Improvements on dipole shower colour

Abstract

The dipole formalism provides a powerful framework from which parton showers can be constructed. In a recent paper (Forshaw et al. 2020), we proposed a dipole shower with improved colour accuracy and in this paper we show how it can be further improved. After an explicit check at $${\mathcal {O}}(\alpha _{\mathrm {s}}^{2})$$ O ( α s 2 ) we confirm that our original shower performs as it was designed to, i.e. inheriting its handling of angular-ordered radiation from a coherent branching algorithm. We also show how other dipole shower algorithms fail to achieve this. Nevertheless, there is an $${\mathcal {O}}(\alpha _{\mathrm {s}}^{2})$$ O ( α s 2 ) topology where it differs at sub-leading $$N_{\mathrm {c}}$$ N c from a coherent branching algorithm. This erroneous topology can contribute a leading logarithm to some observables and corresponds to emissions that are ordered in $$k_t$$ k t but not angle. We propose a simple, computationally efficient way to correct this and assign colour factors in accordance with the coherence properties of QCD to all orders in $$\alpha _{\mathrm {s}}$$ α s .

Cuts for two-body decays at colliders

“…However, typically Drell-Yan measurements at low and moderate p t, are not statistics limited, so one may anticipate that this would not be an issue. 27 The characteristic that we intended to obtain, and that has been obtained, is that at central y rapidities, f (0,1,2) are now all identically zero for p t, 2∆, and f (u) is independent of p t, in that same range. This guarantees that the fiducial cross section at those rapidities is independent of p t, up to roughly 2∆, within the approximation that the harmonic decomposition of eq.…”

“…We believe this to be a valid approach, and it is probably the only robust option available for interpreting fiducial results measured with today's widespread cut choices. However, in general, it seems less than ideal to give up on the use of pure fixed order calculations for predicting hard cross sections, especially as fixed order calculations are conceptually simpler than resummation, and in many respects more flexible (though if a sufficiently accurate resummation can be achieved through a parton shower [23][24][25][26][27][28][29] together with high-order matching, cf. the approaches of refs.…”

Hadronic decays of Higgs boson at NNLO matched with parton shower

“…However, they can certainly help with evaluations of the physics performances of the detector designs which are under investigation. On another hand, with recent progresses on developments of parton shower MCs [101][102][103][104][105][106][107] and given the available matrix elements at higher orders [37], we expect further improvements on modeling of hadronic decays of the Higgs boson in the near future.…”

Dissecting the collinear structure of quark splitting at NNLL

“…including also subleading colour effects and spin correlations [50][51][52]. Other candidates for NLL accurate showers have also been proposed and analytically demonstrated, to achieve NLL accuracy for the thrust [53][54][55][56] and the jet multiplicity [53,54].…”