Fiducial Higgs and Drell-Yan distributions at N3LL′+NNLO with RadISH

We present state-of-the-art predictions for transverse observables relevant to colour-singlet production at the LHC, in particular the transverse momentum of the colour singlet in gluon-fusion Higgs production and in neutral Drell-Yan lepton-pair production, as well as the $$ {\phi}_{\eta}^{\ast } $$ ϕ η ∗ observable in Drell Yan. We perform a next-to-next-to-next-to-leading logarithmic (N3LL) resummation of such observables in momentum space according to the RadISH formalism, consistently including in our prediction all constant terms of relative order $$ {\alpha}_s^3 $$ α s 3 with respect to the Born, thereby achieving N3LL′ accuracy. The calculation is fully exclusive with respect to the Born kinematics, which allows the application of arbitrary fiducial selection cuts on the decay products of the colour singlet. We supplement our results with a transverse-recoil prescription, accounting for dominant classes of subleading-power corrections in a fiducial setup. The resummed predictions are matched with fixed-order differential spectra at next-to-next-to-leading order (NNLO) accuracy. A phenomenological comparison is carried out with 13 TeV LHC data relevant to the Higgs to di-photon channel, as well as to neutral Drell-Yan lepton-pair production. Overall, the inclusion of $$ \mathcal{O} $$ O ($$ {\alpha}_s^3 $$ α s 3 ) constant terms, and to a lesser extent of transverse-recoil effects, proves beneficial for the comparison of theoretical predictions to data, leaving a residual theoretical uncertainty in the resummation region at the 2–5% level for Drell-Yan observables, and 5–7% in Higgs production.

Next-to-leading power threshold corrections for finite order and resummed colour-singlet cross sections

We study next-to-leading-power (NLP) threshold corrections in colour-singlet production processes, with particular emphasis on Drell-Yan (DY) and single-Higgs production. We assess the quality of the partonic and hadronic threshold expansions for each process up to NNLO. We determine numerically the NLP leading-logarithmic (LL) resummed contribution in addition to the leading-power next-to-next-to-leading logarithmic (LP NNLL) resummed DY and Higgs cross sections, matched to NNLO. We find that the inclusion of NLP logarithms is numerically more relevant than increasing the precision to N3LL at LP for these processes. We also perform an analytical and numerical comparison of LP NNLL + NLP LL resummation in soft-collinear effective theory and direct QCD, where we achieve excellent analytical and numerical agreement once the NLP LL terms are included in both formalisms. Our results underline the phenomenological importance of understanding the NLP structure of QCD cross sections.

Two-loop splitting in double parton distributions

Double parton distributions (DPDs) receive a short-distance contribution from a single parton splitting to yield the two observed partons. We investigate this mechanism at next-to-leading order (NLO) in perturbation theory. Technically, we compute the two-loop matching of both the position and momentum space DPDs onto ordinary PDFs. This also yields the 1 \to 21→2 splitting functions appearing in the evolution of momentum-space DPDs at NLO. We give results for the unpolarised, colour-singlet DPDs in all partonic channels. These quantities are required for calculations of double parton scattering at full NLO. We discuss various kinematic limits of our results, and we verify that the 1 \to 21→2 splitting functions are consistent with the number and momentum sum rules for DPDs.

Transverse Momentum Dependence in Double Parton Scattering

In this review, we describe the status of transverse momentum dependence (TMD) in double parton scattering (DPS). The different regions of TMD DPS are discussed, and expressions are given for the DPS cross section contributions that make use of as much perturbative information as possible. The regions are then combined with each other as well as single parton scattering to obtain a complete expression for the cross section. Particular emphasis is put on the differences and similarities to transverse momentum dependence in single parton scattering. We further discuss the status of the factorisation proof for double colour singlet production in DPS, which is now on a similar footing to the proofs for TMD factorisation in single Drell-Yan, discuss parton correlations, and give an outlook on possible research on DPS in the near future.

Compact Exotic Tetraquark Mesons in Large-Nc QCD

We embark on systematic explorations of the behaviour of tetraquark mesons, i.e., colour-singlet bound states of two quarks and two antiquarks, in the (idealized) limit of a large number of colour degrees of freedom, Nc,; of quantum chromodynamics, QCD. Considering the scattering of two ordinary mesons into two ordinary mesons, we start off with formulating a set of selection criteria that should enable us to unambiguously single out precisely those contributions to all encountered scattering amplitudes that potentially will develop tetraquark poles. Assuming that tetraquark mesons do exist and, if so, emerge in the contributions compatible with our criteria at largest admissible order of Nc; we deduce, for the categories of tetraquarks that exhibit either four or only two different open quark flavours, that the decay rates of these tetraquark types are, at least, of order 1/N2c and that internal consistency requires all the members of the first species to exist pairwise, distinguishable by their favoured two-ordinary-meson decay channels.