50 research outputs found
Bounding the Higgs width at the LHC using full analytic results for gg → e − e + μ − μ +
A Formalism for the Systematic Treatment of Rapidity Logarithms in Quantum Field Theory
Many observables in QCD rely upon the resummation of perturbation theory to
retain predictive power. Resummation follows after one factorizes the cross
section into the rele- vant modes. The class of observables which are sensitive
to soft recoil effects are particularly challenging to factorize and resum
since they involve rapidity logarithms. In this paper we will present a
formalism which allows one to factorize and resum the perturbative series for
such observables in a systematic fashion through the notion of a "rapidity
renormalization group". That is, a Collin-Soper like equation is realized as a
renormalization group equation, but has a more universal applicability to
observables beyond the traditional transverse momentum dependent parton
distribution functions (TMDPDFs) and the Sudakov form factor. This formalism
has the feature that it allows one to track the (non-standard) scheme
dependence which is inherent in any scenario where one performs a resummation
of rapidity divergences. We present a pedagogical introduction to the formalism
by applying it to the well-known massive Sudakov form factor. The formalism is
then used to study observables of current interest. A factorization theorem for
the transverse momentum distribution of Higgs production is presented along
with the result for the resummed cross section at NLL. Our formalism allows one
to define gauge invariant TMDPDFs which are independent of both the hard
scattering amplitude and the soft function, i.e. they are uni- versal. We
present details of the factorization and resummation of the jet broadening
cross section including a renormalization in pT space. We furthermore show how
to regulate and renormalize exclusive processes which are plagued by endpoint
singularities in such a way as to allow for a consistent resummation.Comment: Typos in Appendix C corrected, as well as a typo in eq. 5.6
How do aggregated patient reported outcome measures (PROMs) data stimulate health care improvement? A realist synthesis
Objectives: Internationally, there has been considerable debate about the role of data in supporting quality improvement in health care. Our objective was to understand how, why and in what circumstances the feedback of aggregated patient-reported outcome measures data improved patient care. Methods: We conducted a realist synthesis. We identified three main programme theories underlying the use of patient-reported outcome measures as a quality improvement strategy and expressed them as nine ‘if then’ propositions. We identified international evidence to test these propositions through searches of electronic databases and citation tracking, and supplemented our synthesis with evidence from similar forms of performance data. We synthesized this evidence through comparing the mechanisms and impact of patient-reported outcome measures and other performance data on quality improvement in different contexts. Results: Three programme theories were identified: supporting patient choice, improving accountability and enabling providers to compare their performance with others. Relevant contextual factors were extent of public disclosure, use of financial incentives, perceived credibility of the data and the practicality of the results. Available evidence suggests that patients or their agents rarely use any published performance data when selecting a provider. The perceived motivation behind public reporting is an important determinant of how providers respond. When clinicians perceived that performance indicators were not credible but were incentivized to collect them, gaming or manipulation of data occurred. Outcome data do not provide information on the cause of poor care: providers needed to integrate and interpret patient-reported outcome measures and other outcome data in the context of other data. Lack of timeliness of performance data constrains their impact. Conclusions: Although there is only limited research evidence to support some widely held theories of how aggregated patient-reported outcome measures data stimulate quality improvement, several lessons emerge from interventions sharing the same programme theories to help guide the increasing use of these measures
Measurements of fiducial and differential cross sections for Higgs boson production in the diphoton decay channel at s√=8 TeV with ATLAS
Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of s√=8 TeV. The analysis is performed in the H → γγ decay channel using 20.3 fb−1 of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The pp → H → γγ fiducial cross section is measured to be 43.2 ±9.4(stat.) − 2.9 + 3.2 (syst.) ±1.2(lumi)fb for a Higgs boson of mass 125.4GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations
Interference effects for H -> WW/ZZ -> 2l 2nu searches in gluon fusion at the LHC
WW/ZZ interference for Higgs signal and continuum background as well as
signal-background interference is studied for same-flavour l anti-nu_l anti-l
nu_l final states produced in gluon-gluon scattering at the LHC for light and
heavy Higgs masses with minimal and realistic experimental selection cuts. For
the signal cross section, we find WW/ZZ interference effects of O(5%) at M_H =
126 GeV. For M_H >= 200 GeV, we find that WW/ZZ interference is negligible. For
the gg continuum background, we also find that WW/ZZ interference is
negligible. As general rule, we conclude that non-negligible WW/ZZ interference
effects occur only if at least one weak boson of the pair is dominantly
off-shell due to kinematic constraints. The subdominant weak boson pair
contribution induces a correction to the signal-background interference, which
is at the few percentage point level before search selection cuts. Optimised
selection cuts for M_H >~ 600 GeV are suggested.Comment: 22 pages, 2 figures, 9 tables; added 2 references, version to appear
in JHE
Two-loop planar master integrals for the production of off-shell vector bosons in hadron collisions
Measurement of the WW plus WZ cross section and limits on anomalous triple gauge couplings using final states with one lepton, missing transverse momentum, and two jets with the ATLAS detector at root s=7 TeV
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