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Satoshi X. Nakamura

Publications and source records attributed to Satoshi X. Nakamura.

33 records · Page 2Linked to original sources
arXiv2016

Coupled-channel analysis of $D^+\to K^- π^+π^+$ decay

We perform a coupled-channel analysis of pseudodata for the D+-> K-pi+pi+ Dalitz plot. The pseudodata are generated from the isobar model of the E791 Collaboration, and are reasonably realistic. We demonstrate that it is feasible to analyze the high-quality data within a coupled-channel framework that describes the final state interaction of D+-> K-pi+pi+ as multiple rescatterings of three pseudoscalar mesons through two-pseudoscalar-meson interactions in accordance with the two-body and three-body unitarity. The two-pseudoscalar-meson interactions are designed to reproduce empirical pi pi and pi bar K scattering amplitudes. Furthermore, we also include mechanisms that are beyond simple iterations of the two-body interactions, i.e., a three-meson force, derived from the hidden local symmetry model. A picture of hadronic dynamics in D+-> K-pi+pi+ described by our coupled-channel model is found to be quite different from those of the previous isobar-type analyses. For example, we find that the D+-> K-pi+pi+ decay width can get almost triplicated when the rescattering mechanisms are turned on. Among the rescattering mechanisms, those associated with the rho(770) bar K0 channel, which contribute to D+-> K-pi+pi+ only through a channel coupling, give a large contribution, and significantly improve the quality of the fits. The K-pi+ s-wave amplitude from our analysis is reasonably consistent with those extracted from the E791 model independent partial-wave analysis; the hadronic rescattering and the coupling to the rho(770) bar K0 channel play a major role here. We also find that the dressed D+ decay vertices have phases, induced by the strong rescatterings, that strongly depend on the momenta of the final pseudoscalar mesons. Although the conventional isobar-type analyses have assumed the phases to be constant, this common assumption is not supported by our more microscopic viewpoint.

hep-ph↗
arXiv2015

Neutrino-induced meson productions

We develop a dynamical coupled-channels (DCC) model for neutrino-nucleon reactions in the resonance region, by extending the DCC model that we have previously developed through an analysis of $πN, γN\to πN, ηN, KΛ, KΣ$ reaction data for $W\le 2.1$ GeV. We analyze electron-induced reaction data for both proton and neutron targets to determine the vector current form factors up to $Q^2\le$ 3.0 (GeV/$c$)$^2$. Axial-current matrix elements are derived in accordance with the Partially Conserved Axial Current (PCAC) relation to the $πN$ interactions of the DCC model. As a result, we can uniquely determine the interference pattern between resonant and non-resonant amplitudes. Our calculated cross sections for neutrino-induced single-pion productions are compared with available data, and are found to be in reasonable agreement with the data. We also calculate the double-pion production cross sections in the resonance region, for the first time, with relevant resonance contributions and channel couplings. The result is compared with the double-pion production data. For a future development of a neutrino-nucleus reaction model and/or a neutrino event generator for analyses of neutrino experiments, the DCC model presented here can give a useful input.

hep-ph↗
arXiv2013

Theoretical analysis of Lambda(1405) photoproduction

We develop a model that describes the gamma p -> K^+ pi Sigma reaction in the Lambda(1405) region. The model consists of gauge invariant photo-production mechanisms, and the chiral unitary model that gives the rescattering amplitudes where Lambda(1405) is contained. The model also contains phenomenological parameters, associated with short-range dynamics, to be used in fitting data. We successfully fit recent CLAS data for the pi-Sigma invariant mass distributions (line-shape) in the gamma p -> K^+ pi Sigma reaction for all the charge states. We find that the higher mass pole for Lambda(1405) of the chiral unitary model plays an important role in the reaction. We also find the non-resonant background contribution is not negligible, and its sizable effect shifts the Lambda(1405) peak position by several MeV. This work sets a starting point for a fuller analysis in which line-shape as well as K^+ angular distribution data are simultaneously analyzed for extracting Lambda(1405) pole(s).

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arXiv2012

Meson spectroscopy with unitary coupled-channels model for heavy-meson decay into three mesons

We develop a model for describing excited mesons decay into three mesons. The properties of the excited mesons can be extracted with this model. The model maintains the three-body unitarity that has been missed in previous data analyses based on the conventional isobar models. We study an importance of the three-body unitarity in extracting hadron properties from data. For this purpose, we use the unitary and isobar models to analyze the same pseudo data of gamma p -> pi+pi+pi-n, and extract the properties of excited mesons. We find a significant difference between the unitary and isobar models in the extracted properties of excited mesons, such as the mass, width and coupling strength to decay channels.

hep-ph↗
arXiv2011

Dynamical Model for Meson Production off Nucleon and Application to Neutrino-Nucleus Reactions

I explain the Sato-Lee (SL) model and its extension to the neutrino-induced pion production off the nucleon. Then I discuss applications of the SL model to incoherent and coherent pion productions in the neutrino-nucleus scattering. I mention a further extension of this approach with a dynamical coupled-channels model developed in Excited Baryon Analysis Center of JLab.

nucl-th↗
arXiv2011

Effect of three-pion unitarity on resonance poles from heavy meson decays

We study the final state interaction in 3-pion decay of meson resonances at the Excited Baryon Analysis Center (EBAC) of JLab. We apply the dynamical coupled-channels formulation which has been extensively used by EBAC to extract N* information. The formulation satisfies the 3-pion unitarity condition which has been missed in the existing works with the isobar models. We report the effect of the 3-pion unitarity on the meson resonance pole positions and Dalitz plot.

hep-ph↗
arXiv2009

Consistency between renormalization group running of chiral operator and counting rule -- Case of chiral pion production operator --

In nuclear chiral perturbation theory (ChPT), an operator is defined in a space with a cutoff which may be varied within a certain range. The operator runs as a result of the variation of the cutoff [renormalization group (RG) running]. In order for ChPT to be useful, the operator should run in a way consistent with the counting rule; that is, the running of chiral counter terms have to be of natural size. We vary the cutoff using the Wilsonian renormalization group (WRG) equation, and examine this consistency. As an example, we study the s-wave pion production operator for NN\to d pi, derived in ChPT. We demonstrate that the WRG running does not generate any chiral-symmetry-violating (CSV) interaction, provided that we start with an operator which does not contain a CSV term. We analytically show how the counter terms are generated in the WRG running in case of the infinitesimal cutoff reduction. Based on the analytic result, we argue a range of the cutoff variation for which the running of the counter terms is of natural size. Then, we numerically confirm this.

nucl-th↗
arXiv2008

Bridging over p-wave pi-production and weak processes in few-nucleon systems with chiral perturbation theory

I study an aspect of chiral perturbation theory (χPT) which enables one to ``bridge'' different reactions. That is, an operator fixed in one of the reactions can then be used to predict the other. For this purpose, I calculate the partial wave amplitude for the p-wave pion production (pp\to pnπ^+) using the pion production operator from the lowest and the next nonvanishing orders. The operator includes a contact operator whose coupling has been fixed using a matrix element of a low-energy weak process (pp\to de^+ν_e). I find that this operator does not reproduce the partial wave amplitude extracted from experimental data, showing that the bridging over the reactions with significantly different kinematics is not necessarily successful. I study the dependence of the amplitude on the various inputs such as the NN potential, the πNΔcoupling, and the cutoff. I argue the importance of a higher order calculation. In order to gain an insight into a higher order calculation, I add a higher order counter term to the operator used above, and fit the couplings to both the low-energy weak process and the pion production. The energy dependence of the partial wave amplitude for the pion production is described by the operator consistently with the data. However, I find a result which tells us to be careful about the convergence of the chiral expansion for the pp\to pnπ^+ reaction.

nucl-th↗
arXiv2007

Renormalization group analysis of the chiral pion production operator for NN\to dπ

We are interested in the consistency between the cutoff, chiral symmetry, and the power counting. For this purpose, we apply the Wilsonian renormalization group (RG) to an operator and then decrease the Wilsonian cutoff. As an example, we study the s-wave pion production operator for NN\to dπ, derived in chiral perturbation theory. We find that the renormalized part of the RG effective operator is accurately absorbed by chiral counter terms of higher order with natural coefficients. Thus, the use of the (sharp) cutoff regularization does not require us to introduce chiral-symmetry-breaking counter terms, at least in the case of the NN\to dπreaction.

nucl-th↗
arXiv2006

Renormalization group analysis of nuclear current operators

We review our study of the Wilsonian renormalization group (WRG) analysis for nuclear current operators. We apply WRG method to axial-current operators derived from various approaches and obtain the unique effective low-energy operator.

nucl-th↗
arXiv2006

Renormalization group analysis of nuclear force

We study a relation between nuclear forces based on phenomenological approach (V_ph) and nuclear effective field theory (V_EFT) from a viewpoint of renormalization group. We find the relation between these two types of nuclear force using Wilsonian renormalization group equation. Considering the fact that V_EFT is defined in a certain small model space, we show that a simple contact interaction accurately simulates short-distance physics, and that V_EFT is free from dependence on modelling the details of the short-distance physics. Based on our result, we discuss some features of nuclear effective field theory.

nucl-th↗
arXiv2006

Renormalization group analysis of nuclear current operators

A Wilsonian renormalization group (WRG) equation for nuclear current operators in two-nucleon systems is derived. Nuclear current operators relevant to low-energy Gamow-Teller transitions are analyzed using the WRG equation. We employ the axial two-body current operators from phenomenological models and heavy-baryon chiral perturbation theory, which are quite different from one another in describing small scale physics. After reducing the model space of the operators using the WRG equation, we find that there still remains a significant model dependence at Λ= 200 MeV, where Λis the sharp cutoff specifying the size of the model space. A model independent effective current operator is found at a rather small cutoff value, Λ= 70 MeV. By simulating the effective current operator at Λ=70 MeV, we obtain a current operator based on a pionless theory, thereby arguing an equivalence relation between nuclear current operators of phenomenological models and those of effective field theories.

nucl-th↗
arXiv2005

Explanation of more effective effective field theory

We show that the so-called more effective effective field theory (MEEFT) is essentially equivalent to the proper nuclear effective field theory (NEFT) in describing low-energy electroweak processes in nuclei. A key to understanding their equivalence is the relation between a NEFT-based NN-potential and a phenomenological potential through the Wilsonian renormalization group equation.We also discuss an important advantage of MEEFT.

nucl-th↗
arXiv2005

Consideration of Nuclear Forces from the Viewpoint of the Renormalization Group - Relation of Nuclear Forces between Phenomenological Approach and Nuclear Effective Field Theory -

A relation between nuclear forces derived using a phenomenological approach and nuclear effective field theory (NEFT) is proposed from a renormalization group point of view. A phenomenological nuclear force (V_ph) and an NEFT-based NN-potential (V_EFT) are satisfactorily related to each other through the Wilsonian renormalization group (WRG) method. It is clearly shown that use of the simple contact interactions in NEFT is adequate to simulate small scale phenomena, and that an NEFT-based NN-potential (V_EFT) is free from dependence on the model used to describe small scale phenomena. We study the characteristics of V_EFT from a WRG point of view, emphasizing points that have not previously been fully recognized. We also use the V_{low k} method and a unitary transformation method to relate V_ph to V_EFT. It is found that they are not appropriate for this purpose.

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