Session S9: Single Top and Theory

Measurement of t-channel Single Top Quark Production at the D0 Experiment

We present the results of a measurement of t-channel production of single top quarks at the D0 experiment using 2.3/fb of data from Fermilab's proton-antiproton Tevatron collider. For this measurement, no assumption was made about the rate of s-channel single top quark production. The resulting cross sections are compared to standard model predictions and to several models with new physics that might also produce single top quark events.   

Measurement of the t-channel Single Top Quark Cross Section at D0

Single top quark production occurs via three different production modes with the relative contributions being sensitive to physics beyond the standard model. We present a measurement of the t channel cross section based on 5.4/fb of data at the D0 experiment at the Fermilab Tevatron proton-antiproton collider. The signal is separated from the background by use of a multivariate discriminant.   

Single Top Quark Production at D0 Using Boosted Decision Trees

We present a method to measure the cross section for single top quark production at the D0 experiment at the Fermilab Tevatron. We have preformed the measurement using Boosted Decision Trees to separate signal from background with 5.4/fb of data.   

Single Top Quark Production at D0 Using Bayesian Neural Networks

We present a measurement of the single top production cross section based on 5.4/fb of data collected by the D0 experiment at the Fermilab Tevatron proton-antiproton collider. The signal is separated from the background using a Bayesian Neural Network.   

Beyond the standard model searches in single top events

We present a summary of results in searches for new phenomena in the single top topology. New particles are searched for in the final state with lepton, missing energy, and 2 jets. Limits are derived for their cross section as a function of mass.   

Combined Single-Top Search with Early ATLAS Data

We use simulated events to examine the potential to observe the production of a single-top quark in the early ATLAS data. For integrated luminosities of less than $\rm 100~pb^{-1}$, multivariate techniques are used to extract the single-top quark signal, which is small compared to the background. Two separate samples are considered, one containing 1 $b$-tagged jet and another containing 2 $b$-tagged jets. In both samples, the three single-top channels are combined to allow for consideration of the full single-top quark signal.   

Next-to-leading order QCD corrections to s-channel single top quark production and decay at the LHC

We present a study of electroweak production of top and antitop quarks in the s-channel mode at the LHC, including next-to-leading order (NLO) quantum chromodynamics (QCD) corrections to the production and decay of the single (anti)top quark. The spin is preserved in production and decay by using the narrow width approximation for the (anti)top quark. We show the effect of different $O(\alpha_{s})$ contributions on the inclusive cross section and various kinematic distributions at parton level after imposing relevant kinematic cuts to select s-channel single top quark events. We also discuss several possibilities for measuring the top quark polarization.   

Renormalization Group Fixed Point with a Fourth Generation

In the Standard Model with four generations, at the two-loop level, we study the renormalization group equations for the Higgs quartic and Yukawa couplings and gauge couplings. The Yukawa sector is found to have a nontrivial fixed point structure. As the masses of the fourth family becomes sufficiently heavy, it will contain a natural scale $\Lambda_{FP} $ in the range of a few TeV to the order of $10^3$ TeV, above which the Higgs quartic and Yukawa couplings become practically constant. Around $\Lambda_{FP}$ the Yukawa couplings are strong and make it possible for the fourth generation to form bound states, including composite extra Higgs doublets.   

The four-dimensional effective action of a multibrane world in five dimensions

We present an analysis of the gravitational behaviour of an $N$-brane model in five dimensions under general conditions. A two-lengthscale expansion is used to obtain a low-energy description of the model, allowing us to compute a four-dimensional effective theory in this regime. We find $N-1$ radion modes in a non-linear sigma model with the target space being hyperbolic space. Our analysis produces exact solutions of the five-dimensional equations of motion, although the stability of these solutions is known to break down in the case of a black hole on a brane.   

Synthetic gauge fields and Dirac physics in ultracold atoms

Optical lattices provide defect-free substrates for ultracold atoms, which move within the lattice much like electrons in an ideal crystal. Beyond emulating condensed matter systems, ultracold atoms can be used to implement variants of the Dirac equation and quite general gauge potentials, Abelian and non- Abelian. We present several recent examples of work along these lines, such as the realization of {\it Zitterbewegung} [1], field-effect spin transistors [2] and topological insulators [3], and discuss possibilities for realizing relativistic wave equations for particles with intrinsic angular momentum greater than $\hbar/2$. \\[4pt] [1] J. Y. Vaishnav and C. W. Clark, {\it Phys. Rev. Lett} {\bf 100}, 153002 (2008)\newline [2] J. Y. Vaishnav, {\it et al.}, {\it Phys. Rev. Lett} {\bf 101}, 265302 (2008)\newline [3] T. D. Stanescu, {\it et al.}, {\it Phys. Rev. A} {\bf 79}, 053639 (2009)   

The Electroweak Single Production of $t'$ Quarks at the CERN Large Hadron electron Collider

We study the electroweak single production of $t'$ quarks via the process $ep\to t'\nu$ at Large Hadron electron Collider (LHeC). We calculate the background and signal cross sections for the mass range 300-800 GeV. It is shown that the LHeC can discover single $t'$ quark up to the mass of $750$ GeV for the optimized mixing parameters.