Treballs Finals de Grau (TFG) - Física

URI permanent per a aquesta col·leccióhttps://diposit.ub.edu/handle/2445/59725

Treballs Finals del Grau de Física de la Facultat de Físca de la Universitat de Barcelona.

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Mostrant 1 - 20 de 1023

Study of ϒ(𝑛𝑆), 𝐽/𝜓 and 𝜓(2𝑆) production in PbPb collisions at LHCb
(2025-01) Zian Jamoldinova, Salma; Vázquez Gómez, Ricard
The production of ϒ(𝑛𝑆) (𝑛 = 1, 2, 3), 𝐽/𝜓, and 𝜓(2𝑆) mesons has been studied in lead-lead collisions at the LHCb. In the search for Quark-Gluon Plasma, which suppresses more considerably excited states, the yield ratio between 𝑞¯𝑞(2𝑆) and 𝑞¯𝑞(1𝑆) (𝑞 = 𝑏, 𝑐) has been computed. The dimuon decay channel is considered to reconstruct the invariant mass of the quarkonia states, and unbinned maximum-likelihood fits are used to extract the yields. For ϒ(𝑛𝑆), we find insufficient evidence for the production of ϒ(2𝑆), leading to an upper bound on the excited-to-ground state ratio of 0.09, significantly lower than the corresponding proton-proton collision value of 0.25 ± 0.01, suggesting suppression. For charmonium, we distinguish between prompt and non-prompt production using the pseudo decay time and report a 𝜓(2𝑆)-to-𝐽/𝜓 yield ratio of 0.022 ± 0.004, which remains inconclusive but compatible with previous results from 𝑝𝑝 collisions.
Characterization of candidate stellar merger progenitors
(2025-06) Zhang Guo, Hui Hui; Blagorodnova Mujortova, Nadejda
Stellar mergers have traditionally been detected because of their outbursts. A study by Addison et al.(2022) proposed a method to select them based on their position in the Hertzsprung Gap and an increase in luminosity, although without extinction values, resulting in 21 progenitor candidates for Luminous Red Novae. We present their characterization study based on new photometric and spectroscopic data. Initially identified as yellow stars, all candidates were found to be B-type stars, most of them Be stars, which makes them unlikely to be genuine LRNe progenitors. These results underscore the need to incorporate extinction corrections to avoid mischaracterization due to reddening effects. We also compute variation in radial velocities in order to decide if they may be binary systems and rotation velocities for the sources without emission lines, since Be stars are usually fast rotators. As expected, their rotational velocity to critical velocity ratio is 0.47−0.64.
Impact of neuronal aggregation: burst-originating neurons
(2025-06) Vilchez Costa, Àlex; Casademunt i Viader, Jaume; Soriano i Fradera, Jordi
This study explores the spatial distribution of burst-initiating neurons in simulated 2D neuronal cultures with a toroidal topology, in relation to the global network structure and its activity dynamics. A total of 25 simulations were conducted with varying levels of spatial aggregation, using the Izhikevich model, which is inspired by real neurons. The results show that, as the overall population becomes more spatially aggregated, the burst-initiating neurons also tend to cluster, reaching a plateau for population Gini coefficients above 0.5. In vivo results for the homogeneous case are consistent with this study, lending support to the non-experimentally tested scenarios. Moreover, more aggregated networks tend to exhibit higher burst frequencies, although a stable frequency of approximately 3.9 bursts per second is maintained.
Émilie du Châtelet and Newton on the spheroid’s problem: from geometry to calculus
(2025-06) Vilanova Martínez, Adrià; Pérez Canals, Enric
This paper analyzes and compares the resolution made by Newton in the Principia and Du Châtelet in the commentary of her Principes of the problem of finding the attraction exerted by a spheroid on a corpuscle on its axis. We find her solution to be simpler and more complete
Radio variability in the young stellar cluster Ophiuchus A
(2025-06) Vicente Bou, Arnau; Busquet Rico, Gemma
Utilizing VLA X-band (∼ 10 GHz) observations of the Ophiuchus A young stellar cluster, we study the flux variability of the sources in that region for 17 different epochs spanning approximately one month. In the first part of this work we perform an iterative self-calibration procedure of the visibilities to correct phase and amplitude artifacts, generating 2-field mosaics for each epoch. In the second part, we extract de fluxes of the 22 objects detected across all epochs and establish a variability classification scheme based on comparing each source’s maximum flux difference to a threshold that takes into account both rms and calibration uncertainties. Our results reveal variability in 15 out of the 22 detected sources, with particularly notable cases such as pronounced emission peaks in GGS29 and GGS30-IRS2, as well as a variable flux from the VLA1623A binary system. Furthermore, the sample studied seems to be consistent with the idea that Young Stellar Objects’ (YSOs) variability increases with their evolutionary stage
Singular Potentials and Anomalous Symmetry Breaking
(2025-06) Vega Casanovas, Andreu; Fiol Núñez, Bartomeu
This work investigates attractive potentials of the form 1/rN for N ≥ 2 in Quantum Mechanics. For the inverse square potential (N = 2) with sufficiently strong coupling, we examine how classical scale symmetry is broken through the renormalization process, representing the simplest example of a quantum anomaly and touching upon the fundamental question of what symmetries are present in reality. This anomaly is exemplified by the existence of a critical dipole moment required to bind an electron to a polar molecule. In contrast, singular potentials with N > 2 exhibit stronger divergences, and we argue why a complete theory cannot be recovered with finitely many parameters, drawing an analogy with nonrenormalizable theories in quantum field theory
Study of the diagonal ridges in metallicity for different star populations
(2025-06) Ubach Raya, Pau; Antoja Castelltort, M. Teresa
Various surveys, like Gaia, GALAH and LAMOST, have uncovered many features of the Milky Way. In particular, they have uncovered diagonal ridges in metallicity in the (R, Vϕ) plane. In this thesis, we use a realistic N-body simulation to study these ridges. We calculate the metallicity residuals for different age populations and azimuth sectors. We find that residuals decrease with age and change with azimuth. Finally, we calculate the angular momenta of the resonances of the bar and spiral arms, and we find that there is a relation between the residuals and the resonances, but it is not conclusive
The Zeno Paradox in Quantum Mechanics
(2025-01) Trullols Puigcerver, Albert; Juliá-Díaz, Bruno; Briongos-Merino, Héctor
The Quantum Zeno Effect slows the evolution of a quantum system through frequent measurements, preventing state transitions. In the limit of infinitely fast measurements, the evolution effectively freezes. Quantum Zeno Dynamics (QZD) extends this by confining the system to a subspace of its Hilbert space. This work examines QZD through position and momentum measurements modeled as Von Neumann projections. Frequent measurements confine the system within the projection subspace, leading to remarkable effects near its boundaries. Position measurements on a free particle induce momentum reversals, whereas momentum measurements on a particle in a symmetric potential give rise to the novel phenomenon of equipotential translocation.
Mechanical exfoliation and characterization of 2D materials
(2025-06) Tresserras Gonzalo, Bernat; Figueroa Garcia, Adriana Isabel
In this work, mechanical exfoliation of two-dimensional materials has been performed through the “scotch-tape” method with the objective of producing few-layer flakes and characterize them via optical and atomic force microscopy. The studied materials were MoS2 and PtSe2 and the substrate used for characterization was Si coated with SiOX. MoS2 showed good adhesion to the substrate and some few-layer flakes were obtained and analysed, with results suggesting a correlation between both methods of characterization. On the other hand, PtSe2 exhibited poor adhesion onto the substrate and flakes were thick and broken unevenly, making it very difficult to characterize, indicating that alternative methods for producing flakes, or other substrates for their transfer should be explored in order to achieve better results for this material.
Characterization of the elastocaloric effects in 3D printable silicone
(2025-06) Torres Padilla, Marc; Vives i Santa-Eulàlia, Eduard
The elastocaloric effect has been studied in a 3D printable silicone sample submitted to an adiabatic (fast) variation of uniaxial stress. During this process, the sample temperature has been measured by using an infrared camera allowing to obtain thermal maps of the sample surface. With the help of a custom-designed program, the average temperature over a rectangular area has been determined. The estimated adiabatic temperature change is ΔTad = 0.99◦C when the sample is elongated 388% and ΔTad = −0.75◦C when the sample is unstretched back to its original length
Chern number in the Kitaev honeycomb lattice model
(2025-06) Tomas Prats, Pere; Iblisdir, Sofyan
We study a topological invariant in the 2D Kitaev honeycomb model: the Chern number. This model consists of a spin 1 2 hexagonal lattice that can be divided into two triangular sublattices. By applying an external perturbation we can induce a non-trivial phase for some coupling configurations that yields a non-zero Chern number. First we set a theoretical basis in order to understand the results. Then we study how different parameters affect the Chern number. More exactly; finite-size effects, an external perturbation, different coupling configurations and strengths.We will see how each of these variations change the Chern number
Quantum Key Distribution with BB84: Breidbart-Based Eavesdropping and Channel Noise Effects
(2025-06) Simón Codina, María Lourdes; Juliá-Díaz, Bruno; Garcia Saez, Artur
This work presents a security analysis of the BB84 quantum key distribution protocol, focusing on intercept-and-resend attacks and the effects of channel noise. We study two eavesdropping strategies—naive and Breidbart-based—and evaluate the probabilities of Eve (the spy) correctly measuring Alice’s (the sender) bit and Bob (the receiver) measuring an incorrect one. We analyze the impact of bit-flip, phase-flip, and combined noise, derive theoretical expressions, and identify optimal attack parameters. A cost function is introduced to balance Eve’s information gain and detectability. Finally, simulations carried out confirm the theoretical predictions. The results offer insight into the robustness of BB84 under both ideal and noisy conditions and confirm its security against intercept-and-resend attacks.
Distortion of the Wigner distribution by a Coulomb interaction
(2025-06) Seara Rodríguez, Elena; Escobedo Espinosa, Miguel Ángel
The goal of this work is to study the distortion of the Wigner function of a heavy quark interacting by a Coulomb potential in a quark gluon plasma. To carry it out, we programmed a model using FORTRAN 77 that integrates the Wigner function for a Coulomb wave function. With that we want to test if the approximation of using a free particle wave function to calculate the Wigner function of the unbound particles in the Coalescence model is a good approximation
Sequential detuning of a drumhead with a lock-in amplifier
(2025-06) Sánchez Elias, Ricard; Hernández Ferràs, Joan Manel
Whenever a drumhead is tuned, a perturbation in the tension of the membrane induces the splitting of frequencies for the degenerated asymmetric modes (m, n), with m ̸= 0. With the use of a lock-in amplifier and piezoelectric sensors and actuators attached at the head, the amplitude of the signal generated by the sensors is recorded as the membrane is forced to vibrate over a range of frequencies, answering noticeably when mode’s harmonics are reached. The progression from uniform conditions where the modes are accessible, to the measure of frequency splitting when the drum’s lugs are symmetrically tightened demonstrates the functionality of the system and the behavior of non-uniform tension for a vibrating membrane.
The unique conformally and duality-invariant theory of non-linear electrodynamics
(2025-06) San Gil Pascual, Álvaro; Murcia Gil, Ángel Jesús
We study extensions of Maxwell electrodynamics which respect Lorentz invariance, gauge symmetry, conformal symmetry and are invariant under electromagnetic duality rotations. We carefully derive and show that there exists a unique one-parameter family of theories that preserves all these properties. It receives the name of ModMax and we examine how Coulomb’s law is modified within this set of theories and the appearance of birefringence in vacuum
Study of the B+ → π+μ+μ− decay with the LHCb experiment
(2025-06) Salvador Carreté, Marc; Marín Benito, Carla; Olivart Pino, Ernest
In this work, a study of the B+ → π+μ+μ− decay is performed in the new data collected during Run 3 of the LHCb experiment. A Boosted Decision Tree (BDT) algorithm is used to select the events corresponding to this decay and mass fits are performed to extract its yield. The B+ → π+J/ψ(→ μ+μ−) decay is used as a control channel. Using the yield of the control channel, the expected signal yield is found to be 1.64±0.22. No signal events have been found by performing a fit directly, which is compatible with the expectations.
Theoretical study of the mixing of the π0-η-η′-axion system
(2025-06) Salomon Pagespetit, Josep; Gonzàlez-Solís, Sergi
The mass term of the Chiral Lagrangian at leading order mixes the strangeness-zero states. In order to perform calculations of physical quantities such as decay rates and scattering amplitudes involving the neutral π0, η and η′ mesons, the mass matrix of the Lagrangian needs to be diagonalized. In this work, we find the relation between the Lagrangian and physical states in terms of mixing angles as well as the expressions for the corresponding physical meson masses. We also incorporate mixing with the axion, thus preparing the Lagrangian for applications in axion phenomenology.
Getting to know the winter North Atlantic Oscillation
(2025-01) Ruiz Herbón, Eva; García Serrano, Javier
The North Atlantic Oscillation (NAO) is a key atmospheric phenomenon that shapes winter climate patterns in the Northern Hemisphere, affecting sea level pressure, temperature, and precipitation. This study explores the NAO using ERA5 reanalysis data, and coupled atmosphereocean and atmosphere-only simulations to analyse its dynamics and impacts. Empirical Orthogonal Function analysis identifies the NAO as the dominant mode of variability, explaining up to 50% of sea level pressure variations in the North Atlantic-European region during boreal winter. Results illustrate that the NAO is primarily an atmospheric phenomenon, independent of oceanic coupling, as evidenced by consistent patterns across datasets. The study highlights the crucial role of the NAO in modulating regional precipitation and temperature patterns, with significant implications for climate research and socio-economic sectors
Ultracold atoms in a 1D optical lattice: Mott-Superfluid transition
(2025-01) Rubio Jiménez, Víctor; Guilleumas, Montserrat
In this project, the transition between different quantum phases of ultracold bosonic systems trapped in an optical lattice is studied using the exact diagonalization method. First, the Mott Insulator to Superfluid transition is analyzed. Afterwards, the Density Wave phase is also considered. Specifically, a Julia programming language code is used to find the ground state of a system defined by a Bose-Hubbard Hamiltonian and the phase of this state is determined by means of specific observables derived from the occupation levels.
Study of bounded confidence models of opinion dynamics on networks
(2025-06) Rovira Yélamos, Néstor; Cozzo, Emanuele
Using the Deffuant model of opinion dynamics, in which the agents in a network can only influence each other if the discrepancy in their opinions is less than the confidence bound parameter, we observe the formation of clusters during the dynamic. In this process there is a fraction of agents that stay isolated and don’t change their opinion or they form really small clusters that barely change their opinion from the start and stay in the extreme opinions. This work is centered on studying this fraction of isolated agents, how the probability changes for different topologies, dynamics and stages.

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