Boosted top production: factorization and resummation for single-particle inclusive distributions

Journal of High Energy Physics, Jan 2014

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.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://link.springer.com/content/pdf/10.1007%2FJHEP01%282014%29028.pdf

Boosted top production: factorization and resummation for single-particle inclusive distributions

Andrea Ferroglia 2 Simone Marzani 3 Ben D. Pecjak 3 Li Lin Yang 0 1 4 0 Collaborative Innovation Center of Quantum Matter , Beijing, China 1 Center for High Energy Physics, Peking University , Beijing 100871, China 2 New York City College of Technology , 300 Jay Street, Brooklyn, NY 11201, U.S.A 3 Institute for Particle Physics Phenomenology, University of Durham , DH1 3LE Durham, U.K 4 School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University , Beijing 100871, China 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 pT 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. Contents 1 Introduction 2 3 4 Kinematics and factorization Factorizing soft real radiation in the small-mass limit 3.1 NLO phase space integrals and momentum regions 3.2 All-order factorization in the small-mass limit Fixed-order expansions and resummation Heavy-quark loops Conclusions A The massless soft function to NNLO Matching coefficients and anomalous dimensions Introduction Nowadays, top-quark production is of great interest in elementary particle phenomenology at hadron colliders. This is due to the fact that top-quark physics is closely connected to the study of the recently discovered Higgs boson [1, 2] and to the search for new particles. Millions of top-quark pair events have already been produced at the Large Hadron Collider (LHC). For this reason, the ATLAS and CMS collaborations were able to measure the topquark pair production cross section with remarkable precision, e.g. [38]. On the theoretical side, precise measurements require calculations of the measured observables which include corrections beyond the next-to-leading-order (NLO) in QCD. As an example, the total cross section, which can be measured with a relative error of approximately 5%, was recently evaluated at next-to-next-to-leading order (NNLO) in perturbation theory [9]. Differential distributions, such as the pair invariant mass distribution, the top-quark rapidity distribution, and the distributions with respect to the transverse momentum (both of the individual top quark or of the tt system) are also of great interest, especially in the search for new physics. The ATLAS and CMS collaborations already measured several differential distributions [10, 11]. To date, the full set of NNLO QCD corrections to these observables is not known. However, studies of the soft gluon emission corrections to the toppair invariant mass distribution up to next-to-next-to-leading-logarithmic (NNLL) accuracy were presented in [12, 13]. In those works, the resummation of the soft corrections was carried out in momentum space by employing methods developed in [1416]. In the same papers, approximate formulas including all of the terms proportional to logarithmic (plus distribution) corrections up to NNLO were obtained starting from the NNLL resummation formulas. A study of the top-quark transverse momentum and rapidity distributions within the same approach was carried out in [17].1 The NNLL resummation of the transverse momentum distribution of the tt system, which presents additional technical complications with respect to the two distributions mentioned above, was considered in [20, 21]. A kinematic situation of special interest for new physics searches is the so-called boosted regime, where the top quarks are produced with energies much larger than their mass. Examples of boosted top production include the differential distribution at high values of pair invariant mass M , or the high-pT tail of the top-quark transverse momentum distribution. The presence of new heavy particles decaying into pairs of energetic top quarks could generate bumps or more subtle distortions of differential distributions in this kinematic region. The LHC at center-of-mass energies of 7 TeV and 8 TeV has started to explore boosted top production experimentally, and more data will become available with the future 14 TeV run. At the same time, highl (...truncated)


This is a preview of a remote PDF: https://link.springer.com/content/pdf/10.1007%2FJHEP01%282014%29028.pdf

Andrea Ferroglia, Simone Marzani, Ben D. Pecjak. Boosted top production: factorization and resummation for single-particle inclusive distributions, Journal of High Energy Physics, 2014, pp. 28, Volume 2014, Issue 1, DOI: 10.1007/JHEP01(2014)028