No Arabic abstract
We present a study of the polarization observables of the $W$ and $Z$ bosons in the process $p p to W^pm Zto e^pm u_e mu^+mu^-$ at the 13 TeV Large Hadron Collider. The calculation is performed at next-to-leading order, including the full QCD corrections as well as the electroweak corrections, the latter being calculated in the double-pole approximation. The results are presented in the helicity coordinate system adopted by ATLAS and for different inclusive cuts on the di-muon invariant mass. We define left-right charge asymmetries related to the polarization fractions between the $W^+ Z$ and $W^- Z$ channels and we find that these asymmetries are large and sensitive to higher-order effects. Similar findings are also presented for charge asymmetries related to a P-even angular coefficient.
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 provide a description of the transverse momentum spectrum of single inclusive forward jets produced at the LHC, at the center-of-mass energies of 7 and 13 TeV, using the high energy factorization (HEF) framework. We subsequently study double inclusive forward jet production and, in particular, we calculate contributions to azimuthal angle distributions coming from double parton scattering. We also compare our results for double inclusive jet production to those obtained with the Pythia Monte Carlo generator. This comparison confirms that the HEF resummation acts like an initial state parton shower. It also points towards the need to include final state radiation effects in the HEF formalism.
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.
We discuss briefly a recent study of new observables in LHC inclusive events with three tagged jets. One jet is in the forward direction, the second is in the backward direction and well-separated in rapidity from the first, whereas, the third tagged jet is to be found in more central regions of the detector. Taking into consideration that non-tagged mini-jet emissions are allowed and that they may be accounted for by the BFKL gluon Green function, we project the cross sections on azimuthal-angle components and define suitable ratios based on these projections which can provide several distinct tests of the BFKL dynamics.
Accessing the polarization of weak bosons provides an important probe for the mechanism of electroweak symmetry breaking. Relying on the double-pole approximation and on the separation of polarizations at the amplitude level, we study WZ production at the LHC, with both bosons in a definite polarization mode, including NLO QCD effects. We compare results obtained defining the polarization vectors in two different frames. Integrated and differential cross-sections in a realistic fiducial region are presented.