Constraints on the offshell Higgs boson signal strength in the highmass $ZZ$ and $WW$ final states with the ATLAS detector
Abstract
Measurements of the $ZZ$ and $WW$ final states in the mass range above the $2m_Z$ and $2m_W$ thresholds provide a unique opportunity to measure the offshell coupling strength of the Higgs boson. This paper presents constraints on the offshell Higgs boson event yields normalised to the Standard Model prediction (signal strength) in the $ZZ \to 4\ell$, $ZZ\to2\ell2\nu$ and $WW\to e\nu\mu\nu$ 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$^\text{1}$ at a collision energy of $\sqrt{s}$=8 TeV. Using the $CL_s$ method, the observed 95% confidence level (CL) upper limit on the offshell signal strength is in the range 5.18.6, with an expected range of 6.711.0. In each case the range is determined by varying the unknown $gg\to ZZ$ and $gg\to WW$ background Kfactor from higherorder QCD corrections between half and twice the value of the known signal Kfactor. Assuming the relevant Higgs boson couplings are independent of the energy scale of the Higgs production, a combination with the onshell measurements yields an observed (expected) 95\% CL upper limit on $\Gamma_H/\Gamma_H^{\mathrm{SM}}$ in the range 4.5 7.5 (6.5 11.2) using the same variations of the background Kfactor. Assuming that the unknown $gg\rightarrow VV$ background Kfactor is equal to the signal Kfactor,this translates into an observed (expected) 95% CL upper limit on the Higgs boson total width of 22.7 (33.0) MeV.
 Publication:

arXiv eprints
 Pub Date:
 March 2015
 DOI:
 10.48550/arXiv.1503.01060
 arXiv:
 arXiv:1503.01060
 Bibcode:
 2015arXiv150301060A
 Keywords:

 High Energy Physics  Experiment
 EPrint:
 34 pages plus author list + cover pages (50 pages total), 12 figures, 6 tables, submited to The European Physical Journal C, All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG201410/