近似树衰变B- -> pi-pi 0/rho-rho 0可以作为检验强子B介子衰变中强相互作用动力学的各种理论描述的基准通道。强子和微分半轻子B -> pi l nu/rho l nu在最大反冲时的衰变率之比为QCD动力学提供了特别清晰的探针。我们将最近的NNLO计算结果与实验数据进行了比较，发现QCD因子分解假设得到了支持。对所有树主导的B -> pi pi/pi rho/rho rho衰变模式的详细分析似乎有利于某种程度上增强的颜色抑制振幅，这可以通过B介子光锥分布振幅的一阶倒数矩的小值λ_B ~ 250 MeV在QCD因子分解中容纳。B -ρ nu光谱的精确测量可以帮助澄清这一点。
英文摘要：
The approximate tree decays B- -> pi- pi0/rho- rho0 may serve as benchmark channels for testing the various theoretical descriptions of the strong interaction dynamics in hadronic B meson decays. The ratios of hadronic and differential semileptonic B -> pi l nu/rho l nu decay rates at maximum recoil provide particularly clean probes of the QCD dynamics. We confront the recent NNLO calculation in the QCD factorization framework with experimental data and find support for the factorization assumption. A detailed analysis of all tree-dominated B -> pi pi/pi rho/rho rho decay modes seems to favour somewhat enhanced colour-suppressed amplitudes, which may be accommodated in QCD factorization by a small value of the first inverse moment of the B meson light-cone distribution amplitude, lambda_B ~ 250 MeV. Precise measurements of the B -> rho l nu spectrum could help to clarify this point.
We evaluate in the framework of QCD factorization the two-loop vertex corrections to the decays $\bar{B}_{(s)}\to D_{(s)}^{(\ast)+} \, L^-$ and $Λ_b \to Λ_c^+ \, L^-$, where $L$ is a light meson from the set $\{π,ρ,K^{(\ast)},a_1\}$. These decays are paradigms of the QCD factorization approach since only the colour-allowed tree amplitude contributes at leading power. Hence they are sensitive to the size of power corrections once their leading-power perturbative expansion is under control. Here we compute the two-loop ${\cal O}(α_s^2)$ correction to the leading-power hard scattering kernels, an…
NNLO Vertex Corrections in charmless hadronic B decays: Imaginary part
我们在QCD因式分解框架下计算了强子二体衰变的2圈顶点修正的虚部B -> pi pi。这完成了拓扑树振幅虚部的NNLO计算，并代表了QCD因式分解中直接CP不对称性的NNLO预测的重要一步。关于技术方面，我们发现，软共线红外发散取消硬散射内核，这表明因式分解在2圈顺序。所有的结果得到解析，包括依赖于粲夸克质量。数值的NNLO校正的影响被认为是显着的，特别是它们导致增强的强相位的颜色抑制树振幅。
Exclusive non-leptonic two-body decays of $B$ mesons have been studied extensively in the past two decades within the framework of factorization. However, the exploration of the corresponding three-body case has only started recently, in part motivated by new data. We consider here the simplest non-leptonic three-body $B$ decays from the point of view of factorization, namely heavy-to-heavy transitions. We provide a careful derivation of the SCET/QCDF factorized amplitudes to NNLO in $α_s$, and discuss the numerical impact of NLO and NNLO corrections. We then study the narrow-width limit, show…
NNLO corrections to inclusive semileptonic B decays in the shape-function region
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We construct predictions for top quark pair differential distributions at hadron colliders that combine state-of-the-art NNLO QCD calculations with double resummation at NNLL' accuracy of threshold logarithms arising from soft gluon emissions and of small mass logarithms. This is the first time a resummed calculation at full NNLO+NNLL' accuracy in QCD for a process with non-trivial color structure has been completed at the differential level. Of main interest to us is the stability of the M_{tt} and top-quark p_T distributions in the boosted regime where fixed order calculations may become str…
We present numerical calculations of the partial width of the charged Higgs boson decay into a top quark, $H^- \rightarrow \bar{t} + b + X$, and the partial width of the top quark decay into a light charged Higgs boson $t \rightarrow H^+ + b + X$ at next-to-next-to-leading order (NNLO) in QCD, based on a factorization formula of the jet mass. The NNLO corrections significantly reduce the renormalization scale dependence of the partial decay width in both cases. We show relative size of the NNLO corrections for different charged Higgs boson masses and for different renormalization scales. The N…
In this paper we calculate the next-to-leading-order (NLO) corrections to $ρ$-meson electromagnetic form factors by employing the $k_T$ factorization approach. We find that the NLO correction to $F_i (Q^2)(i=LT,TL)$ is around $30\%$ of the leading-order (LO) contributionin the region $Q^2>2GeV^2$. The NLO correction to $F_{LL}(Q^2)$ is close to $20\%$ of the LO one in the region $Q^2>3GeV^2$. The NLO radiative corrections to the electric, magnetic, and quadruple form factors $F_j(Q^2) (j=1,2,3)$ are sizeable in magnitude and agree with those from other approaches.
Based on the nonrelativistic QCD factorization theorem, we resum QCD corrections to the inclusive decay rate of $η_c$ and $η_b$ in the large-$n_f$ limit using bubble chain resummation. By employing dimensional regularization, we show explicitly the cancellation of the infrared renormalon ambiguity in the factorization formula at leading order in $v$ in the large-$n_f$ limit, where $v$ is the typical heavy quark velocity inside the meson. We also make predictions of the ratio of the inclusive decay rate to the decay rate into two photons. By comparing our results with a fixed-order calculation …
Within the nonrelativistic QCD (NRQCD) factorization framework, we compute the long-awaited ${\mathcal O}(α_s^2)$ correction for the exclusive double charmonium production process at $B$ factories, {\it i.e.}, $e^+e^-\to J/ψ+η_c$ at $\sqrt{s}=10.58$ GeV. For the first time, we confirm that NRQCD factorization does hold at next-to-next-to-leading-order (NNLO) for exclusive double charmonium production. It is found that including the NNLO QCD correction considerably reduces the renormalization scale dependence, and also implies the reasonable perturbative convergence behavior for this process. O…
We present cross section predictions for the isolated diphoton production in next-to-next-to-leading order (NNLO) QCD using the computational framework MATRIX. Both the integrated and the differential fiducial cross sections are calculated. We found that the arbitrary setup of the isolation procedure introduces uncertainties with a size comparable to the estimation of the theoretical uncertainties obtained with the customary variation of the factorization and renormalization scales. This fact is taken into account in the final result.
In this work, we study the radiative decay of $Z$ boson to a $P$-wave quarkonium $H$ in association with a photon, where $H$ can be $χ_{QJ}$, $h_Q$ with $Q=c,b$ and $J=0,1,2$. The helicity amplitudes and the unpolarized decay widths are evaluated up to QCD next-to-next-to-leading order (NNLO) within the framework of nonrelativistic QCD (NRQCD). For the first time, we check the NRQCD factorization for $h_Q$ exclusive production at two-loop order. The leading logarithms (LL) of $m_Z^2/m_Q^2$ in the leading-twist short-distance coefficients, which may potentially ruin the perturbative convergence…
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…
We present for first time the computation at large $q_T$ (or small $b_T$) matching coefficients of Transverse Momentum Dependent Parton Distribution Function (TMDPDF) for linearly polarised to the integrated gluon distribution at next-to-next-to leading order (NNLO). The computation is performed using the modified $δ$-regulator for rapidity divergences and dimensional regularization. This TMDPDF matriz element presnts phenomenological interest in two kind of processes. The factorization of the Higgs production transverse momentum ($q_T$) distribution through gluon-gluon fusion and the quarkoni…
NNLO QCD corrections to hadron production in DIS at finite transverse momentum
Shanghai Jiao Tong University（上海交通大学）；Fudan University（复旦大学）；Shandong University（山东大学）；Peking University（北京大学）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）
