B.S. Nielsen

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

AbstractIn a study ofpp collisions atn

Properties of a Fine Sampling Uranium - Copper Scintillator Hadron Calorimeter

sqrt s = 63

Bose-Einstein correlations in αα, pp and pp interactions

n 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.

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

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).

The dominance of jets at large transverse energy in a full-azimuth hadron calorimeter at ISR energies

Abstract We present results obtained with a uranium/copper scintillator fine-sampling calorimeter with wavelength shifter readout. Test beam measurements made with e±, π± and protons in the momentum range 0.3–40 GeV/c are presented. The calorimeter achieves energy resolutions of σ(E) E = 0.36 √E and 0.16 √E for hadrons and electrons, respectively. The measured ratio of response for electrons to that for hadrons is 1.11, for energies of 2 GeV or more. The spatial resolution achieved for single particles at normal incidence is ∼1 cm for electromagnetic showers and ∼3 cm for hadronic showers. Operational experience over three years of running at the CERN ISR, including operation at very high luminosities (∼1.4×1032 cm−2 s−1) is described.

Inclusive vector-meson production in the central region of pp collisions at √s = 63 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.

Antibaryon production in the central region at the ISR

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.

Multiplicity distributions in p-α and α-α collisions in the CERN ISR

Abstract The detailed shape of events triggered by a 1.7 sr hadron calorimeter is studied using charged track information in the Axial Field Spectrometer at the CERN ISR. With increasing transverse energy (ET) a large fraction of the events are seen to have a limited transverse momentum relative to the trigger direction. A comparison of the circularity of the events with a prediction of a QCD-motivated Monte Carlo model shows that at high ET the events originate predominantly from two-constituent scattering.