Charged-current neutrino interactions with nucleons and nuclei at intermediate energies

Nowadays, the interest in neutrinos extends to a large variety of fields in Astrophysics, Nuclear Physics and Particle Physics. One of the open questions in theoretical physics is the description of neutrino oscillations for which an accurate interpretation of neutrino- nucleus reactions is crucial. In this context, recent years have witnessed an intense ex- perimental and theoretical activity to determine the properties of neutrinos and their interaction with matter. This PhD Thesis is thus focused on the analysis of charged-current neutrino-nucleus reactions at kinematics of interest for neutrino oscillation experiments, where the neu- trino energy is typically in the GeV region. Additionally, weak interactions in the nuclear medium at intermediate energies are an extraordinary opportunity to study the dynamics of the nuclear many-body system, beyond the information accesible from electron and hadron probes, and to gain a deeper knowledge of the axial structure and the strangeness content of the nucleons. In any accelerator-based neutrino oscillation experiment, neutrinos are produced as the decay products of successive reactions, thus implying a wide-ranged energy beam. Hence, when interacting with the nuclear matter, a large variety of nuclear effects come into play, going from quasielastic scattering to deep inelastic processes, multi-nucleon ex- citations or meson production via nucleon resonances. Accordingly, robust models that properly describe neutrino-nucleus interactions over the whole experimental range (of the order of 10s of MeV up to 10s of GeV) are required for the experimental analyses. Notice also that the kinematics involved demand a relativistic description of the microscopic nu- clear structure. In this thesis, the analysis of these processes are addressed by using realistic models that provide, within a fully relativistic framework, an accurate description of the different reaction mechanisms of relevance for neutrino oscillation measurements. We begin ana- lyzing neutrino scattering off free nucleons and describing the weak hadronic responses together with the inner structure of the nucleons. With the aim of achieveing a consis- tent analysis of charged-current quasielastic (CCQE) neutrino interactions with nuclei, we present the so-called SuSAv2 model, which is based on the superscaling behavior exhib- ited by electron scattering data and makes use of the relativistic mean field (RMF) theory to describe the nuclear effects arising in neutrino-nucleus interactions. This prescription accounts for the final-state interactions (FSI) between the outgoing nucleon and the resid- ual nucleus and allows for a description in terms of the different isovector/isoscalar and axial/vector reaction channels that play a role in weak interactions. At very high kine- matics, where FSI are negligible, we approach our model to the relativistic plane wave impulse approximation (RPWIA) where no FSI affect the outgoing nucleon. Furthermore, a basic feature in this thesis also concerns the evaluation of multi-nucleon excitations, in particular two-body meson exchange currents (2p-2h MEC) contributions, which are proved to be an essential ingredient to interpret neutrino cross section measure- ments at intermediate energies. In this regard, we develop a highly accurate parametriza- tion of the 2p-2h MEC nuclear responses based on a fully relativistic microscopic calcu- lation. In order to test the reliability of this SuSAv2-MEC model, we firstly compare our pre- dictions with the large amount of existing inclusive 12C(e, e ′) data over the whole energy spectrum. In this connection, we also extend our description to the complete inelastic regime performing a detailed analysis of the inelastic structure functions for protons and neutrons. All this provides a solid benchmark to assess the validity of our model for the analysis of charged-current neutrino-nucleus cross sections. Regarding this point, we com- pare our calculations with recent CCQE and inclusive _μ and ¯_μ measurements on 12C from different collaborations: MiniBooNE, T2K, MINER_A, NOMAD and SciBooNE, covering an energy range from a few MeV to tens of GeV. This comparison also allows us for a deeper understanding of the nuclear reaction mechanisms at different kinematics as well as their influence in terms of the energy and momentum transfers to the nucleus. In this regard, the SuSAv2-MEC approach is applied to the analysis of diverse nuclei of relevance for future neutrino oscillation experiments with the aim of shedding light on the experimental uncertainties arising from nuclear effects in both initial and final states. Furthermore, the SuSAv2-MEC can easily make predictions at high kinematics in which other microscopic-based models would require demanding, time-consuming calculations. Moreover, we also focus on the difference between electron and muon neutrino reac- tions, where a detailed knowledge of _μ and _e cross sections is decisive in connection to the _μ ! _e oscillation experiments aiming at the determination of the neutrino mass hierarchy and the search for CP violation in the leptonic sector. In summary, this PhD thesis constitutes an extensive analysis of the different neutrino- nucleus interaction mechanisms of interest for neutrino oscillation experiments and con- forms an open window for further works and collaborations in hadronic and nuclear physics.Premio Extraordinario de Doctorado U

Analysis of Charged-Current Neutrino-Nucleus Cross Section

A study of the cross section for chaged-current quasielastic (CCQE) scattering on nuclei has been performed using a description of nuclear dynamics based on the Relativistic Fermi Gas model (RFG). The role played by different parametrizations for the weak nucleon form factors is analyzed taking into account the relevance of the axial mass value. The results obtained are compared with the recent data for neutrinos measured by the MiniBooNE Collaboration.Dirección General de Investigación (DGI). España FIS2011-28738-C02-01Centro Nacional de Física de Partículas, Astropartículas y Nuclear (CPAN) CSD2007- 0004

SuSAv2 Model for Inelastic Neutrino-nucleus Scattering

The susperscaling model SuSAv2, already available for charged-current neutrino-nucleus cross sections in the quasielastic region, is extended to the full inelastic regime. In the model the resonance production and deep inelastic reactions are described through the extension to the neutrino sector of the SuSAv2 inelastic model developed for (e, e′) reactions, which combines phenomenological structure functions with a nuclear scaling function. This work also compares two different descriptions of the Δ resonance region, one based on a global scaling function for the full inelastic spectrum and the other on a semiphenomenological Δ scaling function extracted from (e, e′) data for this specific region and updated with respect to previous work. The results of the model are tested against (e, e′) data on C12, O16, Ca40, and Ar40 and applied to the study of the charged current inclusive neutrino cross-section on C12 and Ar40 measured by the T2K, MicroBooNE, ArgoNEUT, and MINERvA experiments, thus covering several kinematical regions.Ministerio de Ciencia e Innovación PID2020–114687 GB-I00Ministerio de Ciencia, Innovación y Universidades FIS2017-88410-Junta de Andalucía FQM160, SOMM17/6105/UGR, USE-21618-KUniversity of Tokyo FY2020, FY2021European Union 83948

Semi-inclusive charged-current neutrino-nucleus reactions: Analysis of data in the Relativistic Plane-Wave Impulse Approximation

Semi-inclusive neutrino-nucleus cross sections within the plane-wave impulse approximation (PWIA) for three nuclear models: relativistic Fermi gas (RFG), independent-particle shell model (IPSM) and natural orbitals shell model (NO) are compared with the available CC0π measurements from the T2K, MINERνA and MicroBooNE collaborations where a muon and at least one proton were detected in the final state. Results are presented as a function of the momenta and angles of the final particles, as well as in terms of the imbalances between proton and muon kinematics. The analysis reveals that contributions beyond PWIA are crucial to explain the experimental measurements and that the study of correlations between final-state proton and muon kinematics can provide valuable information on relevant nuclear effects such as initial state dynamics and final state interactions.Ministerio de Ciencia, Innovación y Universidades FIS2017-88410-PJunta de Andalucía PID2020-114687GB-10

Star formation across the w3 complex

We present a multi-wavelength analysis of the history of star formation in the W3 complex. Using deep, near-infrared ground-based images combined with images obtained with Spitzer and Chandra observatories, we identified and classified young embedded sources. We identified the principal clusters in the complex and determined their structure and extension. We constructed extinction-limited samples for five principal clusters and constructed K-band luminosity functions that we compare with those of artificial clusters with varying ages. This analysis provided mean ages and possible age spreads for the clusters. We found that IC 1795, the centermost cluster of the complex, still hosts a large fraction of young sources with circumstellar disks. This indicates that star formation was active in IC 1795 as recently as 2 Myr ago, simultaneous to the star-forming activity in the flanking embedded clusters, W3-Main and W3(OH). A comparison with carbon monoxide emission maps indicates strong velocity gradients in the gas clumps hosting W3-Main and W3(OH) and shows small receding clumps of gas at IC 1795, suggestive of rapid gas removal (faster than the T Tauri timescale) in the cluster-forming regions. We discuss one possible scenario for the progression of cluster formation in the W3 complex. We propose that early processes of gas collapse in the main structure of the complex could have defined the progression of cluster formation across the complex with relatively small age differences from one group to another. However, triggering effects could act as catalysts for enhanced efficiency of formation at a local level, in agreement with previous studies.Consejo Nacional de Ciencias y Tecnología (CONACYT) CB2010-15216

Mean-field and two-body nuclear effects in inclusive electron scattering on argon, carbon, and titanium: The superscaling approach

We compare the predictions of the superscaling approach (SuSAv2) model including two-particle two-hole meson-exchange currents with the recent JLab data for inclusive electron scattering on three different targets (C, Ar, and Ti). The agreement is very good over the full energy spectrum, with some discrepancy seen only in the deep inelastic region. The 2p2h response, peaked in the dip region between the quasielastic and Δ-resonance peak, is essential to reproduce the data. We also analyze the kF (Fermi momentum) dependence of the data in terms of scaling of the second kind, showing that the 2p2h response scales very differently from the quasielastic one, in full accord with what is predicted by the model. The results represent a valuable test of the applicability of the model to neutrino scattering processes on different nuclei.Spanish Ministerio de Economia y Competitividad y ERDF (European Regional Development Fund) FIS2017-88410-PJunta de Andalucía FQM160U.S. Department of Energy United States Department of Energy (DOE), DE-FC0294ER4081

Emission of neutron–proton and proton–proton pairs in neutrino scattering

We use a recently developed model of relativistic meson-exchange currents to compute the neutron–proton and proton–proton yields in (νμ,μ−) scattering from 12C in the 2p–2h channel. We compute the response functions and cross sections with the relativistic Fermi gas model for different kinematics from intermediate to high momentum transfers. We find a large contribution of neutron–proton configurations in the initial state, as compared to proton–proton pairs. In the case of charge-changing neutrino scattering the 2p–2h cross section of proton–proton emission (i.e., np in the initial state) is much larger than for neutron–proton emission (i.e., two neutrons in the initial state) by a (ω,q)-dependent factor. The different emission probabilities of distinct species of nucleon pairs are produced in our model only by meson-exchange currents, mainly by the Δ isobar current. We also analyze other effects including exchange contributions and the effect of the axial and vector currents.Dirección General de Investigación Científica y Técnica FIS2014-59386-P y FIS2014-53448-C2-1Agencia de Innovación y Desarrollo de Andalucía FQM225 y FQM160Ministerio de Economía y Competitividad IJCI-2014-20038Instituto Nazionale di Fisica Nucleare IS-MANYBODYU.S. Department of Energy DE-FC02-94ER4081

Asymmetric relativistic Fermi gas model for quasielastic lepton-nucleus scattering

We develop an asymmetric relativistic Fermi gas model for the study of the electroweak nuclear response in the quasielastic region. The model takes into account the differences between neutron and proton densities in asymmetric (N>Z) nuclei, as well as differences in the neutron and proton separation energies. We present numerical results for both neutral and charged-current processes, focusing on nuclei of interest for ongoing and future neutrino oscillation experiments. We point out some important differences with respect to the commonly employed symmetric Fermi gas model.University of Turin BARM-RILO-17Junta de Andalucía FQM160Spanish Ministerio de Economía y Competitividad and ERDF (European Regional Development Fund) FIS2014-53448-C2-1, FIS2017-88410-

Charged-current inclusive neutrino cross sections in the SuperScaling model

SuperScaling model (SuSA) predictions to neutrino-induced charged-current π+ production in the Δ-resonance region are explored under MiniBooNE experimental conditions. The SuSA charged-current π+ results are in good agreement with data on neutrino flux-averaged double-differential cross sections. The SuSA model for quasielastic scattering and its extension to the pion production region are used for predictions of charged-current inclusive neutrino- nucleus cross sections. The contribution of two-particle-two-hole vector meson-exchange current excitations is also considered within a fully relativistic model. Results are compared with the T2K experimental data for inclusive scattering.España, DGI y Fundación FEDER FIS2011-28738-C02-01, FPA2013-41267Junta de Andalucía CSD2007-0004

Scintillator ageing of the T2K near detectors from 2010 to 2021

The T2K experiment widely uses plastic scintillator as a target for neutrino interactions and an active medium for the measurement of charged particles produced in neutrino interactions at its near detector complex. Over 10 years of operation the measured light yield recorded by the scintillator based subsystems has been observed to degrade by 0.9-2.2% per year. Extrapolation of the degradation rate through to 2040 indicates the recorded light yield should remain above the lower threshold used by the current reconstruction algorithms for all subsystems. This will allow the near detectors to continue contributing to important physics measurements during the T2K-II and Hyper-Kamiokande eras. Additionally, work to disentangle the degradation of the plastic scintillator and wavelength shifting fibres shows that the reduction in light yield can be attributed to the ageing of the plastic scintillator. The long component of the attenuation length of the wavelength shifting fibres was observed to degrade by 1.3-5.4% per year, while the short component of the attenuation length did not show any conclusive degradation.Ministerio de Ciencia e Innovación SEV-2016-0588, PID2019-107564GB-I00, PGC2018-099388-BI00European Union 713673, 754496, RISE-GA822070-JENNIFER2 2020, RISE-GA872549-SK2HKJSPS KAKENHI (JP16H06288, JP18K03682, JP18H03701, JP18H05537, JP19J01119, JP19J22440, JP19J22258, JP20H00162, JP20H00149, JP20J2030