Inclusive charged particle cross sections in full phase space from proton proton interactions at ISR energies

Measurements are presented of inclusive charged particle production in proton-proton collisions at √s=31, 44 and 62 GeV at the CERN ISR. The large acceptance of the Split Field Magnet detector allows a single experimental setup to cover almost the full longitudinal phase space up to a transverse momentum of 3 GeV/c.     

A study of gluon scattering and gluon fragmentation in highp T interactions at the ISR

Gluon scattering processes are studied in hadronic highp _T events using data obtained with the Split Field Magnet detector (SFM) at the CERN ISR. The experimental set-up allowed the scanning of a wide range of parton energies and scattering angles. It is shown that for positive pions as trigger particles, the parton composition of the recoil jet is correlated with the polar angle and transverse momentum of the triggering pion. Over the kinematical region studied, the recoil jet originates predominantly from scatered gluons, with an increasing prevalence of the gluon component towards forward triggering angles. The variation of the momentum structure of the recoil jet with the trigger angle indicates that the fragmentation function of gluons is softer than that of quarks.     

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.     

Higher order QCD effects in inclusive annihilation and deep inelastic scattering

We present a parton model interpretation of the predictions of quantum chromodynamics in the process e⁺e^?→hadron + anything. We give thecomplete list of parameters needed for the study of the scaling violations of fragmentation functions up to the next-to-leading logarithmic approximation. This includes flavour non-singlet and flavour singlet anomalous dimensions up to order α² and coefficient functions up to order α. We also present results for the deep inelastic scattering e^?h→e^? + anything. We find that in e⁺e^? annihilation the ratio of scaling violations of second order to first order is in general bigger than the corresponding ratio for deep inelastic scattering. The Gribov-Lipatov relation is thus violated in second order. We also find that a modified Drell-Yan analytic continuation relation holds between the deep inelastic and annihilation structure functions for quarks and gluons. In x space we give detailed numerical evaluation of the QCD effects for non-singlet and singlet densities, in the space-like and time-like regions.     

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.     

Higher order corrections and the scale parameter in QCD

I estimate the influence of the higher order corrections on the determination of the scale parameter Λ². I find a sizeable effect (a reduction of Λ² by a factor 3 to 4). This factor can be relevant in the comparison of Λ² with the characteristic confinement parameters.     

Higher order QCD corrections to the photoproduction of a direct photon at HERA

The contribution of resolved photons to the photoproduction cross section of direct photons is reexamined. Higher order,O(α ² α _s), QCD corrections to this contribution are calculated and turn out to be important at HERA energies. The observation of direct photons in the medium-p _⊥ range (p _⊥～5 GeV/c) should provide the opportunity to measure the gluon content of the photon.     

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.     

Positive particle production in the fragmentation region at the CERN ISR

Cross sections for the production of positive pions, kaons and protons in proton-proton collisions at the CERN ISR have been measured. These measurements extend to transverse momenta p_T of 2.5 GeV and span the range in $\text{x = 2p}{}_{\mathrm{<mtext>L</mtext>}}\text{/}\text{s}$ between 0.3 and 0.8 For transverse momenta larger than ～ 1 GeV the cross sections show an increase relative to low-energy data, but are consistent with scaling within the energy range measured here, $\text{31 <}\text{s}\text{< 63}\text{GeV}$.     

Inclusive single particle density in configuration space from the QCD-cascade in DLA approximation

The structure of the QCD gluonic cascade in configuration space is investigated. The explicit form of the inclusive single particle density matrix and single particle density in configuration space transverse coordinates is derived in the double logarithmic approximation (DLA) of QCD. The possible simplification of the multiparton density matrix formalism for DLA approach is found and discussed. Received: 18 November 1997 / Published online: 26 February 1998     

Charged particle spectra in αα and αp collisions at the CERN ISR

Momenta of charged particles produced in inelastic αα, αp, andpp collisions were measured using the Split-Field-Magnet detector at the CERN Intersecting Storage Rings. Inclusive and semi-in-clusive spectra are presented as a function of rapidityy, Feynman-x, and transverse momentump _T . The inclusivey distributions agree well with predictions of the dual parton model; the highest particle densities are reached aty?0 and the momenta of leading protons decrease significantly for increasing total multiplicity. ‘Temperatures’ are equal in αα, αp, andpp interactions. Thep _T distributions depend weakly on the multiplicity.     

Hadronic matter at high energy density and the search for the hadron–parton QCD phase transition

Recent progress is reviewed concerning the evidence for a phase change in strongly interacting matter, as predicted by Lattice QCD theory to occur at an energy density of about 2–3 GeV per cubic fermi. Experiments at the CERN SPS with Lead (208 Pb) beams show that such densities have been reached, and suggest a set of observable quantities to bear first evidence concerning the transition.     

Large transverse momentum particle production at 90° in proton-proton collisions at the ISR

Total charged particle fluxes above 1.2 GeV/c transverse momentum at 90° have been measured at the CERN Intersecting Storage Rings for c.m. energies between 23.2 and 52.7 GeV. In addition, charged pion spectra above 3 GeV/c have been obtained at 44.4 and 52.7 GeV, as well as gamma-ray spectra at the same energies. The upper limit to produce a single electron above 3 GeV/c at 90° is less than 1.2 × 10^?33cm²/sr at 90% confidence level.