Soft and hard interactions in p \bar p collisions at \sqrt s = 1800 and 630 GeV

We present a study of p $\bar p$ collisions at $\sqrt s = 1800$ and 630 GeV collected using a minimum bias trigger by the CDF experiment in which the data set is divided into two classes corresponding to “soft” and “hard” interactions. For each subsample, the analysis includes measurements of the multiplicity, transverse momentum (p _T ) spectrum, and the average p _T and event-by-event p _T dispersion as a function of multiplicity. A comparison of results shows distinct differences in the behavior of the two samples as a function of the center-of-mass (CM) energy. We find evidence that the properties of the soft sample are invariant as a function of CM energy.     

Measurement and QCD analysis of jet cross sections in deep-inelastic positron-proton collisions at \sqrt{s} of 300 GeV

Jet production is studied in the Breit frame in deep-inelastic positron-proton scattering over a large range of four-momentum transfers and transverse jet energies GeV. The analysis is based on data corresponding to an integrated luminosity of taken in the years 1995–1997 with the H1 detector at HERA at a center-of-mass energy GeV. Dijet and inclusive jet cross sections are measured multi-differentially using and angular ordered jet algorithms. The results are compared to the predictions of perturbative QCD calculations in next-to-leading order in the strong coupling constant . QCD fits are performed in which and the gluon density in the proton are determined separately. The gluon density is found to be in good agreement with results obtained in other analyses using data from different processes. The strong coupling constant is determined to be . In addition an analysis of the data in which both and the gluon density are determined simultaneously is presented.     

The influence of Bose-Einstein correlations on intermittency inp\bar p collisions at\sqrt s = 630 GeV

The influence of Bose-Einstein correlations on the rise of factorial moments is small in the 1-dimensional phase space given by the pseudorapidity η, where the 2-body correlation function is dominated by unlike-sign particle correlations. Contraily, the influence is dominant in the higher dimensional phase space. This is shown by using correlation integrals. They exhibit clear power law dependences on the four-momentum transferQ ² for all orders investigated (i=2–5). When searching for the origin of this behaviour, we found that the Bose-Einstein ratio itself shows a steep rise forQ ²→0, compatible with a power law.     

Benchmark cross sections forp \bar p collisions at 1.8 TeV

High-energyp \(\bar p\) collisions provide many quantitative tests of the standard model. Of particular interest are “hard scattering” processes, which test not only standard model matrix elements and higher order perturbative corrections, but also the distributions of quarks and gluons in the colliding hadrons. We present detailed comparisons of data from the CERNSp \(\bar p\) S collider with theory, incorporating up-to-date parton distributions derived from recent deep inelastic scattering data. Encouraged by the excellent agreement between data and theory at \(\sqrt s \) =630GeV, we present a complete set of “benchmark” predictions for the FNALp \(\bar p\) collider at \(\sqrt s \) =1.8TeV.     

Multi-photon production in ee collisions at \sqrt{s} = 181-209 GeV

The process is studied using data collected by the OPAL detector at LEP between the years 1997 and 2000. The data set corresponds to an integrated luminosity of 672.3 pb^-1 at centre-of-mass energies lying between 181 GeV and 209 GeV. Total and differential cross-sections are determined and found to be in good agreement with the predictions of QED. Fits to the observed angular distributions are used to set limits on parameters from several models of physics beyond the Standard Model such as cut-off parameters, contact interactions of the type , gravity in extra spatial dimensions and excited electrons. In events with three photons in the final state the mass spectrum of photon pairs is investigated. No narrow resonance is found and limits are placed on the product of the production cross-section and branching ratio. Received: 22 July 2002 / Published online: 8 November 2002