1,871 research outputs found
Alpha_s: from DIS to LEP
The strong coupling alpha_s is a fundamental parameter of the Standard Model.
In comparison to parameters like alpha_em and M_Z it is relatively poorly
known. However the precision of alpha_s measurements has improved dramatically
in recent years. More than twenty different types of process, from lattice QCD
studies to the highest energy colliders, can be used to measure alpha_s
accurately. The most precise determinations now quote uncertainties in
alpha_s(M_Z) of less than 5%. There is also a remarkable consistency between
the various measurements. The present review provides an update on alpha_s
measurements from the past year.Comment: 12 pages LaTeX and 4 encapsulated postscript figures, using epsfig
and (modified) l-school macros. Based on a talk presented at the conference
on New Non-Perturbative Methods and Quantisation on the Light Cone, Les
Houches, March 199
On the Resummation of Subleading Logarithms in the Transverse Momentum Distribution of Vector Bosons Produced at Hadron Colliders
The perturbation series for electroweak vector boson production at small
transverse momentum is dominated by large double logarithms at each order in
perturbation theory. An accurate theoretical prediction therefore requires a
resummation of these logarithms. This can be performed either directly in
transverse momentum space or in impact parameter (Fourier transform) space.
While both approaches resum the same leading double logarithms, the subleading
logarithms are, in general, treated differently. We comment on two recent
approaches to this problem, emphasising the particular subleading logarithms
resummed in each case and the numerical differences in the cross sections which
result.Comment: 13 (Latex) pages, including 5 embedded figures, uses epsfig.st
Electroweak gauge boson polarisation at the LHC
We study the polarisation of gauge bosons produced at the LHC. Polarisation
effects for W bosons manifest themselves in the angular distributions of the
lepton and in the distributions of lepton transverse momentum and missing
transverse energy. The distributions also depend on the selection cuts, with
kinematic effects competing with polarisation effects. The polarisation is
discussed for a range of different processes producing W bosons: W+jets, W from
top (single and pair) production, W pair production and W production in
association with a Z or Higgs boson. The relative contributions of the
different polarisation states varies from process to process, reflecting the
dynamics of the underlying hard-scattering process. We also present results for
the polarisation of the Z boson produced in association with QCD jets at the
LHC, and comment on the differences between W and Z production.Comment: 27 pages, 25 figure
BFKL Physics in Jet Production at e+e- colliders
Virtual photon scattering in collisions can result in events with
the electron-positron pair at large rapidity separation with hadronic activity
in between. The BFKL equation resums large logarithms that dominate the cross
section for this process. We report here on a Monte Carlo method for solving
the BFKL equation that allows kinematic constraints to be taken into account
and show results for collisions.Comment: 3 pages, Latex, talk presented at the 2000 Meeting of the Division of
Particles and Fields of the APS, Columbus, OH, August 9--12, 200
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