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Natsumi Ikeno

Publications and source records attributed to Natsumi Ikeno.

At least 37 records · Page 2Linked to original sources
arXiv2022

$Z_{cs}$ states from the $D^{*}_s \bar D^*$ and $J/ψK^*$ coupled channels: Signal in $B^+ \to J/ψϕK^+$ decay

We study the $D^{*}_s \bar D^*$ system in connection with the $J/ψK^*$ in coupled channels and observe that, within reasonable values of the cut-off used to regularize the loops, the system does not develop a bound state. However, the $J^P = 2^+$ channel has enough attraction to create a strong cusp structure that shows up in the $J/ψK^+$ invariant mass distribution in the $B^+ \to J/ψϕK^+$ decay at the $D^*_s \bar D^*$ threshold. Such structure is visible in the experimental $B^+ \to J/ψϕK^+$ and $\bar B^0 \to J/ψK^+ K^-$ decays, with small statistics, and our results should stimulate further measurements around this region, given the fact that cusp effects provide as valuable information on hadron dynamics as resonances themselves.

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arXiv2021

Triangle singularity mechanism for the $pp \to π^+ d$ fusion reaction

We develop a model for the $pp \to π^+ d$ reaction based on the $pp \to Δ(1232) N$ transition followed by $Δ(1232) \to πN'$ decay and posterior fusion of $N N'$ to give the deuteron. We show that the triangle diagram depicting this process develops a triangle singularity leading to a large cross section of this reaction compared to ordinary fusion reactions. The results of the calculation also show that the process is largely dominated by the $pp$ system in $L=2, S=0$, which transfers $J=2$ to the final $π^+ d$ system. This feature is shown to be well suited to provide $L=2,S=1$, $J^\mathrm{tot}=3$ for $np$ in the $np(I=0) \to π^- pp$ followed by $pp \to π^+ d$ reaction, which has been proposed recently, as a means of describing the so far assumed dibaryon $d^*(2380)$ peak.

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arXiv2021

Structure of double pionic atoms

We study theoretically the structure of double pionic atoms, in which two negatively charged pions ($π^-$) are bound in the atomic orbits. The double pionic atom is considered to be an interesting system from the point of view of the multi bosonic systems. In addition, it could be possible to deduce valuable information on the isospin $I = 2$ $ππ$ interaction and the pion-nucleus strong interaction. In this paper, we take into account the $ππ$ strong and electromagnetic interactions, and evaluate the effects on the binding energies by perturbation theory for the double pionic atoms in heavy nuclei. We investigate several combinations of two pionic states and find that the order of magnitude of the energy shifts due to the $ππ$ interaction is around 10 keV for the strong interaction and around 100 keV for the electromagnetic interaction for the ground states.

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arXiv2021

The $Z_{cs}(3985)$ as a threshold effect from the $\bar D_s^* D + \bar D_s D^*$ interaction

We study the $e^+ e^- \to K^+ ( D_s^{*-} D^0 + D_s^- D^{*0})$ reaction recently measured at BESIII, from where a new $Z_{cs}$ state has been reported. We study the interaction of $\bar D_s D^*$ with the coupled channels $J/ψK^-$, $K^{*-} η_c$, $D_s^- D^{*0}$, $D_s^{*-} D^0$ by means of an extension to the charm sector of the local hidden gauge approach. We find that the $D_s^- D^{*0}+ D_s^{*-} D^0$ combination couples to $J/ψK^-$ and $K^{*-} η_c$, but the $D_s^- D^{*0}- D_s^{*-} D^0$ combination does not. The coupled channels help to build up strength in the $D_s^- D^{*0}+ D_s^{*-} D^0$ diagonal scattering matrix close to threshold and, although the interaction is not strong enough to produce a bound state or resonance, it is sufficient to produce a large accumulation of strength at the $\bar D_s D^*$ threshold in the $e^+ e^- \to K^+ ( D_s^{*-} D^0 + D_s^- D^{*0})$ reaction in agreement with experiment.

hep-ph↗
arXiv2021

Combined theoretical study of the $D^+ \to π^+ ηη$ and $D^+ \to π^+ π^0 η$ reactions

We study the $D^+ \to π^+ ηη$ and $D^+ \to π^+ π^0 η$ reactions, which are single Cabibbo suppressed and can proceed both through internal and external emission. The primary mechanisms at quark level are considered, followed by hadronization to produce three mesons in the $D^+$ decay, and after that the final state interaction of these mesons leads to the production of the $a_0(980)$ resonance, seen in the $π^+ η$, $π^0 η$ mass distributions. The theory has three unknown parameters to determine the shape of the distributions and the ratio between the $D^+ \to π^+ ηη$ and $D^+ \to π^+ π^0 η$ rates. This ratio restricts much the sets of parameters but there is still much freedom leading to different shapes in the mass distributions. We call for a measurement of these mass distributions that will settle the reaction mechanism, while at the same time provide relevant information on the way that the $a_0(980)$ resonance is produced in the reactions.

hep-ph↗
arXiv2020

Symmetry energy investigation with pion production from Sn+Sn systems

In the past two decades, pions created in the high density regions of heavy ion collisions have been predicted to be sensitive at high densities to the symmetry energy term in the nuclear equation of state, a property that is key to our understanding of neutron stars. In a new experiment designed to study the symmetry energy, the multiplicities of negatively and positively charged pions have been measured with high accuracy for central $^{132}$Sn+$^{124}$Sn, $^{112}$Sn+$^{124}$Sn, and $^{108}$Sn+$^{112}$Sn collisions at $E/A=270~\mathrm{MeV}$ with the S$π$RIT Time Projection Chamber. While the uncertainties of individual pion multiplicities are measured to 4\%, those of the charged pion multiplicity ratios are measured to 2\%. We compare these data to predictions from seven major transport models. The calculations reproduce qualitatively the dependence of the multiplicities and their ratios on the total neutron to proton number in the colliding systems. However, the predictions of the transport models from different codes differ too much to allow extraction of reliable constraints on the symmetry energy from the data. This finding may explain previous contradictory conclusions on symmetry energy constraints obtained from pion data in Au+Au system. These new results call for better understanding of the differences among transport codes, and new observables that are more sensitive to the density dependence of the symmetry energy.

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arXiv2020

Theoretical study of the $D^0 \to K^- π^+ η$ reaction

We develop a model to study the $D^0 \to K^- π^+ η$ 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 $K^- π^+ η$ 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 $κ$ ($K^*_0(700)$) and the $a_0(980)$ resonances, very well visible in the invariant mass distributions. We also introduce the $\bar{K}^{*0} η$ 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 $κ$ 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.

hep-ph↗
arXiv2020

Molecular picture for the $Ω(2012)$ revisited

We conduct a study of the interaction of the $\bar K Ξ^*$, $ηΩ$($s$-wave) and $\bar K Ξ$($d$-wave) channels within a coupled channel unitary approach where the transition potential between the $\bar K Ξ^*$ and $ηΩ$ channels is obtained from chiral Lagrangians. The transition potential between $\bar K Ξ^*$, $ηΩ$ and $\bar K Ξ$ is taken in terms of free parameters, which together with a cut off to regularize the meson-baryon loops are fitted to the $Ω(2012)$ data. We find that all data including the recent Belle experiment on $Γ_{Ω^* \to π\bar K Ξ}/ Γ_{Ω^* \to \bar K Ξ}$, are compatible with the molecular picture stemming from meson baryon interaction of these channels.

hep-ph↗
arXiv2020

Effects of Pauli blocking on pion production in central collisions of neutron-rich nuclei

Pauli blocking is carefully investigated for the processes of $NN \rightarrow N Δ$ and $Δ\rightarrow N π$ in heavy-ion collisions, aiming at a more precise prediction of the $π^-/ π^+$ ratio which is an important observable to constrain the high-density symmetry energy. We use the AMD+JAM approach, which combines the antisymmetrized molecular dynamics for the time evolution of nucleons and the JAM model to treat processes for $Δ$ resonances and pions. As is known in general transport-code simulations, it is difficult to treat Pauli blocking very precisely due to unphysical fluctuations and additional smearing of the phase-space distribution function, when Pauli blocking is treated in the standard method of JAM. We propose an improved method in AMD+JAM to use the Wigner function precisely calculated in AMD as the blocking probability. Different Pauli blocking methods are compared in heavy-ion collisions of neutron-rich nuclei, ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$, at 270 MeV/nucleon. With the more accurate method, we find that Pauli blocking is stronger, in particular for the neutron in the final state in $NN \rightarrow N Δ$ and $ Δ\to Nπ$, compared to the case with a proton in the final state. Consequently, the $π^-/π^+$ ratio becomes higher when the Pauli blocking is improved, the effect of which is found to be comparable to the sensitivity to the high-density symmetry energy.

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arXiv2020

$Υ(nl)$ decay into $ B^{(*)} \bar B^{(*)}$

We have evaluated the decay modes of the $Υ(4s), Υ(3d), Υ(5s), Υ(6s)$ states into $B\bar B, B\bar B^*+c.c., B^* \bar B^*, B_s \bar B_s, B_s \bar B^*_s +c.c., B^*_s \bar B_s^* $ using the $^3P_0$ model to hadronize the $b\bar b$ vector seed, fitting some parameters to the data. We observe that the $Υ(4s)$ state has an abnormally large amount of meson-meson components in the wave function, while the other states are largely $b\bar b$. We predict branching ratios for the different decay channels which can be contrasted with experiment for the case of the $Υ(5s)$ state. While globally the agreement is fair, we call the attention to some disagreement that could be a warning for the existence of more elaborate components in the state.

hep-ph↗
arXiv2019

Comparison of heavy-ion transport simulations: Collision integral with pions and $Δ$ resonances in a box

We compare ten transport codes for a system confined in a box, aiming at improved handling of the production of $Δ$ resonances and pions, which is indispensable for constraining high-density symmetry energy from observables such as the $π^-/π^+$ yield ratio in heavy-ion collisions. The system in a box is initialized with nucleons at saturation density and at 60 MeV temperature. The reactions $NN\leftrightarrow NΔ$ and $Δ\leftrightarrow Nπ$ are implemented, but the Pauli blocking and the mean-field potential are deactivated in the present comparison. Results are compared to those from the two reference cases of a chemically equilibrated ideal gas mixture and of the rate equation. In the results of the numbers of $Δ$ and $π$, deviations from the reference values are observed in many codes, and they depend significantly on the size of the time step. These deviations are tied to different ways in ordering the sequence of collisions and decays, that take place in the same time step. Better agreements are seen in the reaction rates and the number ratios among the isospin species of $Δ$ and $π$. These are, however, affected by the correlations, which are absent in the Boltzmann equation, but are induced by the way particle scatterings are treated in transport calculations. The uncertainty in the transport-code predictions of the $π^-/π^+$ ratio for the system initialized at n/p = 1.5, after letting the existing $Δ$ resonances decay, is found to be within a few percent, which is sufficiently small so that it does not strongly impact constraining the high-density symmetry energy from heavy-ion collisions. Most of the sources of uncertainties have been understood, and individual codes may be further improved. This investigation will be extended in the future to heavy-ion collisions to ensure the problems identified here remain under control.

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arXiv2019

$χ_{c1}$ decays into a pseudoscalar meson and a vector-vector molecule

We evaluate ratios of the $χ_{c1}$ decay rates to $η$ ($η', K^-$) and one of the $f_0(1370)$, $f_0(1710)$, $f_2(1270)$, $f_2'(1525)$, $K^{*}_2(1430)$ resonances, which in the local hidden gauge approach are dynamically generated from the vector-vector interaction. With the simple assumption that the $χ_{c1}$ is a singlet of SU(3), and the input from the study of these resonances as vector-vector molecular states, we describe the experimental ratio $\mathcal{B}(χ_{c1} \rightarrow ηf_2(1270))/ \mathcal{B}(χ_{c1} \rightarrow η' f_2'(1525))$ and make predictions for six more ratios that can be tested in future experiments.

hep-ph↗
arXiv2019

Meson exchange between initial and final state and the $R_D$ ratio in the $\bar{B} \to D \barν \ell (\barν_ττ)$ reactions

We perform a calculation of the strong interaction effects between the $B$ and $D$ mesons in the $\bar{B} \to D \barν \ell$ reaction, as a crossing process of reactions with $BD$ in the final state, where the strong interaction between the mesons leads to a bound $BD$ state. We find corrections to the tree level amplitude of the order of $15-25\%$. We further see the effect of the corrections studied in the $R_D$ ratio for the rates of $\bar{B} \to D \barν_ττ$ and $\bar{B} \to D \barν_e \ell$ decays and find corrections of the order of $10\%$. Given the claims of $1.5\%$ precision in this ratio from fits to data within the standard model, any theoretical model aiming at describing this ratio within the same precision must take into account the corrections described in the present work.

hep-ph↗
arXiv2019

Origin of energy shift in kaonic atom and kaon-nucleus interaction

The $K^-$-nucleus optical potential is revisited to investigate its global feature phenomenologically. It is a puzzle that the energy shift is found to be repulsive in all of the observed kaonic atom, although the $K^-N$ interaction is known to be so attractive as to form the $Λ(1405)$ resonance. To solve this puzzle, we examine the $K^-$ optical potential in the linear density approximation and determine the potential parameters of each kaonic atom so as to reproduce the observed energy shift and absorption width. We find two types of the potentials. One potential has a so large real part as to provide nuclear states with the same quantum number to the atomic state in the last orbit. The level repulsion between the atomic state and the nuclear states takes place due to their mixing, and it makes the atomic state shifted repulsively. The other type of the potential has a large imaginary part and the imaginary part works repulsively for atomic states. We find that only the latter solution reproduce a wide of the observed data, and thus is realized as a $K^-$-nucleus potential for kaonic atom. In the linear nuclear density optical potential, the picture that the repulsive shifts in the atomic states stem from the existence of the nuclear states does not globally stand up. This implies that the $K^-$-nucleus optical potential should have a large imaginary part. We examine some nonlinear density effects and find that the conclusion does not change. We also confirm that the conventionally known optical potentials are categorized into the latter type of the potential.

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arXiv2018

Comparison of heavy-ion transport simulations: Collision integral in a box

Simulations by transport codes are indispensable to extract valuable physics information from heavy ion collisions. In order to understand the origins of discrepancies between different widely used transport codes, we compare 15 such codes under controlled conditions of a system confined to a box with periodic boundary, initialized with Fermi-Dirac distributions at saturation density and temperatures of either 0 or 5 MeV. In such calculations, one is able to check separately the different ingredients of a transport code. In this second publication of the code evaluation project, we only consider the two-body collision term, i.e. we perform cascade calculations. When the Pauli blocking is artificially suppressed, the collision rates are found to be consistent for most codes (to within $1\%$ or better) with analytical results, or completely controlled results of a basic cascade code after eliminating the correlations within the same pair of colliding particles. In calculations with active Pauli blocking, the blocking probability was found to deviate from the expected reference values. The reason is found in substantial phase-space fluctuations and smearing tied to numerical algorithms and model assumptions in the representation of phase space. This results in the reduction of the blocking probability in most transport codes, so that the simulated system gradually evolves away from the Fermi-Dirac towards a Boltzmann distribution. As a result of this investigation, we are able to make judgements about the most effective strategies in transport simulations for determining the collision probabilities and the Pauli blocking. Investigation in a similar vein of other ingredients in transport calculations, like the mean field propagation or the production of nucleon resonances and mesons, will be discussed in the future publications.

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arXiv2018

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 $Δ$ resonances in the reaction process are handled by JAM. We see the mechanism how the $Δ$ 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 $Δ^-/Δ^{++}$ 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 $Δ$ production ratio, and therefore $(N/Z)^2$, are directly reflected in the $π^-/π^+$ ratio, with modification in the final stage of the reaction.

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arXiv2018

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

We study the semileptonic decay of $B^{-}_c$ meson into $\barν l^-$ 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 $B^{-}_c \rightarrow \barν_{l} l^- D^{*}\bar{D^{*}}$ and $B^{-}_c \rightarrow \barν_{l} l^- D^{*}_{s}\bar{D_{s}^{*}}$ 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.

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