Combinations of single-top-quark production cross-section measurements and |f_LV V_tb| determinations at √s = 7 and 8 TeV with the ATLAS and CMS experiments

This paper presents the combinations of single-top-quark production cross-section measurements by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at (\sqrt{s}) = 7 and 8 TeV corresponding to integrated luminosities of 1.17 to 5.1 fb⁻¹ at (\sqrt{s}) = 7 TeV and 12.2 to 20.3 fb⁻¹ at (\sqrt{s})=8TeV. These combinations are performed per centre-of-mass energy and for each production mode: (t)-channel, (tW), and (s)-channel. The combined (t)-channel cross-sections are 67.5 ± 5.7 pb and 87.7 ± 5.8 pb at (\sqrt{s}) = 7 and 8 TeV respectively. The combined (tW) cross-sections are 16.3 ± 4.1 pb and 23.1 ± 3.6 pb at (\sqrt{s}) = 7 and 8 TeV respectively. For the (s)-channel cross-section, the combination yields 4.9 ± 1.4 pb at (\sqrt{s})=8TeV. The square of the magnitude of the CKM matrix element (V_{tb}) multiplied by a form factor f LV is determined for each production mode and centre-of-mass energy, using the ratio of the measured cross-section to its theoretical prediction. It is assumed that the top-quark-related CKM matrix elements obey the relation (|V_{td}|,|V_{ts}| ≪ |V_{tb}|). All the (|f_{LV}V_{tb}|^2) determinations, extracted from individual ratios at (\sqrt{s}) = 7 and 8 TeV, are combined, resulting in (|f_{LV}V_{tb}|) = 1.02 ± 0.04 (meas.) ± 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions.