arXiv subjects

A. Mariano

Publications and source records attributed to A. Mariano.

At least 19 recordsLinked to original sources

arXiv2022

Neutrino-induced single pion production and the reanalyzed bubble chamber data

In this work we report the calculation of the charged current total and differential cross sections for weak pion-production with neutrinos and antineutrinos, with the final pion-nucleon pair invariant mass $W_{πN}\lesssim2$GeV. Our results are compared with the recent reanalyzed data from the old bubble chamber experiments, that solved the discrepancy between the ANL and BNL data. We implement a model previously tested for the cuts $W_{πN}<1.4,1.6$ Gev which includes explicitly resonances in the first and second resonance regions, within different approaches for the resonances self energy and $\frac{3}{2}$-vertexes and propagators, a fact not usually analyzed. Our model leans on consistent effective Lagrangians that generate resonant amplitudes together non resonant plus resonant backgrounds. Effects of hadrons finite extension and more energetic resonances corresponding to the emitted pion-nucleon invariant mass in the $1.6<W_{πN}<2$ GeV region, are taking into account using appropiate form factors in consistency with previous results on neutral current pion production calculations. Our results reproduce well the reanalysed data without cuts and are compared with another models.

hep-ph↗

arXiv2022

Weak pion-production and the second resonance region

In this work we report the calculation of the total cross section for pion-production by the dispersion of neutrinos on nucleons. We use a consistent formalism for the intermediate resonance states of spin $3/2$ , taking care on the conditions imposed by the invariance on contact transformations and using the Sachs parametrization for the form factors. In addition, we incorporate states in the second resonance region up to 1.6 GeV and implement different approaches for all the dressed resonance propagators. In addition to the $Δ$(1232), we include the N$^*$(1440),N$^*$(1535)and N$^*$(1520) resonance contributions, and it is shown that this inclusion improve the description of the total cross section regards a model where only the $Δ$(1230) resonance is considered. Also results for antineutrinos are properly described.

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arXiv2016

Inconsistency of the interactions between pseudoscalar, spinor and Rarita-Schwinger fields

We perform the Dirac quantization of RS fields interacting with a spinor and the first derivative of a pseudoscalar field. We achieve the calculations for two forms of this interaction: first we review the conventional coupling of lowest derivative order, reproducing the well known inconsistencies in its anticommutator algebra. Then, we perform the analysis on the next order term popularly known as spin 3/2 gauge invariant interaction, which is claimed to be free of these inconsistencies. Nevertheless we find that the direct application of the Dirac formalism leads to inconsistencies in complete analogy to the previous case. This is of high relevance in the particle phenomenology field, where these interactions are used to interpret experimental data involving Delta(1232) resonances.

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arXiv2015

About consistence between pi N Delta spin-3/2 gauge couplings and electromagnetic gauge invariance

We analyze the consistence between the recently proposed "spin 3/2 gauge" interaction for the Delta resonance with nucleons and pions, and the fundamental electromagnetic gauge invariance in any radiative amplitude. Chiral symmetric pion-derivative pi N Delta couplings can be substituted through a linear transformation to get Delta-derivative ones, which have the property of decoupling the 1/2 field components of the Delta propagator. Nevertheless, the electromagnetic gauge invariance introduced through minimal substitution in all derivatives, can only be fulfilled at a given order n without destroying the spin 3/2 one by dropping n+1 order terms within an effective field theory (EFT) framework with a defined power counting. In addition, we show that the Ward identity for the gamma Delta gamma vertex cannot be fulfilled with a trimmed 3/2 propagator, which should be necessary in order to keep the spin 3/2 gauge symmetry in the radiative case for the gamma Delta gamma amplitude. Finally, it is shown that radiative corrections of the spin 3/2 gauge strong vertexes at one loop, reintroduce the conventional interaction.

nucl-th↗

arXiv2014

Relic density calculations beyond tree-level, exact calculations versus effective couplings: the ZZ final state

The inferred value of the relic density from cosmological observations has reached a precision that is akin to that of the LEP precision measurements. This level of precision calls for the evaluation of the annihilation cross sections of dark matter that goes beyond tree-level calculations as currently implemented in all codes for the computation of the relic density. In supersymmetry radiative corrections are known to be large and thus must be implemented. Full one-loop radiative corrections for many annihilation processes have been performed. It is important to investigate whether the bulk of these corrections can be parameterised through an improved Born approximation that can be implemented as a selection of form factors to a tree-level code. This paper is a second in a series that addresses this issue. After having provided these form factors for the annihilation of the neutralinos into fermions, which cover the case of a bino-like LSP (Lightest Supersymmetric Particle), we turn our attention here to a higgsino-like dark matter candidate through its annihilation into $ZZ$. We also investigate the cases of a mixed LSP. In all cases we compare the performance of the form factor approach with the result of a full one-loop correction. We also study the issue of the renormalisation scheme dependence. An illustration of the phenomenon of non decoupling of the heavy sfermions that takes place for the annihilation of the lightest neutralino into $ZZ$ is also presented.

hep-ph↗

arXiv2013

One pion production in neutrino-nucleon scattering and the different parametrizations of the weak $N\rightarrowΔ$ vertex

The $N \to Δ$ weak vertex provides an important contribution to the one pion production in neutrino-nucleon and neutrino-nucleus scattering for $πN$ invariant masses below 1.4 GeV. Beyond its interest as a tool in neutrino detection and their background analyses, one pion production in neutrino-nucleon scattering is useful to test predictions based on the quark model and other internal symmetries of strong interactions. Here we try to establish a connection between two commonly used parametrizations of the weak $N \to Δ$ vertex and form factors (FF) and we study their effects on the determination of the axial coupling $C_5^A(0)$, the common normalization of the axial FF, which is predicted to hold 1.2 by using the PCAC hypothesis. Predictions for the $ν_μ p \to μ^- pπ^+$ total cross sections within the two approaches, which include the resonant $Δ^{++}$ and other background contributions in a coherent way, are compared to experimental data.

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arXiv2013

2p2h effects on the weak pion production cross section

The neutrino-nucleon --> lepton pion QE reaction on the A-target is used as a signal event or/and to reconstruct the neutrino energy, using two-body kinematics. Competition of another processes could lead to misidentification of the arriving neutrinos, being important the fake events coming from the CC1-pion background. A precise knowledge of cross sections is a prerequisite in order to make simulations in event generators to substract the fake ones from the QE countings, and in this contribution we analyze the different nuclear effects on the CC1-pion channel. Our calculations also can be extended for the NC case.

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arXiv2013

Matrix elements of four-quark operators and ΔL=2 hyperon decays

The study of neutrinoless double beta decays of nuclei and hyperons require the calculation of hadronic matrix elements of local four-quark operators that change the total charge by two units ΔQ=2 . Using a low energy effective Lagrangian that induces these transitions, we compute these hadronic matrix elements in the framework of the MIT bag model. As an illustrative example we evaluate the amplitude and transition rate of Σ- -> p e- e-, a decay process that violates lepton number by two units (ΔL=2). The relevant matrix element is evaluated without assuming the usual factorization approximation of the four-quark operators and the results obtained in both approaches are compared.

hep-ph↗

arXiv2012

Single photon production $ν_l N\rightarrow ν_l N γ$ in neutrino-nucleon scattering

The quasielastic charged current (CCQE) $ν_e n \rightarrow e^- p$ scattering is the dominant mechanism to detect appearance of a $ν_e$ in an almost $ν_μ$ flux at the 1 GeV scale. Actual experiments show a precision below 1% and between less known background contributions, but necessary to constraint the event excess, we have the radiative corrections. A consistent model recently developed for the simultaneous description of elastic and radiative $πN$ scattering, pion-photoproduction and single pion production processes, both for charged and neutral current neutrino-nucleon scattering, is extended for the evaluation of the radiative $ν_l N\rightarrow ν_l N γ$ cross section. Our results are similar to a previous (but inconsistent) theoretical evaluation in the low energy region, and show an increment in the upper region where the $Δ$ resonance becomes relevant.

nucl-th↗

arXiv2010

Analysis of one hadron rich event

In this report arguments are presented to classify this hadron rich event as an interaction event and the consequences of this statement. For instance the total invariant mass would be estimated as ~ 61 GeV/c^2 and the pair of hadrons used for height estimation have invariant mass = 2.2 GeV/c^2. Besides, tables showing the parametric and non-parametric analysis resulting in a criteria table and the resulting tables for the discrimination of $γ$ or hadron induced showers were presented at the 16th ISVHECRI, held at Batavia, USA. The main point of hadron rich and Centauro events is the identification of the nature of the observed showers. The identification and energy determination of $γ$ or hadron induced showers was made using 2 simulations. Complemented with the observation of photosensitive material under microscope it was determined that the event C16S086I037 could be classified as a hadron rich event. We used 10 reasonable scenarios for $γ$/hadron discrimination and obtained that the event is composed of 25 $γ$'s, 36 hadrons and 1 surviving and leading hadron. All these scenarios were reported at the 14th ISVHECRI, held in Weihai, China and resulted in rather constant values of physical quantities, like the mean transverse momentum of hadrons, $ $, and the mean inelasticity of $γ$-ray, $ $.

astro-ph.HE↗

arXiv2010

Evaluation of coincidence number of pairs and asymmetry parameter in nonmesonic hypernuclear decay

We develop a theoretical framework for the evaluation of the coincidence number of pairs, $N_{nN}$, and the asymmetry parameter, $a_Λ$, in nonmesonic hypernuclear decay $ΛN\rightarrow nN$. The primary nomesonic weak hyperon-nucleon decay process is described through the independent particle shell model. When the effect of the strong interactions experimented by the two nucleons leaving the residual nucleus is included, we have in addition to the $2p1h$ primary configuration $2p'1h'$, $3p2h$, $4p3h$, $\cdots$, etc secondary ones. We work within the $2p'1h'$ subspace of final states assuming a simple approach for finite nuclei based on the eikonal approximation. An optical potential including the nucleon-nucleus isoscalar and isovector interaction is introduced to take into account the minimum nuclear medium effects and to describe the nucleon-nucleus dispersion process along the outgoing path. We applied the proposed description to the calculation of the observables in $^{5}_ΛHe$ and $^{12}_ΛC$ nonmesonic decays. The calculated results show that our treatment of FSI even considered as restricted to a subspace of states gives a good agreement with experimental data, similar to that ones presented by more elaborated evaluations. This indicates that the developed theoretical scheme seems to be appropriated to include more complex configurations. We also discuss the ground state normalization effects at the moment of including the two-nucleon induced decay ($ΛNN \rightarrow nNN$) contribution.

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arXiv2007

$ΔL=2$ hyperon semileptonic decays

We compute the rates of semileptonic B_A \to B_Bl^-l^- (l=e or μ) hyperon transitions in a model where intermediate states involve loops of baryons and a Majorana neutrino. These rates turn out to be well below present experimental bounds and other theoretical estimates. From the experimental upper limit on the Ξ^- \to pμ^-μ^- decay, we derive the bound < 22 TeV for the effective Majorana mass of the muon neutrino. Also, an estimate of background contributions for these decays due to the allowed B_A \to B_Bl^-l^-\barν\barν decays are provided.

hep-ph↗

arXiv2006

A Reanalysis of the LSND Neutrino Oscillation Experiment

We reanalyse the LSND neutrino oscillation results in the framework of the Projected Quasiparticle Random Phase Approximation (PQRPA), which is the only RPA model that treats the Pauli Principle correctly, and accounts satisfactorily for great majority of the weak decay observables around 12C. We have found that the employment of the PQRPA inclusive DIF 12C(nu_e,e-)12N cross-section, instead of the CRPA used by the LSND collaboration in the (nu_mu ->nu_e) oscillations study of the 1993-1995 data sample, leads to the following: 1) the oscillation probability is increased from (0.26 +/- 0.10 +/- 0.05) percents to (0.33 +/- 0.10 +/- 0.13) percents, and 2) the previously found consistence between the (sin^2 2theta, Delta m^2) confidence level regions for the (nu_mu -> nu_e) and the (bar{nu}_mu -> bar{nu}_e) oscillations is significantly diminished. These effects are not due to the difference in the uncertainty ranges for the neutrino-nucleus cross-section, but to the difference in the cross-sections themselves.

nucl-th↗

arXiv2005

$σ$ meson exchange effect on nonmesonic hypernuclear weak decay observables

We analyze the influence of $σ$ meson exchange on the main nonmesonic hypernuclear weak decay observables: the total rate, $Γ_{NM}$, the neutron-to-proton branching ratio, $Γ_{n/p}$, and the proton asymmetry parameter, $a_Λ$. The $σ$ meson exchange is added to the standard strangeness-changing weak $ΛN\to NN$ transition potential, which includes the exchange of the complete pseudoscalar and vector mesons octet ($π$, $η$, $K$, $ρ$, $ω$, $K^*$). Using a shell model formalism, the $σ$ meson weak coupling constants are adjusted to reproduce the recent $Γ_{NM}$ and $Γ_{n/p}$ experimental data for $^5_ΛHe$. Numerical results for the remaining observables of $^5_ΛHe$ and all the observables of $^{12}_ΛC$ decays are presented. They clearly show that the addition of the $σ$ meson, in spite of improving some observables values, is not enough to reproduce simultaneously all the measurements, and the puzzle posed by the experimental data remains unexplained.

nucl-th↗

arXiv2005

Neutrino-Nucleus Reactions and Muon Capture in 12C

The neutrino-nucleus cross section and the muon capture rate are discussed within a simple formalism which facilitates the nuclear structure calculations. The corresponding formulae only depend on four types of nuclear matrix elements, which are currently used in the nuclear beta decay. We have also considered the non-locality effects arising from the velocity-dependent terms in the hadronic current. We show that for both observables in 12C the higher order relativistic corrections are of the order of ~5 only, and therefore do not play a significant role. As nuclear model framework we use the projected QRPA (PQRPA) and show that the number projection plays a crucial role in removing the degeneracy between the proton-neutron two quasiparticle states at the level of the mean field. Comparison is done with both the experimental data and the previous shell model calculations. Possible consequences of the present study on the determination of the $ν_μ->ν_e$ neutrino oscillation probability are briefly addressed.

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arXiv2003

A new Fermi smearing approach for scattering of multi-GeV electrons by nuclei

The cross section for electron scattering by nuclei at high momentum transfers is calculated within the Fermi smearing approximation (FSA), where binding effects on the struck nucleon are introduced via the relativistic Hartree approximation (RHA). The model naturally preserves current conservation, since the response tensor for an off-shell nucleon conserves the same form that for a free one but with an effective mass. Different parameterizations for the inelastic nucleon structure function, are analyzed. The smearing at the Fermi surface is introduced through a momentum distribution obtained from a perturbative nuclear matter calculation. Recent CEBAF data on inclusive scattering of 4.05 GeV electrons on $^{56}$Fe are well reproduced for all measured geometries for the first time, as is evident from the comparison with previous calculations.

nucl-th↗

arXiv2003

Unstable particles, gauge invariance and the Delta^{++} resonance parameters

The elastic and radiative pion(+)-proton scattering are studied in the framework of an effective Lagrangian model for the Delta^{++} resonance and its interactions. The finite width effects of this spin-3/2 resonance are introduced in the scattering amplitudes through a complex mass scheme to respect electromagnetic gauge invariance. The resonant pole (Delta^{++}) and background contributions (rho^0, sigma, Delta and neutron states) are separated according to the principles of the analytic S-matrix theory. The mass and width parameters of the Δ^{++} obtained from a fit to experimental data on the total cross section are in agreement with the results of a model-independent analysis based on the analytic S-matrix approach. The magnetic dipole moment determined from the radiative pion-proton scattering is mu_Delta^{++}=(6.14 +/- 0.51) nuclear magnetons.

hep-ph↗

arXiv2002

Double beta decay of sigma^- hyperons

We compute the strangeness-conserving double beta decay of $Σ^-$ hyperons, which is the only hadronic system that can undergo such decays. We consider both, the lepton number conserving %$Σ^-\go Σ^++2e^-+2 \barν$ $Σ^-\go Σ^+e^-e^-\barν\barν$ ($ββ_{Σ_{2ν}}$) and the lepton number violating $Σ^-\go Σ^+e^-e^-$ ($ββ_{Σ_{0ν}}$) modes. The branching ratios of these $ββ$ decays are suppressed at the level of $10^{-30}$ considering a light neutrino scenario in the case of the $ββ_{Σ_{0ν}}$ channel. The dynamical origin of such low rates and their possible enhancements are briefly discussed. Given its simplicity those decays can be used also for the purposes of illustrating the main features of double beta decays.

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