E. Dahl-Jensen

A search for glueballs and a study of doouble pomeron exchange at the CERN intersecting storage rings

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 axial field spectrometer at the CERN ISR

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.

Studies of proton-proton collisions at the CERN ISR with an identified charged hadron of high transverse momentum at 90°: (II) On the distribution of charged particles in the central region

Abstract Results are reported from an investigation of proton-proton collisions at a c.m. energy of 52.6 GeV, in which a charged hadron with large transverse momentum is produced near 90° in the c.m.s. We have studied the momentum and charge correlations between identified high- p T trigger particles and other charged particles in the central region (rapidity | y | p T particles with charge opposite to that of the trigger particle in a small solid angle around the trigger particle. The sum of the momenta of charged particles inside | y | c per GeV/ c increase of the trigger momentum. Opposite in azimuth to the trigger particle we observe close pairs of high- p T particles in both neutral and doubly charged combinations. In this region we see an indication of scaling in the x E variable for trigger momenta exceeding 3 GeV/ c . The distribution of charge is strongly correlated with the charge of the trigger particle. Otherwise the type of trigger particle does not affect strongly the observed event structure, but for trigger momenta above 3 GeV/ c , K − and p triggers are observed to have fewer negative high- p T recoil particles within | y |

Direct evidence for the emergence of jets in events triggered on large transverse energy in 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.

Evidence for dominant vector-meson production in inelastic proton-proton collisions at 53 GeV c.m. energy

Abstract The Split Field Magnet facility at the CERN ISR has been used to measure inclusive resonance production in inelastic p-p collisions at a c.m. energy of 53 GeV. The mass spectrum of pairs of oppositely charged hadrons shows a strong correlation, which can be explained as a consequence of dominant vector meson production, accounting for more than 60% of all pions and kaons produced.

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.

The forward ring imaging Cherenkov detector of DELPHI

The Forward Ring Imaging Cherenkov detector of the DELPHI experiment at LEP provides hadron identification at polar angles15° < θ < 35° and 145° < θ < 165°. Two radiator media, a layer of liquid C6F14 and a volume of gaseous C4F10, in combination provide coverage of momenta up to 40 GeV/c. A single array of photosensitive Time Projection Chambers registers the impact points of ultraviolet photons from both radiators. The design of the detector and of its readout system is described. First results obtained with a partly installed detector are reported.

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

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.

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

Abstract Events with a large transverse energy in a calorimeter with full azimuthal coverage and |y|

A study of exclusive central hadron production at the ISR as a search for gluonium states

Abstract We present first results from a study of the exclusive reaction pp→pπ + π − p at √s=63 GeV with π + and π − produced in the central region. This reaction has been suggested as a method of searching for gluonium states. The π + π − mass distribution shows rapid order of magnitude decreases in cross section at both 1000 MeV/ c 2 and 1500 MeV/ c 2 . Further structure is observed above 2000 MeV/ c 2 .