11,573 research outputs found
Single-top-quark production at hadron colliders
Single-top-quark production probes the charged-current weak interaction of
the top quark, and provides a direct measurement of the CKM matrix element
V_{tb}. We perform two independent analyses to quantify the accuracy with which
the W-gluon fusion (gq -> t\bar{b}q) and (q\bar{q} -> t\bar{b}) signals can be
extracted from the backgrounds at both the Tevatron and the LHC. Although
perturbation theory breaks down at low transverse momentum for the W-gluon
fusion \bar{b} differential cross section, we show how to obtain a reliable
cross section integrated over low \bar{b} transverse momenta up to a cutoff. We
estimate the accuracy with which V_{tb} can be measured in both analyses,
including theoretical and statistical uncertainties. We also show that the
polarization of the top quark in W-gluon fusion can be detected at the Fermilab
Tevatron and the CERN LHC.Comment: Version to appear in PRD, 31 pages, LaTeX, 8 ps figure
Becoming Psychotherapists: Experiences of Novice Trainees in a Beginning Graduate Class
The authors investigated the experiences related to becoming psychotherapists for 5 counseling psychology doctoral trainees in their first prepracticum course. Qualitative analyses of weekly journals indicated that trainees discussed challenges related to becoming psychotherapists (e.g., being self-critical, having troubling reactions to clients, learning to use helping skills), gains made during the semester related to becoming psychotherapists (e.g., using helping skills more effectively, becoming less self-critical, being able to connect with clients), as well as experiences in supervision and activities that helped them cope with their anxieties. Results are discussed in 5 broad areas: feelings about self in role of psychotherapist, awareness of reactions to clients, learning and using helping skills, reactions to supervision, and experiences that fostered growth. Implications for training and research are provided
Heavy-quark parton distribution functions and their uncertainties
We investigate the uncertainties of the heavy-quark parton distribution functions in the variable flavor number scheme. Because the charm- and bottom-quark parton distribution functions (PDFs) are constructed predominantly from the gluon PDF, it is a common practice to assume that the heavy-quark and gluon uncertainties are the same. We show that this approximation is a reasonable first guess, but it is better for bottom quarks than charm quarks. We calculate the PDF uncertainty for t-channel single-top-quark production using the Hessian matrix method, and predict a cross section of 2.12+0.32-0.29 pb at run II of the Tevatron
Understanding single-top-quark production and jets at hadron colliders
I present an analysis of fully differential single-top-quark production plus
jets at next-to-leading order. I describe the effects of jet definitions,
top-quark mass, and higher orders on the shapes and normalizations of the
kinematic distributions, and quantify all theoretical uncertainties. I explain
how to interpret next-to-leading-order jet calculations, and compare them to
showering event generators. Using the program ZTOP, I show that HERWIG and
PYTHIA significantly underestimate both s-channel and t-channel
single-top-quark production, and propose a scheme to match the relevant samples
to the next-to-leading-order predictions.Comment: 40 pgs., revtex4, 35 ps figs; added Fig. 4, 1 Ref., minor
clarifications, to appear in Phys. Rev.
Constraints on UED from W' searches
We obtain contraints on three Universal Extra Dimensional models utilizing
limits from the CMS Collaboration on W' production and decay into a
single-top-quark final state. We find a weak constraint on the Minimal
Universal Extra Dimensions model due to small Kaluza-Klein number violating
terms. In contrast, the W' search puts a strong limit on the size of the Dirac
mass term of the quarks in Split Universal Extra Dimension models. In
Non-minimal Universal Extra Dimension models the W' search constrains the
splitting between the boundary localized kinetic terms of the gauge bosons and
the quarks. Each of these bounds can be translated into constraints on the mass
splitting between the Kaluza-Klein excitations of the SU(2) charged quarks and
the Klauza-Klein excitations of the W boson.Comment: 7 pages, 5 figures; Updated Draft and Figure
Fully differential QCD corrections to single top quark final states
A new next-to-leading order Monte Carlo program for calculation of fully
differential single top quark final states is described and first results
presented. Both the s- and t-channel contributions are included.Comment: 3 pages, 3 figures, talk presented at DPF2000, August 9-12, 2000. To
appear in International Journal of Modern Physics
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