Electron identification using the TOPAZ detector at TRISTAN

We present an electron-identification method using the time-projection chamber and the lead-glass calorimeter in the TOPAZ detector system. Using this method we have achieved good electron identification against hadron backgrounds over a wide momentum range in the hadronic events produced by both single-photon exchange and two-photon processes. Pion-rejection factors and electron efficiencies were 163 and 68.4\% for high-$P_T$ electrons and 137 and 42.7\% for low-$P_T$ electrons in the single-photon-exchange process, and 8600 and 36.0\% for the two-photon process, respectively.Comment: 32 pages, latex format (article), 24 figures, submitted for publication

New GUT predictions for quark and lepton mass ratios confronted with phenomenology

Group theoretical factors from GUT symmetry breaking can lead to predictions for the ratios of quark and lepton masses (or Yukawa couplings) at the unification scale. Due to supersymmetric (SUSY) threshold corrections the viability of such predictions can depend strongly on the SUSY parameters. For three common minimal SUSY breaking scenarios with anomaly, gauge and gravity mediation we investigate which GUT scale ratios $m_e/m_d$, $m_\mu/m_s$, $y_\tau/y_b$ and $y_t/y_b$ are allowed when phenomenological constraints from electroweak precision observables, $B$ physics, $(g-2)_\mu$, mass-limits on sparticles from direct searches as well as, optionally, constraints from the observed dark matter density are taken into account. We derive possible new predictions for the GUT scale mass ratios and compare them with the phenomenologically allowed ranges. We find that new GUT scale predictions such as $m_\mu/m_s = 9/2$ or 6 and $y_\tau/y_b = 3/2$ or 2 are often favoured compared to the ubiquitous relations $m_\mu/m_s = 3$ or $y_\tau/y_b =1$. They are viable for characteristic SUSY scenarios, testable at the CERN LHC and future colliders.Comment: 33 pages, 5 figures; references added; version to appear in Phys. Rev.

Inclusive One- and Two-Jet Cross sections in γγ\gamma\gamma Reactions at e+e−e^+e^- Colliders

We have calculated inclusive one-- and two--jet production in photon--photon collisions superimposing direct, single resolved and double resolved cross sections for center of mass energies of the LEP1, LEP2 and NLC range. The direct and single resolved cross sections are calculated up to next--to--leading order. The double resolved two--jet cross section is calculated only in LO with a $k$ factor estimated from the NLO one--jet cross section. Various differential cross sections as functions of transverse momenta and rapidities of the jets are evaluated.Comment: 25 pages, latex, 15 figures appended as uuencoded fil

Measurement of inclusive electron cross section in γγ\gamma \gamma collisions at TRISTAN

We have studied open charm production in $\gamma \gamma$ collisions with the TOPAZ detector at the TRISTAN $e^{+}e^{-}$ collider. In this study, charm quarks were identified by electrons (and positrons) from semi-leptonic decays of charmed hadrons. The data corresponded to an integrated luminosity of 95.3 pb$^{-1}$ at a center-of-mass energy of 58 GeV. The results are presented as the cross sections of inclusive electron production in $\gamma \gamma$ collisions with an anti-tag condition, as well as the subprocess cross sections, which correspond to resolved-photon processes. The latter were measured by using a sub-sample with remnant jets. A comparison with various theoretical predictions based on direct and resolved-photon processes showed that our data prefer that with relatively large gluon contents in a photon at small $x (x \le 0.1)$, with the next-to-leading order correction, and with a charm-quark mass of 1.3 GeV.Comment: 26 pages, Latex format (article), 5 figures included, to be published in Phys. Lett.

On the Determination of the Gluon Density of the Proton from Heavy-Flavour Production at HERA

Using a recent next-to-leading-order calculation of the photoproduction double differential cross section for heavy quarks, we study the possibility of extracting the gluon density of the proton from heavy-quark photoproduction data. We discuss the theoretical uncertainties connected with this method, and we conclude that they are well under control in a wide $x$ domain.Comment: CERN-TH.6864/93, GeF-TH-12/93. Latex, 5 topdrawer figures appended at the en

Search for neutrinoless tau decays tau -> 3l and tau -> l K0S

Neutrinoless tau-lepton decays into either three leptons (tau- -> l1- l2 l3) or one lepton and one K0S meson(tau- -> l- K0S) where lepton l means either an electron or muon, have been searched for using 48.6 fb^{-1} of data collected with the Belle detector at the KEKB e+e- collider. No evidence for candidate decays are found in any channel. Therefore we set 90% confidence level upper limits on the branching fraction for 8 different decay modes. These limits are more stringent than those set previously and reach to the 10^{-7} level.Comment: Invited talk at the Seventh International Workshop on Tau Lepton Physics (TAU02), Santa Cruz, Ca, USA, Sept 2002, 7 pages, LaTeX, 3 eps figure