arXiv subjects

S. Kumano

Publications and source records attributed to S. Kumano.

At least 55 records · Page 3Linked to original sources

arXiv2017

3D structure of hadrons by generalized distribution amplitudes and gravitational form factors

Generalized distribution amplitudes (GDAs) are one type of three-dimensional structure functions, and they are related to the generalized distribution functions (GPDs) by the $s$-$t$ crossing of the Mandelstam variables. The GDA studies provide information on three-dimensional tomography of hadrons. The GDAs can be investigated by the two-photon process $γ^* γ\to h\bar h$, and the GPDs are studied by the deeply virtual Compton scattering $γ^* h \to γh$. The GDA studies had been pure theoretical topics, although the GPDs have been experimentally investigated, because there was no available experimental measurement. Recently, the Belle collaboration reported their measurements on the $γ^* γ\to π^0 π^0$ differential cross section, so that it became possible to find the GDAs from their measurements. Here, we report our analysis of the Belle data for determining the pion GDAs. From the GDAs, the timelike gravitational form factors $Θ_1 (s)$ and $Θ_2 (s)$ can be calculated, which are mechanical (pressure, shear force) and mass (energy) form factors, respectively. They are converted to the spacelike form factors by using the dispersion relation, and then gravitational radii are evaluated for the pion. The mass and mechanical radii are obtained from $Θ_2$ and $Θ_1$ as $\sqrt {\langle r^2 \rangle_{\text{mass}}} =0.56 \sim 0.69$ fm and $\sqrt {\langle r^2 \rangle_{\text{mech}}} =1.45 \sim 1.56$ fm, whereas the experimental charge radius is $\sqrt {\langle r^2 \rangle_{\text{charge}}} =0.672 \pm 0.008$ fm for the charged pion. Future developments are expected in this new field to explore gravitational physics in the quark and gluon level.

hep-ph↗

arXiv2017

Standard convolution description of deuteron tensor spin structure

Spin-1 hadrons have additional structure functions not present for spin 1/2 hadrons. These could probe novel aspects of hadron structure and QCD dynamics. For the deuteron, the tensor structure function $b_1$ inherently mixes quark and nuclear degrees of freedom. These proceedings discuss two standard convolution models applied to calculations of the deuteron $b_1$ structure functions. We find large differences with the existing HERMES data and other convolution model calculations. This leaves room for non-standard contributions to $b_1$ in the deuteron. We also discuss the influence of higher twist nuclear effects in the model calculations and data extraction at kinematics covered in HERMES and Jefferson Lab.

hep-ph↗

arXiv2017

Tensor-polarized structure function $b_1$ in the standard convolution description of the deuteron

Tensor-polarized structure functions of a spin-1 hadron are additional observables which do not exist for the spin-1/2 nucleon. They could probe novel aspects of the internal hadron structure. Twist-2 tensor-polarized structure functions are $b_1$ and $b_2$, and they are related by the Callan-Gross-like relation in the Bjorken scaling limit. In this work, we theoretically calculate $b_1$ in the standard convolution description for the deuteron. Two different theoretical models, a basic convolution description and a virtual nucleon approximation, are used for calculating $b_1$ and their results are compared with the HERMES measurement. We found large differences between our theoretical results and the data. Although there is still room to improve by considering higher-twist effects and in the experimental extraction of $b_1$ from the spin asymmetry $A_{zz}$, there is a possibility that the large differences require physics beyond the standard deuteron model for their interpretation. Future $b_1$ studies could shed light on a new field of hadron physics. In particular, detailed experimental studies of $b_1$ will start soon at the Thomas Jefferson National Accelerator Facility. In addition, there are possibilities to investigate tensor-polarized parton distribution functions and $b_1$ at Fermi National Accelerator Laboratory and a future electron-ion collider. Therefore, further theoretical studies are needed for understanding the tensor structure of the spin-1 deuteron, including a new mechanism to explain the large differences between the current data and our theoretical results.

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arXiv2017

Towards a Unified Model of Neutrino-Nucleus Reactions for Neutrino Oscillation Experiments

A precise description of neutrino-nucleus reactions will play a key role in addressing fundamental questions such as the leptonic CP violation and the neutrino mass hierarchy through analyzing data from next-generation neutrino oscillation experiments. The neutrino energy relevant to the neutrino-nucleus reactions spans a broad range and, accordingly, the dominant reaction mechanism varies across the energy region from quasi-elastic scattering through nucleon resonance excitations to deep inelastic scattering. This corresponds to transitions of the effective degree of freedom for theoretical description from nucleons through meson-baryon to quarks. The main purpose of this review is to report our recent efforts towards a unified description of the neutrino-nucleus reactions over the wide energy range; recent overall progress in the field is also sketched. Starting with an overview of the current status of neutrino-nucleus scattering experiments, we formulate the cross section to be commonly used for the reactions over all the energy regions. A description of the neutrino-nucleon reactions follows and, in particular, a dynamical coupled-channels model for meson productions in and beyond the $Δ$(1232) region is discussed in detail. We then discuss the neutrino-nucleus reactions, putting emphasis on our theoretical approaches. We start the discussion with electroweak processes in few-nucleon systems studied with the correlated Gaussian method. Then we describe quasi-elastic scattering with nuclear spectral functions, and meson productions with a $Δ$-hole model. Nuclear modifications of the parton distribution functions determined through a global analysis are also discussed. Finally, we discuss issues to be addressed for future developments.

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arXiv2017

Tensor-polarized structure function $b_1$ by convolution picture for deuteron

There are polarized structure functions $b_{1-4}$ for the spin-1 deuteron. We calculated the leading-twist tensor structure function $b_1$ by using convolution description for the deuteron. We found large differences between our theoretical functions and HERMES experimental data on $b_1$. Although higher-twist effects should be considered in obtaining experimental $b_1$, it suggests a possible existence of new hadron physics mechanism for spin-1 hadrons. Furthermore, we found that there are significant distributions at large Bjorken $x$. In future, an experimental measurement is planned at JLab for $b_1$ and there is a possibility of a proton-deuteron Drell-Yan experiment at Fermilab with the tensor-polarized deuteron, so that further theoretical studies are needed for clarifying the physics origin of tensor structure in terms of quark and gluon degrees of freedom.

hep-ph↗

arXiv2017

Spin asymmetry for proton-deuteron Drell-Yan process with tensor-polarized deuteron

Tensor structure of the deuteron can be studied by deep inelastic scattering and Drell-Yan process to understand it in terms of quark and gluon degrees of freedom. It probes interesting features in the deuteron including a D-wave contribution. In the charged-lepton DIS, twist-two structure functions $b_1$ and $b_2$ are expressed by tensor-polarized parton distribution functions (PDFs). We note that the HERMES experimental measurement of $b_1$ seems to be much different from a conventional theoretical prediction. This puzzling situation should be significantly improved in the near future by an approved experiment to measure $b_1$ at JLab. On the other hand, the tensor-polarized PDFs, especially antiquark distributions, could be measured by spin asymmetries in the Drell-Yan process with a tensor-polarized deuteron at Fermilab. In this work, we estimate tensor-polarization asymmetries for the Fermilab Drell-Yan experiment by using a parametrization for the tensor-polarized PDFs to explain the HERMES $b_1$ data. Obtained spin asymmetries are typically a few percent order and they could be measured by the Fermilab-E1039 experiment. Since the tensor-polarized antiquark distributions will play an important role to solve the puzzle, further theoretical and experimental efforts are needed toward the Drell-Yan experiment at Fermilab and other hadron facilities.

nucl-th↗

arXiv2016

Hadron tomography studies by generalized parton distributions and distribution amplitudes

We discuss hadron-tomography studies for the nucleon and exotic hadrons by high-energy hadron reactions. First, the constituent-counting rule is explained for determining internal quark configurations of exotic-hadron candidates by scaling properties of high-energy exclusive cross sections. Next, possibilities are discussed for investigating the generalized parton distributions (GPDs) of the nucleon and exotic hadrons at J-PARC. In particular, we study hadronic $2 \to 3$ process $p+p \to N+π+B$, exclusive Drell-Yan process, and exotic-hadron GPDs. For determining three-dimensional structure of unstable exotic hadrons, we consider $s$-$t$ crossed quantities of the GPDs called generalized distribution amplitudes (GDAs), which can be investigated at KEKB. We explain possible studies of the GDAs by two-photon processes.

hep-ph↗

arXiv2016

Exotic-Hadron Signature by Constituent-Counting Rule in Perturbative QCD

We explain a method to find internal quark configurations of exotic hadron candidates by using the constituent counting rule. The counting rule was theoretically predicted in perturbative QCD for hard exclusive hadron reactions, and it has been tested in experiments for stable hadrons including compound systems of hadrons such as the deuteron, $^3$H, and $^3$He. It indicates that the cross section scales as $dσ/dt \sim 1/s^{n-2}$, where $s$ is the center-of-mass energy squared and $n$ is the total number of constituents. We apply this method for finding internal configurations of exotic hadron candidates, especially $Λ(1405)$. There is a possibility that $Λ(1405)$ could be five-quark state or a $\bar K N$ molecule, and scaling properties should be different between the ordinary three-quark state or five-quark one. We predict such a difference in $π^- + p \to K^0 + Λ(1405)$, and it could be experimentally tested, for example, at J-PARC. On the other hand, there are already measurements for $γ+ p \to K^+ + Λ(1405)$ as well as the ground $Λ$ in photoproduction reactions. Analyzing such data, we found an interesting indication that $Λ(1405)$ looks like a five-quark state at medium energies and a three-quark one at high energies. However, accurate higher-energy measurements are necessary for drawing a solid conclusion, and it should be done at JLab by using the updated 12 GeV electron beam. Furthermore, we discuss studies of exotic hadron candidates, such as $f_0 (980)$ and $a_0 (980)$, in electron-positron annihilation by using generalized distribution amplitudes and the counting rule. These studies should be possible as a KEKB experiment.

hep-ph↗

arXiv2016

Estimate on Spin Asymmetry for Drell-Yan Process at Fermilab with Tensor-Polarized Deuteron

There are four new structure functions for the spin-1 deuteron in comparison with the ones for the spin-1/2 proton, and they are called $b_1$, $b_2$, $b_3$, and $b_4$. The twist-2 structure functions $b_1$ and $b_2$ are expressed by tensor-polarized parton distribution functions in the deuteron. HERMES measurements of $b_1$ are much different from the prediction of the standard deuteron model with D-state admixture. It indicates that the structure functions $b_1$ and $b_2$ probe an interesting new aspect in the deuteron. There is an approved experiment at JLab to measure $b_1$ and it is expected to start in 2019. On the other hand, the measurement of tensor-polarized distributions is under consideration at Fermilab by the Drell-Yan process with the unpolarized proton beam and tensor-polarized deuteron target. It is expected to provide crucial information on tensor-polarized antiquark distributions. Since the distributions are small quantities, it is important to estimate the tensor-polarized spin asymmetry theoretically to find experimental feasibility for an actual proposal at Fermilab.

hep-ph↗

arXiv2016

Impacts of B-factory measurements on determination of fragmentation functions from electron-positron annihilation data

Fragmentation functions are determined for the pion and kaon by global analyses of charged-hadron production data in electron-positron annihilation. Accurate measurements were reported by the Belle and BaBar collaborations for the fragmentation functions at the center-of-mass energies of 10.52 GeV and 10.54 GeV, respectively, at the KEK and SLAC B factories, whereas other available $e^+e^-$ measurements were mostly done at higher energies, mainly at the $Z$ mass of 91.2 GeV. There is a possibility that gluon fragmentation functions, as well as quark fragmentation functions, are accurately determined by scaling violation. We report our global analysis of the fragmentation functions especially to show impacts of the B-factory measurements on the fragmentation function determination. Our results indicate that the fragmentation functions are determined more accurately not only by the scaling violation but also by high-statistical nature of the Belle and BaBar data. However, there are some tensions between the Belle and BaBar data in comparison with previous measurements. We also explain how the flavor dependence of quark fragmentation functions and the gluon function are separated by using measurements at different $Q^2$ values. In particular, the electric and weak changes are different depending on the quark type, so that a light-quark flavor separation also became possible in principle due to the precise data at both $\sqrt{s}\simeq 10.5$ GeV and 91.2 GeV.

hep-ph↗

arXiv2016

Theoretical estimate on tensor-polarization asymmetry in proton-deuteron Drell-Yan process

Tensor-polarized parton distribution functions are new quantities in spin-one hadrons such as the deuteron, and they could probe new quark-gluon dynamics in hadron and nuclear physics. In charged-lepton deep inelastic scattering (DIS), they are studied by the twist-two structure functions $b_1$ and $b_2$. The HERMES collaboration found unexpectedly large $b_1$ values than a naive theoretical expectation based on the standard deuteron model. The situation should be significantly improved in the near future by an approved experiment to measure $b_1$ at JLab (Thomas Jefferson National Accelerator Facility). There is also an interesting indication in the HERMES result that finite antiquark tensor polarization exists. It could play an important role in solving a mechanism on tensor structure in the quark-gluon level. The tensor-polarized antiquark distributions are not easily determined from the charged-lepton DIS; however, they can be measured in a proton-deuteron Drell-Yan process with a tensor-polarized deuteron target. In this article, we estimate the tensor-polarization asymmetry for a possible Fermilab Main-Injector experiment by using optimum tensor-polarized PDFs to explain the HERMES measurement. We find that the asymmetry is typically a few percent. If it is measured, it could probe new hadron physics, and such studies could create an interesting field of high-energy spin physics. In addition, we find that a significant tensor-polarized gluon distribution should exist due to $Q^2$ evolution, even if it were zero at a low $Q^2$ scale. The tensor-polarized gluon distribution has never been observed, so that it is an interesting future project.

hep-ph↗

arXiv2016

First Monte Carlo analysis of fragmentation functions from single-inclusive $e^+ e^-$ annihilation

We perform the first iterative Monte Carlo (IMC) analysis of fragmentation functions constrained by all available data from single-inclusive $e^+ e^-$ annihilation into pions and kaons. The IMC method eliminates potential bias in traditional analyses based on single fits introduced by fixing parameters not well contrained by the data and provides a statistically rigorous determination of uncertainties. Our analysis reveals specific features of fragmentation functions using the new IMC methodology and those obtained from previous analyses, especially for light quarks and for strange quark fragmentation to kaons.

hep-ph↗

arXiv2016

Nuclear effects in deep inelastic scattering and transition region

We discuss nuclear effects on neutrino-nuclear interactions in a wide kinematical range from shallow to deep inelastic scattering (DIS) region. There is necessity from neutrino communities to have precise neutrino-nucleus cross sections for future measurements on neutrino oscillations and leptonic CP violation. We try to create a model to calculate neutrino cross sections in the wide kinematical range, from quasi-elastic scattering and resonance productions to the DIS. In this article, nuclear modifications of structure functions are mainly discussed, and a possible extension to the $Q^2 \to 0$ region is explained. We also comment on the transition region between baryon resonances and the DIS. There are ongoing experimental efforts on nuclear modifications of structure functions or parton distribution functions such as by pA reactions at RHIC and LHC, Drell-Yan measurements at Fermilab, Miner$ν$a neutrino DIS, and charged-lepton DIS at JLab.

hep-ph↗

arXiv2016

Progress on nuclear modifications of structure functions

We report progress on nuclear structure functions, especially on their nuclear modifications and a new tensor structure function for the deuteron. To understand nuclear structure functions is an important step toward describing nuclei and QCD matters from low to high densities and from low to high energies in terms of fundamental quark and gluon degrees of freedom beyond conventional hadron and nuclear physics. It is also practically important for understanding new phenomena in high-energy heavy-ion collisions at RHIC and LHC. Furthermore, since systematic errors of current neutrino-oscillation experiments are dominated by uncertainties of neutrino-nucleus interactions, such studies are valuable for finding new physics beyond current framework. Next, a new tensor-polarized structure function $b_1$ is discussed for the deuteron. There was a measurement by HERMES; however, its data are inconsistent with the conventional convolution estimate based on the standard deuteron model with D-state admixture. This fact suggests that a new hadronic phenomenon should exist in the tensor-polarized deuteron at high energies, and it will be experimentally investigated at JLab from the end of 2010's.

hep-ph↗

arXiv2016

Constituent-counting rule in photoproduction of hyperon resonances

We analyze the CLAS data on the photoproduction of hyperon resonances, as well as the available data for the ground state $Λ$ and $Σ^{0}$ of the CLAS and SLAC-E84 collaborations, by considering constituent-counting rule suggested by perturbative QCD. The counting rule emerges as a scaling behavior of cross sections in hard exclusive reactions with large scattering angles, and it enables us to determine the number of elementary constituents inside hadrons. Therefore, it could be used as a new method for identifying internal constituents of exotic-hadron candidates. From the analyses of the $γ\, p \to K^{+} Λ$ and $K^{+} Σ^{0}$ reactions, we find that the number of the elementary constituents is consistent with $n_γ = 1$, $n_{p} = 3$, $n_{K^{+}} = 2$, and $n_Λ = n_{Σ^{0}} = 3$. Then, the analysis is made for the photoproductions of the hyperon resonances $Λ(1405)$, $Σ(1385)^{0}$, and $Λ(1520)$, where $Λ(1405)$ is considered to be a $\bar K N$ molecule and hence its constituent number could be five. However, we find that the current data are not enough to conclude the numbers of their constituent. It is necessary to investigate the higher-energy region at $\sqrt{s} > 2.8$ GeV experimentally beyond the energy of the available CLAS data for counting the number of constituents clearly. We also mention that our results indicate energy dependence in the constituent number, especially for $Λ(1405)$. If an excited hyperon is a mixture of three-quark and five-quark states, the energy dependence of the scaling behavior could be valuable for finding its composition and mixture.

hep-ph↗

arXiv2015

The Physics of the B Factories

This work is on the Physics of the B Factories. Part A of this book contains a brief description of the SLAC and KEK B Factories as well as their detectors, BaBar and Belle, and data taking related issues. Part B discusses tools and methods used by the experiments in order to obtain results. The results themselves can be found in Part C. Please note that version 3 on the archive is the auxiliary version of the Physics of the B Factories book. This uses the notation alpha, beta, gamma for the angles of the Unitarity Triangle. The nominal version uses the notation phi_1, phi_2 and phi_3. Please cite this work as Eur. Phys. J. C74 (2014) 3026.

hep-ex↗

arXiv2015

Constraint on K Kbar compositeness of the a0(980) and f0(980) resonances from their mixing intensity

Structure of the $a_{0}(980)$ and $f_{0}(980)$ resonances is investigated with the $a_{0}(980)$-$f_{0}(980)$ mixing intensity from the viewpoint of compositeness, which corresponds to the amount of two-body states composing resonances as well as bound states. For this purpose we first formulate the $a_{0}(980)$-$f_{0}(980)$ mixing intensity as the ratio of two partial decay widths of a parent particle, in the same manner as the recent analysis in BES experiments. Calculating the $a_{0}(980)$-$f_{0}(980)$ mixing intensity with the existing Flatte parameters from experiments, we find that many combinations of the $a_{0}(980)$ and $f_{0}(980)$ Flatte parameters can reproduce the experimental value of the $a_{0}(980)$-$f_{0}(980)$ mixing intensity by BES. Next, from the same Flatte parameters we also calculate the $K \bar{K}$ compositeness for $a_{0}(980)$ and $f_{0}(980)$. Although the compositeness with the correct normalization becomes complex in general for resonance states, we find that the Flatte parameters for $f_{0}(980)$ imply large absolute value of the $K \bar{K}$ compositeness and the parameters for $a_{0}(980)$ lead to small but nonnegligible absolute value of the $K \bar{K}$ compositeness. Then, connecting the mixing intensity and the $K \bar{K}$ compositeness via the $a_{0}(980)$- and $f_{0}(980)$-$K \bar{K}$ coupling constants, we establish a relation between them. As a result, a small mixing intensity indicates a small value of the product of the $K \bar{K}$ compositeness for the $a_{0}(980)$ and $f_{0}(980)$ resonances. Moreover, the experimental value of the $a_{0}(980)$-$f_{0}(980)$ mixing intensity implies that the $a_{0}(980)$ and $f_{0}(980)$ resonances cannot be simultaneously $K \bar{K}$ molecular states.

hep-ph↗

arXiv2015

Spin Physics at J-PARC

Spin-physics projects at J-PARC are explained by including future possibilities. J-PARC is the most-intense hadron-beam facility in the high-energy region above multi-GeV, and spin physics will be investigated by using secondary beams of kaons, pions, neutrinos, muons, and antiproton as well as the primary-beam proton. In particle physics, spin topics are on muon $g-2$, muon and neutron electric dipole moments, and time-reversal violation experiment in a kaon decay. Here, we focus more on hadron-spin physics as for future projects. For example, generalized parton distributions (GPDs) could be investigated by using pion and proton beams, whereas they are studied by the virtual Compton scattering at lepton facilities. The GPDs are key quantities for determining the three-dimensional picture of hadrons and for finding the origin of the nucleon spin including partonic orbital-angular-momentum contributions. In addition, polarized parton distributions and various hadron spin topics should be possible by using the high-momentum beamline. The strangeness contribution to the nucleon spin could be also investigated in principle with the neutrino beam with a near detector facility.

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