Wγ and Zγ production at the LHC in NNLO QCD

Abstract

Abstract:We consider the production of W γ and Zγ pairs at hadron colliders. We report on the complete fully differential computation of radiative corrections at next-to-next-toleading order (NNLO) in QCD perturbation theory. The calculation includes the leptonic decay of the vector boson with the corresponding spin correlations, off shell effects and final-state photon radiation. We present numerical results for pp collisions at 7 and 8 TeV and we compare them with available LHC data. In the case of Zγ production, the impact of NNLO corrections is generally moderate, ranging from 8% to 18%, depending on the applied cuts. In the case of W γ production, the NNLO effects are more important, and range from 19% to 26%, thereby improving the agreement of the theoretical predictions with the data. As expected, the impact of QCD radiative corrections is significantly reduced when a jet veto is applied.

Multiboson interactions at the LHC

“…As illustrated in Figure 7, CMS finds the cross section to be compatible with the MCFM prediction at NLO in QCD as a function of the photon E T out to 100 GeV, while ATLAS measures inclusive cross sections higher than the NLO prediction in the inclusive process for high-E T photons. NNLO corrections are found to increase the NLO prediction by ≈ 20%, hence improving the agreement with the measured cross sections (Grazzini et al, 2015a).…”

“…For diboson production, the state of the art QCD calculation is NNLO for W + W − Grazzini et al, 2016a), W ± γ (Denner et al, 2015;Grazzini et al, 2015a), Grazzini et al, 2015a) and γγ (Campbell et al, 2016). There has been recent rapid progress on this front using q T subtraction techniques and in the near future public codes, such as MATRIX (Wiesemann et al, 2016), should be available to automate event generation.…”

Diboson Results from CMS

“…Experimental backgrounds from beam halo and light spikes in the electromagnetic calorimeter (ECAL) are rejected with cuts on the ECAL signals' timing and shape, and remaining contributions are estimated with fits to the timing signal shapes. The fiducial cross section is found to be σ fid (pp → Zγ → ννγ) = 66.5 ± 13.6 (stat) ± 14.3 (syst) ± 2.2 (lumi) fb, (5.1) which is compatible with the NNLO prediction of 65.5 ± 3.3 fb from MATRIX [13].…”

Measurements ofW±Zproduction cross sections inppcollisions ats=8<

“…In addition, new perturbative effects appearing at NNLO could enhance the SM prediction compared to the NLO calculation. Indeed, for the other diboson final states ZZ, WW, Zγ, and Wγ NNLO calculations have recently become available [70,[76][77][78], and in all cases the NNLO corrections were found to be positive and larger than the uncertainty on the NLO calculation estimated by the conventional independent up and down variations of μ R and μ F by a factor of 2. The ratio of W þ Z to W − Z production cross sections is also measured in the fiducial phase space and yields…”