Vol. 4 No. 2 (2023): Suplemento de la Revista Mexicana de Física. XVIII Mexican Workshop on Particles and Fields 2022 and XXXVI Annual Meeting of the Division of Particles and Fields 2022

Preface.

Proceedings of the XVIII Mexican Workshop on Particles and Fields 2022 and the XXXVI Annual Meeting of the Division of Particles and Fields 2022

The Unruh effect predicts how uniformly accelerated observers will perceive a change in the vacuum state. This shows that the concept of particle number depends on the acceleration of the reference frame. Although this is a result of quantum field theory, its experimental verification is still questioned, mainly due to the high accelerations required. In this work we study a quantum oscillator with only one complex coordinate and a damping term acting as perturbation, which has all the characteristics of the Unruh effect in second quantization for an accelerated observer. The Bogoliubov transformation connecting the two different vacuum states is obtained. This leads to an explicit formula for the particle occupation number as a function of energy and acceleration. Furthermore, it is shown that our analogue system contains an effective temperature that depends on the observer's sudden acceleration, seen as a friction force. The purpose of this work is to demonstrate that quanta production (particles or energy packets) is inevitable under the premises of quantum field theory.

In this contribution, We revisit the effect of electric eE and magnetic field eB and on the critical temperature T χ,C c of the chiral symmetry breaking/restoration and confinement/deconfinement phase transition in the QCD Phase diagram. In this context, we use the symmetrypreserving vector-vector contact interaction model of quarks, in the Schwinger-Dyson equations framework and in the proper time regularization scheme. We also describe the phenomenon of inverse electric catalysis in the pure electric case, magnetic catalysis (and inverse magnetic catalysis) in the pure magnetic case and inverse electromagnetic catalysis in the presence of both electric and magnetic background fields.

The calculation of higher-order corrections in Quantum Field Theories is a challenging task. In particular, dealing with multiloop and multileg Feynman amplitudes leads to severe bottlenecks and a very fast scaling of the computational resources required to perform the calculation. With the purpose of overcoming these limitations, we discuss efficient strategies based on the Loop-Tree Duality, its manifestly causal representation and the underlying geometrical interpretation. In concrete, we exploit the geometrical causal selection rules to define a Hamiltonian whose ground-state is directly related to the terms contributing to the causal representation. In this way, the problem can be translated into a minimization one and implemented in a quantum computer to search for a potential speed-up.

I review recent advances in the computation of radiative corrections in one- and two-meson tau decays and sketch their main applications in new physics tests: of lepton universality and CKM unitarity, as well as searching for non-standard interactions.

We use the most general four-lepton effective interaction Hamiltonian to investigate the impact of massive Dirac and Majorana neutrinos on the leptonic decays of muons and taus. Our analysis encompasses the specific energy and angular distribution of the resulting charged lepton, accounting for both the initial and final polarizations of the charged leptons. Additionally, we identify the emergence of novel generalized Michel parameters and concentrate on the influence of the heavy neutrino masses, which can make significant contributions in cases where new sterile neutrinos exhibit non-negligible mixing. Our analysis reveals that the most promising scenario occurs in the case of τ decays, featuring one heavy neutrino with a mass approximately ranging from 10^2 to 10^3 MeV. In this setting, the discrepancy between the Dirac and Majorana cases could reach an order of magnitude of 10^−4, which is significant enough to be detected in present and future experiments.

The ALICE experiment is devoted to the study of the quark-gluon plasma (QGP) created in heavy-ion collisions at the CERN LHC. The experimental setup allows for the study of many different observables that contributed to the characterization of the properties of the QGP. The ALICE experiment went through a major upgrade during LS2 to profit from the increased LHC luminosity and to improve the tracking resolution. An additional upgrade is planned for LS3. A new experiment, ALICE 3, was proposed as next major upgrade in LS4. In this contribution, a selection of recent physics results was presented together with a glimpse of the next upgrades during LS3 and LS4, with the main focus on ALICE 3 and its physics program

Measuring the mass of particles whose decay products cannot be detected poses a significant challenge due to the complexity of reconstructing these decays and measuring various parameters. However, studying processes involving undetectable particles is crucial as it enables us to delve deeper into familiar decays involving energy loss, such as Standard Model processes involving neutrinos. Additionally, it provides an opportunity to test models associated with physics beyond the Standard Model that can be generated in leptonic colliders. In this study, the mass of the tau lepton was determined by comparing three different methods for decays with semi-invisible final states. Specifically, the measurement focused on the decay τ − → π −ντ (signal). Among the three methods employed, the most accurate result was obtained using the Mmin method, yielding a tau lepton mass value of Mτ = 1777.06 ± 0.44 MeV. The measurement utilized official Monte Carlo data provided by the Belle II collaboration, specifically from the MC13a campaign conducted until 2020, with an integrated luminosity of 100fb⁻¹ .

Heavy ion collisions are rich and complex systems that involve different aspects of QCD and electromagnetic phenomena. From head-on collisions to the case in which the nuclei miss each other, many of QCD and photo-induced probes are being actively investigated. In this contribution we briefly discuss both of these different topics and some of the CMS results on top quark production and vector meson photo-production, as well as the physics motivation to study these processes are presented.

We report on the core-corona model developed to describe the main features of hyperon global polarization in semicentral relativistic heavy-ion collisions as a function of the collision energy. We first neglect the contribution to polarization from hyperons produced in the corona. In this scenario, the global polarization turns out to be described by a delicate balance between the vorticity-to-spin transferring reactions in the core and the predominance of corona over core matter at low energies. We show how this last feature provides a key ingredient missing in our original model that helps to better describe the excitation function for Λ and Λ global polarization. To improve the description, we then introduce the contribution to the global polarization coming from the transverse polarization of Λs produced in the corona, which is hereby assumed to be similar to the well-known polarization produced in p + p reactions. The results show a small positive contribution to the global polarization, however they are not yet conclusive due to the small size of the MC sample used in the analysis.

We investigate the proposal by Kharzeev and Levin of a maximally entangled proton wave function in Deep Inelastic Scattering of electrons and proton in the region of low Bjorken x. Using their proposed relation between parton number and entanglement entropy, we determine the latter using both conventional parton distribution functions and parton distribution functions obtained from an unintegrated gluon distribution subject to next-to-leading order Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution as well as from a dipole cross-section, subject to running coupling Balitsky-Kovchegov (rcBK) evolution. We compare our results to hadronic entropy obtained from final state hadron multiplicity.

In this work we analyze cLFV processes using a low-energy EFT that induces the effective interaction between two charged leptons of different flavor and two photons. We compute ℓ_i → ℓ_jγ, ℓ_i → ℓ_jγγ decays and ℓ_i → ℓ_j conversion in nuclei. We derived indirect upper limits on the double photon decays, which turned out to be below current experimental bounds. Our prediction for ℓ → τ conversion in nuclei is below the expected sensitivity of the NA64 experiment

We estimate the squared speed of sound for the hot and dense QCD states formed in ion collisions at very high energies by exploring the implications of small-bounded and geometry effects in the String Percolation Model. The squared sound velocity shows signals of a local minimum (knee point) below the critical temperature consistent with the softest point in the equation of state and the onset of quark deconfinement that characterizes the quark-gluon plasma phase transition.

The determination of fundamental properties of hadrons is important to clearly understand the experimental measurements such as the anomalous magnetic moment of the muon. However, since a first principle approach is hard to find, several groups among the world are approaching phenomenologically to such description of hadrons. In this poster, we present a comprehensive survey of electromagnetic form factors of all light, heavy and heavy-light ground-state pseudoscalar and scalar mesons. Specifically, in this work we are interested on the determination of Elastic Meson Form Factors (EFF) for Scalar (S) and Pseudoscalar (PS) mesons. However, the calculation of all EFF requires the computation of the quark propagator, the Bethe-Salpeter (BS) equation and the Bethe-Salpeter Amplitudes (BSA) of mesons, their masses as well as the knowledge of the quark-photon interaction at different probing momenta.

We present the calculation of charged pion and kaon electromagnetic form factors in the time-like regime using Schwinger-Dyson equations and the Poincare covariant Bethe-Salpeter equations within an SU(2) isospin symmetric limit. To accurately represent the behavior of a time-like photon, we have incorporated non-valence contributions into the system of equations, enabling the decays ρ → ππ and φ → KK. The inclusion of these decay mechanisms is essential for capturing the expected behavior of the electromagnetic pion and kaon form factors. Our results for the form factors reasonably reproduce the experimental data for a time-like photon.

We revisit the isospin-breaking and electromagnetic corrections of some hadronic tau decays, which can also be employed to extract the Cabibbo-Kobayashi-Maskawa (CKM) matrix element V_us. We extend former analyses by Antonelli et al. working with ChPT with resonances. We find that going beyond the Low approximation, these corrections play an important role between the π⁻ K⁰ and K⁻ π⁰ modes. The K⁻ K⁰ channel is also discussed.

Over the last years, Machine Learning (ML) methods have been successfully applied to a wealth of problems in high-energy physics. In this work, we discuss the extraction of the average number of Multiparton Interactions (⟨Nmpi⟩) from minimum-bias pp data at LHC energies using a regression based on Boosted Decision Trees (BDT). Using the available ALICE data on transverse momentum spectra as a function of multiplicity, we report that for minimum-bias pp collisions at √s = 7 TeV the average Nmpi is 3.98 ± 1.01, which complements our previous results for pp collisions at √s = 5.02 and 13 TeV. The comparisons indicated a modest center-of-mass energy dependence of ⟨Nmpi⟩. The study is further extended extracting the multiplicity dependence of Nmpi for the three center-of-mass energies. These results are qualitatively consistent with the existing ALICE measurements sensitives to Multiparton Interactions (MPI). Through the ML method applied to pp collisions at √s = 13 TeV, we also show that computing the multiplicity in the forward region the extraction of Nmpi is improved. This result opens the possibility to extract the number of MPI event-by-event, and in this way study the particle production as a function of MPI. Our results provide additional evidence of the presence of MPI in hadronic interactions and can help to the understanding of the heavy-ion-like behaviour observed in pp collisions data.

Standard model-dark matter particles, mediated by spin one fields, are analyzed within the effective field theory framework. We [1, 2] consider dark particles masses from few MeV to 6.4 TeV. We restrict the EFT using bounds from relic density, Z invisible decay width, direct and indirect detection limits and collider constraints. Solutions below mZ are found for two operators. Others, around the electroweak scale or slightly above, are also compatible with all present limits.

Jets are commonly used to study Quantum Chromodynamics and search for physics beyond the Standard model. Recent experimental results are analyzed to study hard and soft hadron production mechanisms within and out of the jets. The result of this work is the study of hadron production within and out of the jets produced in proton-proton collisions generated using Pythia 8.3 event generator. We report color reconnection effects on jet multiplicity, multiplicity for identified particles within the jets and transverse momenta distributions at 7 and 13 TeV.

We describe the discovery of the colorless C-odd gluonic compound, the odderon, by the D0 and TOTEM Collaborations by comparing elastic differential cross sections measured in pp and pp¯ interactions at high energies. We also discuss the reach on quartic anomalous couplings and the sensitivity to axion like particle production by using the LHC as a γγ collider and detecting the intact protons at high luminosity.

In this work we investigate the possibility that one neutrino mirror plays the role of a sterile neutrinos with mass on the scale of a few eV ′ s, that is, mˆ ₁ ∼ O(1 eV ). We consider the extension of the Standard Model with gauge symmetry SU(2)_L ⊗ SU(2)_R ⊗ U(1)_Y ′ and additional exotic fermions known as mirror fermions. A double application of the seesaw type I approximation to the most general Majorana-type neutrino mass matrix and diagonalization is performed to study neutrino masses and mixing.

We study the energy dependence of the cross-section for exclusive photo-production of vector mesons J/Ψ and Ψ(2s) and search for signs for the onset of non-linear QCD dynamics in this observable. Our study is based on two dipole models: the Golec-Biernat, Wuesthoff Model (GBW) and the Bartels, Golec-Biernat, Kowal- ski Model (BGK). We find that differences between linear and non-linear implementations of these models are relatively small in the kinematic region probed by both HERA and LHC experiments if the energy dependence of the photo-production cross-section is being considered. We however find that the ratio of both cross-sections grows with energy in the presence of non-linear effects, while it remains approximately constant in the linearized case. The ratio of photo-production cross-sections might therefore provide a suitable tool to characterize the size of non-linear QCD effects at current collider energies.

We present our results on the top quark chromomagnetic dipole moment, which is based on the 5-dimension effective Lagrangian operator that characterizes the chromodipolar vertex functions gtt and ggtt. The chromomagnetic dipole mu_t is derived via quantum fluctuation at the 1-loop level. We evaluate µˆt(s) as a function of the energy scale s=+-E², for E=[10,1000] GeV. In particular we focus on the conventional high-energy scale E=mZ, analogously as with alpha_s(mZ²) and s_W(mZ²). The spacelike evaluation matches quite well with the experimental central value, while the timelike case deviates from it.

This contribution presents the recent research developments within the Cosmic Ray Extremely Distributed Observatory in the search for resolution of various scientific puzzles, ranging from fundamental physical questions to applications like the determination of earthquake precursors. The state-of-the art theoretical, numerical and computational aspects of these phenomena are addressed, as well as recent experimental developments for detection.

We study the evolution of light quarks with isospin symmetry and the pion masses in the presence of a thermal bath and study their temperature dependence. In addition, we analyze the inclusion of a coupling with temperature dependence. We attempt to study the dissolution of bound-states at temperatures higher than the critical temperature, but we found that the model shows that the bound-state's mass increases. We base our study on a momentum-independent symmetry-preserving truncation scheme contact interaction in the Schwinger-Dyson equations framework.

We discuss the conditions for QGP formation under the Color String Percolation Model. Since the observables in the percolation theory are sensitive to the system size, we expect the finite size effects take a relevant contribution to the estimation of the color string observables, such as the transition temperature or the center of mass energy needed for the QGP formation.
We observe that pp collisions (small systems) require around 20 times bigger center of mass energy than heavy ion collisions. Our results are consistent with the experiments claiming that the QGP has been observed.

Discrete Flavor Symmetries are often employed in BSM constructions to successfully recreate fermion masses and mixing patterns through several known mechanisms. Obvious constraints on these types of scenarios are the non-observation of Flavour Changing Neutral Currents which set stringent limits. In this talk I will discuss the strategy of using the scalar sector phenomenology predicted by such BSM models, and its correlation with the dark matter sector, to further strengthen the constraints by exploiting the large data available from heavy scalar searches in colliders including recent likelihood profiles provided by ATLAS and CMS.

We discuss extensions to the Standard Model that increase only the scalar sector, specifically with a singlet and doublet fields. We consider the current values and limits for the Dark Matter (DM) observables in order to constraint the model parameters. We also take into account the latest data related to the physics of the Higgs. We find an update allowed regions for the masses of the DM particle for each extended model in this work.

Collisions of electrons against muons provide a very clean environment for many beyond SM signals. We consider the case of two-to-two flavor changing processes that are absent in the SM. The sensitivity of the e-muon collider to the four-fermion dimension six operators is about the same order of magnitude as the one based on low energy measurements.

In this work we briefly review dark matter evidence, in the Weakly Interacting Massive Particles (WIMP) paradigm we study the cases of scalar and fermion dark matter candidates. Our study introduces effective couplings between dark matter and Standard Model matter, it is intended as an exercise for academic purposes setting up the required tools for a further analysis. Under the last assumption, we calculate the relic density in order to constrain the model parameter space.

By understanding neutrino masses via an inverse seesaw mechanism, the Littlest Higgs model with T parity is enlarged. Promising predictions for lepton flavor violating processes within this setting (see refs.~\cite{IvanPachecoZ,Ivan2}) are reviewed.

The theoretical predictions presented in this work are integral to the ongoing and planned experiments at RHIC and CERN-LHC laboratory. The innovation of the research lies in the possibility of making distributions of many measurable kinematic variables, which are often key to better understanding the reaction mechanism, rather than being limited to presenting only the value of the total cross section. The presented aspect of the research can be used to plan future experiments as well as to interpret already existing experimental results. The correctness of the results is strongly influenced by the type of nuclear form factor used.

We summarize the quantitative results of our analysis [1] of top-pair photoproduction in semileptonic mode in pe collisions at the LHeC and FCC-he. We define three photoproduction regions, based on the rapidity acceptance range of the electron tagger, that provide different degrees of sensitivity to top-quark effective couplings. We focus on the ttγ dipole couplings and the left-handed vector tbW coupling, for which we determine limits at both energies in the different photoproduction regions. Furthermore, we find that the LHeC and FCC-he will yield tight direct bounds on top dipole moments, greatly improving on current direct limits from hadron colliders, and direct limits on the tbW coupling as restrictive as those expected from the HL-LHC. We also consider indirect limits from b → sγ branching ratio and CP asymmetry, that are well known to be very sensitive probes of top electromagnetic dipole moments.

In this article, two image reconstruction techniques for radiography and tomography using cosmic ray muons are presented. The simulation is carried out using the Geant4 package, simulating a multiple coincidence system of four RPCs (Resistive Plate Chambers). The reconstruction techniques presented are based on particle trajectory reconstruction and localization of a single center of dispersion. Two functional cases are displayed for each technique.

High Energy collider experiments are moving to the highest precision frontier quickly. The predictions of observables are based on the factorization formula which helps to connect small to large distances. These predictions can be contrasted with experimental measurements and the success of this phenomenological approach is based on the correct description of nature. The application of the method to proton-proton colliders brings new challenges due to the proton structure and the detectors efficiency on reconstructing hadrons. Furthermore, since the non-perturbative distribution functions takes an important role to describe the experimental distributions, the presence of them makes the information of the partons diluted. At Leading Order (LO) in perturbative calculations, the momentum fractions involved in hard scattering processes are known exactly in terms of kinematical variables of initial and final states hadrons. However, at Next-to-Leading Order (NLO) and beyond, a closed analytical formula is not available. Furthermore, from the pure theoretical calculation, the exact definition of the momentum fraction is very challenging. In this work, we report a methodology based on Machine Learning techniques for the extraction of momentum fractions for $p+p\to\pi^++\gamma$ using a Monte Carlo simulation including quantum corrections up to Next-to-Leading Order in Quantum Chromodynamics and Leading Order in Quantum Electrodymics. Our findings point towards a methodology to find the fundamental properties of the internal structure of hadrons because the reconstructed momentum fractions deeply relate our perturbative models with experimental measurements.

We present the motivation and use-case for the proposed CODEX-b detector, as well as its description. We also describe the design and status of a smaller demonstrator detector, CODEX-beta, as of the time of the conference associated with these proceedings.

We describe the phenomenology of the scalar and dark matter sectors of a BSM theory with Q4 symmetry among the SM fermions. The model features a Higgs portal to a dark sector comprised of heavy right handed neutrinos. We discuss relic abundance as well as direct detection constraints on the DM candidate.