Differential distributions for top-quark hadro-production with a running mass

Abstract

We take a look at how the differential distributions for top-quark production are affected by changing to the running mass scheme. Specifically we consider the transverse momentum, rapidity and pair-invariant mass distributions at next-to-leading order for the top-quark mass in the MS scheme. It is found that, similar to the total cross section, the perturbative expansion converges faster and the scale dependence improves using the mass in the MS scheme as opposed to the on-shell scheme. We also update the analysis for the total cross section using the now available full next-to-next-to-leading order contribution.The measurement of top-quark pair production cross sections at hadron colliders has entered the era of precision physics with the analysis of data available from the Large Hadron Collider (LHC) in the runs at center-of-mass energies √ S = 7 and 8 TeV. Measurements of the total cross section for tt-production from ATLAS and CMS reach by now an accuracy of typically better than O(10 %), with the systematic and luminosity uncertainties already dominating over the small statistical uncertainty, see, e.g., [1][2][3]. First results of differential distributions for tt-production from the LHC are appearing as well [4,5]. Thus, given the present experimental accuracy hadro-production of tt-pairs is currently being established as a standard model (SM) benchmark process.This has motivated tremendous activity on the theory side to match the experimental precision by computing higher order corrections in quantum chromodynamics (QCD) and we briefly recapitulate the status for inclusive tt-pair production, i.e., no tagged final states. Predictions for the total cross section are complete to next-to-next-to-leading order (NNLO) [6][7][8][9] while differential distributions are known to next-to-leading order (NLO) [10,11], including top-quark decay [12][13][14][15][16], though. Additional corrections beyond NLO based on threshold logarithms have been obtained for distria e-mail: matthew.dowling@desy.de butions in the top-quark's transverse momentum and rapidity, p t T and y t , as well as in the invariant mass m tt of the top-quark pair [17][18][19][20].Comparison of these theory predictions to experimental data can be used to determine parameters such as the strong coupling constant, the parton luminosity and the top-quark mass and to study their correlations. Of these parameters, the top-quark mass is certainly the most interesting one with prominent implications for the electro-weak vacuum of the SM, see, e.g., [21,22]. It is a particularly attractive feature of cross sections measurements that they offer the opportunity for an unambiguous and theoretically well-defined determination of the top-quark mass in a particular renormalization scheme [23,24].The conventional scheme choice for the quark mass renormalization is the pole mass, which has its short-comings [25,26], though, since it is based on the idea of quarks appearing as asymptotic states. It exhibits poor convergence of the perturbative series and ...

Improved constraints on parton distributions using LHCb, ALICE and HERA heavy-flavour measurements and implications for the predictions for prompt atmospheric-neutrino fluxes

“…These are calculated using the MNR code [28], with the single-particle inclusive distributions computed using the pole mass scheme for the heavy quarks, and translated into the MS mass scheme expressions using the MS mass m Q (m Q ) and following Ref. [29]. The MS mass scheme is then consistently used in the calculations for all used processes.…”

Dynamical scales for multi-TeV top-pair production at the LHC

“…In particular, we notice that our best scales have a feature that may well be processindependent: they tend to reflect the observable already encoded in the LO kinematics. Second, in the past [83,84] the use of the MS scheme for the top-quark mass has been advocated for, among others, improved convergence of the perturbative series. Our work shows that in order to achieve good convergence no special choice for m t is needed.…”

Differential top-antitop cross-section measurements as a function of observables constructed from final-state particles using pp collisions at s = 7 $$ \sqrt{s}=7 $$ TeV in the ATLAS detector

“…Both experiments have recently published measurements of the inclusive tt production cross-section in proton-proton (pp) collisions at centre-of-mass energies, √ s, of 7 and 8 TeV [3][4][5][6][7][8][9][10][11][12][13][14] as well as differential crosssection measurements as functions of the top-quark transverse momentum (p T ) and rapidity (y), and of the mass (m tt ) and y of the tt system [15][16][17]. These cross-section measurements triggered recent work on Quantum Chromodynamics (QCD) calculations of heavy quark production [18][19][20][21][22][23]. Precision measurements of tt production provide the opportunity to conduct tests of predictions based on perturbative QCD and gain direct information on the gluon parton distribution function (PDF) at large momentum fractions (x Bj ) of about 0.1-0.5 [24].…”