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Double Beta Decay without Neutrino Emission: Mechanism for Studying Physics Beyond the Standard Model


The Standard Model of Elementary Particles


The Standard Model of particles is the theory that best explains the nature of matter, accurately describing subatomic particles and their interactions [1]. Everything is governed by forces, at least for now, encompassing three of the four fundamental forces of nature along with their messengers, particles that transmit interactions between elementary particles [2]. In the Standard Model of Particle Physics, the neutrino is a particle with no electric charge, no color charge, and assumed to be massless, interacting only weakly, known as a Dirac particle, fundamentally distinct from its antiparticle. However, with the discovery of neutrino oscillations and consequently massive neutrino states, there arose the need to postulate mechanisms for generating mass beyond the Higgs Mechanism, thus beyond the Standard Model [3].


It is known that the neutrino is the only fermion lacking any conserved quantum number that distinguishes it from its antiparticle (antineutrino). This makes it possible for the neutrino to be a Majorana particle, meaning the neutrino is identical to its antiparticle (ν = ν̃). In this case, Double Beta Decay without Neutrino Emission (0νDBD) would also be allowed, where the neutrino emitted by one neutron is absorbed by another neutron within the nucleus, as depicted in Figure 1.


On May 11 (Thursday), from 2:00 PM to 3:30 PM, the seminar "Double Beta Decay without Neutrino Emission: Mechanism for Studying Physics Beyond the Standard Model" will be held entirely online. The seminar will be conducted by Prof. Dr. Vitor dos Santos Ferreira, a graduate of the PROFÍSICA Academic Master's program, Ph.D. in Physics from UERJ, and currently a Substitute Professor at the Federal University of Recôncavo da Bahia (UFRB).


This seminar will discuss a nuclear process that, if detected, could serve as a gateway to physics beyond the Standard Model. But before delving deeper: what exactly is the Standard Model of particles?

Figure 1: Feynman diagram for the modes of double beta decay: On the left is decay with emission of two neutrinos (2ν−DBD), and on the right is decay without emission of neutrinos (0ν−DBD).



Double Beta Decay without Neutrino Emission: Mechanism for Studying Physics Beyond the Standard Model


Double beta decay without neutrino emission is an example of a second-order electroweak process that violates lepton number conservation by two units. This process occurs when two neutrons simultaneously decay into two protons within the nucleus with the emission of two electrons. This happens if the neutrino is treated as a Majorana fermion. Majorana neutrinos are key to obtaining answers about the asymmetry between matter and antimatter in the universe, as they allow for the creation of matter without the presence of antimatter. Therefore, the best way to find answers about the nature of the neutrino (Dirac or Majorana) or the existence of right-handed neutrino currents and to understand the non-conservation of lepton number is through the transition rates of double beta decay without neutrino emission, as these rates depend on various unknown parameters (right-handed coupling constants of the electroweak Hamiltonian or the effective neutrino mass), which can be extracted from the decay half-lives.


Large research groups are striving to detect the primary experimental signature consisting of a monoenergetic signal with the reaction Q value intensity, carried by the two electrons together, but so far this signature has not been achieved (see Figure 2). If this were to happen, it would imply the first observation of a matter creation process without the balance of antimatter emission and consequently establish the nature of Majorana neutrinos.

Figure 2: Sum of the energy spectra of the two electrons emitted in double beta decay: i) Blue line for the mode with emission of two neutrinos, and ii) Red line for the mode without emission of neutrinos. Source: https://physics.aps.org/articles/v11/30



What is a Majorana Fermion?


A Majorana fermion is a hypothetical elementary particle that is its own antiparticle, meaning it has neutral charge. This type of particle was proposed by the Italian physicist Ettore Majorana in 1937 and has not yet been experimentally detected. The existence of Majorana fermions has significant implications in particle physics and cosmology, including the potential to explain the matter-antimatter asymmetry of the universe and the existence of dark matter. Research to detect these particles is ongoing in particle physics laboratories worldwide.


Nuclear Physics and its Importance to Human Life


All that has been explained above occurs within Nuclear Physics, which aims to investigate the origin, evolution, structure, and phases of nuclear matter subject to strong interaction, through the development of predictive models.


Fundamental open questions have led Nuclear Physics to broaden its horizons, and today its scope ranges from the study of the most fundamental particles, such as quarks, to gigantic structures in the universe, such as supernovas.


Nuclear Physics has enabled, through nuclear medicine, the development of technologies with significant impact on human health, such as the improvement of increasingly effective medical tests, producing high-resolution images with minimal impact on human skin.

Moreover, it should not be forgotten that about 11% of the world's energy is produced by nuclear reactors. Currently, nuclear energy is increasingly being studied as the best future alternative for sustainable energy, due to its high efficiency and low emission of greenhouse gases. Although there are concerns regarding the safe management of nuclear waste, many countries are investing in solutions to address this issue.



Double Beta Decay without Neutrino Emission will be the theme of the 2nd PROFÍSICA Seminar - 2023 Season


On May 11 (Thursday), from 2:00 PM to 3:30 PM, the seminar "Double Beta Decay without Neutrino Emission: Mechanism for Studying Physics Beyond the Standard Model" will be held entirely online. It will be conducted by Prof. Dr. Vitor dos Santos Ferreira, a graduate of the Academic Master's in PROFÍSICA, Ph.D. in Physics from UERJ, and currently Substitute Professor at the Federal University of Recôncavo da Bahia (UFRB).


This seminar will discuss a nuclear process that, if detected, could be considered a gateway to physics beyond the standard model. But before delving deeper: what is the standard model of particles?



Academic Profile of Prof. Dr. Vitor dos Santos Ferreira


Ph.D. in Physics from the University of the State of Rio de Janeiro (2020), Master's in Physics (2016), and Bachelor's in Physics (2014) from the State University of Santa Cruz. Recently completed a 10-month postdoctoral internship at UESC (2022) and currently serves as a substitute professor at the Federal University of Recôncavo da Bahia. He specializes in Nuclear Physics, focusing on nuclear structure transitions with double charge exchange, utilizing the following microscopic models: Quasiparticle Tamm-Dancoff Approximation (QTDA), Quasiparticle Random Phase Approximation (QRPA), and extensions.



Written by:

Prof. Dr. Vitor dos Santos Ferreira, UFRB

Prof. Dr. André Luis Ribeiro, UESC-PROFÍSICA

Flávia Vitória, MBA, Communication Advisory @adeccua


Sources:

[2] MOREIRA, Marco Antonio. O modelo padrão da física de partículas. Revista Brasileira de Ensino de Física, v. 31, p. 1306.1-1306.11, 2009.

[3] NOGUEIRA, Higo Barros. Neutrinos massivos e mecanismo de geração de massa em uma extensão abeliana do modelo padrão. 2023.

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