Measurements of the pp → W±γγ and pp → Zγγ cross sections at $$ \sqrt{\mathrm{s}} $$ = 13 TeV and limits on anomalous quartic gauge couplings

Abstract

The cross section for W or Z boson production in association with two photons is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data set corresponds to an integrated luminosity of 137 fb−1 collected by the CMS experiment at the LHC. The W → ℓν and Z → ℓℓ decay modes (where ℓ = e, μ) are used to extract the Wγγ and Zγγ cross sections in a phase space defined by electron (muon) with transverse momentum larger than 30 GeV and photon transverse momentum larger than 20 GeV. All leptons and photons are required to have absolute pseudorapidity smaller than 2.5. The measured cross sections in this phase space are σ(Wγγ) = $$ {13.6}_{-1.9}^{+1.9}{\left(\mathrm{stat}\right)}_{-4.0}^{+4.0} $$ 13.6 − 1.9 + 1.9 stat − 4.0 + 4.0 (syst) ± 0.08 (PDF + scale) fb and σ(Zγγ) = $$ {5.41}_{-0.55}^{+0.58}{\left(\mathrm{stat}\right)}_{-.070}^{+0.64} $$ 5.41 − 0.55 + 0.58 stat − .070 + 0.64 (syst) ± 0.06 (PDF + scale) fb. Limits on anomalous quartic gauge couplings are set in the framework of an effective field theory with dimension-8 operators.

Multiboson production at the LHC

“…An observation of the inclusive 𝑽𝜸𝜸 process, 𝑽 = 𝑾, 𝒁 [18], was made by the CMS experiment, with the signal significance of 3.1 and 4.8 standard deviations for 𝑊 𝛾𝛾 and 𝑍𝛾𝛾, respectively. This process is sensitive to anomalous QGC that can be generated by dimension-6 or dimension-8 EFT operators.…”

New Higgs decays to axion-like particles

“…The most promising LHC analysis to constrain our 2µ2γ ALP signal is the CMS search targeting events with a leptonically decaying Z boson and two photons [72] 1 . However, its cut on the transverse momentum of the two photons, p γ T > 20 GeV, is only rarely passed for the photons resulting from the decay of a low-mass ALP a → γγ.…”

“…To increase the sensitivity on Higgs decays to ALPs via the h → a2µ channel, we design our own analysis based on Ref. [72]. We relax the cuts m > 55 GeV and p γ T > 20 GeV in the experimental reference to make the analysis more inclusive:…”

“…To account for the Z+jets background, we have multiplied the generated background distribution by a factor 1.7. This factor is based on the Z+ jets production background contribution in Zγγ production [72], which is ∼ 62 % the size of the signal. We conservatively assume a 25% systematic uncertainty on the background prediction based on the uncertainty of Z+ jets production background contribution; see Ref.…”

“…We conservatively assume a 25% systematic uncertainty on the background prediction based on the uncertainty of Z+ jets production background contribution; see Ref. [72].…”