76,497 research outputs found
Determination of the strong coupling alpha_s from the QCD static energy
We obtain a determination of the strong coupling alpha_s in quantum
chromodynamics, by comparing perturbative calculations for the short-distance
part of the static energy with lattice computations. Our result reads
alpha_s(1.5GeV)=0.326\pm0.019, and when evolved to the scale M_Z (the Z-boson
mass) it corresponds to alpha_s(M_Z)=0.1156^{+0.0021}_{-0.0022}.Comment: 8 pages, 2 figures. Contribution to the proceedings of Quark
Confinement and the Hadron Spectrum
Review of the measurements of the strong coupling constant at LEP 2
Since 1995, LEP has steadily increased the center of mass energy of the
colliding beams, from the M_Z resonance to 133, 161 and 172 GeV. New
measurements of the strong coupling constant, alpha_s, at these energies have
been performed by the LEP experiments, L3, ALEPH, OPAL and DELPHI. In this
article, the new results are summarized, and combined with the previous LEP
measurement of alpha_s(M_Z) in order to obtain an updated LEP average of
alpha_s(M_Z) = 0.120 +- 0.005.Comment: 5-6 pages, 3 figures. Talk given at the DIS 97 conference, Chicago,
April 1997.Replacement: update figure 1. Also available here
http://hep.ph.liv.ac.uk/~martis
The twisted gradient flow coupling at one loop
We compute the one-loop running of the 't Hooft coupling in a finite
volume gradient flow scheme using twisted boundary conditions. The coupling is
defined in terms of the energy density of the gradient flow fields at a scale
given by an adequate combination of the torus size and the rank of
the gauge group, and is computed in the continuum using dimensional
regularization. We present the strategy to regulate the divergences for a
generic twist tensor, and determine the matching to the
scheme at one-loop order. For the particular case in which the twist tensor is
non-trivial in a single plane, we evaluate the matching coefficient numerically
and determine the ratio of parameters between the two schemes. We
analyze the dependence of the results and the possible implications for
non-commutative gauge theories and volume independence.Comment: 52 pages, 12 figure
Factorization and resummation for transverse thrust
We analyze transverse thrust in the framework of Soft Collinear Effective
Theory and obtain a factorized expression for the cross section that permits
resummation of terms enhanced in the dijet limit to arbitrary accuracy. The
factorization theorem for this hadron-collider event-shape variable involves
collinear emissions at different virtualities and suffers from a collinear
anomaly. We compute all its ingredients at the one-loop order, and show that
the two-loop input for next-to-next-to-leading logarithmic accuracy can be
extracted numerically, from existing fixed-order codes.Comment: 47 pages, 12 figures. v2: journal versio
Semi-inclusive radiative decays of Upsilon 1S
We discuss in detail the photon spectrum of radiative Upsilon 1S decays
taking into account a number of results that have recently appeared in the
literature. In particular, we show how to consistently combine expressions
which are valid in the upper end-point region, where NRQCD factorization breaks
down, with those of the central region, where NRQCD factorization holds. An
excellent description of data is achieved, but theoretical errors are large.Comment: 18 pages, 7 figures. Minor modifications. References added and
corrected. Journal versio
Addendum: Electroweak Sudakov effects in W, Z and gamma production at large transverse momentum
In this addendum to Phys. Rev. D 88, no. 1, 013009 (2013), we give results
for the electroweak Sudakov corrections in gauge-boson production at large
transverse momentum p_T at proton colliders. In order for the results to be
easily usable, we provide a simple and accurate parameterization of the
corrections as a function of p_T and the center-of-mass energy \sqrt{s}.
Additionally, we also discuss the dependence of the electroweak corrections on
the rapidity of the produced boson, and comment on the complications that arise
in the photon-production case due to isolation requirementsComment: 4 pages, 4 figure
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