Semileptonic decay of Bc−B^{-}_c into X(3930)X(3930), X(3940)X(3940), X(4160)X(4160)

We study the semileptonic decay of $B^{-}_c$ meson into $\bar{\nu} l^-$ and the isospin zero $X(3930)~(2^{++})$, $X(3940)~(0^{++})$, $X(4160)~(2^{++})$ resonances. We look at the reaction from the perspective that these resonaces appear as dynamically generated from the vector-vector interaction in the charm sector, and couple strongly to $D^{*}\bar{D^{*}}$ and $D^{*}_{s}\bar{D_{s}^{*}}$. We also look into the $B^{-}_c \rightarrow \bar{\nu}_{l} l^- D^{*}\bar{D^{*}}$ and $B^{-}_c \rightarrow \bar{\nu}_{l} l^- D^{*}_{s}\bar{D_{s}^{*}}$ reactions close to threshold and relate the $D^{*}\bar{D^{*}}$ and $D^{*}_{s}\bar{D_{s}^{*}}$ mass distribution to the rate of production of the $X$ resonances.Comment: 7 pages, 9 figure

Collision integral with momentum-dependent potentials and its impact on pion production in heavy-ion collisions

The momentum dependence of the nucleon mean-field potential in a wide momentum range can be an important factor to determine the $\Delta$ resonance and pion production in intermediate-energy heavy-ion collisions. In particular, in neutron-rich systems such as ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ collisions, we need to carefully treat the momentum dependence because the neutron and proton potentials can have different momentum dependence, as characterized at low momenta by effective masses. In the present work, we rigorously calculate the collision terms of $NN \leftrightarrow N \Delta$ and $\Delta \leftrightarrow N \pi$ processes with the precise conservation of energy and momentum under the presence of momentum-dependent potentials for the initial and final particles of the process. The potentials affect not only the threshold condition for the process but also the cross section in general as a function of the momenta of the initial particles, which is treated in a natural way in the present work. Calculations are performed by combining the nucleon dynamics obtained by the antisymmetrized molecular dynamics (AMD) model with a newly developed transport code which we call sJAM. The calculated results for central ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ collisions at 270 MeV/nucleon clearly show that the momentum dependence of the neutron and proton potentials has a significant impact on the $NN \to N \Delta$ process, and this information is strongly reflected in the charged pion ratio ($\pi^-/\pi^+$). We also investigate the effects of the high-density symmetry energy and the isovector part of the potential of $\Delta$ resonances on pion production, which we find are relatively small compared to the effect of the momentum dependence of the neutron and proton potentials.Comment: 18 pages, 13 figures, 1 tabl

Probing neutron-proton dynamics by pions

In order to investigate the nuclear symmetry energy at high density, we study the pion production in central collisions of neutron-rich nuclei ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ at 300 MeV/nucleon using a new approach by combining the antisymmetrized molecular dynamics (AMD) and a hadronic cascade model (JAM). The dynamics of neutrons and protons is solved by AMD, and then pions and $\Delta$ resonances in the reaction process are handled by JAM. We see the mechanism how the $\Delta$ resonance and pions are produced reflecting the dynamics of neutrons and protons. We also investigate the impacts of cluster correlations as well as of the high-density symmetry energy on the nucleon dynamics and consequently on the pion ratio. We find that the $\Delta^-/\Delta^{++}$ production ratio agrees very well with the neutron-proton squared ratio $(N/Z)^2$ in the high-density and high-momentum region. We show quantitatively that $\Delta$ production ratio, and therefore $(N/Z)^2$, are directly reflected in the $\pi^-/\pi^+$ ratio, with modification in the final stage of the reaction.Comment: 14 pages, 10 figures; Figures 3-8 are updated with corrected numerical results. No change in the main conclusion

η′\eta^\prime meson under partial restoration of chiral symmetry in nuclear medium

In-medium modification of the eta' mass is discussed in the context of partial restoration of chiral symmetry in nuclear medium. We emphasize that the U_A(1) anomaly effects causes the eta'-eta mass difference necessarily through the chiral symmetry breaking. As a consequence, the eta' mass is expected to be reduced by order of 100 MeV in nuclear matter where about 30% reduction of chiral symmetry takes place. The strong attraction relating to the eta' mass generation eventually implies that there should be also a strong attractive interaction in the scalar channel of the eta'-N two-body system. We find that the attraction can be strong enough to form a bound state.Comment: 4 pages, 3 figures. Talk given at the XI International Conference on Hypernuclear and Strange Particle Physics (HYP2012), Oct. 1-5, 2012, Barcelona, Spain. Accepted version. Some typos were correcte

Theoretical study of the D0→K−π+ηD^0 \to K^- \pi^+ \eta reaction

We develop a model to study the $D^0 \to K^- \pi^+ \eta$ weak decay, starting with the color favored external emission and Cabibbo favored mode at the quark level. A less favored internal emission decay mode is also studied as a source of small corrections. Some pairs of quarks are allowed to hadronize producing two pseudoscalar mesons, which posteriorly are allowed to interact to finally provide the $K^- \pi^+ \eta$ state. The chiral unitary approach is used to take into account the final state interaction of pairs of mesons, which has as a consequence the production of the $\kappa$ ($K^*_0(700)$) and the $a_0(980)$ resonances, very well visible in the invariant mass distributions. We also introduce the $\bar{K}^{*0} \eta$ production in a phenomenological way and show that the $s$-wave pseudoscalar interaction together with this vector excitation mode are sufficient to provide a fair reproduction of the experimental data. The agreement with the data, in particular the relative weight of the $a_0(980)$ to the $\kappa$ excitation, provides extra support to the picture used, in which these two resonances are a consequence of the interaction of pseudoscalar mesons and not ordinary $q \bar{q}$ mesons.Comment: 13 pages, 13 Figure

Role of f0(980)f_0(980) and a0(980)a_0(980) in the B−→π−K+K−B^- \to \pi ^- K^+ K^- and B−→π−K0Kˉ0B^- \to \pi ^- K^0 \bar K^0 reactions

In this work we study the role of the $f_0(980)$ and $a_0(980)$ resonances in the low $K ^{+} K^{-}$ and $K^0 \bar K^0$ invariant-mass region of the $B^- \to \pi ^- K^+ K^-$ and $B^- \to \pi ^- K^0 \bar K^0$ reactions. The amplitudes are calculated by using the chiral unitary $\rm SU(3)$ formalism, in which these two resonances are dynamically generated from the unitary pseudocalar-pseudoscalar coupled-channel approach. The amplitudes are then used as input in the evaluation of the mass distributions with respect to the $K^{+}K^{-}$ and $K^{0}\bar K^{0}$ invariant-masses, where the contributions coming from the $I=0$ and $I=1$ components are explicitly assessed. Furthermore, the contribution of the $K^{\ast }(892)^0 K^-$ production and its influence on the $\pi^{-} K^+$ and $K^{+} K^-$ systems are also evaluated, showing that there is no significant strength for small $K^{+} K^-$ invariant mass. Lastly, the final distributions of $M_{\rm inv}^2( K^{\pm}K^{\mp} )$ for the $B^{\mp} \to \pi ^{\mp} K^{\pm}K^{\mp}$ reactions are estimated and compared with the LHCb data. Our results indicate that the $I=0$ component tied to the $f_0(980)$ excitation generates the dominant contribution in the range of low $K ^{+} K^{-}$ invariant-mass.Comment: 11 pages, 10 figure