Measurement of the four-lepton invariant mass spectrum in 13 TeV proton-proton collisions with the ATLAS detector

Abstract

A measurement of the four-lepton invariant mass spectrum is made with the ATLAS detector, using an integrated luminosity of 36.1 fb −1 of proton-proton collisions at √ s = 13 TeV delivered by the Large Hadron Collider. The differential cross-section is measured for events containing two same-flavour opposite-sign lepton pairs. It exhibits a rich structure, with different mass regions dominated in the Standard Model by single Z boson production, Higgs boson production, and Z boson pair production, and non-negligible interference effects at high invariant masses. The measurement is compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. These calculations are used to interpret the data in terms of gg → Z Z → 4 and Z → 4 subprocesses, and to place constraints on a possible contribution from physics beyond the Standard Model.

Event generation with Sherpa 2.2

“…Note, a very recent experimental measurement of this channel at √ s = 13 TeV, including an extensive comparison of state-of-the-art theoretical predictions with data, among them those from SHERPA, has been presented by the ATLAS collaboration in [175]. A similar study but for the final state of four charged leptons has been presented in [176].…”

NNLO QCD + NLO EW with Matrix+OpenLoops: precise predictions for vector-boson pair production

“…Since all quarks of the first two generations are treated as massless, the unitarity of the CKM matrix ensures the independence of all physical results of the Cabibbo angles for charge-neutral processes. 11 Hence, for ZZ and W W production the choice of a diagonal CKM matrix is fully justified. The effects from a non-trivial CKM matrix for W Z production are also quite small, being below −1% in case of the NLO QCD cross section and negligible for the NLO QCD K-factor [20,25].…”

BSM W W production with a jet veto

“…In other words, for a Gaussian theory term our treatment is equivalent to the common prescription to combine theoretical and experimental errors in quadrature. 8 With our choice of bins, we can approximate ∆ i (κ t , κ g ) ∆…”

“…The solid contour for W W in figure 14 corresponds to an estimated theoretical uncertainty of 3% in every bin, which is approximately the one you need for W W to be competitive with current ZZ predictions. Based again on 8 In fact, (5.6) itself can similarly be obtained as follows: (i) introduce separate δ -23 - Figure 13. Exclusion contours at 95% level for W W and ZZ production, corresponding to different ways of estimating theoretical uncertainties, see the main text for details.…”

“…Di-boson production at the Large Hadron Collider constitutes a promising window into physics beyond the SM. This is particularly true for di-boson pairs with high invariant mass, which have been already probed by a number of recent experimental analyses [1][2][3][4][5][6][7][8][9][10][11]. On the one hand, their production through gluon fusion receives contributions from an off-shell Higgs boson [12][13][14].…”