Jets from Massive Unstable Particles: Top-Mass Determination

We construct jet observables for energetic top quarks that can be used to determine a short distance top quark mass from reconstruction in e+ e- collisions with accuracy better than Lambda_{QCD}. Using a sequence of effective field theories we connect the production energy, mass, and top width scales, Q>> m>> Gamma, for the top jet cross section, and derive a QCD factorization theorem for the top invariant mass spectrum. Our analysis accounts for: alpha_s corrections from the production and mass scales, corrections due to constraints in defining invariant masses, non-perturbative corrections from the cross-talk between the jets, and alpha_s corrections to the Breit-Wigner line-shape. This paper mainly focuses on deriving the factorization theorem for hemisphere invariant mass distributions and other event shapes in e+e- collisions applicable at a future Linear Collider. We show that the invariant mass distribution is not a simple Breit-Wigner involving the top width. Even at leading order it is shifted and broadened by non-perturbative soft QCD effects. We predict that the invariant mass peak position increases linearly with Q/m due to these non-perturbative effects. They are encoded in terms of a universal soft function that also describes soft effects for massless dijet events. In a future paper we compute alpha_s corrections to the jet invariant mass spectrum, including a summation of large logarithms between the scales Q, m and Gamma.Comment: 54 pages, 10 figures, typos corrected, figures update

Case studies to enhance online student evaluation: Bond University – Surveying students online to improve learning and teaching

One of the most sensible ways of improving learning and teaching is to ask the students for feedback. At the end of each teaching period (i.e. semester or term) all universities and many schools survey their students. Usually these surveys are managed online. Questions ask for student perceptions about teaching, assessment and workload. The survey administrators report four common problems

The Accuracy of Perturbative Master Equations

We consider open quantum systems with dynamics described by master equations that have perturbative expansions in the system-environment interaction. We show that, contrary to intuition, full-time solutions of order-2n accuracy require an order-(2n+2) master equation. We give two examples of such inaccuracies in the solutions to an order-2n master equation: order-2n inaccuracies in the steady state of the system and order-2n positivity violations, and we show how these arise in a specific example for which exact solutions are available. This result has a wide-ranging impact on the validity of coupling (or friction) sensitive results derived from second-order convolutionless, Nakajima-Zwanzig, Redfield, and Born-Markov master equations.Comment: 6 pages, 0 figures; v2 updated references; v3 updated references, extension to full-time and nonlocal regime

Exclusive Radiative Decays of Upsilon in SCET

We study exclusive radiative decays of the $\Upsilon$ using soft-collinear effective theory and non-relativistic QCD. In contrast to inclusive radiative decays at the endpoint we find that color-octet contributions are power suppressed in exclusive decays, and can safely be neglected, greatly simplifying the analysis. We determine the complete set of Lorentz structures that can appear in the SCET Wilson coefficients and match onto them using results from a previous calculation. We run these coefficients from the scale \mups to the scale $\Lambda \sim 1 \textrm{GeV}$, thereby summing large logarithms. Finally we use our results to predict the ratio of branching fractions $B(\Upsilon \to \gamma f_2)/B(J/\psi \to \gamma f_2)$, $B(J/\psi \to \gamma f_2)/B(\psi' \to \gamma f_2)$, and the partial rate for $\Upsilon \to \gamma \pi \pi$.Comment: 17 pages, 2 figures. Updated to reflect published versio

Flavor-singlet light-cone amplitudes and radiative Upsilon decays in SCET

We study the evolution of flavor-singlet, light-cone amplitudes in the soft-collinear effective theory (SCET), and reproduce results previously obtained by a different approach. We apply our calculation to the color-singlet contribution to the photon endpoint in radiative Upsilon decay. In a previous paper, we studied the color-singlet contributions to the endpoint, but neglected operator mixing, arguing that it should be a numerically small effect. Nevertheless the mixing needs to be included in a consistent calculation, and we do just that in this work. We find that the effects of mixing are indeed numerically small. This result combined with previous work on the color-octet contribution and the photon fragmentation contribution provides a consistent theoretical treatment of the photon spectrum in radiative Upsilon decay.Comment: 19 pages with 8 figure

Use of computer-aided analysis techniques for cover type mapping in areas of mountainous terrain

There are no author-identified significant results in this report

Electromagnetic Production of Quarkonium in Z0Z^{0} decay

The decay $Z^{0}\rightarrow Q+ \ell^{+}\ell^{-}$, where $Q$ is a $J^{PC}=1^{--}$ quarkonium state, has a very clean final state, which should make it easy to detect. The branching ratio of this mode is greater than $10^{-6}$ for $\rho$, $\phi$, and $\psi$, indicating that these processes may be detectable at LEP.Comment: Latex, 6 pages, 2 figure in postscript format (uuencoded), (or available upon request), NUHEP-TH-93-1

Pion Interactions in the X(3872)

We consider pion interactions in an effective field theory of the narrow resonance X(3872), assuming it is a weakly bound molecule of the charm mesons D^{0} \bar D^{*0} and D^{*0} \bar D^{0}. Since the hyperfine splitting of the D^{0} and D^{*0} is only 7 MeV greater than the neutral pion mass, pions can be produced near threshold and are non-relativistic. We show that pion exchange can be treated in perturbation theory and calculate the next-to-leading-order correction to the partial decay width \Gamma[X \to D^0 \bar D^{0} \pi^0].Comment: 26 pages, 11 figures, revtex4, to appear in Phys. Rev.