Higgs-boson production induced by bottom quarks

Abstract

Bottom-quark-induced processes are responsible for a large fraction of the CERN Large Hadron Collider ͑LHC͒ discovery potential, in particular, for supersymmetric Higgs bosons. Recently, the discrepancy between exclusive and inclusive Higgs boson production rates has been linked to the choice of an appropriate bottom factorization scale. We investigate the process kinematics at hadron colliders and show that it leads to a considerable decrease in the bottom factorization scale. This effect is the missing piece needed to understand the corresponding higher order results. Our results hold generally for charged and for neutral Higgs boson production at the LHC as well as at the Fermilab Tevatron. The situation is different for single top quark production, where we find no sizable suppression of the factorization scale. Turning the argument around, we can specify how large are the collinear logarithms that can be resummed using the bottom parton picture. I. HIGGS BOSONS AT THE LARGE HADRON COLLIDERThe combined CERN e ϩ e Ϫ collider LEP precision measurements ͓1͔ suggest the existence of a light Higgs boson. In the case of a single standard model Higgs boson the CERN Large Hadron Collider ͑LHC͒ promises multiple coverage for any Higgs boson mass, which will enable us to measure its different decay modes and extract the couplings ͓2͔. For a supersymmetric Higgs sector this coverage has to rely on fewer Higgs boson decay channels ͓2,3͔. This is a direct consequence of the structure of the Higgs sector: while the minimal supersymmetric standard model ͑MSSM͒ predicts a light Higgs boson, it also predicts an enhancement of the coupling to down-type fermions, at the expense of the branching fractions to gauge bosons. This enhancement is an outcome of the two Higgs doublet structure in the MSSM: one doublet is needed to give mass to up-type and the other to down-type fermions. The vacuum expectation values of the two doublets are different, parameterized by tan ␤ ϭv 2 /v 1 . In addition to a light scalar Higgs boson, the two Higgs doublet model includes a heavy scalar, a pseudoscalar, and a charged Higgs boson. None of these additional particles has a mass bounded from above, apart from triviality or unitarity bounds.Of course, observables linked to properties of a light Higgs boson can serve as a probe of whether a new scalar particle is indeed consistent with the standard model Higgs boson ͓4,5͔. There is, however, only one way to conclusively tell the supersymmetric Higgs sector from its standard model counterpart: to discover the additional heavy Higgs bosons and determine their properties.At the LHC, the possible enhancement of down-type fermion Yukawa couplings by powers of tan ␤ can render the search for a heavy scalar and pseudoscalar Higgs boson promising. For small values of tan ␤ the Yukawa coupling of the charged Higgs boson is governed by the top quark mass m t /tan ␤, whereas for larger values of tan ␤ the bottom Yukawa coupling m b tan ␤ dominates. While the chances of finding a heavy Higgs boson with a smal...

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

“…14 in [54]), the Principle of Minimal Sensitivity [56,58]; the Complete Renormalization Group Improvement approach [59] which provides a factorisation scale based on an alternative collinear factorisation scheme [60], extending earlier work on factorisation scale setting in Higgs production [61,62]. Finally, the Brodsky-Lepage-Mackenzie scale setting approach [63] (and its further refinement known as Principle of Maximum Conformality ) [64][65][66][67][68][69] is based on the idea of restoring the conformal symmetry of the QCD Lagrangian in observables.…”

Towards precise predictions for Higgs-boson production in the MSSM

“…By default, we use the MSTW2008 set of PDFs [133], and we fix the renormalization and factorization scales entering the gluon-fusion cross section to µ R = µ F = m φ /2 [19,134], where φ = {h, H, A} denotes the considered Higgs boson. For bottom-quark annihilation, the central values of the scales are chosen as µ R = m φ and µ F = m φ /4 [72][73][74]135]. In the calculation of the gluon-fusion cross section we relate the bottom Yukawa coupling to the pole mass M b , computed at the three-loop level [136,137] from the input value for the running mass, m b (m b ).…”

“…Our default choice for the central scales isμ R = m φ andμ F = m φ /4, following the observation that radiative corrections are particularly small for this value of the factorization scale [72][73][74]135]. To study the uncertainty associated to the variation of the scales, we consider seven combinations corresponding to all possible pairings of µ R = {m φ /2, m φ , 2 m φ } and µ F = {m φ /8, m φ /4, m φ /2}, with the additional constraint that 2 ≤ µ R /µ F ≤ 8 (again, we discard the two pairs with the largest variation of µ R /µ F around its central value, which in this case is 4).…”

Analytic results for Higgs production in bottom fusion

“…It was thus proposed in refs. [19,[22][23][24] that when using the five flavour scheme the appropriate central scale is m H /4. Indeed, the NNLO result [25] in the 5FS seems to confirm this choice.…”