Infrared renormalons in kinematic distributions for hadron collider processes

Infrared renormalons in Quantum Chromodynamics are associated with non-perturbative corrections to short distance observables. Linear renormalons, i.e. such that the associated non-perturbative corrections scale like one inverse power of the hard scale, can affect at a non-negligible level even the very high-energy phenomena studied at the Large Hadron Collider. Using an Abelian model, we study the presence of linear renormalons in the transverse momentum distribution of a neutral vector boson Z produced in hadronic collisions. We consider a process where the Z transverse momentum is balanced by a sizable recoil against a coloured final state particle. One may worry that such a colour configuration, not being azimuthally symmetric, could generate unbalanced soft radiation, associated in turn with linear infrared renormalons affecting the transverse momentum distribution of the vector boson. We performed a numerical calculation of the renormalon effects for this process in the so-called large b0 limit. We found no evidence of linear renormalons in the transverse momentum distribution of the Z in the large transverse-momentum region, irrespective of rapidity cuts.

Resummed Drell-Yan cross-section at N3LL

We present the resummed predictions for inclusive cross-section for Drell-Yan (DY) production as well as onshell Z, W± productions at next-to-next-to-next-to leading logarithmic (N3LL) accuracy. Using the standard techniques, we derive the N-dependent coefficients in the Mellin-N space as well as the N-independent constants and match the resummed result through the minimal prescription procedure with the fixed order results. In addition to the standard ln N exponentiation, we study the numerical impacts of exponentiating N-independent part of the soft function and the complete $$ {\overline{g}}_0 $$ g ¯ 0 that appears in the resummed predictions in N space. All the analytical pieces needed in these different approaches are extracted from the soft-virtual part of the inclusive cross section known to next-to-next-to-next-to leading order (N3LO). We perform a detailed analysis on the scale and parton distribution function (PDF) variations and present predictions for 13 TeV LHC for the neutral Drell-Yan process as well as onshell charged and neutral vector boson productions.

First results on precision constraints on Z - Z′ mixing with ATLAS and CMS diboson production data at the LHC at 13 TeV and predictions for Run II

The study of electroweak boson pair production provides a powerful tool to search for new phenomena beyond the Standard Model (SM). Extra neutral vector bosons Z′ decaying to charged gauge vector boson pairs W+W- are predicted in many scenarios of new physics, including models with an extended gauge sector. The diboson production allows to place stringent constraints on the Z-Z′ mixing parameter ξ and Z′ mass, MZ′. We present the Z′ exclusion region in the ξ - MZ′ plane for the first time by using data comprised of pp collisions at √s = 13 TeV and recorded by the ATLAS and CMS detectors at the CERN LHC, with integrated luminosities of 36.1 and 35.9 fb-1, respectively. The exclusion region has been significantly extended compared to that obtained from the previous analysis performed with Tevatron data, as well as with LHC data collected at 7 and 8 TeV. Also, we found that these constraints on the Z-Z′ mixing factor are more severe than those derived from the global analysis of electroweak data. Further improvement on the constraining of this mixing can be achieved from the analysis of data to be collected at higher luminosity expected in Run II.