23,130 research outputs found
Nucleon form factors, B-meson factories and the radiative return
The feasibility of a measurement of the electric and magnetic nucleon form
factors at -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 values up to 8 or even 9 GeV
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.
Heart of Darkness: The Significance of the Zeptobarn Scale for Neutralino Direct Detection
The direct detection of dark matter through its elastic scattering off
nucleons is among the most promising methods for establishing the particle
identity of dark matter. The current bound on the spin-independent scattering
cross section is sigma^SI < 10 zb for dark matter masses m_chi ~ 100 GeV, with
improved sensitivities expected soon. We examine the implications of this
progress for neutralino dark matter. We work in a supersymmetric framework
well-suited to dark matter studies that is simple and transparent, with models
defined in terms of four weak-scale parameters. We first show that robust
constraints on electric dipole moments motivate large sfermion masses mtilde >
1 TeV, effectively decoupling squarks and sleptons from neutralino dark matter
phenomenology. In this case, we find characteristic cross sections in the
narrow range 1 zb 70 GeV. As sfermion masses are
lowered to near their experimental limit mtilde ~ 400 GeV, the upper and lower
limits of this range are extended, but only by factors of around two, and the
lower limit is not significantly altered by relaxing many particle physics
assumptions, varying the strange quark content of the nucleon, including the
effects of galactic small-scale structure, or assuming other components of dark
matter. Experiments are therefore rapidly entering the heart of dark
matter-favored supersymmetry parameter space. If no signal is seen,
supersymmetric models must contain some level of fine-tuning, and we identify
and analyze several possibilities. Barring large cancellations, however, in a
large and generic class of models, if thermal relic neutralinos are a
significant component of dark matter, experiments will discover them as they
probe down to the zeptobarn scale.Comment: 35 pages, 11 figures; v2: references added, figures extended to 2 TeV
neutralino masses, XENON100 results included, published versio
Production of J/psi Mesons at HERA
Inelastic and diffractive production of J/psi mesons at HERA is reviewed. The
data on inelastic photoproduction are described well within errors by the
Colour Singlet Model in next-to-leading order. A search for colour octet
processes predicted within the NRQCD/factorisation approach is conducted in
many regions of phase space. No unambiguous evidence has been found to date.
Diffractive elastic production of J/psi mesons has been measured in the limit
of photoproduction up to the highest photon proton center of mass energies. The
increase of the cross section is described by pQCD models. At larger Q^2, the W
dependence is found to be similar to that observed in photoproduction. First
analyses of data at high t yield a powerlike dependence on |t|. A LO BFKL
calculation gives a good description of the data.Comment: 14 pages, 12 figures, contribution to Ringberg 200
B decays to final states including D_s^{(*)} and D^*
The e^+e^- annihilation data recorded with the BABAR detector has been used
to study B decays to D_s^(*) and D^* mesons. The production fraction of
inclusive D_s^(*) and the corresponding momentum spectra have been determined.
Exclusive decays B^0 --> D^{*-}D_s^{(*)+} have been identified with a partial
reconstruction technique and their branching fractions have been measured. We
also report branching fraction measurements for the exclusive hadronic modes
B^0 --> D^{*-} pi^+ and B^0 --> D^{*-} rho^+.Comment: 5 pages, 4 postscript figures, contributed paper to DPF200
NLO photon parton parametrization using ee and ep data
An NLO photon parton parametrization is presented based on the existing
measurements from data and the low- proton structure
function from interactions. Also included in the extraction of the NLO
parton distribution functions are the dijets data coming from . The new parametrization is compared to other NLO parametrizations.Comment: 22 pages, 7 figures, 2 table
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