which are characterized by a large transverse momentum. A specially shaped magnet together with an “imaging” drift chamber is used for efficient detection and momentum analysis of high multiplicity events at interaction rates of up to 5 × 106 s. Particle identification is accomplished over 1 sr; an uranium/scintillator hadron calorimeter will cover more than 8 sr in 1982 to provide an unbiased energy measurement.

e^{+}e^{-}

Abstract In four-jet events from e+e− →Z0 →multihadrons one can separate the three principal contributions from the triple-gluon vertex, double gluon-bremsstrahlung and the secondary quark-antiquark production, using the shape of the two-dimensional angular distributions in the generalized Nachtmann-Reiter angle θ NR ∗ and the opening angle of the secondary jets. Thus one can identify directly the contribution from the triple-gluon vertex without comparison with a specific non-QCD model. Applying this new method to events taken with the DELPHI-detector we get for the ratio of the colour factor Nc to the fermionic Casimir operator C F : N c C F = 2.55 ± 0.55 ( stat. ) ± 0.4 ( fragm. + models ) ± 0.2 ( error in bias ) in agreement with the value 2.25 expected in QCD from Nc=3 and C F = 4 3 .

collisions at energies from 130 to 183 GeV

We present data obtained from a 1.7 sr hadron calorimeter, triggered on transverse energy, in pp collisions at s=63 GeV at the CERN-ISR. From the change in the distribution of energy in the calorimeter, we extract the cross section for two-constituent hard scattering for pT between 6 and 14 GeV at y = 0. The decrease of this jet cross section over this pT range is consistent with exp (−bpT), with b = (1.02 ± 0.09) GeV−1. The slope and normalization of the cross section agree well with a QCD motivated Monte Carlo model. The ratio between jet and single particle cross sections [dσJET/dpT)/(dσπ0/dpT)]| y = 0 changes from about 200 at 6 GeV to about 1500 at 14 GeV.

Further evidence for jet production from the charged particles produced in pp collisions at triggered on large transverse energy

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.