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Catani, S., Cieri, L., Colferai, D., & Coradeschi, F. (2023). Soft gluon-quark-antiquark emission in QCD hard scattering. Eur. Phys. J. C, 83(1), 38–18pp.
Abstract: We consider the radiation of a soft gluon (g) and a soft quark-antiquark (qq & macr;) pair in QCD hard scattering. In the soft limit the scattering amplitude has a singular behaviour that is factorized and controlled by a soft current, which has a process-independent structure in colour space. We evaluate the soft gqq & macr; current at the tree level for an arbitrary multiparton scattering process. The irreducible correlation component of the current includes strictly nonabelian terms and also terms with an abelian character. Analogous abelian correlations appear for soft photon-lepton- antilepton emission in QED. The squared current for soft gqq & macr; emission produces colour dipole and colourtripole interactions between the hard-scattering partons. The colour tripole interactions are odd under charge conjugation and lead to charge asymmetry effects. We consider the specific applications to processes with two and three hard partons, and we discuss the structure of the corresponding charge asymmetry contributions. We also generalize our QCD results to the cases of QED and mixed QCD x QED radiative corrections.
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Catani, S., & Cieri, L. (2022). Multiple soft radiation at one-loop order and the emission of a soft quark-antiquark pair. Eur. Phys. J. C, 82(2), 97–27pp.
Abstract: We consider the radiation of two or more soft partons in QCD hard-scattering at one-loop order. The corresponding scattering amplitude is singular, and the singular behaviour is controlled by a process-independent soft current. Using regularization in d = 4 – 2 epsilon space-time dimensions, we explicitly evaluate the ultraviolet and infrared divergent (epsilon-pole) terms of the one-loop soft current for emission of an arbitrary number of soft partons in a generic hard-scattering process. Then we consider the specific case of soft quark-antiquark (q (q) over bar) emission and we compute the one-loop current by including the finite terms. We find that the one-loop soft-q (q) over bar current exhibits a new type of transverse-momentum singularity, which has a quantum (absorptive) origin and a purely non-abelian character. At the squared amplitude (cross section) level, this transverse-momentum singularity produces contributions to multijet production processes in hadron collisions. The one-loop squared current also leads to charge asymmetry terms, which are a distinctive features of soft-q (q) over bar radiation. We also extend these results to the cases of QED and mixed QCDxQED radiative corrections for soft fermion-antifermion emission.
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Autieri, A., Cieri, L., Ferrera, G., & Sborlini, G. F. R. (2023). Combining QED and QCD transverse-momentum resummation for W and Z boson production at hadron colliders. J. High Energy Phys., 07(7), 104–30pp.
Abstract: In this article, we consider the transverse momentum (qT) distribution of W and Z bosons produced in hadronic collisions. We combine the qT resummation for QED and QCD radiation including the QED soft emissions from the W boson in the final state. In particular, we perform the resummation of enhanced logarithmic contributions due to soft and collinear emissions at next-to-leading accuracy in QED, leading-order accuracy for mixed QED-QCD and next-to-next-to-leading accuracy in QCD. In the small-qT region we consistently include in our results the next-to-next-to-leading order (i.e. two loops) QCD corrections and the next-to-leading order (i.e. one loop) electroweak corrections. The matching with the fixed-order calculation at large qT has been performed at next-to-leading order in QCD (i.e. at O(alpha(2)(S))) and at leading order in QED. We show numerical results for W and Z production at the Tevatron and the LHC. Finally, we consider the effect of combined QCD and QED resummation for the ratio of W and Z qT distributions, and we study the impact of the QED corrections providing an estimate of the corresponding perturbative uncertainties.
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Becchetti, M., Bonciani, R., Cieri, L., Coro, F., & Ripani, F. (2023). Two-loop form factors for diphoton production in quark annihilation channel with heavy quark mass dependence. J. High Energy Phys., 12(12), 105–28pp.
Abstract: We present the computation of the two-loop form factors for diphoton production in the quark annihilation channel. These quantities are relevant for the NNLO QCD corrections to diphoton production at LHC recently presented in [1]. The computation is performed retaining full dependence on the mass of the heavy quark in the loops. The master integrals are evaluated by means of differential equations which are solved exploiting the generalised power series technique.
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Camarda, S., Cieri, L., Ferrera, G., & Urtasun-Elizari, J. (2022). Higgs boson production at the LHC: fast and precise predictions in QCD at higher orders. Eur. Phys. J. C, 82(5), 492–8pp.
Abstract: We present a new numerical program, HTurbo, which provides fast and numerically precise predictions for Higgs boson production cross sections. The present version of the code implements the perturbative QCD expansion up to the next-to-next-to-leading order also combined with the resummation of the large logarithmic corrections at small transverse momenta up to next-to-next-to-leading logarithmic accuracy and it includes the Higgs boson production through gluon fusion and decay in two photons with the full dependence on the final-state kinematics. Arbitrary kinematical cuts can be applied to the final states in order to obtain fiducial cross sections and associated kinematical distributions. We present a benchmark comparison with the predictions obtained with the numerical programs HRes and HNNLO programs for which HTurbo represents an improved reimplementation.
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