arXiv subjects
Publications and source records attributed to Lynne H. Orr.
In this talk we discuss gluon radiation in top production and decay. After reviewing results for hadron colliders we consider soft gluon radiation at lepton colliders and present gluon distributions that are potentially sensitive to production-decay interference effects.
Understanding the pattern of gluon radiation in $t \bar t$ production processes is important for making an accurate determination of the top mass from the measurement of its decay products. In a recent paper we showed that the exact matrix element and parton shower (HERWIG) calculations gave very different results for the distribution of gluon jets in $t \bar t$ production at the Tevatron $p \bar p$ collider. By repeating the calculation for the simpler $e^+e^- \to b \bar b W^+W^-g$ process, we reveal even more dramatic differences between the two approaches. We conclude that there are significant differences in gluon radiation between HERWIG and the matrix element calculation in regions of phase space where one would expect agreement.
We present a complete calculation of the matrix elements for the processes $q \bar q, gg \to b W^+ \bar b W^- g$ and $qg \to b W^+ \bar b W^- q$ which are relevant for the study of events with an additional jet in $t \bar t$ production at the Tevatron $p \bar p $ collider. Our calculation includes (i) the contributions from gluons emitted during the top production and decay stages and the interference between these, and (ii) the complete set of Feynman diagrams corresponding to both resonant and non-resonant top production. We study the distribution in phase space of the additional parton jet and make comparisons with previous studies based on the soft-gluon approximation and with results from parton-shower Monte Carlo simulations. The implications for top mass measurements are briefly discussed.
Extra soft jets in top events in $p \bar p$ collisions may arise not only from gluons radiated off initial state partons or final state $b$ quarks, but may also be radiated from the $t$ quarks themselves. We discuss predictions for distributions of soft gluons in $t \bar t$ production at the Tevatron and the implications for attempts to measure the top mass by reconstructing the invariant mass of its decay products.
This talk is an overview of prospects for measuring the top mass $m_t$ at present and future colliders. Methods for extracting $m_t$ appropriate to experiments at the Tevatron, Large Hadron Collider, and Next Linear Collider are discussed, with examples given for each. Sources of systematic uncertainties specific to each method and experiment are identified.
Top pairs produced at the Tevatron may be accompanied by extra jets due to radiation of soft gluons. Whether these jets should be included in top momentum reconstruction depends on the source of the gluons, which can be radiated off the initial partons, the final state $b$ quarks, or the intermediate top quarks. We compute soft gluon distributions and discuss their implications for top mass measurements.
A large fraction of top quark events in $\pp$ collisions at $1.8\ \TeV$ will contain additional soft hadronic jets from gluon bremsstrahlung off the quarks and gluons in the hard processes $\qq, gg \to \tt \to \bb \ww$. These extra jets can cause complications when attempting to reconstruct $m_t$ from the invariant mass of combinations of final-state quarks and leptons. We show how such soft radiation cannot be unambiguously associated with either initial-state radiation or or with final-state radiation off the $b$ quarks. The top quarks can radiate too, and in fact the pattern of radiation has a very rich structure, which depends on the orientation of the final-state particles with respect to each other and with respect to the beam. We calculate the full radiation pattern of soft jets in the soft gluon approximation and compare with several approximate forms which are characteristic of parton shower Monte Carlos. The implications for top mass measurements are discussed.
Soft gluons radiated in top quark production and decay can interfere in a way that is sensitive to the top width. We show how the width affects the gluon distribution in $e^+e^- \rightarrow t {\bar t}$ and discuss prospects for measuring $Γ$ from gluons radiated near $\tt$ threshold.