arXiv subjects

Antonio Paz

Publications and source records attributed to Antonio Paz.

4 recordsLinked to original sources

arXiv2026

Design and performance of a large-area scintillator-based chamber for the MID subsystem of ALICE 3

This paper reports on the design and construction of a chamber for the muon identifier detector (MID) of the ALICE 3 upgrade project. The chamber consists of two sensitive layers separated by a 1 cm air gap. Each layer holds 24 scintillator bars ($1\times4\times100$ cm$^3$) manufactured by FNAL-NICADD. The bars are equipped with Kuraray wavelength shifting fibers and the readout is provided by a silicon photomultiplier from Hamamatsu. The bars in the second layer are orthogonal to the bars in the first layer, thus providing an overlapping cell size of 4$\times$4 cm$^{2}$. The bar assembly as well as the design of the mechanical structure is described. The design of the chamber is close to that considered in the ALICE 3 letter of intent. The chamber was tested at the CERN T10 beamline using 3 GeV/$c$ pion-enriched and muon beams. The chamber was placed behind an iron absorber, with different absorber lengths considered in the test. The muon identification is performed using a Machine Learning algorithm, which was trained and tested using muon (signal) and pion (background) data (50% of the available statistics). The trained ML algorithm was applied to muon data, yielding a muon efficiency above 99% for the OR condition (detection in either layer 1 or 2). The implementation in the pion-beam data gives the fake-muon efficiency as a function of the absorber length that is well described by an exponential function with a slope parameter of 18.79 cm. The next steps towards finalizing the optimization are outlined.

physics.ins-det↗

arXiv2021

Particle production as a function of the underlying event in pp collisions simulated with PYTHIA 8

In this work we present the production of charged particles associated with high-$p_{\rm T}$ trigger particles ($8<p_{\rm T}^{\rm trig.}<15$ GeV /$c$) at mid-pseudorapidity in proton-proton collisions at $\sqrt{s}=5.02$\,TeV simulated with the \textsc{PYTHIA 8} Monte Carlo model. The study is performed as a function of the relative transverse activity classifier, $R_{\rm T}$, which is the relative charged-particle multiplicity in the transverse region ($π/3 <|Δϕ| <2π/3$) of the di-hadron correlations, and it is sensitive to the Multi-Parton Interactions. The evolution of the yield of associated particles on both the toward and the away regions with $3\leq p_{\rm T}^{\rm assoc.}<8$ GeV/$c$ as a function of $R_{\rm T}$ is investigated. We propose a strategy which allows for the modelling and subtraction of the Underlying Event (UE) contribution from the toward and the away regions in challenging environments like those characterised by large $R_{\rm T}$. We found that the signal in the away region becomes broader with increasing $R_{\rm T}$. Contrarily, the yield increases with $R_{\rm T}$ in the toward region. This effect is reminiscent of that seen in heavy-ion collisions, where an enhancement of the yield in the toward region for $0-5\%$ central Pb--Pb collisions at $\sqrt{s}_{\rm NN}=2.76$\,TeV was reported. To further understand the role of the UE and additional jet activity, the transverse region is divided into two one-sided sectors, "trans-max" and "trans-min" selected in each event according to which region has larger or smaller charged particle multiplicity. Based on this selection criterion, the observables are studied as a function of $R_{\rm T}^{\rm max}$ and $R_{\rm T}^{\rm min}$, respectively. The presented results have been published in J. Phys. G 48, no.1, 015007 (2020) and Phys. Rev. D 104, no.1, 016017 (2021).

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↗

arXiv2020

Multi-Parton Interactions in pp collisions from Machine Learning-based regression

Multi-Parton Interactions (MPI) in pp collisions have attracted the attention of the heavy-ion community since they can help to elucidate the origin of collective-like effects discovered in small collision systems at the LHC. In this work, we report that in PYTHIA 8.244, the charged-particle production in events with a large number of MPI (${\rm N}_{\rm mpi}$) normalized to that obtained in minimum-bias pp collisions shows interesting features. After the normalization to the corresponding $\langle {\rm N}_{\rm mpi} \rangle$, the ratios as a function of $p_{\rm T}$ exhibit a bump at $p_{\rm T}\approx3$ GeV/$c$; and for higher $p_{\rm T}$ ($>8$ GeV/$c$), the ratios are independent of ${\rm N}_{\rm mpi}$. While the size of the bump increases with increasing ${\rm N}_{\rm mpi}$, the behavior at high $p_{\rm T}$ is expected from the "binary scaling" (parton-parton interactions), which holds given the absence of any parton-energy loss mechanism in PYTHIA. The bump at intermediate $p_{\rm T}$ is reminiscent of the Cronin effect observed for the nuclear modification factor in p--Pb collisions. In order to unveil these effects in data, we propose a strategy to construct an event classifier sensitive to MPI using Machine Learning-based regression. The study is conducted using TMVA, and the regression is performed with Boosted Decision Trees (BDT). Event properties like forward charged-particle multiplicity, transverse spherocity and the average transverse momentum ($\langle p_{\rm T} \rangle$) are used for training. The kinematic cuts are defined in accordance with the ALICE detector capabilities. In addition, we also report that if we apply the trained BDT on existing (${\rm INEL}>0$) pp data, i.e. events with at least one primary charged-particle within $|η|<1$, the average number of MPI in pp collisions at $\sqrt{s}=5.02$ and 13 TeV are 3.76$\pm1.01$ and 4.65$\pm1.01$, respectively.

hep-ph↗