Probing the interaction of semi-hard quarks and gluons with the underlying event in light- and heavy-flavor triggered proton-proton collisions

We study underlying-event observables in inelastic proton-proton (pp) collisions at a centre-of-mass energy of $$\sqrt{s} = 13$$ s = 13 TeV with identified light and heavy-flavor triggers using the PYTHIA 8 event generator. The study is performed as a function of the transverse momentum of the leading particle ($$p_\mathrm {T}^\mathrm{trigger}$$ p T trigger ). While at high $$p_\mathrm {T}^\mathrm{trigger}$$ p T trigger ($$>10$$ > 10 GeV/c) the underlying-event activity is independent of the leading particle species, at intermediate $$p_\mathrm {T}^\mathrm{trigger}$$ p T trigger ($$2<p_\mathrm {T}^\mathrm{trigger} <8$$ 2 < p T trigger < 8 GeV/c) it is larger in pion-triggered events than in events triggered with B mesons. Moreover, the underlying event in pion-triggered events, the majority of which are initiated by gluons, shows a stronger effect of color reconnection than events triggered with B-hadrons, that are mostly initiated by quark jets. The effect is observed at both hadronic and partonic level. Given that color reconnection affects the interaction among final partons before the hadronization, and that in the string model quarks (gluons) are connected to one (two) string piece(s), we conclude that the observed effect can be attributed to differences in the interactions of gluon and quark jets with the underlying event.

Soft-drop grooming for hadronic event shapes

Soft-drop grooming of hadron-collision final states has the potential to significantly reduce the impact of non-perturbative corrections, and in particular the underlying-event contribution. This eventually will enable a more direct comparison of accurate perturbative predictions with experimental measurements. In this study we consider soft-drop groomed dijet event shapes. We derive general results needed to perform the resummation of suitable event-shape variables to next-to-leading logarithmic (NLL) accuracy matched to exact next-to-leading order (NLO) QCD matrix elements. We compile predictions for the transverse-thrust shape accurate to NLO + NLL′ using the implementation of the Caesar formalism in the Sherpa event generator framework. We complement this by state-of-the-art parton- and hadron-level predictions based on NLO QCD matrix elements matched with parton showers. We explore the potential to mitigate non-perturbative corrections for particle-level and track-based measurements of transverse thrust by considering a wide range of soft-drop parameters. We find that soft-drop grooming indeed is very efficient in removing the underlying event. This motivates future experimental measurements to be compared to precise QCD predictions and employed to constrain non-perturbative models in Monte-Carlo simulations.

Development and validation of HERWIG 7 tunes from CMS underlying-event measurements

This paper presents new sets of parameters (“tunes”) for the underlying-event model of the $${\textsc {herwig}} \,7$$ H E R W I G 7 event generator. These parameters control the description of multiple-parton interactions (MPI) and colour reconnection in $${\textsc {herwig}} \,7$$ H E R W I G 7 , and are obtained from a fit to minimum-bias data collected by the CMS experiment at $$\sqrt{s}=0.9$$ s = 0.9 , 7, and $$13 \,\text {Te}\text {V} $$ 13 Te . The tunes are based on the NNPDF 3.1 next-to-next-to-leading-order parton distribution function (PDF) set for the parton shower, and either a leading-order or next-to-next-to-leading-order PDF set for the simulation of MPI and the beam remnants. Predictions utilizing the tunes are produced for event shape observables in electron-positron collisions, and for minimum-bias, inclusive jet, top quark pair, and Z and W boson events in proton-proton collisions, and are compared with data. Each of the new tunes describes the data at a reasonable level, and the tunes using a leading-order PDF for the simulation of MPI provide the best description of the data.

Forms of Discussion Maintenance in the Conditions of Public Internet Communication

The thematic arrangement as a structural element of Internet discourse has been noted several times by researchers. The aim of this article was to analyse the forms of the thematic maintenance of discourse in the conditions of public internet communication. The study was run in the framework of a discursive approach. The basis is represented by news publications on Facebook, and online comments to them. The discourse was analysed via a structure-composite method. The findings allowed two forms of thematic maintenance of discourse in the Internet to be defined: in spiral order, and in chain order. Spiralling discourse occurs when the event being described is localised in time and its circumstances become the thematic core around which the conversation revolves, both in journalistic Internet publications and in the commentaries to them. However, this is practically a conversation about nothing: the introduction of new topics is aimed at keeping the audience interested in the underlying event, but clarifies nothing about the circumstances of the case. This form of discussion maintenance was extensively exemplified through the ‘Skripal case’. Its indicators are a lack of information regarding the main event, thematic incompleteness, repetition, the struggle of meanings, thematic diversity, introducing new themes. The second form of discourse maintenance, namely in chain order, was described through the example of the coronavirus topic. In this case, the topic development reflects the spread of the disease across the planet. The linguistic indicators of this form of discourse are indications of time, space and morbidity. The analysis of discourse maintenance forms in public internet communication enables the revelation of some laws in the arrangement of such seemingly sporadic speech constructs as online comments.