Measurement of the τ lepton polarization in Z boson decays in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV

Medientyp: E-Artikel
Titel: Measurement of the τ lepton polarization in Z boson decays in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV
Beteiligte: Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Damanakis, K.; Dragicevic, M.; Escalante Del Valle, A.; Hussain, P. S.; Jeitler, M.; Krammer, N.; Liko, D.; Mikulec, I.; Schieck, J.; Schöfbeck, R.; Schwarz, D.; Sonawane, M.; Templ, S.; Waltenberger, W.; Wulz, C.-E.; Darwish, M. R.; Janssen, T.; Van Mechelen, P.; [...]
Erschienen: Springer Science and Business Media LLC, 2024
Erschienen in: Journal of High Energy Physics
Sprache: Englisch
DOI: 10.1007/jhep01(2024)101
ISSN: 1029-8479
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Beschreibung: <jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>The polarization of <jats:italic>τ</jats:italic> leptons is measured using leptonic and hadronic <jats:italic>τ</jats:italic> lepton decays in Z → <jats:italic>τ</jats:italic><jats:sup>+</jats:sup><jats:italic>τ</jats:italic><jats:sup><jats:italic>−</jats:italic></jats:sup> events in proton-proton collisions at <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \sqrt{s} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math></jats:alternatives></jats:inline-formula> = 13 TeV recorded by CMS at the CERN LHC with an integrated luminosity of 36.3 fb<jats:sup><jats:italic>−</jats:italic>1</jats:sup>. The measured <jats:italic>τ</jats:italic><jats:sup><jats:italic>−</jats:italic></jats:sup> lepton polarization at the Z boson mass pole is <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {\mathcal{P}}_{\tau}\left(\textrm{Z}\right) $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>P</mml:mi> <mml:mi>τ</mml:mi> </mml:msub> <mml:mfenced> <mml:mi>Z</mml:mi> </mml:mfenced> </mml:math></jats:alternatives></jats:inline-formula> = −0.144 ± 0.006 (stat) ± 0.014 (syst) = −0.144 ± 0.015, in good agreement with the measurement of the <jats:italic>τ</jats:italic> lepton asymmetry parameter of <jats:italic>A</jats:italic><jats:sub><jats:italic>τ</jats:italic></jats:sub> = 0.1439 ± 0.0043 = <jats:inline-formula><jats:alternatives><jats:tex-math>$$ -{\mathcal{P}}_{\tau}\left(\textrm{Z}\right) $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>−</mml:mo> <mml:msub> <mml:mi>P</mml:mi> <mml:mi>τ</mml:mi> </mml:msub> <mml:mfenced> <mml:mi>Z</mml:mi> </mml:mfenced> </mml:math></jats:alternatives></jats:inline-formula> at LEP. The <jats:italic>τ</jats:italic> lepton polarization depends on the ratio of the vector to axial-vector couplings of the <jats:italic>τ</jats:italic> leptons in the neutral current expression, and thus on the effective weak mixing angle sin<jats:sup>2</jats:sup><jats:inline-formula><jats:alternatives><jats:tex-math>$$ {\theta}_{\textrm{W}}^{\textrm{eff}} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>θ</mml:mi> <mml:mi>W</mml:mi> <mml:mi>eff</mml:mi> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula>, independently of the Z boson production mechanism. The obtained value sin<jats:sup>2</jats:sup><jats:inline-formula><jats:alternatives><jats:tex-math>$$ {\theta}_{\textrm{W}}^{\textrm{eff}} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>θ</mml:mi> <mml:mi>W</mml:mi> <mml:mi>eff</mml:mi> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> = 0.2319 ± 0<jats:italic>.</jats:italic>0008(stat) ± 0<jats:italic>.</jats:italic>0018(syst) = 0<jats:italic>.</jats:italic>2319 ± 0<jats:italic>.</jats:italic>0019 is in good agreement with measurements at <jats:italic>e</jats:italic><jats:sup>+</jats:sup><jats:italic>e</jats:italic><jats:sup><jats:italic>−</jats:italic></jats:sup> colliders.</jats:p>
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