We extend our previous results on small-x resummation in the pure Yang--Mills theory to full QCD with nf quark flavours, with a resummed two-by-two matrix of resummed quark and gluon splitting functions. We also construct the corresponding deep-inelastic coefficient functions, and show how these can be combined with parton densities to give fully resummed deep-inelastic structure functions F_2 and F_L at the next-to-leading logarithmic level. We discuss how this resummation can be performed in different factorization schemes, including the commonly used MSbar scheme. We study the importance of the resummation effects by comparison with fixed-order perturbative results, and we discuss the corresponding renormalization and factorization scale variation uncertainties. We find that for x below 0.01 the resummation effects are comparable in size to the fixed order NNLO corrections, but differ in shape. We finally discuss the phenomenological impact of the small-x resummation, specifically in the extraction of parton distribution from present day experiments and their extrapolation to the kinematics relevant for future colliders such as the LHC
We explore the effects of the resummation of large logarithmic perturbative corrections to double-longitudinal spin asymmetries for inclusive and semi-inclusive deep inelastic scattering in fixed-target experiments. We find that the asymmetries are overall rather robust with respect to the inclusion of the resummed higher-order terms. Significant effects are observed at fairly high values of x, where resummation tends to decrease the spin asymmetries. This effect turns out to be more pronounced for semi-inclusive scattering. We also investigate the potential impact of resummation on the extrac…
We discuss a model for soft gluon re-summation based on a statistical description of independent emissions during inelastic collisions. The model is applied to estimate Survival Probabilities at the LHC. A comparison with other models and experimental data is presented.
We discuss hadron mass corrections and threshold resummation for deep-inelastic scattering $\ell N\rightarrow\ell' X$ and semi-inclusive annihilation $e^+e^-\rightarrow h X$ processes, and provide a prescription how to consistently combine these two corrections respecting all kinematic thresholds. We find an interesting interplay between threshold resummation and target mass corrections for deep-inelastic scattering at large values of Bjorken $x_B$. In semi-inclusive annihilation, on the contrary, the two considered corrections are relevant in different kinematic regions and do not affect each…
Threshold resummation of Semi-Inclusive Deep-Inelastic Scattering
Università di Milano（米兰大学）；INFN, Sezione di Milano（意大利国家核物理研究所，米兰分部）；Dipartimento di Fisica, Università di Genova（热那亚大学物理系）；INFN, Sezione di Genova（意大利国家核物理研究所，热那亚分部）；II. Institut für Theoretische Physik, Universität Hamburg（汉堡大学第二理论物理研究所）
The off-diagonal parton-scattering channels $g+γ^*$ and $q+ϕ^*$ in deep-inelastic scattering are power-suppressed near threshold $x\to 1$. We address the next-to-leading power (NLP) resummation of large double logarithms of $1-x$ to all orders in the strong coupling, which are present even in the off-diagonal DGLAP splitting kernels. The appearance of divergent convolutions prevents the application of factorization methods known from leading power resummation. Employing $d$-dimensional consistency relations from requiring $1/ε$ pole cancellations in dimensional regularization between momentum …
We present all-order results for the highest three large-x logarithms of the splitting functions P_qg and P_gq and of the coefficient functions C_phi,q, C_2,g and C_L,g for structure functions in Higgs- and gauge-boson exchange DIS in massless perturbative QCD. The corresponding coefficients have been derived by studying the unfactorized partonic structure functions in dimensional regularization independently in terms of their iterative structure and in terms of the constraints imposed by the functional forms of the real- and virtual-emission contributions together with their Kinoshita--Lee-Na…
We present a comprehensive study of high-energy double logarithms in inclusive DIS. They appear parametrically as alpha_s^n ln^{2n-k} x at the n-th order in perturbation theory in the splitting functions for the parton evolution and the coefficient functions for the hard scattering process, and represent the leading corrections at small $x$ in the flavour non-singlet case. We perform their resummation, in terms of modified Bessel functions, to all orders in full QCD up to NNLL accuracy, and partly to N^3LL and beyond in the large-n_c limit, and provide fixed-order expansions up to five loops. …
We present our results on soft gluon resummation in the invariant mass threshold applied to the associated production of a top quark pair with a W boson at the LHC in the Mellin space formalism.
We present our predictions for the inclusive production of two heavy quark-antiquark pairs, separated by a large rapidity interval, in the collision of (quasi-)real photons at the energies of LEP2 and of some future electron-positron colliders. We include in our calculation the full resummation of leading logarithms in the center-of-mass energy and a partial resummation of the next-to-leading logarithms, within the Balitsky-Fadin-Kuraev-Lipatov (BFKL) approach.
We investigate the factorization and resummation of t-channel single top (antitop) quark production in the SM at both the Tevatron and the LHC in SCET. We find that the resummation effects decrease the NLO cross sections by about 3% at the Tevatron and about 2% at the LHC. And the resummation effects significantly reduce the factorization scale dependence of the total cross section. The transfer momentum cut dependence and other matching scale dependencies are also discussed. We also show that when our numerical results for s- and t-channel single top production at the Tevatron are combined, i…
High-energy logarithmic correction are enhanced when the ratio, $x = \frac{Q^2}{s}$ between the typical energy scale of a scattering process $Q$ and the total centre of mass energy available $s$ is small. We discuss recent developments on their resummation in differential cross sections in rapidity, transverse momentum and invariant mass and their application to heavy flavour production at the LHC.
We develop a framework for a systematic resummation of the transverse momentum distribution of top-quark pairs produced at hadron colliders based on effective field theory. Compared to Drell-Yan and Higgs production, a novel soft function matrix is required to account for the soft gluon emissions from the final states. We calculate this soft function at the next-to-leading order, and perform the resummation at the next-to-next-to-leading logarithmic accuracy. We compare our results with parton shower programs and with the experimental data at the Tevatron and the LHC. We also discuss the impli…
In this paper we study the factorization and resummation of s-channel single top quark production in the Standard Model at both the Tevatron and the LHC. We show that the production cross section in the threshold limit can be factorized into a convolution of hard function, soft function and jet function via soft-collinear-effective-theory (SCET), and resummation can be performed using renormalization group equation in the momentum space resummation formalism. We find that in general, the resummation effects enhance the Next-to-Leading-Order (NLO) cross sections by about $3%-5%$ at both the Tev…
The inclusive hadroproduction of two heavy quarks, featuring a large separation in rapidity, is proposed as a novel probe channel of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) approach. In a theoretical setup which includes full resummation of leading logarithms in the center-of-mass energy and partial resummation of the next-to-leading ones, predictions for the cross section and azimuthal coefficients are presented for kinematic configurations typical of current and possible future experimental analyses at the LHC.
We discuss the resummation of the large logarithmic terms appearing in the heavy quark effects on parton distribution functions inside the virtual photon. We incorporate heavy quark mass effects by changing the initial condition of the leading-order DGLAP evolution equation. In a certain kinematical limit, we recover the logarithmic terms of the next-to-leading order heavy quark effects obtained in the previous work. This method enables us to resum the large logarithmic terms due to heavy quark mass effects on the parton distributions in the virtual photon. We numerically calculate parton dist…
I derive an all-order resummation formula for the logarithmically enhanced contributions proportional to $\frac{α_s^n}{x \pm ξ} \log (\frac{ξ\pm x}{2ξ})^k$ in the quark coefficient function of deeply-virtual-Compton scattering and the pion-photon transition form factor in momentum space. The resummation is performed at the next-to-next-to-leading logarithmic accuracy. The key observation is that the quark coefficient function itself factorizes in the $x \rightarrow \pm ξ$ limit, which allows for a resummation using renormalization group equations. A preliminary numerical analysis suggests that…
We investigate the QCD effects in the production of neutral Higgs bosons via bottom quark fusion in both the standard model and the minimal supersymmetric standard model at the CERN Large Hadron Collider. We include the next-to-leading order (NLO) QCD corrections (including supersymmetric QCD) and the threshold resummation effects. We use the soft-collinear effective theory to resum the large logarithms near threshold from soft gluon emission. Our results show that the resummation effects can enhance the total cross sections by about 5% compared with the NLO results.
We consider the quark beam function that describes collinear initial-state radiation that is constrained by a veto on reconstructed jets. As the veto is imposed on the transverse momenta of the jets, the beam function is subject to rapidity divergences, and we use the collinear-anomaly framework to extract the perturbative matching kernels to next-to-next-to-leading order (NNLO) in the strong-coupling expansion. Our calculation is based on a novel framework that automates the computation of beam functions in Mellin space and it provides the ingredients to extend jet-veto resummations for quark…
We present state of the art resummation predictions for differential cross sections in top-quark pair production at the LHC. They are derived from a formalism which allows the simultaneous resummation of both soft and small-mass logarithms, which endanger the convergence of fixed-order perturbative series in the boosted regime, where the partonic center-of-mass energy is much larger than the mass to the top quark. We combine such a double resummation at NNLL$'$ accuracy with standard soft-gluon resummation at NNLL accuracy and with NLO calculations, so that our results are applicable throughou…
We discuss recent progress concerning the resummation of large logarithms at next-to-leading power (NLP) in scattering processes near threshold. We begin by briefly reviewing the diagrammatic and SCET approach, which are used to derive factorization theorems for physical observables in this kinematic limit. Then, we focus on the quark-gluon channel in deep inelastic scattering and Drell-Yan. We show that the use of consistency conditions for the cancellation of leading poles in the hadronic cross section can be used to achieve the resummation of large leading logarithms (LLs) at NLP, both with…
