Search results for "ISOSCALAR"
showing 10 items of 91 documents
Neutral currents in atomic and nuclear physics
1990
Abstract The spin structure function of the proton measured by the EMC collaboration suggests an axial isoscalar neutral current for the nucleon. I study its implications for neutral current phenomena in atomic and nuclear physics. This includes parity-violating observables for transitions between hyperfine multiplets in light muonic atoms, selected inelastic neutrino nuclear reactions and the polarization asymmetry in electron scattering for isoscalar transitions. The neutrino-induced process 7 Li → 7 Li ∗ (0.478 MeV ) is particularly favourable for neutrino reactor experiments. I find that the axial isoscalar coupling extracted from the EMC measurement increases the neutrino cross section…
Exotic bcq¯q¯ four-quark states
2019
We carry out a systematic study of exotic $Q{Q}^{\ensuremath{'}}\overline{q}\overline{q}$ four-quark states containing distinguishable heavy flavors, $b$ and $c$. Different generic constituent models are explored in an attempt to extract general conclusions. The results are robust, predicting the same sets of quantum numbers as the best candidates to lodge bound states independently of the model used, the isoscalar ${J}^{P}={0}^{+}$ and ${J}^{P}={1}^{+}$ states. The first state would be strong and electromagnetic-interaction stable, while the second would decay electromagnetically to $\overline{B}D\ensuremath{\gamma}$. Isovector states are found to be unbound, preventing the existence of ch…
Break-up and Coherent Photoproduction ofηMesons on the Deuteron
1997
We present new break-up and coherent data for $\ensuremath{\eta}$ meson photoproduction on the deuteron, using a deuterium target and tagged bremsstrahlung photons up to 1 GeV. The differential cross sections for the coherent process were measured from threshold to 800 MeV. They are much smaller than those previously reported. The break-up channel provides a direct measurement of the neutron to proton differential cross section ratios. At the ${S}_{11}(1535)$ resonance peak, ${\ensuremath{\sigma}}_{n}/{\ensuremath{\sigma}}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.68\ifmmode\pm\else\textpm\fi{}0.06$ leading to an isoscalar to isovector amplitude ratio of ${A}_{s}{/A}_{\ensurem…
Chiral symmetry amplitudes in the S-wave isoscalar and isovector channels and the σ, f[sub 0](980), a[sub 0](980) scalar mesons
1998
We use a nonperturbative approach which combines coupled channel Lippmann Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the σ, f0 and a0 resonances. The ππ→ππ, ππ→KK phase shifts and inelasticities in the T=0 scalar channel are well reproduced as well as the π0η and KK mass distributions in the T=1 channel. Furthermore, the total and partial decay widths of the f0 and a0 resonances are properly reproduced. The results seem to indicate that chiral symmetry constraint…
DOUBLY CHARMED MESONS
2010
Doubly charmed mesons are studied within a quark model framework. We solve the four-quark Schor\"dinger equation by means of a variational approach by using different interacting potentials. Our results point to the existence of a stable isoscalar doubly charmed four-quark meson with quantum numbers $J^P=1^+$.
Dispersive Evaluation of the Inner Radiative Correction in Neutron and Nuclear $\beta$-decay
2019
We propose a novel dispersive treatment of the so-called inner radiative correction to the neutron and nuclear $\beta$-decay. We show that it requires knowledge of the parity-violating structure function $F_3^{(0)}$ that arises from the interference of the axial vector charged current and the isoscalar part of the electromagnetic current. By isospin symmetry, we relate this structure function to the charged current inelastic scattering of neutrinos and antineutrinos. Applying this new data-driven analysis we obtain a new, more precise evaluation for the universal radiative correction $\Delta_{R}^{V,\,new}=0.02467(22)$ that supersedes the previous estimate by Marciano and Sirlin, $\Delta_R^V…
AN OPERATOR PRODUCT EXPANSION ANALYSIS OF e+e-ANNIHILATION DATA
2013
Perturbative Quantum Chromodynamics combined with the operator product expansion is expected to provide a framework for the description of phenomena in hadron interactions including contributions of nonperturbative origin. Applied to the correlator of two electromagnetic currents, this framework can be confronted with e+e-annihilation into hadrons. Data from the total hadronic e+e-cross-section have become much more precise in recent years and the power corrections in the operator product expansion, i.e. the vacuum condensates are expected to be determined with higher precision than previously. We present an analysis of the condensates of dimensions d = 2, 4 and 6 and find reasonably stable…
Microscopic s-wave optical potential for slow pions scattered by a nucleus.
1989
We have done a microscopic calculation of the {ital s}-wave optical potential for the pion-nucleus system at low energies, 0{le}{ital T}{sub {pi}}{le}100 MeV, using a description based on hadronic degrees of freedom. We have obtained, separately, the real and imaginary parts of the optical potential coming from one-body and two-body processes. We have also separated the imaginary part of the potential associated to absorption and to quasielastic channels. We find that the imaginary part of the absorption channel is independent of the energy (within the range of energies considered here) in agreement with a recent empirical determination. We compare our results with phenomenological potentia…
Prediction of hidden charm strange molecular baryon states with heavy quark spin symmetry
2019
We have studied the meson-baryon $S-$wave interaction, using coupled channels, in the isoscalar hidden-charm strange sector and $J^P = 1/2^-,3/2^-$ and $5/2^-$. We impose constraints of heavy quark spin symmetry in the interaction and obtain the non vanishing matrix elements from an extension of the local hidden gauge approach to the charm sector. The ultraviolet divergences are renormalized using the same meson-baryon-loops regulator previously employed in the non-strange hidden charm sector, where a good reproduction of the properties of the newly discovered pentaquark states is obtained. We obtain five states of $1/2^-$, four of $3/2^-$ and one of $5/2^-$, which could be compared in the …
Nuclear matrix elements for0νββdecays with light or heavy Majorana-neutrino exchange
2015
We compute the nuclear matrix elements (NMEs) corresponding to the neutrinoless double beta ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) decays of nuclei which attract current experimental interest. We concentrate on ground-state-to-ground-state decay transitions mediated by light (l-NMEs) or heavy (h-NMEs) Majorana neutrinos. The computations are done in realistic single-particle model spaces using the proton-neutron quasiparticle random-phase approximation (pnQRPA) with two-nucleon interactions based on the Bonn one-boson-exchange $G$ matrix. Both the l-NMEs and the h-NMEs include the appropriate short-range correlations, nucleon form factors, and higher-order nucleonic weak …