Inclusive cross section ratios in highp T proton-proton scattering at ISR energies

Ratios of inclusive cross sections σ(π⁺)/σ(π⁺+K ⁺+p) and \(\sigma (\pi ^ - )/\sigma (\pi ^ - + K^ - + \bar p)\) were measured for proton-proton interactions with a highp _T hadron in the final state around c.m.s. scattering angles θ?20°, 20° and 45° at two ISR energies \(\sqrt s = 31\) Gev and 62 GeV. Results are shown as functions of transverse and longitudinal momentum and are compared with parton model predictions. The different dependences of positive and negative pion fractions atp _T ?2–3 GeV/c on longitudinal momenta is similar to that observed in soft hadronic interactions at low values ofp _T where the leading proton effect (diquark fragmentation) is known to contribute. The quantitative agreement of the data with diquark model predictions indicates the presence of diquark fragmentation also in highp _T jets.     

Multiplicity dependence of the average transverse momentum and of the particle source size inp−p interactions at\sqrt s =62, 44 and 31 GeV

The average transverse momentum and the size of the particle emitting source (measured via Bose-Einstein correlations) have been studied as functions of the charged particle density in the central region inp-p interactions at \(\sqrt s \) =62, 44 and 31 GeV. Both the average transverse momentum and the source size increase with increasing density at all three energies. This effect, very weak at \(\sqrt s \) =31 GeV, becomes stronger with increasing energy.     

Many-particle rapidity correlations in light-ion interactions at the CERN intersecting storage rings

Many-particle rapidity correlations have been studied for αα,dd, andpp interactions at the CERN Intersecting Storage Rings using the Split-Field Magnet detector, and basing the investigating on the distributions of rapidity gaps between particles. In the framework of a simple cluster model, it is found that all the data samples have similar features and that the events contain clusters of two different types.     

Gluon tagging in hard proton-proton interactions at the ISR

Events obtained by triggering on a single particle with high transverse momentump _T show a four-jet structure. The two transverse jets are due to the fragmentation of point-like scattered partons. Experimental evidence is presented that highp _T K ^? mesons and their associated jets are produced by hard scattering and subsequent fragmentation of flavour neutral partons with a rather soft structure function. Hence, gluons are a natural source of highp _T K ^? mesons which do not share any valence quark with the incoming protons. The analysis is based upon measurements of short-range quantum number correlations within the trigger jet and of long-range correlations between different jets. The data were obtained at \(\sqrt s\) =62 GeV GeV with the Split Field Magnet Detector (SFM) at the CERN ISR.     

Transverse momentum distribution in Pomeron-Pomeron collisions at the CERN ISR

Proton-proton interactions which result in a central cluster of massM _x and two quasi-elastically scattered protons are generally described by Pomeron-Pomeron scattering. A study of this process at ISR energies with the Split Field Magnet detector is carried out in terms of transverse momentum behaviour for the centrally produced system of particles. The inclusivep _T distribution for central hadrons is measured up to 3 GeV/c. Forp _T <1.2 GeV/c, thep _T distribution is exponential. Using a subsample of exclusive events, this exponential shape is shown to originate from a phase-space-like decay ofM _x when convoluted with a transverse component of the pomeron momentum. In the highp _T range, the shape of thep _T distribution strongly depends on Feynman-x of the scattered protons in a way that can be described by hard parton scattering.     

Contribution of single diffraction dissociation to highp T production in proton-proton collisions at\sqrt s = 62 GeV at the CERN ISR

The contribution of single diffraction dissociation to highp _T particle production has been determined with the split field magnet detector. For transverse momentap _T >2 GeV/c and production angles θ>10° it is found to be less than 5% for all types of trigger particles. Specifically, a diffractive origin of the large production cross section for highp _T protons can be excluded. The contributions found to highp _T production are found to be in good agreement with extrapolations of the relative particle yields from single diffraction dissociation observed in inelastic minimum bias events.     

Evidence forf 2 (1720) production in the reaction pomeron-pomeron→π+π−π+π−

Data are presented on pomeron-pomeron interactions which produce a central π⁺π^?π⁺π^? system in proton-proton collisions at √s=62 GeV at the CERN Intersecting Storage Rings. A spin-parity analysis of the π⁺π^?π⁺π^? system shows evidence for the production of the statef ₂ (1720) with decay to ρ⁰π⁺π^?. Since pomeron-pomeron interactions are expected to favor the production of gluonic bound states, observation of thef ₂ (1720) supports earlier interpretations of it as a glueball. In addition, enhancements near threshold give indication of the statef ₂ (1270) decaying to ρ⁰ρ⁰ and the statef ₀ (1400) decaying to ρ⁰π⁺π^?.