Abstract
In this work we explore first necessary steps to contruct a fully massive version of a variable flavour number scheme. In particular we focus, as an example, on an extension of the five-flavour scheme, where instead of neglecting explicit initial state quark mass effects, we retain all massive dependence, while keeping the resummation properties of the massless five-flavour scheme. We name this scheme five-flavour-massive (5FMS) scheme. Apart from consistently modified parton distribution functions, we provide all the ingredients that are needed to implement this scheme at MC@NLO accuracy, in a Monte Carlo event generator. As proof of concept we implement this scheme in SHERPA, and perfom a comparison of the new scheme with traditional ones for the simple process of scalar particle production in bottom quark fusion.
Highlights
Processes with heavy quarks in the initial state present an interesting challenge for theoretical predictions at the LHC and other hadron collider experiments
Apart from consistently modified parton distribution functions, we provide all the ingredients that are needed to implement this scheme at MC@NLO accuracy, in a Monte Carlo event generator
A decision has to be made in how far heavy quarks can act as incident partons—due to their mass being larger than the QCD scale parameter mQ ≫ ΛQCD one could argue that they are disallowed to have a parton distribution function (PDF), thereby decoupling them from the QCD evolution in the initial state, described by the Dokshitzer-GribovLipatov-Altarelli-Parisi (DGLAP) equations
Summary
Processes with heavy quarks (bottom or charm) in the initial state present an interesting challenge for theoretical predictions at the LHC and other hadron collider experiments. For some processes and observables, the effects of the finite heavy quark mass mQ become relevant and in such cases these quarks must be treated as fully massive This immediately translates into the heavy quarks only appearing as final state particles. It gives rise to ongoing comparisons of calculations of the same processes and observables in the five- and four-flavor schemes The former refers to a consistently massless treatment of the b-quark, which can be found in both initial and final states, while the latter treats the b-quarks as massive and allows them to be in the final state only. There we compare our results with the DIRE parton shower, which includes (collinear) NLO corrections to the DGLAP equation [26,27]
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