Spin correlations in final-state parton showers and jet observables

Abstract

As part of a programme to develop parton showers with controlled logarithmic accuracy, we consider the question of collinear spin correlations within the PanScales family of parton showers. We adapt the well-known Collins–Knowles spin-correlation algorithm to PanScales antenna and dipole showers, using an approach with similarities to that taken by Richardson and Webster. To study the impact of spin correlations, we develop Lund-declustering based observables that are sensitive to spin-correlation effects both within and between jets and extend the MicroJets collinear single-logarithmic resummation code to include spin correlations. Together with a 3-point energy correlation observable proposed recently by Chen, Moult and Zhu, this provides a powerful set of constraints for validating the logarithmic accuracy of our shower results. The new observables and their resummation further open the pathway to phenomenological studies of these important quantum mechanical effects.

Cuts for two-body decays at colliders

“…We comment on two features: firstly, f (u) acquires linear dependence at y = y t ≡ y max − arccosh(m /2p t,cut ) 1.42. 25 As with the analogous characteristic seen in sections 4.3 and 4.4, a suitably wide rapidity bin around this point will transform this linear dependence into reasonably tame quadratic dependence. The second feature concerns f (1) , where one sees linear p t, dependence for y ≥ y t .…”

“…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.…”

“…Here, we work in the massless lepton approximation, where rapidity and pseudorapidity are identical 25. In figure16, the feature at that rapidity is sharp, i.e.…”

Next-to-leading non-global logarithms in QCD

“…refs. [4][5][6][7][8][9][10][11][12][13] for recent work). Specifically, the resummation of next-to-leading logarithmic (NLL) non-global logarithms is a crucial ingredient for the development of NNLL algorithms, that are necessary to achieve sufficiently accurate event simulation both at present and future colliders.…”

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].…”