Effective Predictions of Event Shapes: Factorized, Resummed, and Gapped Angularity Distributions
Andrew Hornig, Christopher Lee, Grigory Ovanesyan
备注:
52 pages, 13 figures, 1 table, uses JHEP3.cls. v2: comparison between SCET and QCD clarified, other minor corrections, v3: journal version, references added, minor corrections and clarifications
Using soft-collinear effective theory (SCET), which provides a unified framework for factorization, resummation of logarithms, and incorporation of universal nonperturbative functions in hard-scattering QCD cross-sections, we present a new prediction of angularity distributions in e+e- annihilation. Angularities tau_a are an infinite class of event shapes which vary in their sensitivity to the substructure of jets in the final state, controlled by a continuous parameter a<2. We calculate angularity distributions for all a<1 to first order in the strong coupling alpha_s and resum large logarithms in these distributions to next-to-leading logarithmic (NLL) accuracy. Our expressions for the next-to-leading order (NLO) O(alpha_s) partonic jet and soft functions in the factorization theorem for angularity distributions are given for the first time. We employ a model for the nonperturbative soft function with a gap parameter which cancels the renormalon ambiguity in the partonic soft function. We explore the relation between the SCET approach to resummation and past approaches in QCD, and discuss the advantages of the effective theory approach. In addition, we draw from the NLO calculations of the jet and soft functions an intuitive lesson about how factorization breaks down in the effective theory as a->1.
We present angularity differential cross-section for the deep inelastic scattering process (DIS) in the framework of soft-collinear effective theory (SCET). Using SCET, the cross-section is factorized in terms of hard, jet, beam and soft functions. Our result includes resummation of the large logarithms up to next-to-next leading logarithmic (NNLL) accuracy. The numerical results presented here for DIS angularity cross-section can be explored by the future EIC.
We present predictions for the $e^{+}e^{-}$ event shape angularities at NNLL$^{\prime}$ resummed and $\mathcal{O}(α_s^{2})$ matched accuracy and compare them to LEP data at center-of-mass energies $Q=91.2$ GeV and $Q=197$ GeV. We perform the resummation within the framework of Soft-Collinear Effective Theory, and make use of recent results for the two-loop angularity soft function. We determine the remaining NNLL$^{\prime}$ and $\mathcal{O}(α_s^2)$ ingredients from a fit to the EVENT2 generator, and implement a shape function with a renormalon-free gap parameter to model non-perturbative effec…
Threshold resummed spectra in B -> Xu l nu decays in NLO (II)
我们把不变强子质量mX与强子总能量EX之比的分布和半轻子衰变B -> Xu l nu中mX的分布恢复到次领先级。通过扩展我们的公式,我们得到了O(α S ^2)处所有红外光谱的系数和O(α S ^3)处主要红外光谱的系数。我们明确地表明,这些半轻子谱和辐射衰变B -> Xs γ中的光子谱之间的关系不是一个纯粹的短距离。在半轻子光谱中存在长距离效应,它不能完全被辐射衰变中测量的结构函数分解,必须以某种方式进行建模。
Multivariate analyses are emerging as important tools to understand properties of hadronic jets which play a key role in the LHC experimental program. We take a first step towards precise and differential theory predictions by calculating the cross section for $e^+ e^- \to$ 2 jets differential in the angularities $e_α$ and $e_β$. The logarithms of $e_α$ and $e_β$ in the cross section are jointly resummed to next-to-next-to-leading logarithmic accuracy, using the SCET+ framework we developed, and are matched to the next-to-leading order cross section. We perform analytic one-loop calculations t…
Event shape observables have been widely used for precision QCD studies at various lepton and hadron colliders. We present the most accurate calculation of the transverse-energy-energy correlation event shape variable in deep-inelastic scattering. In the framework of soft-collinear effective theory the cross section is factorized as the convolution of the hard function, beam function, jet function and soft function in the back-to-back limit. A close connection to TMD factorization is established, as the beam function when combined with part of the soft function is identical to the conventional…