Puzzled or surprised by the almost incredible accuracy occasionally claimed in the literature to be achievable for numerical outcomes of QCD sum-rule analyses, we scrutinized the usual procedure employed for the extraction of the parameters of individual bound states from dispersive sum rules by taking advantage of the exact solvability of a quantum-mechanical harmonic-oscillator model: It turns out that the determination of the ground-state parameters (that is, decay constant and form factor) by requiring independence from the Borel mass in its stability window does not necessarily yield their exact numerical values. For instance, the comparison of the sum-rule predictions for bound-state parameters with their numerical values known precisely in our harmonic-oscillator model reveals that standard sum-rule procedures underestimate the ground-state decay constant by some 4% and its form factor by almost 15%; such systematic uncertainties cannot be inferred from our correlators' accuracy better than 1% in the window of Borel stability: they are uncontrollable.
The hadronic contribution to the eight forward amplitudes of light-by-light scattering ($γ^*γ^*\to γ^*γ^*$) is computed in lattice QCD. Via dispersive sum rules, the amplitudes are compared to a model of the $γ^*γ^*\to {\rm hadrons}$ cross sections in which the fusion process is described by hadronic resonances. Our results thus provide an important test for the model estimates of hadronic light-by-light scattering in the anomalous magnetic moment of the muon, $a_μ^{\rm HLbL}$. Using simple parametrizations of the resonance $M\to γ^*γ^*$ transition form factors, we determine the corresponding …
We present the calculation of the next-to-leading order QCD corrections for top-quark pair production in association with an additional jet at hadron colliders, using the modified minimal subtraction scheme to renormalize the top-quark mass. The results are compared to measurements at the Large Hadron Collider run I. In particular, we determine the top-quark running mass from a fit of the theoretical results presented here to the LHC data.
Data from the Belle Collaboration for associated production (with a light unpolarized hadron) and single-inclusive production of transversely polarized $Λ$-hyperons in $e^+e^-$ annihilation processes allowed to extract within a TMD approach, for the first time, the $Λ$ polarizing fragmentation function. Recent theoretical developments on the computation of cross sections for single-inclusive hadron production in $e^+e^-$ annihilation processes, within a Soft Collinear Effective Theory approach, combined with the CSS formalism for the double-hadron production case, can be used to perform a rene…
Memo on Extracting |V(cb)| and |V(ub)/V(cb)| from semileptonic B decays
本文对美强子半轻子衰变的重夸克展开作了简要的评述。分析了如何从$B$介子的半轻子宽度、所有弱衰变美强子的平均半轻子宽度和零反冲下的$B \ra l νD^*$中提取$|V(cb)|$。特别注意目前的理论不确定性（包括它们之间的相关性），以及如何在未来减少它们。最后，我将评论$|V(ub)/V(cb)|$中的理论不确定性。
Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tre（意大利国家核物理研究所罗马三分部）；Physics Department and INFN Sezione di Roma, Università di Roma La Sapienza（罗马大学物理系与INFN罗马分部）
We study the suppressions of high transverse momentum single hadron and dihadron productions in high-energy heavy-ion collisions based on the framework of a next-to-leading-order perturbative QCD parton model combined with the higher-twist energy loss formalism.Our model can provide a consistant description for the nuclear modification factors of single hadron and dihadron productions in central and non-central nucleus-nucleus collisions at RHIC and the LHC energies. We quantitatively extract the value of jet quenching parameter $\hat q$ via a global $χ^2$ analysis, and obtain ${\hat{q}}/{T^3}…
We present a discussion on the methods for extracting a given parameter from measurements of hadronic data, with particular focus on determinations of the strong coupling constant. We show that when the PDF dependency on the determination is adequately taken into account, the dispersion between the results from different measurements is significantly reduced. We speculatively propose the concept of preferred value of a parameter from a particular dataset.
Nuclear modification factors of single hadrons and dihadrons at large transverse momentum ($p_{\rm T}$) in high-energy heavy-ion collisions are studied in a next-to-leading-order (NLO) perturbative QCD parton model. Parton fragmentation functions (FFs) in $A+A$ collisions are modified due to jet energy loss which is proportional to the jet transport coefficient $\hat{q}$ characterizing the interaction between the parton jet and the produced medium. By confronting 6 current sets of NLO parton FFs for large $p_{\rm T}$ hadron productions, we extract $\hat{q}$ quantitatively via a global fit to d…
Precision Corrections to Dispersive Bounds on Form Factors
本文给出了底强子半轻子衰变中色散关系形状因子界的精确修正，并分析了它们对由这些界导出的参数化的影响。我们将QCD两圈和非微扰修正的两点相关，考虑形状因子的衰变率的贡献被抑制轻子质量，并实现更现实的估计截断误差与参数化。我们包括更高的共振在强子的总和，再加上重夸克的对称性关系接近零反冲，进一步收紧总和规则的界限。利用所有这些改进，我们表明，在B --> D l nu和B --> D^* l nu中的六个形状因子中的每一个可以仅使用总体归一化和一个未知参数以3%或更小的精度来描述。一个类似的对Lambda_b --> Lambda_c l nu形状因子的单系数参数化，以及对1/m^2阶有效的重夸克对称关系，用一个未知参数和唯象上有趣的量（\bar Lambda）_Lambda \approx M_{Lambda_b} - m_b来描述微分重子衰变速率。我们讨论的有效性的斜率曲率关系推导出Caprini和Neubert，并提出较弱的，校正的关系。最后，我们提出了目前的实验B --> D^*l nu和B --> D l nu数据的改进的单参数展开的样本拟合。
Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tre（意大利国家核物理研究所罗马第三分部）；Physics Department and INFN Sezione di Roma, Università di Roma La Sapienza（罗马大学物理系及意大利国家核物理研究所罗马分部）
We discuss the simultaneous dispersive analyses of $πK\to πK$ and $ππ\to K \bar{K}$ scattering data and the $κ/K^*_0(700)$ resonance. The unprecedented statistics of present and future Hadron Experiments, modern Lattice QCD calculations, and the wealth of new states and decays, require such precise and model-independent analyses to describe final state interactions. We review the existing and often conflicting data and explain in detail the derivation of the relevant dispersion relations, maximizing their applicability range. Next, we review and extend the caveats on some data, showing their i…
We discuss the specific features of extracting properties of the exotic polyquark hadrons (tetraquarks, pentaquarks) compared to the usual hadrons by the QCD sum-rule approach. In the case of the ordinary hadrons, already the one-loop leading-order correlation functions provide the bulk of the hadron observables, e.g., of the form factor; inclusion of radiative corrections modifies already nonzero one-loop contributions. In the case of an exotic hadron, the situation is qualitatively different: discussing strong decays of an exotic tetraquark meson, which provide the main contribution to its w…
Parton distribution functions (PDFs) are nonperturbative quantities describing the relation between a hadron and quarks and gluons within it. We propose to extract PDFs from QCD global analysis of "data" generated by lattice QCD calculations of good "lattice cross sections", which are basically single-hadron matrix elements that are lattice QCD calculable and perturbative QCD factorizable into the PDFs. To demonstrate the existence of good "lattice cross sections", we take quasi-quark distribution introduced by Ji [1] as a case study to show that it could be factorized into the PDFs to all ord…
We present a new technique for extracting decay and transition rates into final states with any number of hadrons. The approach is only sensitive to total rates, in which all out-states with a given set of QCD quantum numbers are included. For processes involving photons or leptons, differential rates with respect to the non-hadronic kinematics may also be extracted. Our method involves constructing a finite-volume Euclidean four-point function, whose corresponding spectral function measures the decay and transition rates in the infinite-volume limit. This requires solving the inverse problem …
We develop a number of sum rules comparing spectral integrals involving judiciously chosen weights to integrals over the corresponding Euclidean two-point function. The applications we have in mind are to the hadronic vacuum polarization that determines the most important hadronic correction $a_μ^{\rm HVP}$ to the muon anomalous magnetic moment. First, we point out how spectral weights may be chosen that emphasize narrow regions in $\sqrt{s}$, providing a tool to investigate emerging discrepancies between data-driven and lattice determinations of $a_μ^{\rm HVP}$. Alternatively, for a narrow re…
