Properties of $$e^ + e^ - \to h\bar h$$ in the $$\Upsilon (b\bar b)$$ -continuum

Ultrasoft NLL running of the nonrelativistic O(v) QCD quark potential

“…[16] and exhibits a clear instability for ν ∼ α s ∼ 0.15, where the low-energy matrix elements relevant for top threshold production have to be evaluated. This instability is the cause of the relatively large 6-10% uncertainty in the normalization of the top pair threshold cross section [10,19]. Finally, the black solid curve shows c 1 (ν)/c 1 (1) including the full NLL and NNLL non-mixing contributions as well as the ultrasoft NNLL mixing corrections finalized in this work.…”

“…The reason is related to the larger size of the ultrasoft coupling α s (mν 2 ) and to a rather large coefficient multiplying the ultrasoft contributions. These large ultrasoft contributions are responsible for an uncertainty in the normalization of the most up-to-date top pair threshold cross section prediction of at best 6% [19], which is quite far from the required precision (see also Ref. [10]).…”

𝒪(ααs) corrections to the γtt̄ vertex at the top quark threshold

“…The first subscript of h refers to helicity of the electron, and the second one to the vector (J µ V =ψγ µ ψ) or axial-vector coupling (J µ A =ψγ µ γ 5 ψ) of the gauge bosons to the top quark current. 2 For e + R e − L in the initial state a similar expression is obtained by replacing R by L in Eq. (1).…”

“…The feasibility of such high-precision measurements requires a theory prediction of the total cross section σ(e + e − → tt) with high accuracy (preferably δσ/σ ≤ 3%). Current estimates based on (partial) next-to-next-to-leading logarithmic (NNLL) order [2,3] and (partial) next-to-next-to-next-to-leading order (NNNLO) [4,5] QCD corrections lead to an uncertainty of the order of 10%.…”

An optimal scheme for top quark mass measurement near the $\rm{t}\bar{t}$ threshold at future $\rm{e}^{+}{e}^{-}$ colliders

“…It can also be suppressed by other selection cuts [37]. The interference between the resonant top pair decay and the single top decay process is also suppressed by v 2 [38] with v being the top quark velocity. Therefore, the backgrounds can safely be neglected in such a clean experiment.…”