0000000000133325
AUTHOR
Werner Bernreuther
showing 8 related works from this author
QCD corrections to static heavy-quark form factors
2005
Interactions of heavy quarks, in particular of top quarks, with electroweak gauge bosons are expected to be very sensitive to new physics effects related to electroweak symmetry breaking. These interactions are described by the so-called static form factors, which include anomalous magnetic moments and the effective weak charges. We compute the second-order QCD corrections to these static form factors, which turn out to be sizeable and need to be taken into account in searches for new anomalous coupling effects.
The real–virtual antenna functions forS→QQ¯Xat NNLO QCD
2014
Abstract We determine, in the antenna subtraction framework for handling infrared divergences in higher order QCD calculations, the real–virtual antenna functions for processes involving the production of a pair of massive quarks by an uncolored initial state at NNLO QCD. The integrated leading and subleading color real–virtual antenna functions are computed analytically in terms of (cyclotomic) harmonic polylogarithms. As a by-product and check we compute R Q = σ ( e + e − → γ ⁎ → Q Q ¯ X ) / σ ( e + e − → γ ⁎ → μ + μ − ) and compare with existing results. Our result for R Q is exact to order α s 2 .
Top-quark pair production at next-to-next-to-leading order QCD in electron positron collisions
2016
We set up a formalism, within the antenna subtraction framework, for computing the production of a massive quark-antiquark pair in electron positron collisions at next-to-next-to-leading order in the coupling $\alpha_s$ of quantum chromodynamics at the differential level. Our formalism applies to the calculation of any infrared-safe observable. We apply this set-up to the production of top-quark top antiquark pairs in the continuum. We compute the production cross section and several distributions. We determine, in particular, the top-quark forward-backward asymmetry at order $\alpha_s^2$. Our result agrees with previous computations of this observable.
Higgs CP properties using the tau decay modes at the ILC
2013
We investigate the prospects of determining the CP nature of the 126 GeV neutral spin-0 (Higgs) boson h, discovered at the LHC, at a future linear collider. We consider the production of h by the Higgsstrahlung process and its subsequent decays to tau leptons. We investigate how precisely a possible pseudoscalar component of h can be detected by the measurement of a suitably defined angular distribution, if all major decay modes of the tau lepton are used. From our numerical simulations, we estimate the expected precision to the scalar-pseudoscalar mixing angle, including estimates of the background and of measurement uncertainties, to be 2.8 degree for Higgs-boson production at a center-of…
The forward-backward asymmetry for massive bottom quarks at the $Z$ peak at next-to-next-to-leading order QCD
2017
We compute the order $\alpha_s^2$ QCD corrections to the $b$-quark forward-backward asymmetry in $e^+e^-\to b{\bar b}$ collisions at the $Z$ boson resonance, taking the non-zero mass of the $b$ quark into account. We determine these corrections with respect to both the $b$-quark axis and the thrust axis definition of the asymmetry. We compute also the distributions of these axes with respect to the electron beam. If one neglects the flavor singlet contributions to the $b$-quark asymmetry, as was done in previous computations for massless $b$ quarks, then the second-order QCD corrections for $m_b\neq 0$ are smaller in magnitude than the corresponding corrections for $m_b=0$. Including the si…
Determining the CP parity of Higgs bosons at the LHC in the $\tau$ to 1-prong decay channels
2008
We propose a method for determining the CP nature of a neutral Higgs boson or spin-zero resonance $\phi$ at the CERN Large Hadron Collider (LHC) in its $\phi\to\tau^{-}\tau^{+}$ decay channel. The method can be applied to any 1-prong $\tau$-decay mode, which comprise the majority of the $\tau$-lepton decays. The proposed observables allow to discriminate between pure scalar and pseudoscalar Higgs-boson states and/or between a CP-conserving and CP-violating Higgs sector. We show for the decays $\tau\to\pi\nu_{\tau}$ that the method maintains its discriminating power when measurement uncertainties are taken into account. The method will be applicable also at a future linear $e^{+}e^{-}$ colli…
How to pin down theCPquantum numbers of a Higgs boson in itsτdecays at the LHC
2011
We investigate how the $CP$ quantum numbers of a neutral Higgs boson or spin-zero resonance $\ensuremath{\Phi}$, produced at the CERN Large Hadron Collider, can be determined in its $\ensuremath{\tau}$-pair decay mode $\ensuremath{\Phi}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{\ensuremath{-}}{\ensuremath{\tau}}^{+}$. We use a method [S. Berge and W. Bernreuther, Phys. Lett. B 671, 470 (2009).] based on the distributions of two angles and apply it to the major 1-prong $\ensuremath{\tau}$ decays. We show for the resulting dilepton, lepton-pion, and two-pion final states that appropriate selection cuts significantly enhance the discriminating power of these observables. From our analysis we…
Two-parton contribution to the heavy-quark forward–backward asymmetry in NNLO QCD
2006
Forward-backward asymmetries, $A_{FB}^Q$, are important observables for the determination of the neutral-current couplings of heavy quarks in inclusive heavy quark production, $e^+ e^- \to \gamma^*, Z^* \to Q +X$. In view of the measurement perspectives on $A_{FB}^Q$ at a future linear collider, precise predictions of $A_{FB}^Q$ are required for massive quarks. We compute the contribution of the $Q \bar Q$ final state to $A_{FB}^Q$ to order $\as^2$ in the QCD coupling. We provide general formulae, and we show that this contribution to $A_{FB}^Q$ is infrared-finite. We evaluate these two-parton contributions for $b$ and $c$ quarks on and near the $Z$ resonance, and for $t$ quarks above thres…