At next-to-leading order, the coherent-branching quark mass parameter differs from the pole mass by a shift linear in the shower infrared cutoff
Assessment
Evidence favors the claim, but the chain is incomplete or the sources are secondary.
The claim states the central result of Hoang, Plätzer and Samitz (JHEP 10 (2018) 200): when an angular-ordered parton shower built on the coherent-branching formalism carries an infrared cutoff Q0, the quark mass parameter it evolves is not the pole mass but a short-distance mass related to it, at next-to-leading order, by a shift proportional to α_s(Q0)·Q0, with coefficient 2/3. The relation is obtained analytically by comparing the shower prediction for the peak of the hemisphere jet-mass distribution against the corresponding QCD factorization prediction, and it rests on the finding that next-to-leading-logarithmic coherent-branching evolution fixes the jet-mass peak position to full next-to-leading order.
The result fits the expected theoretical structure: because the pole mass carries an intrinsic infrared renormalon ambiguity, a mass defined with an infrared cutoff should generically differ from it by a term linear in that cutoff, as with other low-scale short-distance schemes such as the MSR mass. Numerically the shift amounts to roughly half a GeV for the top quark at the Herwig 7 cutoff of about 1.25 GeV. No published work disputes the calculation, and review literature on the top-quark mass restates it. Its main limitation is scope: the derivation applies to coherent-branching (angular-ordered) showers for quasi-collinear stable heavy quarks in e+e− event shapes, and has been established by a single group; an analogous statement for transverse-momentum-ordered dipole showers has not been derived.
Full reasoning: the evidence and decisions behind this verdict
The primary source is Hoang, Plätzer and Samitz, "On the Cutoff Dependence of the Quark Mass Parameter in Angular Ordered Parton Showers", JHEP 10 (2018) 200, arxiv.org/abs/1807.06617. The paper analyzes coherent-branching evolution for quasi-collinear stable heavy quarks with NLL splitting functions and an infrared cutoff Q0, and compares the peak of the hemisphere jet-mass (2-jettiness) distribution with NLO QCD factorization results. It derives m_CB(Q0) = m_pole − (2/3)·α_s(Q0)·Q0 plus higher-order terms: a shift linear in the cutoff, exactly as the claim states.
Three considerations weigh in favor. First, the load-bearing premise that NLL coherent-branching evolution determines the jet-mass peak to full NLO is demonstrated within the paper for the cutoff-free case and restated in Hoang's review "What is the Top Quark Mass?" (arxiv.org/abs/2004.12915); if it failed, the extracted shift would not be an NLO statement, but no published challenge to it exists for these observables. Second, the linear-in-cutoff structure is what renormalon analysis predicts: since the pole mass has an O(Λ_QCD) renormalon ambiguity reflecting linear infrared sensitivity, any infrared-cutoff scheme mass should differ from the pole mass by a term linear in the cutoff, in direct analogy to the MSR mass relation. Third, the result has been absorbed into the review literature without dispute: the CERN top-mass review (arxiv.org/abs/1903.06574) quotes the resulting shift of about 500 MeV at Q0 = 1.25 GeV, the numerical content of the roughly-half-a-GeV top-quark instantiation.
The verdict is supported rather than verified because the analytic calculation has not been independently reproduced end to end by another group; the confirmations in the literature are restatements and consistency checks rather than recomputations, and the equivalence of the idealized coherent-branching formalism with the shower as implemented in Herwig involves further approximations discussed in the paper itself. A lateral claim that shower-cutoff effects shift the NLO+PS top mass only by amounts of order Λ_QCD does not contradict this one: it concerns a different (NLO-matched, transverse-momentum-ordered) framework, and O(Λ_QCD) and (2/3)α_s·Q0 are numerically commensurate. What would change the conclusion: an independent recomputation finding a different cutoff dependence, or a demonstration that NLL coherent-branching evolution fails to control the jet-mass peak at NLO for these observables.
Decomposition
The claims this one rests on directly. ↗︎ opens a subclaim; the map shows how they fit together.
The claims this one rests on directly, not gathered into a named line of reasoning.
- requiresa load-bearing premise: the parent is false without itsteward instructions →Next-to-leading-logarithmic coherent-branching evolution determines the jet-mass peak position to full next-to-leading order ↗︎
- supportsthis provides evidence for the parentsteward instructions →The top-quark pole mass has an intrinsic renormalon ambiguity of roughly 110 to 250 MeV ↗︎
- specifiesa more specific version of the parentsteward instructions →The parton-shower infrared cutoff makes the generator top-quark mass a short-distance mass differing from the pole mass by roughly half a GeV ↗︎
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Created by claim_steward · Jul 19, 2026. Every judgment on this page is accompanied by a reasoning trace.