We calculate next-to-leading-order (NLO) correction to the pion electromagnetic form factor at leading twist in the $k_T$ factorization theorem. Partons off-shell by $k_T^2$ are considered in both quark diagrams and effective diagrams for the transverse-momentum-dependent (TMD) pion wave function. The light-cone singularities in the TMD pion wave function are regularized by rotating the Wilson lines away from the light cone. The soft divergences from gluon exchanges among initial- and final-state partons cancel exactly. We derive the infrared-finite $k_T$-dependent NLO hard kernel for the pion electromagnetic form factor by taking the difference of the above two sets of diagrams. Varying the renormalization and factorization scales, we find that the NLO correction is smaller, when both the scales are set to the invariant masses of internal particles: it becomes lower than 40% of the leading-order (LO) contribution for momentum transfer squared $Q^2>7$ GeV$^2$. It is observed that the NLO leading-twist correction does not play an essential role in explaining the experimental data, but the LO higher-twist contribution does.
We investigate the theoretical framework of the $\cos 2ϕ$ azimuthal asymmetry contributed by the coupling of two Boer-Mulders functions in the dilepton production unpolarized $πp$ Drell-Yan process by applying the transverse momentum dependent factorization at leading order. We adopt the model calculation results of the unpolarized distribution function $f_1$ and Boer-Mulders function $h_1^\perp$ of pion meson from the light-cone wave functions. We take into account the transverse momentum evolution effects for both the distribution functions of pion and proton by adopting the existed extracti…
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 extract the pion transverse momentum dependent (TMD) parton distribution by fitting the pion-induced Drell-Yan process within the framework of TMD factorization. The analysis is done at the next-to-next-to-leading order (NNLO) with proton TMD distribution and non-perturbative TMD evolution extracted earlier in the global fit. We observe the significant difference in the normalization of transverse momentum differential cross-section measured by E615 experiment and the theory prediction.
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…
Photon-pion transition form factor: BABAR puzzle is cracked
最近,BABAR合作组公布了(arXiv:0905.4778)光子-π介子跃迁形状因子$F_{πγγ^{\ast}}(Q^{2})$的数据,这与微扰QCD的标准因子分解方法的预测是强烈矛盾的。紧接着,提出了两种机制(A.E. Dorokhov,arXiv:0905.4577; A. V. Radyushkin,arXiv:0906.0323),其在数学上增强了形状因子渐近性,因此提供了对BABAR数据的定性满意描述。然而,巴巴尔效应的物理学原理并没有完全阐明。在目前的工作中,基于对QCD真空的非微扰方法和相当普遍的假设,我们证明了π介子跃迁形状因子存在两个渐近区域。一个具有渐近性$F_{πγ^{\ast}γ}(Q^{2})\sim1/Q^{2}$的区域对应于标准QCD因子分解方法的结果,而另一个区域违反标准因子分解并导致渐近行为为$F_{πγ^{\ast}γ}(Q^{2})\sim\ln(Q^{2})Q^{2}$。此外,考虑特定的非定域手征夸克模型,我们找到了参数区域,在该区域成功描述了现有的π介子跃迁形状因子的CELLO、CLEO和BABAR数据。
We present a new determination of unpolarised charged pion and kaon fragmentation functions from a set of single-inclusive electron-positron annihilation and lepton-nucleon semi-inclusive deep-inelastic scattering data. The determination includes next-to-next-to-leading order QCD corrections to both processes, and is carried out in a framework that combines a neural-network parametrisation of fragmentation functions with a Monte Carlo representation of their uncertainties. We discuss the quality of the determination, in particular its dependence on higher order corrections.
In this paper, we investigate the factorization hypothesis step by step for the exclusive process $B \to ρ$ at next-to-leading order (NLO) with the collinear factorization approach, and then we extend our results to the $k_T$ factorization frame. We show that the soft divergence from the specific NLO diagrams will cancel each other at the quark level, while the remaining collinear divergence can be absorbed into the NLO wave functions. The full NLO amplitudes can be factorized into two parts: the NLO $B$ and $ρ$ meson wave functions containing the collinear divergence and the leading order (LO…
The Pion Gravitational Form Factors and the Trace Anomaly in QCD Factorization
Università del Salento(萨伦托大学);INFN Sezione di Lecce(意大利国家核物理研究所莱切分部);National Center for HPC, Big Data and Quantum Computing(高性能计算、大数据与量子计算国家中心);CNR Nanotec(意大利国家研究委员会纳米技术研究所);Institute of Physics, Academia Sinica(中央研究院物理学研究所)
We revisit the evaluations for the spacelike and timelike $ρπ$ transition form factors $F_{ρπ}(Q^2)$ and $G_{ρπ}(Q^2)$ with the inclusion of the the next-to-leading order (NLO) QCD contributions in the framework of the $k_T$ factorization theorem. The infrared divergence is regularized by the transversal momentum carried by external valence quarks, and ultimately absorbed into the meson wave functions. In the region of $ Q^2 \leqslant 2 \, \textrm{GeV}^2 $, where PQCD factorization apporach applicable, the NLO contribution can bring no larger than $ 35\%$ enhancement to the spacelike form fact…
Working in the nonrelativistic-QCD factorization framework at next-to-leading order in $α_s$, we fit the relevant color octet (CO) long-distance matrix elements (LDMEs) of the $ψ(2S)$ meson, $\langle {\cal O}^{ψ(2S)}({^1S}_0^{[8]})\rangle$, $\langle {\cal O}^{ψ(2S)}({^3S}_1^{[8]})\rangle$, and $\langle {\cal O}^{ψ(2S)}({^3P}_0^{[8]})\rangle$, to 1001 data points of upolarized and polarized $ψ(2S)$ inclusive hadroproduction. We do four different fits, with filters on polarization and low to middle transverse momentum $p_T$. We find that a successful description of the data is only possible with…
We have applied the extended factorization scheme to investigate the electroweak pion production on nuclei. The ANL-Osaka model, which was obtained by analyzing the data of $πN$, $γN$, $N(e,e'π)$ and $N(ν,μ\,π) $ reactions up to invariant mass $W=$ 2 GeV, is used to generate the matrix elements of current operators relevant to pion-production off the nucleon. Medium effects on the $Δ$ (1232) component of meson-exchange current are included by using a $Δ$-nucleus potential determined from the previous $Δ$-hole model studies of pion-nucleus reactions. Nuclear correlations in the initial target s…
QCD factorization in gamma* gamma -> pi pi and gamma* N -> pi pi N
在高虚光子与实光子碰撞过程中,在阈附近唯一的2 π介子产生为解开强子的部分子内容提供了新的可能性。我们解释这个政权的动力学,即分离的振幅在QCD微扰理论和广义分布振幅,这是非微扰函数描述的排他性过渡的一个部分子对到两个强子计算的部分子图。在核子的动量转移和π介子对的不变质量都很小的运动学区域中,同样的量也出现在gamma* N -> pi pi N中;这允许将QCD分析扩展到两个产生的π介子的共振区域之外。
We complete the calculation of the QCD penguin amplitude at next-to-next-to-leading order in the QCD factorization approach to non-leptonic B-meson decays. This provides the last missing piece in the computation of the QCD correction to direct CP asymmetries at leading power in the heavy-quark expansion.
We present the next-to-leading power (NLP) factorization formula for the $q\bar{q}\to γ^*+X$ channel of the Drell-Yan production near the kinematic threshold limit. The formalism used for the computation of next-to-leading power corrections within soft-collinear effective field theory is introduced, we discuss the emergence of new objects, the NLP collinear functions, and define them through an operator matching equation. We review the leading power factorization before extending it to subleading powers. We also present the one-loop result for the newly introduced collinear function, and demon…
We present a factorization theorem valid near the kinematic threshold $z=Q^2/\hat{s}\to 1$ of the partonic Drell-Yan process $q\bar q\toγ^*+X$ for general subleading powers in the $(1-z)$ expansion. We then consider the specific case of next-to-leading power. We discuss the emergence of collinear functions, which are a key ingredient to factorization starting at next-to-leading power. We calculate the relevant collinear functions at $\mathcal{O}(α_s)$ by employing an operator matching equation and we compare our results to the expansion-by-regions computation up to the next-to-next-to-leading …
In this paper a new comprehensive analysis of parton-to-pion fragmentation functions (FFs) is performed for the first time by including all experimental data sets on single inclusive pion as well as unidentified light charged hadron production in electron-positron ($e^+e^-$) annihilation. We determine the pion FFs along with their uncertainties using the standard "Hessian" technique at next-to-leading order (NLO) and next-to-next-to leading order (NNLO) in perturabative QCD. It is shown that the determination of pion FFs using simultaneously the data sets from pion and unidentified light charg…