120,054 research outputs found
Unintegrated parton distributions and electroweak boson production at hadron colliders
We describe the use of doubly-unintegrated parton distributions in
hadron-hadron collisions, using the (z,k_t)-factorisation prescription where
the transverse momentum of the incoming parton is generated in the last
evolution step. We apply this formalism to calculate the transverse momentum
(P_T) distributions of produced W and Z bosons and compare the predictions to
Tevatron Run 1 data. We find that the observed P_T distributions can be
generated almost entirely by the leading order q_1 q_2 -> W,Z subprocesses,
using known and universal doubly-unintegrated quark distributions. We also
calculate the P_T distribution of the Standard Model Higgs boson at the LHC,
where the dominant production mechanism is by gluon-gluon fusion.Comment: 20 pages, 8 figures. Version to appear in Phys. Rev. D; correction to
Higgs P_T distribution made in Erratu
Diffractive parton distributions: the role of the perturbative Pomeron
We consider the role of the perturbative Pomeron-to-parton splitting in the
formation of the diffractive parton distributions.Comment: 8 pages, 4 figures. To appear in the proceedings of the 12th
International Conference on Elastic and Diffractive Scattering: Forward
Physics and QCD, DESY, Hamburg, Germany, 21-25 May 200
Effect of absorptive corrections on inclusive parton distributions
We study the effect of absorptive corrections due to parton recombination on
the parton distributions of the proton. A more precise version of the GLRMQ
equations, which account for non-linear corrections to DGLAP evolution, is
derived. An analysis of HERA F_2 data shows that the small-x gluon distribution
is enhanced at low scales when the absorptive effects are included, such that a
negative gluon distribution at 1 GeV is no longer required.Comment: 10 pages, 3 figure
Reputation of Oral and Maxillofacial Surgery in the UK:the patients' perspective
Our intention is to shed theoretical and practical light on the professional reputation of Oral and Maxillofacial Surgery (OMFS) in the UK by drawing on theories from management literature, particularly concerning reputation. Since professional reputation is socially constructed by stakeholders, we used interpretivist methods to conduct a qualitative study of patients (stakeholders) to gain an insight into their view of the profession. Findings from our focus groups highlighted the importance of “soft-wired skills” and showed a perception – reality gap in the interaction between patients and doctors. They also highlighted the importance of consistency, relational coordination, mechanisms to enable transparent feedback, and professional processes of governance. To help understand how best to manage the reputation of the specialty, we also explored how this is affected by the media and the Internet
Treatment of the infrared contribution: NLO QED evolution as a pedagogic example
We show that the conventional prescription used for DGLAP parton evolution at
NLO has an inconsistent treatment of the contribution from the infrared (IR)
region. We illustrate the problem by studying the simple example of QED
evolution, treating the electron and photon as partons. The deficiency is not
present in a physical approach which removes the IR divergency and allows
calculation in the normal 4-dimensional space.Comment: 15 pages, 2 figures, erratum at the end of the articl
Improving alpha_QED(M_Z^2) and the charm mass by analytic continuation
The standard determination of the QED coupling on the Z pole is performed
using the latest available data for R. The direct application of analytic
continuation techniques is found not to improve the accuracy of the value of
\alpha(M_Z^2). However they help to resolve an ambiguity in the values of R in
the energy region \sqrt{s} < 2 GeV, which, in turn, reduces the uncertainty in
\alpha(M_Z^2). Moreover, they provide a sensitive determination of the mass of
the charm quark. The favoured solution, which uses the inclusive data for R for
\sqrt{s} < 2 GeV, has a pole mass m_c = 1.33-1.40 GeV and \alpha^{-1}(M_Z^2) =
128.972 +/- 0.026; whereas if the sum of the exclusive channels is used to
determine R in this region, we find \alpha^{-1}(M_Z^2) = 128.941 +/- 0.029.Comment: LaTeX, 23 pages, 7 eps figures, typos removed, accepted by Eur. Phys.
J.
Improving the Drell-Yan probe of small x partons at the LHC via a k_t cut
We show that the observation of the Drell-Yan production of low-mass
lepton-pairs (M 3) at the LHC can make a
direct measurement of parton distribution functions (PDFs) in the low x region,
x < 10^{-4}. We describe a procedure that greatly reduces the sensitivity of
the predictions to the choice of the factorization scale and, in particular,
show how, by imposing a cutoff on the transverse momentum of the lepton-pair,
the data are able to probe PDFs in the important low scale, low x domain. We
include the effects of the Sudakov suppression factor.Comment: 14 pages, 5 figures, version to be published in EPJC, with expanded
explanatio
Physical factorisation scheme for PDFs for non-inclusive applications
We introduce the physical factorisation scheme, which is necessary to
describe observables which are `not completely inclusive'. We derive the
formulae for NLO DGLAP evolution in this scheme, and also for the `rotation' of
the conventional MSbar PDFs into the physical representation. Unlike, the MSbar
prescription, where, for example, the gluon PDF at NLO obtains an admixture of
the quark-singlet PDF, and vice-versa, the physical approach does not mix
parton PDFs of different types. That is, the physical approach retains the
precise quantum numbers of each PDF. The NLO corrections to DGLAP evolution in
the physical scheme are less than those in the MSbar case, indicating a better
convergence of the perturbative series
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