903 research outputs found
Search for Single Leptoquark Production in Electron-Photon Scattering at = 161 and 172 GeV
A search for a first generation scalar leptoquark (LQ) has been performed using the data collected by the OPAL detector in 1996 at e+e- centre-of-mass energies sqrt{s} of 161 and 172 GeV. It is assumed that a single leptoquark can be produced in the process eq->LQ, where the initial state quark originates from a hadronic fluctuation of a quasi-real photon which has been radiated by one of the LEP beams. Lower limits at the 95 % confidence level on the mass of a first generation scalar leptoquark of 131 GeV for beta=0.5 and beta=1, coupling values lambda larger than sqrt{4*pi*alpha_em) and leptoquark charges -1/3 or -5/3 are obtained
Uncertainties in Atmospheric Muon-Neutrino Fluxes Arising from Cosmic-Ray Primaries
We present an updated calculation of the uncertainties on the atmospheric
muon-neutrino flux arising from cosmic-ray primaries. For the first time, we
include recent measurements of the cosmic-ray primaries collected since 2005.
We apply a statistical technique that allows the determination of correlations
between the parameters of the GSHL primary-flux parametrisation and the
incorporation of these correlations into the uncertainty on the muon-neutrino
flux. We obtain an uncertainty related to the primary cosmic rays of around
, depending on energy, which is about a factor of two smaller
than the previously determined uncertainty. The hadron production uncertainty
is added in quadrature to obtain the total uncertainty on the neutrino flux,
which is reduced by . To take into account an unexpected hardening
of the spectrum of primaries above energies of observed in
recent measurements, we propose an alternative parametrisation and discuss its
impact on the neutrino flux uncertainties
Light Higgs Production at a Photon Collider
We present a preliminary study of the production of a light Higgs boson with
a mass between 120 and 160 GeV in photon-photon collisions at a Compton
collider. The event generator for the backgrounds to a Higgs signal due to
bbbar and ccbar heavy quark pair production in polarized Gamma-Gamma collisions
is based on a complete next-to-leading order (NLO) perturbative QCD
calculation. For J_z=0 the large double-logarithmic corrections up to four
loops are also included. It is shown that the two-photon width of the Higgs
boson can be measured with high statistical accuracy of about 2-10% for
integrated Gamma-Gamma luminosity in the hard part of the spectrum of 43 fb-1.
From this result the total Higgs boson width can be derived in a model
independent way.Comment: 12 pages, submitted to International Workshop on High Energy Photon
Colliders, June 14 - 17, 2000, DESY Hamburg, German
Jet and hadron production in photon-photon collisions
Di-jet and inclusive charged hadron production cross-sections measured in
photon-photon collisions by OPAL are compared to NLO pQCD calculations. Jet
shapes measured in photon-photon scattering by OPAL, in deep-inelastic ep
scattering by H1 and in photon-proton scattering by ZEUS are shown to be
consistent in similar kinematic ranges. New results from TOPAZ on prompt photon
production in photon-photon interactions are presented.Comment: 4 pages, submitted to Proceedings of DIS99, DESY-Zeuthen, Germany,
April 199
and scattering from , forward amplitudes in a QCD eikonal model with a dynamical gluon mass
We examine the photoproduction and the hadronic
total cross sections by means of a QCD eikonal model with a dynamical infrared
mass scale. In this model, where the dynamical gluon mass is the natural
regulator for the tree level gluon-gluon scattering, the and total cross sections are derived from the and forward
scattering amplitudes assuming vector meson dominance and the additive quark
model. We show that the validity of the cross section factorization relation
is
fulfilled depending on the Monte Carlo model used to unfold the hadronic
cross section data, and we discuss in detail the case of
data with GeV
unfolded by the Monte Carlo generators PYTHIA and PHOJET. The data seems to
favor a mild dependence with the energy of the probability () that the
photon interacts as a hadron.Comment: 16 pages, 3 figures; misprints corrected; to appear in Phys. Rev.
Light Higgs production at the Compton Collider
We have studied the production of a light Higgs boson with a mass of 120 GeV
in photon-photon collisions at a Compton collider. The event generator for the
backgrounds to a Higgs signal due to bbbar and ccbar heavy quark pair
production in polarized gamma-gamma collisions is based on a complete
next-to-leading order (NLO) perturbative QCD calculation. For J_z=0 the large
double-logarithmic corrections up to four loops are also included. It is shown
that the two-photon width of the Higgs boson can be measured with high
statistical accuracy of about 2 % for integrated gamma-gamma luminosity in the
hard part of the spectrum of 40 fb**-1. As a result the total Higgs boson width
can be calculated in a model independent way to an accuracy of about 14 %Comment: submitted to the proceedings of the International Workshop on Linear
Colliders (LCWS99) at Sitges, Spain, 28 April - 5 May 199
Direct comparison of sterile neutrino constraints from cosmological data, <i>Îœ</i><sub><i>e</i></sub> disappearance data and <i>Îœ</i><sub><i>ÎŒ</i></sub>â <i>Îœ</i><sub><i>e</i></sub> appearance data in a 3+1 model
Direct comparison of sterile neutrino constraints from cosmological data, disappearance data and appearance data in a model
We present a quantitative, direct comparison of constraints on sterile
neutrinos derived from neutrino oscillation experiments and from Planck data,
interpreted assuming standard cosmological evolution. We extend a model,
which is used to compare exclusions contours at the 95% CL derived from Planck
data to those from -disappearance measurements, to a model. This
allows us to compare the Planck constraints with those obtained through
appearance searches, which are sensitive to more
than one active-sterile mixing angle. We find that the cosmological data fully
exclude the allowed regions published by the LSND, MiniBooNE and Neutrino-4
collaborations, and those from the gallium and rector anomalies, at the 95% CL.
Compared to the exclusion regions from the Daya Bay -disappearance
search, the Planck data are more strongly excluding above and
, with the Daya Bay
exclusion being stronger below these values. Compared to the combined Daya
Bay/Bugey/MINOS exclusion region on appearance,
the Planck data is more strongly excluding above , with the exclusion strengths of the Planck
data and the Daya Bay/Bugey/MINOS combination becoming comparable below this
value.Comment: 9 pages, 4 figures, accepted by Eur. Phys. J.
A Novel Electrical Method to Measure Wire Tensions for Time Projection Chambers
We present a novel electrical technique to measure the tension of wires in
multi-wire drift chambers. We create alternating electric fields by biasing
adjacent wires on both sides of a test wire with a superposition of positive
and negative DC voltages on an AC signal (). The
resulting oscillations of the wire will display a resonance at its natural
frequency, and the corresponding change of the capacitance will lead to a
measurable current. This scheme is scalable to multiple wires and therefore
enables us to precisely measure the tension of a large number of wires in a
short time. This technique can also be applied at cryogenic temperatures making
it an attractive solution for future large time-projection chambers such as the
DUNE detector. We present the concept, an example implementation and its
performance in a real-world scenario and discuss the limitations of the
sensitivity of the system in terms of voltage and wire length.Comment: 7 pages, 8 figures. Accepted by NIM
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