Order QCD Radiative Corrections Research Articles

Far-forward neutrinos at the Large Hadron Collider

We present a new calculation of the energy distribution of high-energy neutrinos from the decay of charm and bottom hadrons produced at the Large Hadron Collider (LHC). In the kinematical region of very forward rapidities, heavy-flavor production and decay is a source of tau neutrinos that leads to thousands of charged-current tau neutrino events in a 1 m long, 1 m radius lead neutrino detector at a distance of 480 m from the interaction region. In our computation, next-to-leading order QCD radiative corrections are accounted for in the production cross-sections. Non-perturbative intrinsic-kT effects are approximated by a simple phenomenological model introducing a Gaussian kT -smearing of the parton distribution functions, which might also mimic perturbative effects due to multiple initial-state soft-gluon emissions. The transition from partonic to hadronic states is described by phenomenological fragmentation functions. To study the effect of various input parameters, theoretical predictions for {D}_s^{pm } production are compared with LHCb data on double-differential cross-sections in transverse momentum and rapidity. The uncertain- ties related to the choice of the input parameter values, ultimately affecting the predictions of the tau neutrino event distributions, are discussed. We consider a 3+1 neutrino mixing scenario to illustrate the potential for a neutrino experiment to constrain the 3+1 parameter space using tau neutrinos and antineutrinos. We find large theoretical uncertainties in the predictions of the neutrino fluxes in the far-forward region. Untangling the effects of tau neutrino oscillations into sterile neutrinos and distinguishing a 3+1 scenario from the standard scenario with three active neutrino flavours, will be challenging due to the large theoretical uncertainties from QCD.

The measurement of the Higgs self-coupling at the LHC: theoretical status

Abstract Now that the Higgs boson has been observed by the ATLAS and CMS experiments at the LHC, the next important step would be to measure accurately its properties to establish the details of the electroweak symmetry breaking mechanism. Among the measurements which need to be performed, the determination of the Higgs self-coupling in processes where the Higgs boson is produced in pairs is of utmost importance. In this paper, we discuss the various processes which allow for the measurement of the trilinear Higgs coupling: double Higgs production in gluon fusion, vector boson fusion, double Higgs-strahlung and associated production with a top quark pair. We first evaluate the production cross sections for these processes at the LHC with center-of-mass energies ranging from the present $ \sqrt{s}=8 $ TeV to $ \sqrt{s}=100 $ TeV, and discuss their sensitivity to the trilinear Higgs coupling. We include the various higher order QCD radiative corrections, at next-to-leading order for gluon and vector boson fusion and at next-to-next-to-leading order for associated double Higgs production with a gauge boson. The theoretical uncertainties on these cross sections are estimated. Finally, we discuss the various channels which could allow for the detection of the double Higgs production signal at the LHC and estimate their potential to probe the trilinear Higgs coupling.

Indirect measurement of quarkonium in the two-photon process

In this paper, we propose a new approach to probe the quarkonium at the BES-III and the B factories. In the two-photon process, e(+)e(-) -> e(+)e(-) + hadron, the signals of the emitted hadron can be reconstructed through investigating the final leptons e(+)e(-). Furthermore, by analyzing the distribution of the relative angle between the final e(+) and e(-), we can determine the quantum number of the final hadron. For those hadrons that are hard to detect directly, this may provide an effective way. We calculate the cross sections as well as the distributions of the eta(c)(1S, 2S) and chi(cJ)(1P, 2P) production at tree level and the next-to-leading order QCD radiative corrections. In addition, the cross sections of bottomonium production are considered at tree level. Unfortunately, they are too tiny to be detected.

Combining next-to-leading order QCD and electroweak radiative corrections toW-boson production at hadron colliders in the powheg framework

The precision measurement of the mass of the $W$ boson is an important goal of the Fermilab Tevatron and the CERN Large Hadron Collider (LHC). It requires accurate theoretical calculations which incorporate both higher-order QCD and electroweak corrections, and also provide an interface to parton-shower Monte Carlo programs which make it possible to realistically simulate experimental data. In this paper, we present a combination of the full ${\cal O}(\alpha)$ electroweak corrections of {\tt WGRAD2}, and the next-to-leading order QCD radiative corrections to $W\to\ell\nu$ production in hadronic collisions in a single event generator based on the {\tt POWHEG} framework, which is able to interface with the parton-shower Monte Carlo programs {\tt Pythia} and {\tt Herwig}. Using this new combined QCD+EW Monte Carlo program for $W$ production we provide numerical results for total cross sections and kinematic distributions of relevance to the $W$ mass measurement at the Tevatron and the LHC for the processes $pp,p\bar p \to W^\pm \to \mu^\pm \nu_\mu$. In particular, we discuss the impact of EW corrections in the presence of QCD effects when including detector resolution effects.

Dijet invariant mass distribution in top quark hadronic decay with QCD corrections

The dijet invariant mass distributions from the hadronic decay of unpolarized top quark ($t\to b W^+$ followed by $W^+\to u \bar{d}$) are calculated, including the next-to-leading order QCD radiative corrections. We treat the top decay in the complex mass scheme due to the existence of the intermediate state W boson. Our analytical expressions are also available in different dimensional regularization schemes and $\gamma_5$ strategies. Finally, in order to construct the jets, we use different jet algorithms to compare their influences on our results. The obtained dijet mass distributions from the top quark decay are useful to distinguish these dijets from those produced via other sources and to clarify the issue about the recent CDF Collaborations' $Wjj$ anomaly.

New QCD sum rule for the structure functions of a photon target

Basing on gauge invariance, renormalizability, asymptotic freedom and conservation of energy-momentum tensor in QCD we deduce QCD sum rule for the leading twist parton structure functions of a real and virtual photon target which accounts for any order QCD radiative corrections.