二重态电磁性质的连通部分

手征区十重态重子的精确电磁结构

Precision electromagnetic structure of decuplet baryons in the chiral regime

重子十重态的电磁性质是在淬火QCD中计算的，在20^3 x 40的晶格上，晶格间距为0.128 fm，使用胖链无关三叶草（FLIC）费米子作用量，夸克质量提供了低至300 MeV的π质量。磁矩和电荷半径从每个单独的夸克扇区的电和磁形状因子中提取。由此构造了相应的重子性质。我们给出了自旋为3/2的重子的高阶矩，包括电四极矩E2和磁八极矩M3。本文报道了世界上第一个确定Delta重子非零M3形状因子的结果。利用这些结果，我们提供了一个结论性的分析，表明十重态重子是变形的。我们比较了八重态重子的十重态重子结果。我们建立的环境敏感性是远不如在八重态重子相比，在十重态重子的情况下明显。一个令人惊讶的结果是，十重态重子的电荷半径通常小于八重态重子的电荷半径。德尔塔^+的磁矩揭示了低夸克质量区域的翻转，使其小于质子的磁矩。这些结果与猝灭手征微扰理论的预期是一致的。在Sigma^*0的磁矩中也观察到类似的翻转，但在Xi^* 中没有，因为在猝灭的QCD中只会出现K介子环。当考虑到负电荷因子时，Ω ^-重子的电四极矩为正，等于0.86 +- 0.12 x 10^-2 fm^2，表明它是扁圆形的。

重子八重态到二重态的电磁跃迁

Baryon Octet to Decuplet Electromagnetic Transitions

利用格点模拟方法研究了$SU(3)$味重子八重态到十重态的电磁跃迁矩。发现$N \; γ\to Δ$通道的磁跃迁矩与最近的实验分析一致。晶格结果表明为$μ_{p Δ} / μ_p = 0.88(15)$。根据粒子数据组约定，$p \; γ\to Δ^+$跃迁的$f_{M1} = 0.231(41)$ GeV ${}^{-1/2}$。超子$M1$跃迁矩的晶格预言与简单夸克模型的预言一致。然而，夸克在晶格模拟中对跃迁矩的贡献方式与夸克模型计算所预期的不同。标量四极形状因子表现出与先前多极分析一致的行为。还确定了$E2/M1$多极跃迁矩比。晶格结果表明，$p \; γ\to Δ^+$的过渡$R_{EM} \equiv -{\cal G}_{E2}/{\cal G}_{M1} = +3\pm 8$ \%。特别感兴趣的是$Ξ^-$和$Σ^-$电磁跃迁中的$E2/M1$比率的显著非零信号。

Isospin splittings in the decuplet baryon spectrum from dynamical QCD+QED

We report a new analysis of the isospin splittings within the decuplet baryon spectrum. Our numerical results are based upon five ensembles of dynamical QCD+QED lattices. The analysis is carried out within a flavour-breaking expansion which encodes the effects of breaking the quark masses and electromagnetic charges away from an approximate SU(3) symmetric point. The results display total isospin splittings within the approximate SU(2) multiplets that are compatible with phenomenological estimates. Further, new insight is gained into these splittings by separating the contributions arising fro…

A relativistic quark model for the Omega- electromagnetic form factors

We compute the Omega- electromagnetic form factors and the decuplet baryon magnetic moments using a quark model application of the Covariant Spectator Theory. Our predictions for the Omega- electromagnetic form factors can be tested in the future by lattice QCD simulations at the physical strange quark mass.

有限晶格间距下的强子电磁性质

Hadronic Electromagnetic Properties at Finite Lattice Spacing

在猝灭和部分猝灭的手征微扰理论中，我们增加了八重态介子以及八重态和十重态重子的电磁性质，使之包括了由于晶格离散化引起的O（a）修正。我们给出了在同位旋极限下SU（3）味群的结果以及在非简并夸克情况下SU（2）味群的结果。这些修正对于用Wilson价夸克和海夸克的晶格计算外推以及用Wilson海夸克和Ginsparg-Wilson价夸克的晶格计算都是有用的。

What is the role of the meson cloud in the $Σ^{*0} \to γΛ$ and $Σ^\ast \to γΣ$ decays?

We study the effect of the meson cloud dressing in the octet baryon to decuplet baryon electromagnetic transitions. Combining the valence quark contributions from the covariant spectator quark model with those of the meson cloud estimated based on the flavor SU(3) cloudy bag model, we calculate the transition magnetic form factors at $Q^2=0$ ($Q^2=-q^2$ and $q$ the four-momentum transfer), and also the decuplet baryon electromagnetic decay widths. The result for the $γ^\ast Λ\to Σ^{\ast 0}$ decay width is in complete agreement with the data, while that for the $γ^\ast Σ^+ \to Σ^{\ast +}$ is un…

介子云对十重态到八重态重子Dalitz衰变的贡献

Meson cloud contributions to the Dalitz decays of decuplet to octet baryons

本研究在夸克模型框架下结合介子云贡献，计算了十重态到八重态重子的Dalitz衰变宽度，预测HADES和PANDA可检验相关结果，并探讨了测量特定衰变道的可能性。

重子手征微扰论中自旋-$\frac{3}{2}$重子的电磁极化率

Electromagnetic polarizabilities of the spin-$\frac{3}{2}$ baryons in heavy baryon chiral perturbation theory

本研究利用重子手征微扰论计算轻味十重态与单重六重态自旋-3/2重子的电磁极化率，推导至$\u0001(p^3)$阶，发现手征修正和M1跃迁影响显著，且Δ重子电极化率远高于核子。

Connected and disconnected quark contributions to hadron spin

By introducing an external spin operator to the fermion action, the quark spin fractions of hadrons are determined from the linear response of the hadron energies using the Feynman-Hellmann (FH) theorem. At our SU(3)-flavour symmetric point, we find that the connected quark spin fractions are universally in the range 55-70\% for vector mesons and octet and decuplet baryons. There is an indication that the amount of spin suppression is quite sensitive to the strength of SU(3) breaking. We also present first preliminary results applying the FH technique to calculations of quark-line disconnected…

静态三夸克系统的自由能

Free energies of static three quark systems

本文研究了有限温度下SU（3）纯规范理论格点上三重夸克组成的重子系统的自由能行为。对于高于$T_c$的所有温度，我们发现三夸克系统的单（十）重态自由能的连通部分由$qq$ -三重态（-六重态）自由能的连通部分之和给出.使用重整化自由能，我们可以比较自由能在不同的颜色通道，以及那些$qq$ -和$qqq$ -系统在一个独特的能量尺度。

Strange nucleon electromagnetic form factors from lattice QCD

We evaluate the strange nucleon electromagnetic form factors using an ensemble of gauge configurations generated with two degenerate maximally twisted mass clover-improved fermions with mass tuned to approximately reproduce the physical pion mass. In addition, we present results for the disconnected light quark contributions to the nucleon electromagnetic form factors. Improved stochastic methods are employed leading to high-precision results. The momentum dependence of the disconnected contributions is fitted using the model-independent z-expansion. We extract the magnetic moment and the elec…

Nucleon electromagnetic form factors using lattice simulations at the physical point

We present results for the nucleon electromagnetic form factors using an ensemble of maximally twisted mass clover-improved fermions with pion mass of about 130 MeV. We use multiple sink-source separations and three analysis methods to probe ground-state dominance. We evaluate both the connected and disconnected contributions to the nucleon matrix elements. We find that the disconnected quark loop contributions to the isoscalar matrix elements are small, giving an upper bound of up to 2$\%$ of the connected contribution and smaller than its statistical error. We present results for the isovect…

Proton and neutron electromagnetic form factors from lattice QCD

The electromagnetic form factors of the proton and the neutron are computed within lattice QCD using simulations with quarks masses fixed to their physical values. Both connected and disconnected contributions are computed. We analyze two new ensembles of $N_f = 2$ and $N_f = 2 + 1 + 1$ twisted mass clover-improved fermions and determine the proton and neutron form factors, the electric and magnetic radii, and the magnetic moments. We use several values of the sink-source time separation in the range of 1.0 fm to 1.6 fm to ensure ground state identification. Disconnected contributions are calc…

The hadronic contribution to the running of the electromagnetic coupling and the electroweak mixing angle

The electromagnetic coupling $α$ and the electroweak mixing angle $θ_{\mathrm{W}}$ are parameters of the Standard Model (SM) that enter precision SM tests and play a fundamental rôle in beyond SM physics searches. Their values are energy dependent, and non-perturbative hadronic contributions are the main source of uncertainty to the theoretical knowledge of the running with energy. We present a lattice study of the leading hadronic contribution to the running of $α$ and $\sin^2θ_{\mathrm{W}}$. The former is related to the hadronic vacuum polarization (HVP) function of electromagnetic currents,…