arXiv subjects

Lizardo Valencia Palomo

Publications and source records attributed to Lizardo Valencia Palomo.

7 recordsLinked to original sources

arXiv2026

Impact of local and global event conditions in prompt charm hadron ratios

Fragmentation functions extracted from electron-proton and electron-positron collisions have shown not to be able to explain prompt charm hadron ratios in proton-proton collisions at the LHC energies. New models and event generator tunes have been developed to correctly describe the data from the ALICE experiment in proton-proton collisions at different center of mass energies. In this work Pythia 8.312 is used to implement two of those models: the SC-CR and BLC-CR + Ropes. Both show a good performance to reproduce the data at \sqrt{s}} = 13 TeV in different event conditions for the $Λ_{c}^{+}/\rm{D}^0$, $Σ_{c}^{0,+,++}/\rm{D}^0$, $\rm{D}^{+}/\rm{D}^0$ and $\rm{D}^{*+}/\rm{D}^0$ ratios. For the particular case when the prompt charm hadrons are within jets, all the ratios show modifications relative to the case where the presence of jets is not required. A study in two different ranges of the relative transverse activity is also conducted. In this case only the baryon to meson ratios show a dependence on the underlying event activity. Results indicate that baryon and meson hadronisation are not affected in the same way by local effects or global event conditions

hep-ph↗

arXiv2026

Multiplicity dependence of $Υ$(nS) mean transverse momentum in proton-proton collisions

Correct description of quarkonia production and kinematics are still one of the most challenging assignments for Quantum Chromodynamics. This document presents a study of the $Υ$(1S), (2S) and (3S) mean transverse momentum ($\langle p_{\mathrm{T}}^Υ \rangle$) as a function of the charged particle multiplicity ($N_{\mathrm{Track}}$) in proton-proton collisions at $\sqrt{s}$ = 7 TeV generated with Pythia 8.312 CUETP8M1 tune. The comparison to real data collected by the CMS experiment indicates that the agreement is much better for the excited states than for the ground state. The observed fast increase of the $\langle p_{\mathrm{T}}^Υ \rangle$ at small values of $N_{\mathrm{Track}}$ is mainly due to the contribution from the away region. Furthermore, when computing the $\langle p_{\mathrm{T}}^Υ \rangle$ from jetty and isotropic events a clear $p_{\mathrm{T}}$ hardening is observed in jetty events. Finally, analyzing the fragmentation of jets containing an $Υ$(nS) it is proposed a method to test the new quarkonia shower present in the Monte Carlo event generator.

hep-ph↗

arXiv2025

J/$ψ$ and $Υ$(1S) production in jets at LHC energies

Quarkonia production in hadronic collisions is far from being understood as none of the existing models can correctly describe the wealth of available data. In particular, LHCb and CMS experiments have reported that PYTHIA 8 cannot reproduce the prompt J/$ψ$ production in jets in proton-proton collisions at two different center of mass energies: the event generator predicts an important amount of the prompt J/$ψ$ to be produced isolated, opposite to the experimental data. This document demonstrates that such effect remains true even if the QCD color reconnection (CR) model is used. Besides that, it is shown that using the new quarkonia parton shower included in PYTHIA 8.312 it is possible to correctly describe the experimental results. This agreement between data and simulation is improved when using the QCD color reconnection approach, opening the possibility to distinguish between the two CR implementations. Finally, a prediction performed for $Υ$(1S) indicates that a higher jet p$_T$ selection should be used by the LHC experiments in order to distinguish between PYTHIA 8 results generated with and without the quarkonia parton shower.

hep-ph↗

arXiv2023

Understanding the transverse-spherocity biased data from pp collisions at the LHC energies

The ALICE collaboration recently reported the mean transverse momentum as a function of charged-particle multiplicity for different pp-collisions classes defined based on the "jettiness" of the event. The event "jettiness" is quantified using transverse spherocity that is measured at midpseudorapidity ($|η|<0.8$) considering charged particles with transverse momentum within $0.15<p_{\rm T}<10$ GeV/$c$. Comparisons to PYTHIA 8 (tune Monash) predictions show a notable disagreement between the event generator and data for jetty events that increases as a function of charged-particle multiplicity. This paper reports on the origin of such a disagreement using PYTHIA 8 event generator. Since at intermediate and high $p_{\rm T}$ ($2<p_{\rm T}<10$ GeV/$c$), the spectral shape is expected to be modified by color reconnection or jets, their effects on the average $p_{\rm T}$ are studied. The results indicate that the origin of the discrepancy is the overpredicted multijet yield by PYTHIA 8 which increases with the charged particle multiplicity. This finding is important to understand the way transverse spherocity and multiplicity bias the pp collisions, and how well models like PYTHIA 8 reproduce those biases. The studies are pertinent since transverse spherocity is currently used as an event classifier by experiments at the LHC.

hep-ph↗

arXiv2019

Probing color reconnection with underlying event observables at the LHC energies

In this work we study the underlying event (UE) activity as a function of the highest jet transverse momentum ($p_{\rm T}^{\rm jet}$) in terms of the number and summed $p_{\rm T}$ densities of charged particles in the azimuthal region transverse to the $p_{\rm T}^{\rm jet}$ direction. The UE observables normalised to the INEL multiplicity obey an approximate Koba-Nielsen-Olesen (KNO) scaling. Based on PYTHIA~8.2 simulations of $pp$ collisions at LHC energies, we show that the remaining imperfection of the KNO scaling is due to the increasing importance of multiple partonic interactions (MPI) at higher $\sqrt{s}$. Motivated by this, we studied the UE activity considering charged particles within different $p_{\rm T}$ intervals in $pp$ collisions at $\sqrt{s}=7$\,TeV. We demonstrate that the saturations of both number and summed $p_{\rm T}$ densities, which are commonly claimed, are only observed for low-\pt charged particles ($0.5 0.5$\,GeV/$c$) the summed $p_{\rm T}$ density is not sensitive to the variation of color reconnection (CR), however at low-p_{\rm T} it is reduced with increasing CR, whereas an opposite behaviour is found at intermediate-$p_{\rm T}$ ($2<p_{\rm T}<10$\,GeV/$c$). Finally, we show that CR produces flow-like behaviour only in the UE region and the effects are reduced with increasing $p_{\rm T}^{\rm jet}$ due to the hardering of UE. The outcomes encourage the measurement of inclusive and identified charged particle $p_{\rm T}$ spectra (over a wide range of $p_{\rm T}$) associated to UE aimed at better understanding the similarities between $pp$ and heavy-ion data discovered at the LHC.

hep-ex↗

arXiv2017

Universality of the underlying event in pp collisions

In this paper we study ATLAS results on underlying event in pp collisions at $\sqrt{s}$=0.9, 7 and 13 TeV. We show that the center-of-mass energy dependences of the charged-particle production sensitive to the underlying event ("transverse" region) and to the hardest partonic interaction ("towards" and "away" regions) in pp collisions can be both understood in terms of the change of the inclusive average multiplicity. Within uncertainties, the corresponding particle production as a function of the leading charged particle shows no significant $\sqrt{s}$-dependence for the three regions once they are scaled according to the relative change in multiplicity. The scaling properties reported here are well reproduced by PYTHIA 8.212 tune Monash 2013 and suggest an universality of the underlying event in hadronic interactions at high $\sqrt{s}$. Based on the simulations, we observed that the same scaling properties are also present in the average number of multi-partonic interactions as a function of the leading charged particle. Moreover, the multiplicity distributions associated to the underlying event exhibit a KNO scaling.

hep-ex↗

arXiv2017

Open heavy flavour and quarkonium production as a function of the multiplicity in pp and p-Pb collisions with ALICE at the LHC

Due to the large masses of beauty and charm quarks, their production cross sections can be computed in the framework of perturbative Quantum Chromodynamics. The correlation of quarkonium and open heavy-flavour hadron yields with charged particles produced in proton-proton (pp) and proton-lead (p-Pb) collisions can shed light on the interplay between hard and soft mechanisms in particle production. In this proceeding the results from D-meson and J/$ψ$ yields as a function of the charged-particle multiplicity in pp and p-Pb collisions are presented. Comparisons to theoretical models are also discussed.

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