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Register a new userUnweighted event generation in hadronic WZ production at order(alpha_S)
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We present an algorithm for unweighted event generation in the partonic process pp -> WZ (j) with leptonic decays at next-to-leading order in alpha_S. Monte Carlo programs for processes such as this frequently generate events with negative weights in certain regions of phase space. For simulations of experimental data one would like to have unweighted events only. We demonstrate how the phase space from the matrix elements can be combined to achieve unweighted event generation using a second stage Monte Carlo integration over a volume of real emissions (jets). Observable quantities are kept fixed in the laboratory frame throughout the integration. The algorithm is applicable to a broader class of processes and is CPU intensive.
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We present a study at next-to-leading-order (NLO) of the process $pp to W^pm Z to ell u_l ell^+ ell^-$, where $ell,ell =e, mu$, at the Large Hadron Collider. We include the full NLO QCD corrections and the NLO electroweak (EW) corrections in the double-pole approximation. We define eight fiducial polarization coefficients directly constructed from the polar-azimuthal angular distribution of the decay leptons. These coefficients depend strongly on the kinematical cuts on the transverse momentum or rapidity of the individual leptons. Similarly, fiducial polarization fractions are also defined and they can be directly related to the fiducial coefficients. We perform a detailed analysis of the NLO QCD+EW fiducial polarization observables including theoretical uncertainties stemming from the scale variation and parton distribution function uncertainties, using the fiducial phase space defined by the ATLAS and CMS experiments. We provide results in the helicity coordinate system and in the Collins-Soper coordinate system, at a center-of-mass energy of 13 TeV. The EW corrections are found to be important in two of the angular coefficients related to the $Z$ boson, irrespective of the kinematical cuts or the coordinate system. Meanwhile, those EW corrections are very small for the $W^pm$ bosons.
The pair production of a $W$ and a $Z$ boson at the LHC is an important process to study the triple-gauge boson couplings as well as to probe new physics that could arise in the gauge sector. In particular the leptonic channel $p p to W^pm Zto 3ell + u + X$ is considered by ATLAS and CMS collaborations. Polarisation observables can help pinning down new physics and give information on the spin of the gauge bosons. Measuring them requires high statistics as well as precise theoretical predictions. We define in this contribution fiducial polarisation observables for the $W$ and $Z$ bosons and we present theoretical predictions in the Standard Model at next-to-leading order (NLO) including QCD as well as NLO electroweak corrections, the latter in the double-pole approximation. We also show that this approximation works remarkably well for $W^pm Z$ production at the LHC by comparing to the full results.
WZ production is an important process at the LHC because it probes the non-Abelian structureof electroweak interactions and it is a background process for many new physics searches. In the quest for new physics, polarization observables of the W and Z bosons can play an important role. They can be extracted from measurements and can be calculated using the Standard Model. In this contribution, we define fiducial polarization observables of the W and Z bosons and discuss the effects of next-to-leading order electroweak and QCD corrections in the Standard Model.
We have developed a Monte Carlo event generator for non-resonant diphoton ($gammagamma$) production at hadron collisions in the framework of GR@PPA, which consistently includes processes having additional one jet radiation. The possible double count problem in the generation of radiative processes is avoided by using the LLL subtraction method that we have applied to the weak-boson production processes. The subtraction method has been extended to the final-state QED divergence that appears in the $qg rightarrow gammagamma + q$ process. Because a parton shower (PS) which regularizes the subtracted QED divergence is still under development, we tried to use PYTHIA for the generation of the fragmentation events to restore the subtracted components. The simulation employing the old PS of PYTHIA shows a reasonable matching with the GR@PPA events, and the combined event sample shows a result in reasonable agreement with ResBos. We found that the contribution from $qg rightarrow gammagamma + q$ is significant in the LHC condition. This event generator must be useful for the background studies in low-mass Higgs boson searches at LHC.
I describe a subtraction scheme for the next-to-next-to-leading order calculation of single inclusive production at hadron colliders. Such processes include Drell-Yan, W^{+/-}, Z and Higgs Boson production. The key to such a calculation is a treatment of initial state radiation which preserves the production characteristics, such as the rapidity distribution, of the process involved. The method builds upon the Dipole Formalism and, with proper modifications, could be applied to deep inelastic scattering and e^+ e^- annihilation to hadrons.
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