Abstract
We present a complete description of top quark pair production in association with a hard photon in the dilepton channel. Our calculation is accurate to NLO in QCD. It is based on matrix elements for {e}^{+}{nu}_e{mu}^{-}{overline{nu}}_{mu }boverline{b}upgamma production and includes all resonant and non-resonant diagrams, interferences, and off-shell effects of the top quarks and the W gauge bosons. This calculation constitutes the first full computation for top quark pair production with a final state photon in hadronic collisions at NLO in QCD. Numerical results for total and differential cross sections are presented for the LHC at a centre-of-mass energy of sqrt{s}=13 TeV. For a few observables relevant for new physics searches, beyond some kinematic bounds, we observe shape distortions of more than 100%. In addition, we confirm that the size of the top quark off-shell effects for the total cross section is consistent with the expected uncertainties of the narrow width approximation. Results presented here are not only relevant for beyond the Standard Model physics searches but also important for precise measurements of the top-quark fiducial cross sections and top-quark properties at the LHC.
Highlights
Of an exotic top-like quark or the top quark with an anomalous electric dipole moment, see e.g. refs. [1,2,3,4]
With the goal of stabilising shapes in the high pT regions, that are relevant for the new physics searches, we have explored a dynamical choice for μR and μF
At the central scale μ0 = mt/2, the gg channel dominates the total leading order (LO) pp cross section by 79%, followed by the qq + qq channel with 21%
Summary
For the kinematic-dependent scale μR = μF = μ0 = HT /4 our results can be summarised as follows. As expected they are in agreement with results provided at LO and at NLO for μ0 = mt/2. Within quoted theoretical errors they agree at the level of 0.2σ at LO and 0.05σ at NLO This time, the full pp cross section receives positive and small NLO corrections of 2.5%. After symmetrisation of theoretical errors the scale uncertainty at LO is estimated to be instead of the order of 28% and at NLO is reduced down to 4%. After all the size of NLO corrections is diminished and the theoretical error is smaller when comparing to the results with the fixed scale choice. Qualitatively our findings remain the same as for the fixed scale choice
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