The $q_{\mathrm{T}}$ and $Δϕ_{t\bar{t}}$ spectra in top-antitop hadroproduction at NNLL+NNLO: the interplay of soft-collinear resummation and Coulomb singularities
In this paper, we present the resummation-improved differential transverse momentum and azimuthal decorrelation cross sections, $dσ_{t\bar{t}}/dq_{\mathrm{T}}$ and $dσ_{t\bar{t}}/dΔϕ_{t\bar{t}}$, in top-antitop pair production at the LHC. Our calculation is based on the observation that both cross sections are dominated by topologies where the top-quark pair is well separated, expressed in their relative velocity $β_{t\bar{t}}\sim\mathcal{O}(1)$, at colliding energies of $\sqrt{s}=13\,\text{TeV}$ or higher. Therefore, the asymptotic behaviour in the limits $q_{\mathrm{T}}\to0$ and $Δϕ_{t\bar{t}}\to0$ can mostly be captured by the soft and collinear resummation in the HQET$+$SCET framework. Nevertheless, starting at NNLL, Coulomb singularities emerge in the threshold regime, $β_{t\bar{t}}\to0$, in both the hard sector and its evolution kernels, leading to unphysical results upon integration over the entire $β_{t\bar{t}}$ range. To this end, two prescriptions, dubbed the D- and R-prescription, are introduced to regularise these Coulomb singularities. They embody two fundamentally different methods to truncate the threshold enhanced terms, rendering their contribution finite. In the absence of a combined threshold and small-transverse-momentum resummation, we present a quantitative assessment of the ambiguity introduced by the choice of prescription, itself a test of the sensitivity of our calculation to such threshold enhancements, for both the $dσ_{t\bar{t}}/dq_{\mathrm{T}}$ and $dσ_{t\bar{t}}/dΔϕ_{t\bar{t}}$ spectra.
Associated production of a top quark pair with a heavy electroweak gauge boson at NLO+NNLL accuracy
我们进行软胶子修正的总截面和不变的质量分布的阈值重建的生产的顶-反顶夸克对与重电弱玻色子$V = W^+$，$W^-$或$Z$在$pp$碰撞在大型强子对撞机。在三粒子不变质量运动学中，使用直接QCD Mellin空间技术，以近-领先对数（NNLL）精度进行重新计算。结果表明，对于$t\bar t Z$过程，软胶子重算对次领先阶（NLO）结果有显著的修正。当中心尺度等于$t\bar t Z$不变质量时，修正值接近30%.对于该过程，相对于NLO结果，在NLO+NNLL水平下，由于尺度选择导致的截面的主要理论不确定性显著降低。在$t\bar t W^{\pm}$病例中，发现再膨胀的影响不太明显。所获得的结果进行比较CMS和ATLAS合作在LHC最近进行的测量。
