Search results for "nucl-th"
showing 10 items of 1223 documents
Looking for a hidden-charm pentaquark state with strangeness $S=-1$ from $��^-_b$ decay into $J/��K^- ��$
2015
Assuming that the recently observed hidden-charm pentaquark state, $P_c(4450)$, is of molecular nature as predicted in the unitary approach, we propose to study the decay of $��^-_b\rightarrow J/��K^- ��$ to search for the strangeness counterpart of the $P_c(4450)$. There are three ingredients in the decay mechanism: the weak decay mechanism, the hadronization mechanism, and the finite state interactions in the meson-baryon system of strangeness $S=-2$ and isospin $I=1/2$ and of the $J/����$. All these have been tested extensively. As a result, we provide a genuine prediction of the differential cross section where a strangeness hidden-charm pentaquark state, the counterpart of the $P_c(445…
The model-discriminating power of lepton flavor violating tau decays
2014
Within an effective field theory framework, we discuss the possibility to discriminate among different operators that contribute to lepton flavor violating (LFV) tau decays. Correlations among decay rates in different channels are shown to provide a basic handle to unravel the origin of LFV in these processes. More information about the underlying dynamics responsible for LFV can be gathered from differential distributions in three-body decays like tau -> mu pi pi or tau -> 3 mu: these are considered in some detail. We incorporate in our analysis recent developments in the determination of the hadronic form factors for tau -> mu pi pi. Future prospects for the observation of LFV ta…
Anomalous f(1) exchange in vector meson photoproduction asymmetries
2000
We perform an analysis of the elastic production of vector mesons with polarized photon beams at high energy in order to investigate the validity of a recently proposed dynamical mechanism based on the dominance of the f_1 trajectory at large momentum transfer. The density matrix characterizing the angular distributions of the vector meson decays is calculated within an exchange model which includes the Pomeron and the f_1. The asymmetries of these decays turn out to be very useful to disentangle the role of these exchanges since their effect depends crucially on their quantum numbers which are different. The observables analyzed are accessible with present experimental facilities.
Neutrino Induced Coherent Pion Production off Nuclei and PCAC
2009
We review the Rein--Sehgal model and criticize its use for low energy neutrino induced coherent pion production. We have studied the validity of the main approximations implicit in that model, trying to compare with physical observables when that is possible and with microscopical calculations. Next, we have tried to elaborate a new improved model by removing the more problematic approximations, while keeping the model still reasonably simple. Last, we have discussed the limitations intrinsic to any approach based on the partial conservation of the axial current hypothesis. In particular, we have shown the inability of such models to determine the angular distribution of the outgoing pion w…
Faddeev fixed-center approximation to the $N\bar{K}K$ system and the signature of a $N^*(1920)(1/2^+)$ state
2010
We perform a calculation for the three body $N \bar{K} K$ scattering amplitude by using the fixed center approximation to the Faddeev equations, taking the interaction between $N$ and $\bar{K}$, $N$ and $K$, and $\bar{K}$ and $K$ from the chiral unitary approach. The resonant structures show up in the modulus squared of the three body scattering amplitude and suggest that a $N\bar{K}K$ hadron state can be formed. Our results are in agreement with others obtained in previous theoretical works, which claim a new $N^*$ resonance around 1920 MeV with spin-parity $J^P=1/2^+$. The existence of these previous works allows us to test the accuracy of the fixed center approximation in the present pro…
Small-$x$ Quark and Gluon Helicity Contributions to the Proton Spin Puzzle
2023
A small-$x$ helicity evolution has been derived in 2016-18 and received an important modification in 2022. This proceedings discusses the setup and summarizes recent results of the theoretical development, including the asymptotic behavior of helicity PDFs and $g_1$ structure function at small $x$. The recent fits to various polarized scattering data are also discussed, together with similar calculations that follow from the same framework. The results from this research program will provide important theoretical inputs for the future polarized small-$x$ measurements at the electron-ion collider (EIC).
Exclusive semileptonic decays of ground-state $cb$ baryons driven by a $c\to s,d$ quark transition
2012
We evaluate semileptonic decays of spin-1/2 and spin-3/2 doubly heavy $cb$ baryons. The decays are driven by a $c\to s,d$ transition at the quark level. We check our results for the form factors against heavy quark spin symmetry constraints obtained in the limit of very large heavy quark masses and near zero recoil.
The low lying scalar resonances in the D0 decays into K0s and f0(500), f0(980), a0(980)
2014
The $D^0$ decay into $K^0_s$ and a scalar resonance, $f_0(500)$, $f_0(980)$, $a_0(980)$, is studied obtaining the scalar resonances from final state interaction of a pair of mesons produced in a first step in the $D^0$ decay into $K^0_s$ and the pair of pseudoscalar mesons. This weak decay is very appropriate for this kind of study because it allows to produce the three resonances in the same decay in a process that is Cabibbo allowed, hence the rates obtained are large compared to those of $\bar{B}^0$ decays into $J/\psi$ and a scalar meson that have at least one Cabibbo suppressed vertex. Concretely the $a_0(980)$ production is Cabibbo allowed here, while it cannot be seen in the $\bar{B}…
Statistical analysis of beta decays and the effective value of g_A in the proton-neutron quasiparticle random-phase approximation framework
2016
We perform a Markov Chain Monte Carlo (MCMC) statistical analysis of a number of measured ground-state-to-ground-state single $\beta^+$/electron-capture and $\beta^-$ decays in the nuclear mass range A = 62 - 142. The corresponding experimental comparative half-lives (log ft values) are compared with the theoretical ones obtained by the use of the proton-neutron quasiparticle random-phase approximation (pnQRPA) with G-matrix based effective interactions. The MCMC analysis is performed separately for 47 isobaric triplets and 28 more extended isobaric chains of nuclei to extract values and uncertainties for the effective axial-vector coupling constant g_A in nuclear-structure calculations per…
Sequential single pion production explaining the dibaryon "d*(2380)" peak*
2023
We study the two step sequential one pion production mechanism, $np(I=0)\to \pi^-pp$, followed by the fusion reaction $pp\to \pi^+d$, in order to describe the $np\to \pi^+\pi^-d$ reaction with $\pi^+\pi^-$ in $I=0$, where a narrow peak, so far identified with a "$d(2380)$" dibaryon, has been observed. We find that the second step $pp\to \pi^+d$ is driven by a triangle singularity that determines the position of the peak of the reaction and the large strength of the cross section. The combined cross section of these two mechanisms produce a narrow peak with the position, width and strength compatible with the experimental observation within the approximations done. This novel interpretation …