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Yoshitaka Hatta

Publications and source records attributed to Yoshitaka Hatta.

At least 19 recordsLinked to original sources
arXiv2026

Spin-spin entanglement at high energy

Spin correlations offer a quantum-information perspective on the partonic final states produced in high-energy scattering. We discuss the spin-density matrix of a heavy quark-antiquark pair in two complementary small-$x$ processes. In coherent diffractive production, color-singlet exchange enforces an unusually strong relation between entanglement and Bell nonlocality: a longitudinal photon creates a maximally entangled pair, whereas for a transverse photon the pair is generically both entangled and Bell nonlocal, with a model-independent point of maximal entanglement. In inclusive back-to-back production, the density matrix factorizes into a hard spin tensor and the unpolarized and linearly polarized Weizsäcker--Williams gluon distributions. The latter generates an azimuthal modulation and can increase the concurrence when the dijet relative momentum and imbalance are approximately orthogonal. Strikingly, in the saturation model considered, nonlinear effects wash out this modulation for $q_\perp\lesssim 3Q_s$, whereas the dilute BFKL limit, in which $G_2/G_0\to1$, yields a maximal modulation independent of the imbalance magnitude. These results connect quantum-information observables with the Pomeron and saturation physics.

hep-ph↗
arXiv2026

Three-qubit entanglement in the Bethe-Heitler process

The familiar Bethe-Heitler process on the proton target $e+p\to e+p+γ$ is transformed into a laboratory for studying multiparticle entanglement. We discuss how bipartite and genuine tripartite entanglement between the final state electron, proton and photon are built up by successive $1\to 2$ and $2\to 2$ elementary interactions. We validate our argument by simulating events. Below 5 GeV center-of-mass energy, we identify more than 900 Greenberger-Horne-Zeilinger (GHZ) states and 1200 W states, each with a fidelty exceeding 99%.

quant-ph↗
arXiv2026

Photon-nucleon entanglement in Compton scattering at low and high energies

We study spin-spin entanglement in the final state photon-nucleon system in Compton scattering, both at low energy below the pion threshold and at high energy in perturbative QCD to next-to-leading order. We first establish a no-go theorem showing that, for any spin-$\frac{1}{2}$ target, entanglement cannot be generated in unpolarized Compton scattering if the scattering amplitudes are real. We then consider polarized Compton scattering off the electron, the proton and the neutron. At low energy, we uncover a rich variety of maximally entangled Bell states and their unitary equivalents realized across different regions of the kinematic plane. Interestingly, the proton and neutron targets exhibit distinct patterns of entanglement. In the neutron case, the electric and magnetic polarizabilities dramatically influence the pattern and even the existence of entanglement. This suggests that entanglement can serve as a novel tool for investigating the detailed electromagnetic properties of the nucleons.

hep-ph↗
arXiv2026

Spin Structure of the Nucleon: Overview

I present a pedagogical review of the decomposition of the proton spin. Both the Jaffe-Manohar and Ji decompositions are discussed. Particular emphasis is placed on the quark and gluon orbital angular momenta, including their gauge invariant definitions, small-$x$ behavior and connection to experimental observables.

hep-ph↗
arXiv2026

Mass radius and D-term of atomic nuclei in relativistic mean field theory

Based on relativistic mean field theory for atomic nuclei, we compute the mass radius and other radii associated with the energy momentum tensor for dozens of spin-0 nuclei across the nuclear chart. We also compute the D-term of these nuclei, the forward limit of the gravitational form factor $D(t=0)=D$. The dependence on the neutron number $N$ is systematically studied for calcium (Ca), nickel (Ni), zirconium (Zr), tin (Sn) and lead (Pb) isotopes. Remarkably, $|D|$ does not monotonically increase with $N$. Instead, it exhibits local maxima and minima when $N$ equals a magic number and even a sub-magic number. This results in characteristic kinks in the mass, scalar, tensor and shear radii of these isotopes. Our work for the first time elucidates the strong sensitivity of the various mechanical properties of nuclei to the nuclear shell structure.

nucl-th↗
arXiv2026

Quantum entanglement in electron-nucleus collisions: Role of the linearly polarized gluon distribution

We calculate the spin density matrix of a back-to-back quark-antiquark pair inclusively produced in electron-nucleus scattering, taking into account the gluon saturation effect and the linearly polarized gluon distribution. We then investigate concurrence and stabilizer Rényi entropy, quantifying entanglement, Bell-nonlocality, and magic. We find that the linearly polarized gluon distribution tends to enhance the entanglement of a heavy quark pair when the total and relative transverse momenta of the pair are orthogonal.

hep-ph↗
arXiv2026

Probing quantum entanglement with Generalized Parton Distributions at the Electron-Ion Collider

Within the collinear factorization framework based on Generalized Parton Distributions (GPDs), we calculate the spin density matrix of exclusively produced quark and antiquark pairs $u\bar{u}$, $d\bar{d}$, $s\bar{s}$, $c\bar{c}$, $b\bar{b}$ in electron-proton scattering. The presence of both real and imaginary parts in the scattering amplitudes leads to a rich pattern of entanglement between the quark and the antiquark. We map out kinematical regions where the pairs exhibit entanglement, Bell nonlocality and non-stabilizerness (`magic'). We also predict that massive quarks and antiquarks are transversely polarized, similar to the well-known transverse hyperon polarization in unpolarized collisions. In strangeness, charm and bottom productions, the polarization can reach 50-80\% in certain kinematic regions in the low-energy runs of the Electron-Ion Collider.

hep-ph↗
arXiv2026

Single spin asymmetry in $e+p\to e'+B^\uparrow+X$

We study an exotic type of single spin asymmetry in unpolarized electron-proton scattering, in which the outgoing electron momentum exhibits a left-right asymmetry relative to the transverse spin of the leading baryon $B$ in the target fragmentation region. We lay out two theoretical frameworks for describing this effect: The twist-three fracture function at high-$Q^2$ and the spin-dependent odderon in the high energy limit.

hep-ph↗
arXiv2026

Spin-spin entanglement in diffractive heavy quark production

We calculate the spin density matrix of a heavy quark-antiquark pair ($b\bar{b}$, $c\bar{c}$ or $s\bar{s}$) diffractively produced in Deep Inelastic Scattering and Ultraperipheral Collisions. We show that the Pomeron exchange leaves characteristic imprints on the entanglement pattern between the quark and the antiquark. For the longitudinally polarized virtual photon, the pair always exhibits maximal entanglement and maximal violation of the Bell-CHSH inequality. For the transversely polarized photon, the pair is always entangled and Bell-violating, reaching maximal entanglement and maximal violation simultaneously when the transverse momentum approximately equals the quark mass.

hep-ph↗
arXiv2026

Deeply virtual $ϕ$-meson production near threshold

We discuss exclusive $ϕ$-meson electroproduction off the proton near threshold within the GPD factorization framework. We propose the `threshold approximation' in which only the leading term of the conformal partial wave expansion of the meson production amplitudes is kept in both the quark and gluon exchange channels. We test the validity of this approximation to next-to-leading order in QCD and demonstrate the strong sensitivity of the cross section to the gluon and strangeness gravitational form factors. We also perform realistic event generator simulations both for Jefferson Lab and EIC kinematics and demonstrate the capabilities of future facilities for measuring near-threshold $ϕ$ electroproduction.

hep-ph↗
arXiv2025

Generalized parton distributions and gravitational form factors at large momentum transfer

Within the soft collinear effective theory (SCET), we derive a factorization theorem which resums Sudakov logarithms $(α_s\ln^2(-t))^n$ to all orders in the quark-in-quark generalized parton distribution (GPD) at large momentum transfer $t$, and perform a consistency check to one-loop. We show that the same Sudakov factor appears in the `Feynman' contribution to the GPDs of the nucleon. Our result enables the resummation of all the large logarithms $\ln Q^2$ and $\ln^2t$ in exclusive processes with two hard scales $Λ_{\rm QCD}^2\ll |t| \ll Q^2$. We also present a SCET power counting analysis of the Feynman contributions to the GPDs and show that the $x$-dependence of GPDs factorizes at large-$t$ with controlled corrections. This in particular implies that any ratio of GPD moments such as the electromagnetic and gravitational form factors (GFF) is perturbatively calculable in this approximation. Furthermore, we identify a novel order $α_s$ power-law $t$-dependence in the GPD and the $D$-type GFF that will dominate over the standard order $(α_s^2)$ `leading twist' asymptotic contribution in the phenomenologically relevant region of $t$.

hep-ph↗
arXiv2025

Realizing the Scientific Program with Polarized Ion Beams at EIC

Polarized ion beams at the Electron Ion Collider are essential to address some of the most important open questions at the twenty-first century frontiers of understanding of the fundamental structure of matter. Here, we summarize the science case and identify polarized $^2$H, $^3$He, $^6$Li and $^7$Li ion beams as critical technology that will enable experiments which address the most important science. Further, we discuss the required ion polarimetry and spin manipulation in EIC. The current EIC accelerator design is presented. We identify a significant R\&D effort involving both national laboratories and universities that is required over about a decade to realize the polarized ion beams and estimate (based on previous experience) that it will require about 20 FTE over 10 years (or a total of about 200 FTE-years) of personnel, including graduate students, postdoctoral researchers, technicians and engineers. Attracting, educating and training a new generation of physicists in experimental spin techniques will be essential for successful realization. AI/ML is seen as having significant potential for both acceleration of R\&D and amplification of discovery in optimal realization of this unique quantum technology on a cutting-edge collider. The R\&D effort is synergistic with research in atomic physics and fusion energy science.

nucl-ex↗
arXiv2025

Directed flow from parton spin-orbit coupling in $pp$ and $pA$ collisions

We point out a novel mechanism to generate $\cos ϕ$ two-particle azimuthal correlation (`directed flow') in unpolarized proton-proton and proton-nucleus collisions in the forward rapidity region of the projectile proton. This is a direct consequence of the recently discovered strong spin-orbit coupling in gluons at small-$x$. The observable simultaneously serves as a unique probe into the double helicity parton distribution functions of the proton.

hep-ph↗
arXiv2025

Sullivan process near threshold and the pion gravitational form factors

We propose a novel method to experimentally access the gravitational form factors (GFFs) of the charged pion $π^+$ through the Sullivan process in electron-proton scattering. We demonstrate that the cross sections of $J/ψ$-photoproduction and $ϕ$-electroproduction near the respective thresholds are dominated by the gluon GFF of the pion to next-to-leading order in perturbative QCD. We predict cross sections for the Electron-Ion Collider and the Jefferson Lab experiments.

hep-ph↗
arXiv2024

Spin-orbit entanglement in the Color Glass Condensate

We compute the spin-orbit correlations of quarks and gluons at small-$x$ and show that the helicity and the orbital angular momentum of individual partons are strongly anti-aligned even in unpolarized or spinless hadrons and nuclei. Combined with the fact that gluons in the Color Glass Condensate are linearly polarized, our finding indicates that the helicity and the orbital angular momentum of single gluons are maximally entangled in a quantum mechanical sense.

hep-ph↗
arXiv2024

Nonlocal chiral anomaly and generalized parton distributions

We discuss the nonlocal generalization of the QCD chiral anomaly along the light-cone and derive relations between twist-two, twist-three and twist-four generalized parton distributions (GPDs) mediated by the anomaly. We further establish the connection to the `anomaly pole' in the GPD $\tilde{E}$ recently identified in the perturbative calculation of the Compton scattering amplitudes, and demonstrate its cancellation at the GPD level. Our work helps elucidate the previously unexplored connection between GPDs, the chiral anomaly, and the mass generation of the $η'$ meson.

hep-ph↗
arXiv2024

Maximally entangled gluons for any $x$

Individual quarks and gluons at small-$x$ inside an unpolarized hadron can be regarded as Bell states in which qubits in the spin and orbital angular momentum spaces are maximally entangled. Using the machinery of quantum information science, we generalize this observation to all values $0<x<1$ and describe gluons (but not quarks) as maximally entangled states between a qubit and a qudit. We introduce the conditional probability distribution $P(l^z|s^z)$ of a gluon's orbital angular momentum $l^z$ given its helicity $s^z$. Restricting to the three states $l^z=0,\pm 1$, which constitute a qutrit, we explicitly compute $P$ as a function of $x$

hep-ph↗