Speaker
Judith Katzy
(DESY, HAMBURG)
Description
Measurements of the ZZ and WW final states in the mass range above the 2mZ and 2mW thresholds
provide a unique opportunity to measure the off-shell coupling strength of the Higgs boson.
This poster presents a determination of the off-shell Higgs boson event yields normalised to the
Standard Model prediction (signal strength) in the ZZ→4ℓ, ZZ→2ℓ2ν and WW→eνμν final states. The
result is based on pp collision data collected by the ATLAS experiment at the LHC, corresponding
to an integrated luminosity of 20.3 fb−1 at a collision energy of s√=8 TeV. Using the CLs method,
the observed 95% confidence level (CL) upper limit on the off-shell signal strength is in the
range 5.1--8.6, with an expected range of 6.7--11.0. In each case the range is determined by
varying the unknown gg→ZZ and gg→WW background K-factor from higher-order QCD corrections between
half and twice the value of the known signal K-factor. Assuming the relevant Higgs boson couplings
are independent of the energy scale of the Higgs production, a combination with the on-shell
measurements yields an observed (expected) 95% CL upper limit on ΓH/ΓSMH in the
range 4.5--7.5 (6.5--11.2) using the same variations of the background K-factor. Assuming that
the unknown gg→VV background K-factor is equal to the signal K-factor, this translates into an
observed (expected) 95% CL upper limit on the Higgs boson total width of 22.7 (33.0) MeV.
Author
Judith Katzy
(DESY, HAMBURG)
