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L. Roca

Publications and source records attributed to L. Roca.

85 records · Page 5Linked to original sources
arXiv2004

Unitary chiral dynamics in $J/Ψ$ decays into $VPP$ and the role of the scalar mesons

We make a theoretical study of the $\J$ decays into $ωππ$, $ϕππ$, $ωK \bar{K}$ and $ϕK\bar{K}$ using the techniques of the chiral unitary approach stressing the important role of the scalar resonances dynamically generated through the final state interaction of the two pseudoscalar mesons. We also discuss the importance of new mechanisms with intermediate exchange of vector and axial-vector mesons and the role played by the OZI rule in the $\Jϕππ$ vertex, quantifying its effects. The results nicely reproduce the experimental data for the invariant mass distributions in all the channels considered.

hep-ph↗
arXiv2004

Decay of axial-vector mesons into VP and P$γ$

We propose a phenomenological Lagrangian for the decay of the SU(3) nonets of the axial-vector mesons of $J^{PC}=1^{+-},1^{++}$ into a vector meson and a pseudoscalar constructed with tensor fields for the vector and axial-vector mesons. The formulation leads to a good reproduction of the different decay branching ratios and assuming vector meson dominance (VMD) it also leads to good results for the radiative decay of the $a_1$ into pion and photon, and in agreement with the structure proposed in the chiral tensor formulation of radiative decay of axial-vector mesons. The two SU(3) parameters and the mixing angle of $K_{1A}$ and $K_{1B}$ needed to give the physical $K_1(1270)$ and $K_1(1400)$ resonances are also determined.

hep-ph↗
arXiv2004

Unitary chiral dynamics in J/Psi to VPP decays and the role of scalar mesons

We make a theoretical study of the J/Psi decays into ωππ, ϕππ, ωK \bar{K} and ϕK\bar{K} using the techniques of the chiral unitary approach stressing the important role of the scalar resonances dynamically generated through the final state interaction of the two pseudoscalar mesons. We also discuss the importance of new mechanisms with intermediate exchange of vector and axial-vector mesons and the role played by the OZI rule in the J/Ψϕππvertex, quantifying its effects. The results nicely reproduce the experimental data for the invariant mass distributions in all the channels considered.

hep-ph↗
arXiv2003

Mass dependence of inclusive nuclear $ϕ$ photoproduction

Based on a prior determination of the $ϕ$ selfenergy in a nuclear medium we perform a theoretical study of inclusive $ϕ$ photoproduction in nuclei, looking at the $A$ dependence of the cross sections for different $ϕ$ momenta. We find sizeable reductions in the nuclear cross sections with respect to the elementary one, using a $ϕ$ selfenergy which implies a width about six times the free one at normal nuclear density. The calculations are done to match the set up for an ongoing experiment at {\it SPring8/Osaka} which should provide valuable information on the renormalization of the $ϕ$ properties in nuclei.

nucl-th↗
arXiv2003

Sequential vector and axial-vector meson exchange and chiral loops in radiative phi decay

We study the radiative $ϕ$ decay into $π^0 π^0 γ$ and $π^0 ηγ$ taking into account mechanisms in which there are two sequential vector-vector-pseudoscalar or axial-vector--vector--pseudoscalar steps followed by the coupling of a vector meson to the photon, considering the final state interaction of the two mesons. There are other mechanisms in which two kaons are produced through the same sequential mechanisms or from $ϕ$ decay into two kaons and then undergo final state interaction leading to the final pair of pions or $π^0 η$, this latter mechanism being the leading one. The results of the parameter free theory, together with the theoretical uncertainties, are compared with the latest experimental results of KLOE at Frascati.

hep-ph↗
arXiv2003

$η\to π^0 γγ$ decay within unitarized chiral perturbation theory

We improve the calculations of the $η\to π^0 γγ$ decay within the context of meson chiral lagrangians. We use a chiral unitary approach for the meson-meson interaction, thus generating the $a_0(980)$ resonance and fixing the longstanding sign ambiguity on its contribution. This also allows us to calculate the loops with one vector meson exchange, thus removing a former source of uncertainty. In addition we ensure the consistency of the approach with other processes. First, by using vector meson dominance couplings normalized to agree with radiative vector meson decays. And, second, by checking the consistency of the calculations with the related $γγ\to π^0 η$ reaction. We find an $η\to π^0 γγ$ decay width of $0.47\pm 0.10$ eV, in clear disagreement with published data but in remarkable agreement with the most recent measurement.

hep-ph↗
arXiv2003

The $(π^-,γγ)$ reaction in nuclei and the $σ$ meson in the medium

A theoretical analysis of the $(π^-,γγ)$ reaction in nuclei is made in order to find the viability of this reaction to test modifications of the $σ$ meson mass in nuclear matter. The $ππ$ correlation in the scalar-isoscalar channel in nuclear matter could, in principle, manifest itself in this reaction since it plays an important role in the $ππ\toγγ$ mechanism. But we conclude that this effect is hardly visible in this reaction due to the strong background of the pion-Bremsstrahlung terms. Only with some special cuts and for some polarization states are the effect visible at the cost of a strong reduction in the cross section.

nucl-th↗
arXiv2002

The $σ$ meson in a nuclear medium through two pion photoproduction

We present theoretical results for $(γ, π^0 π^0)$ production on nucleons and nuclei in the kinematical region where the scalar isoscalar $ππ$ amplitude is influenced by the $σ$ pole. The final state interaction of the pions modified by the nuclear medium produces a spectacular shift of strength of the two pion invariant mass distribution induced by the moving of the $σ$ pole to lower masses and widths as the nuclear density increases.

nucl-th↗
arXiv2002

The sigma meson in a nuclear medium through two pion photoproduction

We present theoretical results for (gamma,pi0 pi0) and (gamma,pi+- pi0) production on nucleons and nuclei in the kinematical region where the scalar isoscalar pi pi amplitude is influenced by the sigma pole. The final state interaction of the pions modified by the nuclear medium produces a spectacular shift of strength of the pi0 pi0 invariant mass distribution induced by the moving of the sigma pole to lower masses and widths as the nuclear density increases.

nucl-th↗
arXiv2001

Two pion photoproduction on nucleons and nuclei in the rho and sigma regions

In this talk we report on two physical processes, the photoproduction of $ρ$ mesons in nuclei and the $π^0 π^0$ photoproduction in nuclei at low energies. In the first case the aim is to observe experimentally the theoretically predicted changes on the $ρ$ properties in the nuclear medium. In the second case one wishes to investigate the modifications of the $ππ$ interaction in the nuclear medium in the region of the $σ$ meson. In the first case we observe that it is quite difficult to see large effects due to the $ρ$ modification in the medium because the detection of the $ρ$ is done through the two pions which are produced in the $Δ$ region and are largely distorted in the medium. In the second case, when the I=0 part of the $ππ$ interaction is substituted by the in medium $ππ$ amplitude, we observe a very large shift of strength in the invariant mass distribution to small values of the mass in $^{12}C$ and $^{208}Pb$ with respect to the distribution of the elementary reaction. This spectacular shift appears to be corroborated by recent experiments at Mainz reported in this same Workshop.

nucl-th↗
arXiv2001

How different Fermi surface maps emerge in photoemission from Bi2212

We report angle-resolved photoemission spectra (ARPES) from the Fermi energy ($E_F$) over a large area of the ($k_x,k_y$) plane using 21.2 eV and 32 eV photons in two distinct polarizations from an optimally doped single crystal of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi2212), together with extensive first-principles simulations of the ARPES intensities. The results display a wide-ranging level of accord between theory and experiment and clarify how myriad Fermi surface (FS) maps emerge in ARPES under various experimental conditions. The energy and polarization dependences of the ARPES matrix element help disentangle primary contributions to the spectrum due to the pristine lattice from those arising from modulations of the underlying tetragonal symmetry and provide a route for separating closely placed FS sheets in low dimensional materials.

cond-mat.supr-con↗
arXiv2001

The role of Delta(1700) excitation and rho production in double pion photoproduction

Recent information on invariant mass distributions of the $γp\toπ^+π^0 n$ reaction, where previous theoretical models had shown deficiencies, have made more evident the need for new mechanisms, so far neglected or inaccurately included. We have updated a previous model to include new necessary mechanisms. We find that the production of the $ρ$ meson, and the $Δ(1700)$ excitation, through interference with the dominant terms, are important mechanisms that solve the puzzle of the $γp\toπ^+π^0 n$ reaction without spoiling the early agreement with the $γp\toπ^+π^- p$ and $γp\toπ^0π^0 p$ reactions.

nucl-th↗