427 research outputs found
Threshold corrections to rapidity distributions of Z and W^\pm bosons beyond N^2 LO at hadron colliders
Threshold enhanced perturbative QCD corrections to rapidity distributions of
and bosons at hadron colliders are presented using the Sudakov
resummed cross sections at NLO level. We have used renormalisation group
invariance and the mass factorisation theorem that these hard scattering cross
sections satisfy to construct the QCD amplitudes. We show that these higher
order threshold QCD corrections stabilise the theoretical predictions for
vector boson production at the LHC under variations of both renormalisation and
factorisation scales.Comment: 17 pages, 8 eps figures. This paper is dedicated to the memory of
W.L.G.A.M. van Neerve
Soft spectator scattering in the nucleon form factors at large within the SCET approach
The proton form factors at large momentum transfer are dominated by two
contributions which are associated with the hard and soft rescattering
respectively. Motivated by a very active experimental form factor program at
intermediate values of momentum transfers, ,
where an understanding in terms of only a hard rescattering mechanism cannot
yet be expected, we investigate in this work the soft rescattering contribution
using soft collinear effective theory (SCET). Within such description, the form
factor is characterized, besides the hard scale , by a semi-hard scale , which arises due to presence of soft spectators, with virtuality
( GeV), such that . We show that in this case a two-step factorization can be
successfully carried out using the SCET approach. In a first step (SCET),
we perform the leading order matching of the QCD electromagnetic current onto
the relevant SCET operators and perform a resummation of large logarithms
using renormalization group equations. We then discuss the further matching
onto a SCET framework, and propose the complete factorization formula
for the Dirac form factor, accounting for both hard and soft contributions. We
also present a qualitative discussion of the phenomenological consequences of
this new framework.Comment: 33 pages, 19 figures; typos corrected, text improved. Version to
appear in Phys.Rev.
A simple shower and matching algorithm
We present a simple formalism for parton-shower Markov chains. As a first
step towards more complete uncertainty bands, we incorporate a comprehensive
exploration of the ambiguities inherent in such calculations. To reduce this
uncertainty, we then introduce a matching formalism which allows a generated
event sample to simultaneously reproduce any infrared safe distribution
calculated at leading or next-to-leading order in perturbation theory, up to
sub-leading corrections. To enable a more universal definition of perturbative
calculations, we also propose a more general definition of the hadronization
cutoff. Finally, we present an implementation of some of these ideas for
final-state gluon showers, in a code dubbed VINCIA.Comment: 32 pages, 6 figure
Jets in Effective Theory: Summing Phase Space Logs
We demonstrate how to resum phase space logarithms in the Sterman-Weinberg
(SW) dijet decay rate within the context of Soft Collinear Effective theory
(SCET). An operator basis corresponding to two and three jet events is defined
in SCET and renormalized. We obtain the RGE of the two and three jet operators
and run the operators from the scale to the phase space scale . This phase space scale, where is the
cone half angle of the jet, defines the angular region of the jet. At we determine the mixing of the three and two jet operators. We
combine these results with the running of the two jet shape function, which we
run down to an energy cut scale . This defines the resumed SW
dijet decay rate in the context of SCET. The approach outlined here
demonstrates how to establish a jet definition in the context of SCET. This
allows a program of systematically improving the theoretical precision of jet
phenomenology to be carried out.Comment: 25 pages, 4 figures, V2: Typos fixed, writing clarified, detail on
PSRG added. Matching onto jet definition changed to taking place at collinear
scal
Sum rule for a difference of proton and neutron total photoproduction cross-sections
Starting from very high energy inelastic electron-nucleon scattering with a
production of a hadronic state to be moved closely to the direction of the
initial nucleon, then utilizing analytic properties of parts of forward virtual
Compton scattering amplitudes on proton and neutron, one obtains the relation
between nucleon form factors and a difference of proton and neutron
differential electroproduction cross-sections. In particular, for the case of
small transferred momenta, one finally derives sum rule, relating Dirac proton
mean square radius and anomalous magnetic moments of proton and neutron to the
integral over a difference of the total proton and neutron photoproduction
cross-sections.Comment: LaTeX2e, 7 pages, 1 eps figure (revised version
Bremsstrahlung and pair production processes at low energies, multi-differential cross section and polarization phenomena
Radiative electron-proton scattering is studied in peripheral kinematics,
where the scattered electron and photon move close to the direction of the
initial electron. Even in the case of unpolarized initial electron the photon
may have a definite polarization. The differential cross sections with
longitudinally or transversal polarized initial electron are calculated. The
same phenomena are considered for the production of an electron-positron pair
by the photon, where the final positron (electron) can be also polarized.
Differential distributions for the case of polarized initial photon are given.
Both cases of unscreened and completely screened atomic targets are considered.Comment: 15 pages, 6 figure
Vacuum polarization radiative correction to the parity violating electron scattering on heavy nuclei
The effect of vacuum polarization on the parity violating asymmetry in the
elastic electron-nucleus scattering is considered. Calculations are performed
in the high-energy approximation with an exact account for the electric field
of the nucleus. It is shown that the radiative correction to the parity
violating asymmetry is logarithmically enhanced and the value of the correction
is about -1%.Comment: 6 pages, 3 figures, REVTex
Цивилизационный процесс и его социальная драматургия в условиях глобальных и региональных трансформаций
Book Review: Mikhalchenko N.I. The great civilizational explosion at the turn of the 20th and 21st centuries / NI Mikhalchenko. – К.: Parliamentary publishing house, 2016. – 504 p. [in Russian]Рецензия на книгу: Михальченко Н. И. Великий цивилизационный взрыв на рубеже ХХ и ХХІ веков / Н. И. Михальченко. – К. : Парламентское издательство, 2016. – 504 с
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