We compute the O(αsα2) and O(αs2α) contributions to the production cross section of a Z boson with one b jet at the Large Hadron Collider (LHC) and study their phenomenological relevance for LHC ...physics. The accurate prediction of hadronic Z+b-jet production is needed to control a background that greatly affects both the measurement of Higgs-boson properties and the searches of new physics at the LHC. At the same time it could enable the first precise measurement of the b-quark parton distribution function. In this context b-quark mass effects become relevant and need to be studied with care, both at the level of the hard process and at the level of the initial- and final-state parton evolution. It is the aim of this paper to explore some of these issues in the framework of a massive five-flavor scheme and to assess the need for the inclusion of both electroweak corrections, in addition to QCD corrections, and b-quark mass effects in the prediction of total and differential cross sections for hadronic Z+b-jet production.
In QCD, we are used to describing the SU(3) color space in terms of a flow of color. At the algebra level, the Lorentz group consists of two copies of the (complexified) su(2) algebra, so one may ...anticipate that a similar way of thinking about the spacetime structure of scattering amplitudes should exist. In this article, we argue that this is indeed the case, and introduce the chirality-flow formalism for massless tree-level QED and QCD. Within the chirality-flow formalism, scattering amplitudes can directly be written down in terms of Lorentz-invariant spinor inner products, similar to how the color structure can be described in terms of a color flow.
A
bstract
We calculate the process
pp
→
W
+
W
−
→
e
+
ν
e
μ
−
ν
¯
μ
at NLO QCD, including also effective field theory (EFT) operators mediating the
ggW
+
W
−
interaction, which first occur at ...dimension eight. We further combine the NLO and EFT matrix elements produced by G
o
S
am
with the H
erwig
7/M
atchbox
framework, which offers the possibility to study the impact of a parton shower. We assess the effects of the anomalous couplings by comparing them to top-mass effects as well as uncertainties related to variations of the renormalisation, factorisation and hard shower scales.
We present an update of the Binoth Les Houches Accord (BLHA) to standardise the interface between Monte Carlo programs and codes providing one-loop matrix elements.
After a brief introduction to the state of the art of theoretical predictions for electroweak vector-boson production with both top and bottom quarks at the LHC, we review the case of Z-boson ...production with b jets, and discuss the impact of NLO QCD+EW corrections and finite b-quark mass effects on the theoretical prediction for Z+b jet production.
In this talk we discuss a purely numerical approach to next-to-leading order calculations in QCD. We present a simple formula, which provides a local infrared subtraction term for the integrand of a ...one-loop amplitude. In addition we briefly comment on local ultraviolet subtraction terms and on the required deformation of the contour of integration.
We discuss an algorithm for the numerical evaluation of NLO multiparton processes. We focus hereby on the virtual part of the NLO calculation, i.e. on evaluating the one-loop integration numerically. ...We employ and extend the ideas of the subtraction method to the virtual part and we use subtraction terms for the soft, collinear and ultraviolet regions, which allows us to evaluate the loop integral numerically in four dimensions. A second ingredient is a method to deform the integration contour of the loop integration into the complex plane. The algorithm is derived on the level of the primitive amplitudes, where we utilise recursive relations to generate the corresponding one-loop off-shell currents. We discuss the numerical behavior of the approach and the application to the leading colour contribution in e+ e- --> n jets, with n up to seven.
In this talk we discuss an algorithm for the numerical calculation of one-loop QCD amplitudes and present results at next-to-leading order for jet observables in electron-positron annihilation ...calculated with the above-mentioned method. The algorithm consists of subtraction terms, approximating the soft, collinear and ultraviolet divergences of QCD one-loop amplitudes, as well as a method to deform the integration contour for the loop integration into the complex plane to match Feynman's i delta rule. The algorithm is formulated at the amplitude level and does not rely on Feynman graphs. Therefore all ingredients of the algorithm can be calculated efficiently using recurrence relations. The application of this method to the leading-colour contribution of e+ e- --> n jets, with n up to seven, demonstrates the efficiency of the approach.
PDF
