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Register a new userBoosted top production: factorization and resummation for single-particle inclusive distributions
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We study single-particle inclusive (1PI) distributions in top-quark pair production at hadron colliders, working in the highly boosted regime where the top-quark p_T is much larger than its mass. In particular, we derive a novel factorization formula valid in the small-mass and soft limits of the differential partonic cross section. This provides a framework for the simultaneous resummation of soft gluon corrections and small-mass logarithms, and also an efficient means of obtaining higher-order corrections to the differential cross section in this limit. The result involves five distinct one-scale functions, three of which arise through the subfactorization of soft real radiation in the small-mass limit. We list the NNLO corrections to each of these functions, building on results in the literature by performing a new calculation of a soft function involving four light-like Wilson lines to this order. We thus obtain a nearly complete description of the small-mass limit of the differential partonic cross section at NNLO near threshold, missing only terms involving closed top-quark loops in the virtual corrections.
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We investigate the production of highly energetic top-quark pairs at hadron colliders, focusing on the case where the invariant mass of the pair is much larger than the mass of the top quark. In particular, we set up a factorization formalism appropriate for describing the differential partonic cross section in the double soft and small-mass limit, and explain how to resum simultaneously logarithmic corrections arising from soft gluon emission and from the ratio of the pair-invariant mass to that of the top quark to next-to-next-to-leading logarithmic accuracy. We explore the implications of our results on approximate next-to-next-to-leading order formulas for the differential cross section in the soft limit, pointing out that they offer a simplified calculational procedure for determining the currently unknown delta-function terms in the limit of high invariant mass.
We address the potential of measurements with boosted single-top final states at the high-luminosity LHC (HL-LHC) and possible future hadron colliders: the high-energy LHC (HE-LHC), and the future circular collider (FCC). As new physics examples to assess the potential, we consider the search for $tbW$ anomalous couplings and for a weakly-coupled $W$ boson. The FCC would improve by a factor of two the sensitivity to anomalous couplings of the HL-LHC. For $W$ bosons, the FCC is sensitive to $W$ couplings $2-5$ times smaller than the HL-LHC in the mass range 2-4 TeV, and to masses up to 30 TeV in the case of Standard Model-like couplings.
We present results for the 2-jettiness differential distribution for boosted top quark pairs produced in $e^+e^-$ collisions in the peak region accounting for QCD large-logarithm resummation at next-to-next-to-next-to-leading logarithmic (N$^3$LL) order and fixed-order corrections to matrix elements at next-to-next-to-leading order (NNLO) calculated in the framework of soft-collinear effective theory and boosted heavy quark effective theory. Electroweak and finite-width effects are included at leading order. We study the perturbative convergence of the cross section in the pole and MSR mass schemes, with and without soft gap subtractions. We find that there is a partial cancellation between the pole mass and soft function renormalons. When renormalon subtractions concerning the top mass and the soft function are implemented, the perturbative uncertainties are, however, systematically smaller and an improvement in the stability of the peak position is observed. We find that the top MSR mass may be determined with perturbative uncertainties well below $100$,MeV from the peak position of the 2-jettiness distribution. This result has important applications for Monte Carlo top quark mass calibrations.
We study inclusive production of doubly heavy baryon at a $e^+e^-$ collider and at hadron colliders through fragmentation. We study the production by factorizing nonpertubative- and perturbative effects. In our approach the production can be thought as a two-step process: A pair of heavy quarks can be produced perturbatively and then the pair is transformed into the baryon. The transformation is nonperturbative. Since a heavy quark moves with a small velocity in the baryon in its rest frame, we can use NRQCD to describe the transformation and perform a systematic expansion in the small velocity. At the leading order we find that the baryon can be formed from two states of the heavy-quark pair, one state is with the pair in $^3S_1$ state and in color ${bf bar 3}$, another is with the pair in $^1S_0$ state and in color ${bf 6}$. Two matrix elements are defined for the transformation from the two states, their perturbative coefficients in the contribution to the cross-section at a $e^+e^-$ collider and to the function of heavy quark fragmentation are calculated. Our approach is different than previous approaches where only the pair in $^3S_1$ state and in color ${bf bar 3}$ is taken into account. Numerical results for $e^+e^-$ colliders at the two $B$-factories and for hadronic colliders LHC and Tevatron are given.
The inclusive production of jets in the central region of rapidity is studied in $k_T$-factorization at next-to-leading order (NLO) in QCD perturbation theory. Calculations are performed in the Regge limit making use of the NLO BFKL results. A jet cone definition is introduced and a proper phase--space separation into multi-Regge and quasi-multi-Regge kinematic regions is carried out. Two situations are discussed: scattering of highly virtual photons, which requires a symmetric energy scale to separate the impact factors from the gluon Greens function, and hadron-hadron collisions, where a non--symmetric scale choice is needed.
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