arXiv subjects

M. J. Vicente Vacas

Publications and source records attributed to M. J. Vicente Vacas.

At least 19 recordsLinked to original sources

arXiv2024

Cabibbo suppressed hyperon production off nuclei induced by antineutrinos

In this work we study the production of $Σ$ and $Λ$ hyperons in strangeness changing $ΔS = -1$ charged current interactions of muon antineutrinos on nuclear targets. At the nucleon level, besides quasielastic scattering we consider the inelastic mechanism in which a pion is produced alongside the hyperon. Its relevance for antineutrinos with energies below 2 GeV is conveyed in integrated and differential cross sections. We observe that the distributions on the angle between the hyperon and the final lepton are clearly different for quasielastic and inelastic processes. Hyperon final state interactions, modeled with an intranuclear cascade, lead to a significant transfer from primary produced $Σ$'s into final $Λ$'s. They also cause considerable energy loss, which is apparent in hyperon energy distributions. We have investigated $Λ$ production off ${}^{40}$Ar in the conditions of the recently reported MicroBooNE measurement. We find that the $Λπ$ contribution, dominated by $Σ^*(1385)$ excitation, accounts for about one third of the cross section.

hep-ph↗

arXiv2020

Threshold pion electro- and photoproduction off nucleons in covariant chiral perturbation theory

Pion electro- and photoproduction off the nucleon close to threshold is studied in covariant baryon chiral perturbation theory at O($p^3$) in the extended-on-mass-shell scheme, with the explicit inclusion of the $Δ(1232)$ resonance. The relevant low energy constants are fixed by fitting the available experimental data with the theoretical model. The inclusion of the $Δ$ resonance as an explicit degree of freedom substantially improves the agreement with data and the convergence of the model.

hep-ph↗

arXiv2019

Pion photoproduction off nucleons in covariant chiral perturbation theory

Pion photoproduction off the nucleon close to threshold is studied in covariant baryon chiral perturbation theory at O($p^3$) in the extended-on-mass-shell scheme, with the explicit inclusion of the $Δ(1232)$ resonance using the $δ$ counting. The theory is compared to the available data of cross sections and polarization observables for all the charge channels. Most of the necessary low energy constants are well known from the analysis of other processes and the comparison with data strongly constrains some of the still unknown ones. The $Δ(1232)$ contribution is significant in improving the agreement with data, even at the low energies considered.

hep-ph↗

arXiv2019

Neutral-current weak pion production off the nucleon in covariant chiral perturbation theory

Neutral current single pion production induced by neutrinos and antineutrinos on nucleon targets has been investigated in manifestly relativistic baryon chiral perturbation theory with explicit $Δ(1232)$ degrees of freedom up to $\mathcal{O}(p^3)$. At low energies, where chiral perturbation theory is applicable, the total cross sections for the different reaction channels exhibit a sizable non-resonant contribution, which is not present in event generators of broad use in neutrino oscillation and cross section experiments such as GENIE and NuWro.

hep-ph↗

arXiv2018

Weak pion production off the nucleon in covariant chiral perturbation theory

Weak pion production off the nucleon at low energies has been systematically investigated in manifestly relativistic baryon chiral perturbation theory with explicit inclusion of the $Δ$(1232) resonance. Most of the involved low-energy constants have been previously determined in other processes such as pion-nucleon elastic scattering and electromagnetic pion production off the nucleon. For numerical estimates, the few remaining constants are set to be of natural size. As a result, the total cross sections for single pion production on neutrons and protons, induced either by neutrino or antineutrino, are predicted. Our results are consistent with the scarce existing experimental data except in the $ν_μn\to μ^-nπ^+$ channel, where higher-order contributions might still be significant. The $Δ$ resonance mechanisms lead to sizeable contributions in all channels, especially in $ν_μp\to μ^- pπ^+$, even though the considered energies are close to the production threshold. The present study provides a well founded low-energy benchmark for phenomenological models aimed at the description of weak pion production processes in the broad kinematic range of interest for current and future neutrino-oscillation experiments.

hep-ph↗

arXiv2018

Electromagnetic form factors of spin 1/2 doubly charmed baryons

We study the electromagnetic form factors of the doubly charmed baryons, using covariant chiral perturbation theory within the extended on-mass-shell (EOMS) scheme. Vector-meson contributions are also taken into account. We present results for the baryon magnetic moments, charge and magnetic radii. While some of the chiral Lagrangian parameters could be set to values determined in previous works, the available lattice results for $Ξ_{cc}^+$ and $Ω_{cc}^+$ only allow for robust constraints on the low-energy constant (LEC) combination, $c_{89}(=-\frac{1}{3}c_8+4c_9)$. The couplings of the doubly charmed baryons to the vector mesons have been estimated assuming the Okubo--Zweig--Iizuka (OZI) rule. We also give the expressions for the form factors of the double beauty baryons considering the masses predicted in the framework of quark models. A comparison of our results with those obtained in heavy baryon chiral perturbation theory (HBChPT) at the same chiral order is made.

hep-ph↗

arXiv2017

$ϕ$ meson transparency in nuclei from $ϕN$ resonant interactions

We investigate the $ϕ$ meson nuclear transparency using some recent theoretical developments on the $ϕ$ in medium self-energy. The inclusion of direct resonant $ϕN$-scattering and the kaon decay mechanisms leads to a $ϕ$ width much larger than in most previous theoretical approaches. The model has been confronted with photoproduction data from CLAS and LEPS and the recent proton induced $ϕ$ production from COSY finding an overall good agreement. The results support the need of a quite large direct $ϕN$-scattering contribution to the self-energy.

nucl-th↗

arXiv2017

Peripheral transverse densities of the baryon octet from chiral effective field theory and dispersion analysis

The baryon electromagnetic form factors are expressed in terms of two-dimensional densities describing the distribution of charge and magnetization in transverse space at fixed light-front time. We calculate the transverse densities of the spin-1/2 flavor-octet baryons at peripheral distances b = O(M_π^{-1}) using methods of relativistic chiral effective field theory (χEFT) and dispersion analysis. The densities are represented as dispersive integrals over the imaginary parts of the form factors in the timelike region (spectral functions). The isovector spectral functions on the two-pion cut t > 4 M_π^2 are calculated using relativistic χEFT including octet and decuplet baryons. The χEFT calculations are extended into the ρmeson mass region using an N/D method that incorporates the pion electromagnetic form factor data. The isoscalar spectral functions are modeled by vector meson poles. We compute the peripheral charge and magnetization densities in the octet baryon states, estimate the uncertainties, and determine the quark flavor decomposition. The approach can be extended to baryon form factors of other operators and the moments of generalized parton distributions.

hep-ph↗

arXiv2017

Consistency between SU(3) and SU(2) chiral perturbation theory for the nucleon mass

Treating the strange quark mass as a heavy scale compared to the light quark mass, we perform a matching of the nucleon mass in the SU(3) sector to the two-flavor case in covariant baryon chiral perturbation theory. The validity of the $19$ low-energy constants appearing in the octet baryon masses up to next-to-next-to-next-to-leading order~\cite{Ren:2014vea} is supported by comparing the effective parameters (the combinations of the $19$ couplings) with the corresponding low-energy constants in the SU(2) sector~\cite{Alvarez-Ruso:2013fza}. In addition, it is shown that the dependence of the effective parameters and the pion-nucleon sigma term on the strange quark mass is relatively weak around its physical value, thus providing support to the assumption made in Ref.~\cite{Alvarez-Ruso:2013fza}.

nucl-th↗

arXiv2016

$ϕ$ meson self-energy in nuclear matter from $ϕN$ resonant interactions

The $ϕ$-meson properties in cold nuclear matter are investigated by implementing resonant $ϕN$ interactions as described in effective approaches including the unitarization of scattering amplitudes. Several $N^*$-like states are dynamically generated in these models around $2$ GeV, in the vicinity of the $ϕN$ threshold. We find that both these states and the non-resonant part of the amplitude contribute sizably to the $ϕ$ collisional self-energy at finite nuclear density. These contributions are of a similar strength as the widely studied medium effects from the $\bar K K$ cloud. Depending on model details (position of the resonances and strength of the coupling to $ϕN$) we report a $ϕ$ broadening up to about $40$-$50$ MeV, to be added to the $ϕ\to\bar K K$ in-medium decay width, and an attractive optical potential at threshold up to about $35$ MeV at normal matter density. The $ϕ$ spectral function develops a double peak structure as a consequence of the mixing of resonance-hole modes with the $ϕ$ quasi-particle peak. The former results point in the direction of making up for missing absorption as reported in $ϕ$ nuclear production experiments.

nucl-th↗

arXiv2016

$Δ(1232)$ resonance in the $\vecγp\rightarrow pπ^0$ reaction at threshold

We calculate the neutral pion photoproduction on the proton near threshold in covariant baryon chiral perturbation theory, including the $Δ(1232)$ resonance as an explicit degree of freedom, up to chiral order $p^{7/2}$ in the $δ$ counting. We compare our results with recent low-energy data from the Mainz Microtron for angular distributions and photon asymmetries. The convergence of the chiral series of the covariant approach is found to improve substantially with the inclusion of the $Δ(1232)$ resonance.

hep-ph↗

arXiv2016

Masses of doubly charmed baryons in the extended on-mass-shell renormalization scheme

In this work, we investigate the mass corrections of the doubly charmed baryons up to $N^2LO$ in the extended-on-mass-shell (EOMS) renormalization scheme, comparing with the results of heavy baryon chiral perturbation theory. We find that the terms from the heavy baryon approach are a subset of those obtained in the EOMS scheme. By fitting the lattice data, we can determine the parameters $\tilde{m}$, $α$, $c_1$ and $c_7$ from the Lagrangian, while in the heavy baryon approach no information on $c_1$ can be obtained from the baryons mass. Correspondingly, the masses of $m_{Ξ_{cc}}$ and $m_{Ω_{cc}}$ are predicted, in the EOMS scheme, extrapolating the results from different values of the charm quark and the pion masses of the lattice QCD calculations.

hep-ph↗

arXiv2016

Present Status of Single Pion Production in Neutrino-Nucleus Reactions

Some of the recent progress in the physics of pion production induced by neutrinos on nucleons and nuclei is reviewed from a theoretical perspective. The importance of Watson's theorem to reconcile ANL and BNL data with the off-diagonal Goldberger-Treiman relation for the $Δ(1232)$ is discussed. The disagreement between MiniBooNE data and theoretical calculations is presented in the light of the new MINERvA data. The coherent pion production data on $^{12}$C obtained by MINERvA are also compared to different microscopic and PCAC models.

hep-ph↗

arXiv2016

Watson's theorem and the $NΔ(1232)$ axial transition

We present a new determination of the $NΔ$ axial form factors from neutrino induced pion production data. For this purpose, the model of Hernandez {\it et al.} [Phys. Rev. D76, 033005 (2007)] is improved by partially restoring unitarity. This is accomplished by imposing Watson's theorem on the dominant vector and axial multipoles. As a consequence, a larger $C_5^A(0)$, in good agreement with the prediction from the off-diagonal Goldberger-Treiman relation, is now obtained.

hep-ph↗

arXiv2015

Chiral dynamics in the gamma p --> p pi0 reaction

We investigate the neutral pion photoproduction on the proton near threshold in covariant chiral perturbation theory with the explicit inclusion of Delta degrees of freedom. This channel is specially sensitive to chiral dynamics and the advent of very precise data from the Mainz microtron has shown the limits of the convergence of the chiral series for both the heavy baryon and the covariant approaches. We show that the inclusion of the Delta resonance substantially improves the convergence leading to a good agreement with data for a wider range of energies.

hep-ph↗

arXiv2015

Antineutrino induced Lambda(1405) production off the proton

We have studied the strangeness changing antineutrino induced reactions $\barν_{l} p \rightarrow l^+ ϕB $, with $ϕB = K^-p$, $\bar{K}^0n$, $π^0Λ$, $π^0Σ^0$, $ηΛ$, $ηΣ^0$, $π^+Σ^-$, $π^-Σ^+$, $K^+Ξ^-$ and $K^0Ξ^0$, using a chiral unitary approach. These ten coupled channels are allowed to interact strongly, using a kernel derived from the chiral Lagrangians. This interaction generates two $Λ(1405)$ poles, leading to a clear single peak in the $πΣ$ invariant mass distributions. At backward scattering angles in the center of mass frame, $\barν_μ p \rightarrow μ^+ π^0 Σ^0$ is dominated by the $Λ(1405)$ state at around 1420~MeV while the lighter state becomes relevant as the angle decreases, leading to an asymmetric line shape. In addition, there are substantial differences in the shape of $πΣ$ invariant mass distributions for the three charge channels. If observed, these differences would provide valuable information on a claimed isospin I=1, strangeness S=-1 baryonic state around 1400 MeV. Integrated cross sections have been obtained for the $πΣ$ and $\bar K N$ channels, investigating the impact of unitarization in the results. The number of events with $Λ(1405)$ excitation in $\barν_μp$ collisions in the recent antineutrino run at the MINERvA experiment has also been obtained. We find that this reaction channel is relevant enough to be investigated experimentally and to be taken into account in the simulation models of future experiments with antineutrino beams.

hep-ph↗

arXiv2015

Weak Production of Strange Particles and $η$ Mesons off the Nucleon

The strange particle production induced by (anti)neutrino off nucleon has been studied for $|ΔS|=0$ and $|ΔS|=1$ channels. The reactions those we have considered are for the production of single kaon/antikaon, eta and associated particle production processes. We have developed a microscopical model based on the SU(3) chiral Lagrangian. The basic parameters of the model are $f_π$, the pion decay constant, Cabibbo angle, the proton and neutron magnetic moments and the axial vector coupling constants for the baryons octet. For antikaon production we have also included $Σ^*$(1385) resonance and for eta production $S_{11}$(1535) and $S_{11}$(1650) resonances are included.

hep-ph↗

arXiv2015

Weak Quasielastic Production of Hyperons and Threshold Production of Two Pions

We have studied quasielastic charged current hyperon production induced by $\barν_μ$ on free nucleon and the nucleons bound inside the nucleus and the results are presented for several nuclear targets like $^{40}Ar$, $^{56}Fe$ and $^{208}Pb$. The hyperon-nucleon transition form factors are determined from neutrino-nucleon scattering and semileptonic decays of neutron and hyperons using SU(3) symmetry. The nuclear medium effects(NME) due to Fermi motion and final state interaction(FSI) effect due to hyperon-nucleon scattering have been taken into account. Also we have studied two pion production at threshold induced by neutrinos off nucleon targets. The contribution of nucleon, pion, and contact terms are calculated using Lagrangian given by nonlinear $σ$ model. The contribution of the Roper resonance has also been taken into account. The numerical results for the cross sections are presented and compared with the experimental results from ANL and BNL.

hep-ph↗