Bottom Mass Effects Research Articles

Two-loop bottom mass effects on the Higgs transverse momentum spectrum in top-induced gluon fusion

We compute bottom mass (mb) corrections to the transverse momentum (qT) spectrum of Higgs bosons produced by gluon fusion in the regime qT ∼ mb ≪ mH at leading power in mb/mH and qT/mH, where the gluons couple to the Higgs via a top loop. To this end we calculate the quark mass dependence of the transverse momentum dependent gluon beam functions (aka gluon TMDPDFs) at two loops in the framework of SCET. These functions represent the collinear matrix elements in the factorized gluon-fusion cross section for small qT. We discuss in detail technical subtleties regarding rapidity regulators and zero-bin subtractions in the calculation of the virtual corrections present for massive quarks. Combined with the known soft function for mb ≠ 0 our results allow to determine the resummed Higgs qT distribution in the top-induced gluon fusion channel at NNLL′ (and eventually N3LL) with full dependence on mb/qT. We perform a first phenomenological analysis at fixed order, where the new corrections to the massless approximation lead to percent-level effects in the peak region of the Higgs qT spectrum. Upon resummation they may thus be relevant for state-of-the-art precision predictions for the LHC.

NLO oriented event-shape distributions for massive quarks

In this article we compute the cross section for the process {e}^{+}{e}^{-}to Qoverline{Q}+X , with Q a heavy quark, differential in a given event shape e and the angle θT between the thrust axis and the beam direction. These observables are usually referred to as oriented event shapes, and it has been shown that the θT dependence can be split in two structures, dubbed the unoriented and angular terms. Since the unoriented part is already known, we compute the differential and cumulative distributions in fixed-order for the angular part up to mathcal{O} (αs). Our results show that, for the vector current, there is a non-zero mathcal{O}left({alpha}_s^0right) contribution, in contrast to the axial-vector current or for massless quarks. This entails that for the vector current one should expect singular terms at mathcal{O} (αs) as well as infrared divergences in real- and virtual-radiation diagrams that should cancel when added up. On the phenomenological side, and taking into account that electroweak factors enhance the vector current, it implies that finite bottom-mass effects are an important correction since they are not damped by a power of the strong coupling and therefore cannot be neglected in precision studies. Finally, we show that the total angular distribution for the vector current has a Sommerfeld enhancement at threshold.

Finite quark-mass effects in the NNLOPS POWHEG+MiNLO Higgs generator

We include finite top- and bottom-mass effects in the next-to-next-to-leading order parton shower (NNLOPS) event generator for inclusive Higgs boson production in gluon fusion based upon the POWHEG+MiNLO approach. Since fixed-order results for quark-mass effects only reach NLO accuracy, we add them to the NNLOPS generator at that accuracy. We explore uncertainties related to the unknown all-order logarithmic structure of bottom-mass effects by comparing the assumption of full exponentiation to no exponentiation at all. Phenomenological results showing the effects of finite quark-masses in the NNLOPS simulation are presented. These suggest that the aforementioned uncertainty is well contained within the envelope of plain renormalization and factorization scale uncertainties.

W b b ¯ j $$ W\;b\overline{b}j $$ production at NLO with POWHEG+MiNLO

We present a next-to-leading order plus parton-shower event generator for the production of a W boson plus two bottom quarks and a jet at hadron colliders, implemented in the POWHEG BOX framework. Bottom-mass effects and spin correlations of the decay products of the W boson are fully taken into account. The code has been automatically generated using the two available interfaces to MadGraph4 and GoSam, the last one updated to a new version. We have applied the MiNLO prescription to our Wbbj calculation, obtaining a finite differential cross section also in the limit of vanishing jet transverse momentum. Furthermore, we have compared several key distributions for Wbbj production with those generated with a next-to-leading order plus parton-shower event generator for Wbb production, and studied their factorization- and renormalization-scale dependence. Finally, we have compared our results with recent experimental data from the ATLAS and CMS Collaborations.

Top- and bottom-mass effects in hadronic Higgs production at small transverse momenta through lo+nll

The resummed transverse momentum distribution of the Higgs boson in gluon fusion through LO+NLL for small transverse momenta is considered, where the Higgs is produced through a top- and bottom-quark loop. We study the mass effects with respect to the infinite top-mass approach. The top-mass effects are small and the heavy-top limit is valid to better than 4% as long as the Higgs' transverse momentum stays below 150 GeV. When the bottom loop is considered as well, the discrepancy reaches up to about 10%. We conclude that bottom-mass effects cannot be included in a reasonable manner by a naive reweighting procedure in the heavy-top limit. We compare our results to an earlier, alternative approach based on POWHEG.

Rhad at the B-factory

A systematic theoretical evaluation of the cross section for hadron production in electron-positron collisions in the energy range just below the B meson threshold is presented which includes charm and bottom mass effects and is accurate to order α s 3. The corresponding measurement in the energy region several GeV above the threshold is also discussed.