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| Format: | Preprint |
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2020
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| Online Access: | https://arxiv.org/abs/2011.00530 |
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| _version_ | 1866918125301137408 |
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| author | d'Enterria, David Yan, Cynthia |
| author_facet | d'Enterria, David Yan, Cynthia |
| contents | 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2011_00530 |
| institution | arXiv |
| publishDate | 2020 |
| record_format | arxiv |
| spellingShingle | Revised QCD effects on the $Z\to b\bar{b}$ forward-backward asymmetry in $e^+e^-$ collisions d'Enterria, David Yan, Cynthia High Energy Physics - Phenomenology High Energy Physics - Experiment 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. |
| title | Revised QCD effects on the $Z\to b\bar{b}$ forward-backward asymmetry in $e^+e^-$ collisions |
| topic | High Energy Physics - Phenomenology High Energy Physics - Experiment |
| url | https://arxiv.org/abs/2011.00530 |