论文标题
修订的QCD对$ z \ to b \ bar {b} $ forward-backward不对称$ e^+e^ - $ collision
Revised QCD effects on the $Z\to b\bar{b}$ forward-backward asymmetry in $e^+e^-$ collisions
论文作者
论文摘要
$ e^+e^ - $ e^+e^ - $ quarks的前向后背部（fb）在LEP测量的z极点碰撞，$ a_ \ text {fb}^{0，b} = 0.0992 \ 0.0992 \ pm0.0016 $，如今仍与lar extervision observision observisional tit lar dilectional tath lar dilectional（2.4 $）（2.4） $（a_ \ text {fb}^{0，b}）_ {_ \ text {th}} = 0.1030 \ pm 0.0002 $。除了主要的统计不确定性之外，QCD效应（例如$ b $ quark淋浴和强环化）是$ a_ \ text {fb}^{0，b} $系统不确定性的主要来源，在过去的二十年中尚未对其进行修订。我们使用现代的Parton淋浴Pythia 8和Vincia模拟，重新评估八个原始$ a_ \ text {fb}^{0，B} $ LEP测量的QCD不确定性，并具有九种不同的软辐射和界线辐射以及零件片片的实现。我们的分析与NNLO大量$ b $ quark校正相结合，独立计算，表明$ \ sim $ 0.7 \％\％和$ \ sim $ 0.3 \％的总传播QCD不确定性分别是Lep-and-Jet-charge分析分析，大约是两个小于原始LEP结果的因素。考虑此类更新的QCD效果会导致新的$ a_ \ text {fb}^{0，b} = 0.0995 \ pm0.0016 $平均，数据理论的张力从2.4 $σ$降低到2.2 $σ$。确认或解决这一长期差异需要新的高亮度$ e^+e^ - $ collider收集Z Pole的更多数据，以显着降低主导的$ a_ \ a_ \ text {fb}^{0，b} $统计不确定性，并提高我们对$ b $ $ $ - $ - $ quark淋浴的理解。
The forward-backward (FB) asymmetry of $b$ quarks in $e^+e^-$ collisions at the Z pole measured at LEP, $A_\text{FB}^{0,b} = 0.0992\pm0.0016$, remains today one of the electroweak precision observables with the largest disagreement (2.4$σ$) with respect to the Standard Model prediction, $(A_\text{FB}^{0,b})_{_\text{th}} = 0.1030 \pm 0.0002$. Beyond the dominant statistical uncertainties, QCD effects, such as $b$-quark showering and hadronization, are the leading sources of $A_\text{FB}^{0,b}$ systematic uncertainty, and have not been revised in the last twenty years. We reassess the QCD uncertainties of the eight original $A_\text{FB}^{0,b}$ LEP measurements, using modern parton shower PYTHIA 8 and VINCIA simulations with nine different implementations of soft and collinear radiation as well as of parton fragmentation. Our analysis, combined with NNLO massive $b$-quark corrections independently computed, indicates total propagated QCD uncertainties of $\sim$0.7\% and $\sim$0.3\% for the lepton- and jet-charge analyses, respectively, that are about a factor of two smaller than those of the original LEP results. Accounting for such updated QCD effects leads to a new $A_\text{FB}^{0,b} = 0.0995\pm0.0016$ average, with a data-theory tension slightly reduced from 2.4$σ$ to 2.2$σ$. Confirmation or resolution of this long-term discrepancy requires a new high-luminosity $e^+e^-$ collider collecting orders-of-magnitude more data at the Z pole to significantly reduce the dominant $A_\text{FB}^{0,b}$ statistical uncertainties, and to improve our understanding of $b$-quark showering and hadronization.
