Bump hunting in LHC tt¯ events

Abstract

We demonstrate that a purposefully normalised NNLO m tt differential spectrum can have very small theoretical uncertainty and, in particular, a small sensitivity to the top quark mass. Such observable can thus be a very effective bump-hunting tool for resonances decaying to tt events during LHC Run II and beyond. To illustrate how the approach works, we concentrate on one specific example of current interest, namely, the possible 750 GeV di-gamma excess resonance Φ. Considering only theoretical uncertainties, we demonstrate that it is possible to distinguish pp → Φ → tt signals studied in the recent literature [Hespel, Maltoni and Vryonidou, arXiv:1606.04149] from the pure SM background with very high significance. Alternatively, in case of non-observation, a strong upper limit on the decay rate Φ → tt can be placed.

Latest theory developments for top pair production, generators and showering

“…They were first published for the forward backward top asymmetry in ref. [3], and, very recently, for other (more exclusive) observables [4]. The importance of the latter results can not be underestimated.…”

“…By including NNLO corrections, the agreement is significantly improved, as also shown in ref. [4]. An important refinement of these differential results will be its combination with the NNLO differential computation of the top decay, that was performed in refs.…”

“…In the context of top-pair production, so far results were published only using the MEPS@NLO [41] and FxFx [42] merging methods. 4 The measurement of QCD activity in tt events…”

Summary of the CKM 2016 working group on high-energy flavor physics

“…The measurement of a large top quark forward-backward asymmetry at the Tevatron (see Sec. 4) was one of the motivations to extend these calculations also the differential cross sections, both for the LHC [3] and for the Tevatron [4].…”

Top quark pair production in association with a jet with NLO QCD off-shell effects

“…Important measurements are the determination of the top-quark coupling to gauge bosons and the Higgs boson, spin-correlations of the top-quark decay products as well as fiducial cross sections and differential distributions. For now, the most advanced calculations for stable top-quark pair production are the NNLO+NNLL prediction [1] of the total cross section and NNLO accurate prediction for differential distributions [2,3]. However, top-quarks are extremely unstable particles, and therefore decay before they can hadronize.…”