arXiv subjects

Gyula Bencedi

Publications and source records attributed to Gyula Bencedi.

7 recordsLinked to original sources

arXiv2025

Finite $V_{\rm 2\Delta}$ puzzle in low-multiplicity pp collisions from ultra-long-range azimuthal correlations in the string-shoving model

Ultra-long range angular correlations have been recently reported by the ALICE collaboration in pp collisions at $\sqrt{s}=13$ TeV below ${\rm d}N_{\rm ch}/{\rm d}\eta=7$. The measurements have been performed as a function of the charged-particle multiplicity at midrapidity ($N_{\rm ch}$ in $|\eta|<0.8$), which is known to be strongly sensitive to local multiplicity fluctuations. The present work investigates the impact of the event-activity estimator on ultra-long range angular correlations. The study is conducted in the framework of PYTHIA8 with the string shoving mechanism since it gives a non-zero elliptic flow coefficient, $V_{2\Delta}$. The analysis is conducted as a function of $N_{\rm ch}$, the number of parton-parton scatterings ($N_{\rm mpi}$) and flattenicity. Surprisingly, for ultra-long range correlations, pp collisions with $N_{\rm mpi}=1$ (dijets) seems to be the most sensitive to string shoving. The effect diminishes with increasing $N_{\rm mpi}$. While in data, within uncertainties, $V_{2\Delta}$ exhibits a weak multiplicity dependence; the string shoving mechanism gives a $V_{2\Delta}$ that decreases with the increase in $N_{\rm ch}$. The present work therefore supports the picture stating that mechanisms such as string shoving might explain the low multiplicity limit, whereas, hydro becomes relevant in high-multiplicity pp collisions. This work also suggests that flattenicity might be more effective than $N_{\rm ch}$ to better handle non-flow effects.

hep-ph↗

arXiv2024

Flattenicity as "centrality" estimator in p-Pb collisions simulated with PYTHIA 8.312 Angantyr

In this paper, a "centrality" estimator based on flattenicity ($\rho$) is studied in proton-led (p-Pb) collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV using PYTHIA 8 Angantyr. Although Angantyr is still under development, the existing implementation is enough to study the particle production in systems where medium effects are absent. Firstly, ALICE data on pseudorapidity distributions as a function of the forward multiplicity (V0M), as well as transverse momentum distributions of identified particles in non-single diffractive p-Pb collisions, are compared with Angantyr. Secondly, the average number of binary nucleon-nucleon ($N_{\rm coll}$) collisions for different "centrality" estimators are compared. The studies include the following "centrality" estimators: V0M, $\rho$ and midrapidity multiplicity (CL1). On one hand, the "centrality" dependence of $\langle N_{\rm coll} \rangle$ for the $\rho$ selection shows the smallest deviations ($<8$ %) with respect to that obtained using impact parameter $b$; on the other hand, the V0M and CL1 yield huge deviations (up to a factor 2) with respect to the results using $b$. The particle ratios and nuclear modification factors ($Q_{\rm pPb}$) as a function of $p_{\rm T}$ are also studied. The proton-to-pion ratio exhibits a flow-like peak at intermediate $p_{\rm T}$ (2-8 GeV/$c$) with little or no "centrality" dependence for V0M, $\rho$ and $b$ selections. The kaon-to-pion ratio as a function of $p_{\rm T}$ is "centrality" independent for the same selections. On the contrary, for the CL1 class the ratios exhibit the typical behaviour associated with hard physics. Regarding $Q_{\rm pPb}$, a peak at intermediate $p_{\rm T}$ ($2-8$ GeV/$c$) for different particle species is observed when the "centrality" is obtained with $b$ or $\rho$. The observed features diminish for the selections based on V0M and CL1.

nucl-ex↗

arXiv2022

Unveiling the effects of multiple soft partonic interactions in pp collisions at $\sqrt{{\textit s}}=13.6$ TeV using charged-particle flattenicity

Event classifiers based either on the charged-particle multiplicity or the event shape have been extensively used in proton-proton (pp) collisions by the ALICE collaboration at the LHC. The use of these tools became very instrumental since the observation of fluid-like behavior in high-multiplicity pp collisions. In particular, the study as a function of the charged-particle multiplicity registered in the forward V0 ALICE detector allowed for the discovery of strangeness enhancement in high-multiplicity pp collisions. However, one drawback of the multiplicity-based event classifiers is that requiring a high charged-particle multiplicity biases the sample towards hard processes like multi-jet final states. These biases make it difficult to perform jet-quenching searches in high-multiplicity pp collisions. In this context, the present paper explores the use of the new event classifier, flattenicity; which uses the multiplicity calculated in the forward pseudorapidity region. To illustrate how this tool works, pp collisions at $\sqrt{s}=13.6$ TeV simulated with PYTHIA~8 are explored. The sensitivity of flattencity to multi-partonic interactions as well as to the ``hardness'' of the collision are discussed. PYTHIA 8 predictions for the transverse momentum spectra of light- and heavy-flavored hadrons as a function of flattenicity are presented.

hep-ph↗

arXiv2021

Disentangling the hard gluon Bremsstrahlung effects from the relative transverse activity classifier in pp collisions

Recently, the so-called relative transverse activity classifier, $R_{\rm T}$, has been proposed as a tool to disentangle the particle production originated from the soft and hard QCD processes in proton-proton (pp) collisions. $R_{\rm T}$ is a useful quantity to study particle production in events with exceptionally large or small activity in the transverse region with respect to the event-averaged mean. Contrary to the expectations, the preliminary results of the ALICE Collaboration indicate that, e.g., the proton-to-pion ratio does not exhibit the characteristic enhancement at intermediate $p_{\rm T}$ in events with large $R_{\rm T}$ with respect to minimum-bias pp collisions. In this work, we investigate the origin of this effect using the PYTHIA 8 and HERWIG 7 Monte Carlo event generators. The effect is a consequence of a selection bias attributed to wide-angle gluon emissions which creates jets that populate the transverse region. Therefore, we propose a modified version of $R_{\rm T}$ in order to suppress its sensitivity to hard gluon Bremsstrahlung, and enhance the sensitivity to soft Multiparton Interactions (MPI). This approach could be useful in order to study the particle production in the jet-like region as a function of MPI. The implementation of these ideas in data will provide more insight into the production mechanisms of hadrons in high-multiplicity pp collisions, and its connection with heavy-ion phenomena.

hep-ph↗

arXiv2018

Event-shape- and multiplicity-dependent identified particle production in pp collisions at 13 TeV with ALICE at the LHC

Multiplicity-dependent measurements of identified particle production led to the discovery of collective-like behavior in pp collisions at the LHC. Better understanding of the effects attributed to well-understood physics, like multiple hard scatterings, is required to establish whether this behaviour is truly collective in origin. Experimentally, those effects can be controlled using event shapes, like transverse spherocity, which allows the classification of pp collisions either as jetty or isotropic events. The transverse momentum ($p_{\rm T}$) spectra of light-flavor hadrons in pp collisions measured over a broad range provide important input to study particle production mechanisms in the soft and hard scattering regimes of the QCD. In this work, they are used to perform a comprehensive study as a function of the event multiplicity, collision energy, and event shapes. The proton-to-pion and kaon-to-pion particle ratios as a function of $p_{\rm T}$ are also reported and the results compared to QCD-inspired models.

hep-ex↗

arXiv2018

New results on the multiplicity and centre-of-mass energy dependence of identified particle production in pp collisions with ALICE

The study of identified particle production in proton-proton (pp) collisions as a function of center-of-mass energy ($\sqrt{s}$) and event charged-particle multiplicity is a key tool for understanding similarities and differences between small and large collision systems. We report on new measurements of the production of identified particles and their dependence on multiplicity and $\sqrt{s}$. Latest results for light flavor hadrons, comprising $π^{\pm}$, $\mathrm{K}^{\pm}$, ${\rm p}(\rm \bar{p})$, single-strange ($\mathrm{K_{S}^{0}}$, $\barΛ$, and $Λ$), multi-strange ($Ξ^{-}$, $\overlineΞ^{+}$, $Ω^{-}$, and $\overlineΩ^{+}$) particles as well as resonances ($\mathrm{K^{*0}}$, $\mathrm{\overline{K}^{*0}}$, $ϕ$), are presented for $\sqrt{s}~=~5.02, 7$, and 13 TeV. The measured minimum bias $p_{\rm T}$ spectra and yields were complemented with multiplicity-dependent measurements for single- and multi-strange hadrons at $\sqrt{s}~=~7$ and $\sqrt{s}~=~13$ TeV. Results are compared to measurements at lower $\sqrt{s}$ as well as to those in proton-lead and lead-lead (Pb-Pb) collisions, respectively at $\sqrt{s}_{\rm NN}~=~5.02$ TeV and $\sqrt{s}_{\rm NN}~=~2.76$ TeV. The results unveil intriguing similarities among collision systems at different $\sqrt{s}$. The production rates of strange hadrons are found to increase more than those of non-strange particles, showing an enhancement pattern with multiplicity which does not depend on the collision energy. These yield ratios take values which are alike for small systems at comparable multiplicities and show smooth evolution with multiplicity across all collision systems. Although the multiplicity dependence of spectral shapes can be qualitatively described by general-purpose Monte Carlo (MC) event generators, the evolution of yield ratios is barely (or not) captured by MC model predictions.

hep-ex↗

arXiv2016

Nuclear modification factor of charged particles and light-flavour hadrons in p--Pb collisions measured by ALICE

The hot and dense strongly interacting Quark-Gluon Plasma (sQGP) created in ultra-relativistic heavy-ion collisions can be probed by studying high-$p_{\rm T}$ particle production and parton energy loss. Similar measurements performed in p-Pb collisions may help in determining whether initial or final state nuclear effects play a role in the observed suppression of hadron production at high-$p_{\rm T}$ in Pb--Pb collisions. By examining the nuclear modification factors through the comparison of identified hadron yields in different collision systems one can gain insight into particle production mechanisms and nuclear effects.

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