2,464,650 research outputs found

### Pentaquarks in high-energy colliding experiments: perspectives from HERA

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

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

New experimental results on polarized structure functions, cross sections for
$e^{\pm}p$ neutral and charge current reactions and $\nu$ ($\bar{\nu}$) 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 $p\bar{p}$ collisions and
inclusive $\pi^0$ production in $pp$ 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

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

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
$\gamma \gamma$ 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

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

An NLO photon parton parametrization is presented based on the existing
$F_2^\gamma$ measurements from $e^+e^-$ data and the low-$x$ proton structure
function from $ep$ interactions. Also included in the extraction of the NLO
parton distribution functions are the dijets data coming from $\gamma p \to j_1
+ j_2 +X$. 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

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

The feasibility of a measurement of the electric and magnetic nucleon form
factors at $B$-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 $Q^2$ values up to 8 or even 9 GeV$^2$
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

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 $W_{H}^{\pm}$ 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 $Wqq'$ 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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