Measurement of the ZZ production cross section and Z →ℓ+ℓ−ℓ′+ℓ′− branching fraction in pp collisions at s=13 TeV

Abstract

Four-lepton production in proton-proton collisions, pp → (Z/γ * ) (Z/γ * ) → + − + − , where , = e or µ, is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.6 fb −1 . The ZZ production cross section, σ(pp → ZZ) = 14.6 +1.9 −1.8 (stat) +0.5 −0.3 (syst) ± 0.2 (theo) ± 0.4 (lumi) pb, is measured for events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60 < m + − , m + − < 120 GeV. The Z boson branching fraction to four leptons is measured to be B(Z → + − + − ) = 4.9 +0.8 −0.7 (stat) +0.3 −0.2 (syst) +0.2 −0.1 (theo) ± 0.1 (lumi) × 10 −6 for the four-lepton invariant mass in the range 80 < m + − + − < 100 GeV and dilepton mass m + − > 4 GeV for all opposite-sign, same-flavor lepton pairs. The results are in agreement with standard model predictions.

ZZ production in gluon fusion at NLO matched to parton shower

“…During the Run I of the Large Hadron Collider (LHC), the production of a pair of vector bosons was one of the processes studied in greatest detail [1][2][3][4][5][6]. The Higgs boson was initially discovered through its decay into dibosons, and this decay channel continues to be important for measuring the properties of the Higgs [7][8][9][10].…”

“…The Higgs boson was initially discovered through its decay into dibosons, and this decay channel continues to be important for measuring the properties of the Higgs [7][8][9][10]. First LHC Run II data at 13 TeV recently became available from both ATLAS [11] and CMS [5]. Further LHC results with higher statistics will enable a program of precision Higgs measurements, including its coupling to vector bosons through its decay to ZZ or W þ W − .…”

Branching fraction for Z decays to four leptons and constraints on new physics

“…We define the phase space region for our combined B(Z → 4 ) by the invariant mass requirements 80 < m 4 < 100 GeV for the four-lepton sum and m + − > 4 GeV for all opposite-sign, same-flavor lepton pairs. This region is chosen to most closely match those used for the published measurements, and is identical to that of the CMS results published in 2016 [2] and 2018 [3]. The region used for the 2012 CMS measurement reported in Ref.…”

“…Even so, the high luminosities recorded at the LHC experiments have enabled them to observe Z → 4 decay events in numbers sufficient to measure B(Z → 4 ) precisely. These measurements have been made by the CMS Collaboration, which has published results from data samples at √ s = 7 and 13 TeV [1][2][3], and by the ATLAS Collaboration, which has performed a combined measurement using data samples at √ s = 7 and 8 TeV [4].…”

“…In the case of B(Z → 4 ), such a combination is nontrivial; a naive weighted average of the measured values as reported in Refs. [1][2][3][4] falsely suggests disagreement among them. Care must be taken to account for the particular experimental cuts employed in each analysis in order to appropriately incorporate them in the combined value.…”