We study large-distance contributions to the nucleon parton densities in the transverse coordinate (impact parameter) representation based on generalized parton distributions (GPDs). Chiral dynamics generates a distinct component of the partonic structure, located at momentum fractions x ~< M_pi/M_N and transverse distances b ~ 1/M_pi. We analyze the phenomenological "pion cloud" model of the flavor asymmetry dbar(x) - ubar(x) and quantify what fraction of the calculated asymmetry results from the universal large-distance region. Our findings indicate that a two-component picture of the nucleon's partonic structure, with a "core" antiquark distribution at b < b_core ~= 0.55 fm which vanishes at x -> 0 and the universal large-distance pion cloud, could naturally account for the x-dependence of the measured asymmetry.
Forward-backward (charge) asymmetry in the processes of $e^+e^-$ annihilation into a pair of charged pseudoscalar mesons is recalculated in the one-loop approximation. The exact dependence on the meson masses is taken into account. Results known in the literature are partially corrected. The bulk of the charge asymmetry appears due to double-photon exchange in $s$ channel. Experimental studies of the asymmetry can be used to verify the point-like approximation used in calculation of radiative corrections due to emission of photons by pions or kaons.
The single pion production (SPP) in the charged-current neutrino (antineutrino) scattering off the polarized nucleon is discussed. The spin asymmetry is predicted within two approaches. The spin polarizations of the target nucleon that are longitudinal and perpendicular to the neutrino momentum are considered. It is shown, in several examples, that information about the SPP dynamics coming from the spin asymmetry is complementary to information obtained from measurements of spin averaged cross section. Indeed, the spin asymmetry is sensitive to the nonresonance background description of the SP…
Soft-fermion-pole contribution to single-spin asymmetry for pion production in pp collisions
基于共线因子分解的twist-3机制，研究了核子-核子碰撞中包含π介子产生p^ \uparrow p \to πX的单横自旋不对称性.我们导出了极化核子中软费米子极（SFP）对与扭曲3夸克-胶子关联函数相关的扭曲3单自旋相关截面的贡献。我们发现，尽管SFP函数不像SGP函数那样具有“导数项”，但如果SFP函数与SGP函数具有相似的量级，则SFP函数由于具有大的部分子硬截面和大的色因子而对非对称性A_N产生很大的影响。
In this work, we perform a detailed study of the $τ^-\toπ^-π^0γν$ decay process within the resonance chiral theory. We pay special attention to the triple-product asymmetry in the $τ^-\toπ^-π^0γν$ process. The minimal resonance chiral Lagrangian and the odd-intrinsic parity resonance operators are simultaneously included to calculate the decay amplitudes. Various invariant-mass distributions in the $π^-π^0$, $π^-γ$ and $π^0γ$ systems are studied and they reveal different resonance dynamics. We further predict the intriguing nonzero triple-product asymmetry distributions, which may provide usef…
Soft-Fermion-Pole Mechanism to Single Spin Asymmetry in Hadronic Pion Production
单自旋不对称性（SSA）是在共线因式分解方法中可观察到的扭曲-3。给出了一个与RHIC实验相关的pp碰撞中π介子产生的扭曲3单自旋相关截面公式p^ \uparrow p \to πX.特别地，我们从夸克-胶子关联函数计算了软费米子极（SFP）对散射截面的贡献。我们表明，它的效果可以作为大的软胶子极（SGP）的贡献，由于大SFP部分子硬截面，即使衍生物的SFP功能不参与的截面。
A sizable $\cos 4ϕ$ azimuthal asymmetry in exclusive di-pion production near $ρ^0$ resonance peak in ultraperipheral heavy ion collisions recently has been reported by STAR collaboration. We show that both elliptic gluon Wigner distribution and final state soft photon radiation can give rise to this azimuthal asymmetry. The fact that the QED effect alone severely underestimates the observed asymmetry might signal the existence of the nontrivial correlation in quantum phase distribution of gluons.
We investigate the transverse momentum weighted azimuthal asymmetry with a $\sin\left(3ϕ_h -ϕ_S\right)$ modulation in electroproduction of charged pion production off the transversely polarized proton. The asymmetry is contributed by the product of the second transverse-moment of the pretzelosity distribution function and the first transverse-moment of the Collins function. Using the extracted result for the proton pretzelosity and the available parametrization for the pion Collins function, we numerically predict the $P_{hT}^3$-weighted $\sin\left(3ϕ_h -ϕ_S\right)$ asymmetry for charged pion …
We investigate the single transverse-spin asymmetry with a $\sin (2ϕ-ϕ_S)$ modulation in the pion-induced Drell-Yan process within the theoretical framework of the transverse momentum dependent factorization. The asymmetry is contributed by the convolution of the Boer-Mulders function and the transversity. We adopt the model results for the distributions of the pion meson from the light-cone wavefunction approach and the available parametrization for the distributions of the proton to numerically estimate the $\sin (2ϕ-ϕ_S)$ asymmetry in $π^- p$ Drell-Yan at the kinematics of the COMPASS at CE…
We study the $\sin2ϕ_h$ azimuthal asymmetry of charged and neutral pion productions off the longitudinally polarized nucleon targets in semi-inclusive deeply inelastic scattering (SIDIS) process within the transverse momentum dependent~(TMD) factorization. The asymmetry is contributed by the convolution of the TMD distribution $h_{1L}^{\perp}$ and the Collins fragmentation function $H_{1}^\perp$. We adopt the Wandzura-Wilczek-type~(WW-type) approximation for $h_{1L}^{\perp}$ and two different parametrizations on the nonperturbative part of TMD evolution for $h_{1L}^{\perp}$ and $H_{1}^\perp$. …
We investigate the Sivers asymmetry in the pion-induced single polarized Drell-Yan process in the theoretical framework of the transverse momentum dependent factorization up to next-to-leading logarithmic order of QCD. Within the TMD evolution formalism of parton distribution functions, the recently extracted nonperturbative Sudakov form factor for the pion distribution functions as well as the one for the Sivers function of the proton are applied to numerically estimate the Sivers asymmetry in the $π^- p$ Drell-Yan at the kinematics of the COMPASS at CERN. In the low $b$ region, the Sivers fu…
Predictions for single spin asymmetries in lepton + p(transv. polarized) -> pion + X and gamma^* + p(transv. polarized) -> pion + X
给出了半包容DIS过程中的单横自旋不对称性A_N的预言，指出极化夸克碎裂成相对喷注轴具有横动量k_T的末态强子时的自旋效应，即所谓的Collins效应，可能会产生不可忽略的A_N值。分裂夸克的基本单自旋不对称性在以前的论文中已经被修正，通过拟合p（transv）的数据。极化）+ P -> π介子+ X，并且这里给出的预测唯一地基于这样的假设，即柯林斯效应是所观察到的p（transv）中的单自旋不对称性的唯一原因。极化）+ p -> π介子+ X。最后讨论了夸克分布函数中的自旋和k_T依赖性，即所谓的Sivers效应。
Understanding the proton spin composition from the quarks and gluons spin polarization and their motion is important to test various kinds of sum rules and nonperturbative properties of hadrons. At the Relativistic Heavy Ion Collider (RHIC), we collide longitudinally polarized proton beams and measure the double helicity asymmetry $A_{LL}$, which is an important physical quantity for extracting the polarized parton distribution functions (PDFs) of the proton. Direct photon, jet and charged pion production are good channels to probe the gluon spin polarization inside the proton, with the abilit…
Theoretical Update of Twist-3 Single-Spin Asymmetry in Semi-Inclusive DIS
基于与大横动量π介子产生相关的共线因子分解中的twist-3机制，讨论了半包容DIS（$e p^\uparrow \to e πX$）中的单自旋不对称性.这更新了我们以前的研究，包括，特别是，新的部分子过程引起的贡献，并允许我们推导出完整的公式为相应的单自旋不对称性与一套完整的扭曲3夸克胶子关联函数在横向极化核子。我们讨论了与低横动量π介子产生的横动量相关因子分解结果的对应关系。
We investigate the possible formation of a Bose-Einstein condensed phase of pions in the early Universe at nonvanishing values of lepton flavor asymmetries. A hadron resonance gas model with pion interactions, based on first-principle lattice QCD simulations at nonzero isospin density, is used to evaluate cosmic trajectories at various values of electron, muon, and tau lepton asymmetries that satisfy the available constraints on the total lepton asymmetry. The cosmic trajectory can pass through the pion condensed phase if the combined electron and muon asymmetry is sufficiently large: $|l_e + …
