O. Botner

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).

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 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 .

Evidence for a directional dependence of Bose-Einstein correlations at the CERN intersecting storage rings

Abstract In pp and pp collisions at the CERN Intersecting Storage Rings, a directional dependence of the size of the pion-emitting region is observed using Bose-Einstein interference between identical charged pions. The data reveal a substantially larger dimension in the direction parallel to the beam axis than in the transverse direction, indicating a prolate shape of the emission region. For αα interactions, the data are consistent with a spherical shape.

The production of prompt positrons at low transverse momentum increases with the square of the associated charged multiplicity: Axial field spectrometer collaboration

We have measured the production of prompt positrons in pp collisions at √s = 63 GeV and y = 0 in the pT interval 0.12<pT<1.0 GeV/c. The results indicate that the production of positrons at low pT (<0.4 GeV/c) is proportional to the square of the mean multiplicity in the central region |y| < 1. Such a quadratic dependence is not expected from final-state sources such as hadronic bremsstrahlung or hadronic decays, but is natural in models where low mass electron pairs are produced by interactions of constituents created during the collision.

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.

Charged particle production and correlations at high transverse momentum at the CERN intersecting storage rings

Abstract We study the production of identified charged particles in pp collisions at a c.m. energy of 63 GeV in events with an identified high-pT trigger particle. The measurements were performed at the CERN Intersecting Storage Rings using the Axial Field Spectrometer. Production ratios are presented as a function of pT in the range 2.5 to 8 GeV/c.

The associated charged particle multiplicity of high-pT π0 and single-photon events

Abstract The associated charged particle multiplicities of high-pT π0 and single-photon events were measured at the CERN intersecting storage rings using lead/liquid-argon calorimeters and a scintillation counter array placed around the intersection region. The average multiplicity on the trigger side for the single-photon events was found to be significantly lower than that for the π0 events. The away-side multiplicity for both π0 and single-photon events increases with the trigger particle pT, but, at a fixed pT, the direct photon sample was found to have a slightly lower average multiplicity. The differences in the event structure can be explained if a large fraction of the single photons are produced via qg → γq constituent scattering.

A comparison of hadron production in pp and pp collisions in the central region at s = 53 GeV

We have studied the inclusive production of the hadrons π±, K±, p, p, Λ, Λ, ρ and ⋉ in the central region at the ISR s = 53 GeV, in both pp and pp collisions. Differences are observed only for K±, p, and p production. We then study also correlations between low-pT pp and pp pairs in the two types of collisions, separating the contribution from baryon pair production and from the incident particles (stopping protons). We observe a positive correlation between two stopping protons; between the production of two pairs, and between a stopping proton and a pair production, there are negative correlations.