Search for Single Leptoquark Production in Electron-Photon Scattering at s\sqrt{s} = 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 $(5\text{--}15)\%$, 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 $\approx 5\%$. To take into account an unexpected hardening of the spectrum of primaries above energies of $100$ $\text{GeV}$ 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

γp\gamma p and γγ\gamma \gamma scattering from pˉp\bar{p}p, pppp forward amplitudes in a QCD eikonal model with a dynamical gluon mass

We examine the $\gamma p$ photoproduction and the hadronic $\gamma \gamma$ 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 $\gamma p$ and $\gamma \gamma$ total cross sections are derived from the $pp$ and $\bar{p}p$ forward scattering amplitudes assuming vector meson dominance and the additive quark model. We show that the validity of the cross section factorization relation $\sigma_{pp}/\sigma_{\gamma p}=\sigma_{\gamma p}/\sigma_{\gamma \gamma}$ is fulfilled depending on the Monte Carlo model used to unfold the hadronic $\gamma \gamma$ cross section data, and we discuss in detail the case of $\sigma (\gamma \gamma \to hadrons)$ data with $W_{\gamma \gamma} > 10$ GeV unfolded by the Monte Carlo generators PYTHIA and PHOJET. The data seems to favor a mild dependence with the energy of the probability ($P_{had}$) 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, νe\nu_{e} disappearance data and νμ→νe\nu_{\mu}\rightarrow\nu_{e} appearance data in a 3+13+1 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 $1+1$ model, which is used to compare exclusions contours at the 95% CL derived from Planck data to those from $\nu_{e}$-disappearance measurements, to a $3+1$ model. This allows us to compare the Planck constraints with those obtained through $\nu_{\mu}\rightarrow\nu_{e}$ 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 $\nu_{e}$-disappearance search, the Planck data are more strongly excluding above $|\Delta m^{2}_{41}|\approx 0.1\, \mathrm{eV}^{2}$ and $m_\mathrm{eff}^\mathrm{sterile}\approx 0.2\, \mathrm{eV}$, with the Daya Bay exclusion being stronger below these values. Compared to the combined Daya Bay/Bugey/MINOS exclusion region on $\nu_{\mu}\rightarrow\nu_{e}$ appearance, the Planck data is more strongly excluding above $\Delta m^{2}_{41}\approx 5\times 10^{-2}\,\mathrm{eV}^{2}$, 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 ($V_{\rm AC} \pm V_{\rm DC}$). 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