Unbinned measurement of thrust in $e^+e^-$ collisions at $\sqrt{s}$ = 91.2 GeV with ALEPH archived data
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| Main Authors: | , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866908611509223424 |
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| author | Alliance, The Electron-Positron : Badea, Anthony Baty, Austin Bossi, Hannah Chen, Yu-Chen Chen, Yi Zhang, Jingyu Innocenti, Gian Michele Maggi, Marcello McGinn, Chris Peters, Michael Sheng, Tzu-An Mikuni, Vinicius Avaylon, Matthew Komiske, Patrick Metodiev, Eric Thaler, Jesse Nachman, Benjamin Lee, Yen-Jie |
| author_facet | Alliance, The Electron-Positron : Badea, Anthony Baty, Austin Bossi, Hannah Chen, Yu-Chen Chen, Yi Zhang, Jingyu Innocenti, Gian Michele Maggi, Marcello McGinn, Chris Peters, Michael Sheng, Tzu-An Mikuni, Vinicius Avaylon, Matthew Komiske, Patrick Metodiev, Eric Thaler, Jesse Nachman, Benjamin Lee, Yen-Jie |
| contents | The strong coupling constant ($α_{S}$) is a fundamental parameter of quantum chromodynamics (QCD), the theory of the strong force. Some of the earliest precise constraints on $α_{S}$ came from measurements of event shape observables, such as thrust ($T$), using hadronic $Z$ boson decays produced in $e^+e^-$ collisions. However, recent work has revealed discrepancies between event-shape-based extractions of $α_{S}$ and values determined using other experimental methods. This work reexamines archived $e^+e^-$ data collected at a collision energy of $\sqrt{s}=91.2$ GeV by the ALEPH detector at the Large Electron-Positron Collider. Modern machine learning techniques are used to correct for detector effects in an unbinned manner, allowing the $T$ distribution to be measured with higher granularity than previous ALEPH measurements. The new measurement reveals a small but systematic shift towards larger values of $τ=1-T$, and the potential implications of this shift for $α_{S}$ extractions are illustrated by comparing to state-of-the-art theoretical calculations. In addition, the region of $-6<\logτ<-2$, where poorly-understood non-perturbative effects are large, is compared to modern parton shower Monte Carlo simulations. This measurement provides unique new inputs for $α_{S}$ extractions and also improves constraints on phenomenological models of QCD dynamics such as parton fragmentation and hadronization. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2510_22038 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Unbinned measurement of thrust in $e^+e^-$ collisions at $\sqrt{s}$ = 91.2 GeV with ALEPH archived data Alliance, The Electron-Positron : Badea, Anthony Baty, Austin Bossi, Hannah Chen, Yu-Chen Chen, Yi Zhang, Jingyu Innocenti, Gian Michele Maggi, Marcello McGinn, Chris Peters, Michael Sheng, Tzu-An Mikuni, Vinicius Avaylon, Matthew Komiske, Patrick Metodiev, Eric Thaler, Jesse Nachman, Benjamin Lee, Yen-Jie High Energy Physics - Experiment The strong coupling constant ($α_{S}$) is a fundamental parameter of quantum chromodynamics (QCD), the theory of the strong force. Some of the earliest precise constraints on $α_{S}$ came from measurements of event shape observables, such as thrust ($T$), using hadronic $Z$ boson decays produced in $e^+e^-$ collisions. However, recent work has revealed discrepancies between event-shape-based extractions of $α_{S}$ and values determined using other experimental methods. This work reexamines archived $e^+e^-$ data collected at a collision energy of $\sqrt{s}=91.2$ GeV by the ALEPH detector at the Large Electron-Positron Collider. Modern machine learning techniques are used to correct for detector effects in an unbinned manner, allowing the $T$ distribution to be measured with higher granularity than previous ALEPH measurements. The new measurement reveals a small but systematic shift towards larger values of $τ=1-T$, and the potential implications of this shift for $α_{S}$ extractions are illustrated by comparing to state-of-the-art theoretical calculations. In addition, the region of $-6<\logτ<-2$, where poorly-understood non-perturbative effects are large, is compared to modern parton shower Monte Carlo simulations. This measurement provides unique new inputs for $α_{S}$ extractions and also improves constraints on phenomenological models of QCD dynamics such as parton fragmentation and hadronization. |
| title | Unbinned measurement of thrust in $e^+e^-$ collisions at $\sqrt{s}$ = 91.2 GeV with ALEPH archived data |
| topic | High Energy Physics - Experiment |
| url | https://arxiv.org/abs/2510.22038 |