2,464,650 research outputs found

    Pentaquarks in high-energy colliding experiments: perspectives from HERA

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    Several issues related to pentaquark searches relevant for current and future high-energy colliding experiments are discussed. We make an attempt to explain why pentaquark candidates are not seen by some experiments, and what makes the HERA experiments so special in such searches.Comment: 14 pages, 4 eps figure

    Review of Final LEP Results or A Tribute to LEP

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    After a comment on the performance of LEP some highlights of the LEP1 and LEP2 physics programmes are reviewed. The talk concentrates on the precision measurements at the Z resonance, two fermion production above the Z, W+W- production, ZZ production, indirect limits on the Higgs mass, LEP contributions to the exploration of the CKM matrix, and on the LEP measurements of alpha_s.Comment: Proceedings of the XX International Symposium on Lepton and Photon Interactions at High Energies Rome, Italy, July 200

    The statistical parton distributions: status and prospects

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    New experimental results on polarized structure functions, cross sections for e¬Īpe^{\pm}p neutral and charge current reactions and őĹ\nu (őĹňČ\bar{\nu}) charge current on isoscalar targets are compared with predictions using the statistical parton distributions, which were previously determined. New data on cross sections for Drell-Yan processes, single jet in ppňČp\bar{p} collisions and inclusive ŌÄ0\pi^0 production in pppp collisions are also compared with predictions from this theoretical approach. The good agreement which we find with all these tests against experiment, strenghtens our opinion on the relevance of the role of quantum statistics for parton distributions. We will also discuss the prospects of this physical framework.Comment: 34 pages, 23 figures, references and figures adde

    New NLO Parametrizations of the Parton Distributions in Real Photons

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    We present new NLO sets of parton distributions in real photons based on a scheme invariant definition of the non-perturbative input. We compare the theoretical predictions with LEP data and a best fit allows us to constrain the parameters of the distributions. The shape of the gluon distribution is poorly constrained and we consider the possibility to measure it in photoproduction experiments. Three parametrizations which aim to take into account the scattering of LEP data are proposed. They are compared to other NLO parametrizations.Comment: 38 pages, 23 Postscript figures, fig. 6,7,8,9 improved, comparisons with other NLO parametrizations, added reference

    Recent Low x and Diffractive Collider Data

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    Selected recent data from collider experiments pertaining to the understanding of QCD at low Bjorken-x are reviewed. The status of QCD and Regge factorisation in hard diffractive interactions is discussed in terms of data from HERA and the Tevatron. The possibility of anomalous behaviour in the ő≥ő≥\gamma \gamma total cross section is confronted with the most recent measurements from LEP. Data from all three colliders that are sensitive to possible BFKL effects are presented and different interpretations are discussed.Comment: 9 pages, introductory talk from the 1999 Durham Phenomenology Workshop on Collider Physic

    e+e- --> e+e- pi0 pi0 at Daphne

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    The production of the sigma(500) meson in gamma gamma --> pi0 pi0 is studied. In particular, the KLOE data collected during the DAPHNE run at sqrt(s)= 1 GeV are appropriate to this purpose because of the strong reduction of Kaon backgrounds.Comment: 13 pages, 9 figures, few comments adde

    NLO photon parton parametrization using ee and ep data

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    An NLO photon parton parametrization is presented based on the existing F2ő≥F_2^\gamma measurements from e+e‚ąíe^+e^- data and the low-xx proton structure function from epep interactions. Also included in the extraction of the NLO parton distribution functions are the dijets data coming from ő≥p‚Üíj1+j2+X\gamma p \to j_1 + j_2 +X. The new parametrization is compared to other NLO parametrizations.Comment: 22 pages, 7 figures, 2 table

    A new gamma*-p / pbar-p factorization test in diffraction, valid below Q^2 about 6 GeV^2

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    One of the key experimental issues in high energy hadron physics is the extent to which data from the diffractive interaction mechanism may be described by a factorized formula which is the product of a universal term describing the probability of finding a Pomeron in a proton (loosely referred to as the "Pomeron flux-factor") and a term decribing the Pomeron's interaction with the other incident proton. In the present paper, after demonstrating that existing data on diffractive gamma*-p and pbar-p interactions show that the Pomeron flux-factor is not universal, we present the results of a new test of factorization in these interactions which does not rely on universality of the flux-factor. The test is satisfied to within ~20% for 1 < Q^2 ~ 6 GeV^2 and beta < 0.2 in the gamma*-p interactions, suggesting that the resons for non-universality of the flux-factor have a limited effect on the factorization itself. However, a clear breakdown of this test is observed at larger Q^2. Kharzeev and Levin suggest that this can be attributed to the onset of QCD evolution effects in the Pomeron's structure. The breakdown occurs in a Q^2 region which agrees with their estimates of a small Pomeron size.Comment: 20 pages, 7 Encapsulated Postscript figures, LaTex, submitted to European Phisical Journal

    Nucleon form factors, B-meson factories and the radiative return

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    The feasibility of a measurement of the electric and magnetic nucleon form factors at BB-meson factories through the radiative return is studied. Angular distributions allow a separation of the contributions from the two form factors. The distributions are presented for the laboratory and the hadronic rest frame, and the advantages of different coordinate systems are investigated. It is demonstrated that Q2Q^2 values up to 8 or even 9 GeV2^2 are within reach. The Monte Carlo event generator PHOKHARA is extended to nucleon final states, and results are presented which include Next-to-Leading Order radiative corrections from initial-state radiation. The impact of angular cuts on rates and distributions is investigated and the relative importance of radiative corrections is analysed.Comment: 9 pages, 11 figures. Final version to appear in Eur. Phys. J.

    Little Higgs models and single top production at the LHC

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    We investigate the corrections of the littlest Higgs(LH) model and the SU(3) simple group model to single top production at the CERN Large Hardon Collider(LHC). We find that the new gauge bosons WH¬ĪW_{H}^{\pm} predicted by the LH model can generate significant contributions to single top production via the s-channel process. The correction terms for the tree-level Wqq‚Ä≤Wqq' couplings coming from the SU(3) simple group model can give large contributions to the cross sections of the t-channel single top production process. We expect that the effects of the LH model and the SU(3) simple group model on single top production can be detected at the LHC experiments.Comment: 17pages, 5 figures, discussions and references added, typos correcte
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