b-initiated processes at the LHC: a reappraisal

By Fabio Maltoni, G. Ridolfi, M. Ubiali. 2012

184 citations recorded by the source corpus.

A bstractSeveral key processes at the LHC in the standard model and beyond that involve b quarks, such as single-top, Higgs, and weak vector boson associated production, can be described in QCD either in a 4-flavor or 5-flavor scheme. In the former, b quarks appear only in the final state and are typically considered massive. In 5-flavor schemes, calculations include b quarks in the initial state, are simpler and allow the resummation of possibly large initial state logarithms of the type log $ \frac{{{\mathcal{Q}^2}}}{{m_{{^b}}^2}} $ into the b parton distribution function (PDF), $ \mathcal{Q} $ being the typical scale of the hard process. In this work we critically reconsider the rationale for using 5-flavor improved schemes at the LHC. Our motivation stems from the observation that the effects of initial state logs are rarely very large in hadron collisions: 4-flavor computations are pertubatively well behaved and a substantial agreement between predictions in the two schemes is found. We identify two distinct reasons that explain this behaviour, i.e., the resummation of the initial state logarithms into the b-PDF is relevant only at large Bjorken x and the possibly large ratios $ \frac{{{\mathcal{Q}^2}}}{{m_{{^b}}^2}} $’s are always accompanied by universal phase space suppression factors. Our study paves the way to using both schemes for the same process so to exploit their complementary advantages for different observables, such as employing a 5-flavor scheme to accurately predict the total cross section at NNLO and the corresponding 4-flavor computation at NLO for fully exclusive studies.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/7944ac9da3953fc6b310d73ec693a9ceea81294b

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Citations in the corpus

PDF4LHC recommendations for LHC Run II (2015, methodology): “These are required for consistent calculations where the partonic cross-sections are computed in the nf = 4 scheme, accounting for bottom quark mass effects [134].”
Higgs production in association with bottom quarks (2014, background): “i) Logarithms are dominant, but they are especially so only at large Bjorken x’s, and are always associated with phase-space suppression factors [19].”
Handbook of LHC Higgs Cross Sections: 3. Higgs Properties (2013, methodology): “The renormalization scale is set to μR = (MH± +mt)/2, while the factorization scaleμF = μ̃ is chosen according to the method proposed in [724].”
A critical appraisal and evaluation of modern PDFs (2016, unknown): “[157] for more recent studies and Ref.”
Lepton Number Violation: Seesaw Models and Their Collider Tests (2017, background): “] indicate a loss of perturbative control, not an enhancement, and leads to a signiﬁcant overestimation of their cross sections. As in the case of EW boson production in association with heavy ﬂavors [373,374], the correct treatment requires either a matching/subtraction scheme with top quark PDFs t”
The PDF4LHC report on PDFs and LHC data: Results from Run I and preparation for Run II (2015, background): “These are especially useful to test pQCD calculational schemes [161].”