Effect of color reconnection and rope formation on resonance production in p–p collisions in Pythia 8

Resonance production in proton–proton collisions at $$\sqrt{s} = 7$$ s = 7 TeV and 13 TeV have been investigated using a Pythia 8 event generator within the framework of microscopic processes including color reconnection and rope hadronization. Specifically, the observable effects of different modes of color reconnections on the ratio of yields of mesonic and baryonic resonances with respect to their stable counterpart have been explored as a function of mean charged particle multiplicity. A suppression in the ratio is observed as a function of the mean number of charged particles for mesonic resonances. The $$\phi /\mathrm {K}$$ ϕ / K and $${\phi /\pi }$$ ϕ / π ratios show an enhancement for high-multiplicity events due to enhanced production of strange quarks via the microscopic process of rope hadronization in the partonic phase. The mechanism of the hadronization of color ropes together with the quark–gluon plasma (QCD)-based color reconnection of partons predicted an enhancement in the ratio for baryonic resonances to non-resonance baryons having similar quark content. The yield ratios of resonances are found to be independent of the collision energy and strongly dependent on event activity.

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.

Evolution of strange and multi-strange hadron production with relative transverse multiplicity activity in underlying event

In this work, the relative Underlying event (UE) transverse multiplicity activity classifier ($$R_\mathrm{{T}}$$ R T ) is used to study the strange and multi-strange hadron production in proton-proton collisions. Our study with $$R_\mathrm{{T}}$$ R T would allow to disentangle these particles, which are originating from the soft and hard QCD processes. We have used the PYTHIA 8 Monte-Carlo (MC) with a different implementation of color reconnection and rope hadronization models to demonstrate the proton-proton collisions data at $$\sqrt{s}~$$ s = 13 TeV. The relative production of strange and multi-strange hadrons are discussed extensively in low and high transverse activity regions. In this contribution, the relative strange hadron production is enhanced with increasing $$R_\mathrm{{T}}$$ R T . This enhancement is significant for the strange baryons as compared to mesons. In addition, the particle ratios as a function of $$R_\mathrm{{T}}~$$ R T confirm the baryon enhancement in new Color Reconnection (newCR), whereas the Rope model confirms the baryon enhancement only with strange quark content. Experimental confirmation of such results will provide more insight into the soft physics in the transverse region, which will be useful to investigate various tunes based on hadronization and color reconnection schemes.

Modification of Jet Structure in High-Multiplicity pp Collisions due to Multiple-Parton Interactions and Observing a Multiplicity-Independent Characteristic Jet Size

We study the multiplicity dependence of jet structures in pp collisions using Monte Carlo event generators. We give predictions for multiplicity-differential jet structures and present evidence for a nontrivial jet shape dependence on charged hadron event multiplicity that can be used as a sensitive tool to experimentally differentiate between equally well-preforming simulation tunes. We also propose a way to validate the presence and extent of effects such as multiple-parton interactions (MPI) or color reconnection (CR), based on the detection of nontrivial jet shape modification in high-multiplicity events at high pT. Using multiplicity-dependent jet structure observables in various pT windows might also help understanding the interplay between jet particles and the underlying event (UE). We introduce a multiplicity-independent characteristic jet size measure and use a simplistic model to aid its physical interpretation.