Precise test of lepton flavour universality in <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="0" style="font-size: 113.1%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mtext class="mjx-n" style="color: red;"><mjx-c class="mjx-c5C"></mjx-c><mjx-c class="mjx-c76"></mjx-c><mjx-c class="mjx-c61"></mjx-c><mjx-c class="mjx-c72"></mjx-c><mjx-c class="mjx-c76"></mjx-c><mjx-c class="mjx-c65"></mjx-c><mjx-c class="mjx-c63"></mjx-c></mjx-mtext><mjx-texatom texclass="ORD"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D44A TEX-I"></mjx-c></mjx-mi></mjx-texatom></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mtext mathcolor="red">\varvec</mtext><mrow data-mjx-texclass="ORD"><mi>W</mi></mrow></math></mjx-assistive-mml></mjx-container>-boson decays into muons and electrons in <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="1" style="font-size: 113.1%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mtext class="mjx-n" style="color: red;"><mjx-c class="mjx-c5C"></mjx-c><mjx-c class="mjx-c76"></mjx-c><mjx-c class="mjx-c61"></mjx-c><mjx-c class="mjx-c72"></mjx-c><mjx-c class="mjx-c76"></mjx-c><mjx-c class="mjx-c65"></mjx-c><mjx-c class="mjx-c63"></mjx-c></mjx-mtext><mjx-texatom texclass="ORD"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D45D TEX-I"></mjx-c></mjx-mi><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D45D TEX-I"></mjx-c></mjx-mi></mjx-texatom></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mtext mathcolor="red">\varvec</mtext><mrow data-mjx-texclass="ORD"><mi>p</mi><mi>p</mi></mrow></math></mjx-assistive-mml></mjx-container> collisions at <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="2" style="font-size: 113.1%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true" style="width: 8.975em;"><mjx-mtext class="mjx-n" style="color: red;"><mjx-c class="mjx-c5C"></mjx-c><mjx-c class="mjx-c76"></mjx-c><mjx-c class="mjx-c61"></mjx-c><mjx-c class="mjx-c72"></mjx-c><mjx-c class="mjx-c76"></mjx-c><mjx-c class="mjx-c65"></mjx-c><mjx-c class="mjx-c63"></mjx-c></mjx-mtext><mjx-texatom texclass="ORD"><mjx-msqrt><mjx-sqrt><mjx-surd><mjx-mo class="mjx-n"><mjx-c class="mjx-c221A"></mjx-c></mjx-mo></mjx-surd><mjx-box style="padding-top: 0.281em;"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D460 TEX-I"></mjx-c></mjx-mi></mjx-box></mjx-sqrt></mjx-msqrt></mjx-texatom><mjx-mo class="mjx-n" space="4"><mjx-c class="mjx-c3D"></mjx-c></mjx-mo><mjx-mn class="mjx-n" space="4"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c33"></mjx-c></mjx-mn><mjx-mstyle><mjx-mspace style="width: 0.167em;"></mjx-mspace></mjx-mstyle><mjx-mtext class="mjx-n"><mjx-c class="mjx-c54"></mjx-c></mjx-mtext><mjx-mtext class="mjx-n"><mjx-c class="mjx-c65"></mjx-c></mjx-mtext><mjx-mspace style="margin-right: -0.1em;"></mjx-mspace><mjx-mtext class="mjx-n"><mjx-c class="mjx-c56"></mjx-c></mjx-mtext></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mtext mathcolor="red">\varvec</mtext><mrow data-mjx-texclass="ORD"><msqrt><mi>s</mi></msqrt></mrow><mo>=</mo><mn>13</mn><mstyle scriptlevel="0"><mspace width="0.167em"></mspace></mstyle><mtext>T</mtext><mtext>e</mtext><mspace width="-1.00006pt"></mspace><mtext>V</mtext></math></mjx-assistive-mml></mjx-container> with the ATLAS detector
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Precise test of lepton flavour universality in \varvecW-boson decays into muons and electrons in \varvecpp collisions at \varvecs=13TeV with the ATLAS detector

Abstract

Abstract: The ratio of branching ratios of the W boson to muons and electrons, RWμ/e=B(Wμu) R W μ / e = B ( W → μ ν ) /B(Weu) B ( W → e ν ) , has been measured using 140 fb1 140 fb - 1 of pp collision data at s=13 s = 13  TeV Te V collected with the ATLAS detector at the LHC, probing the universality of lepton couplings. The ratio is obtained from measurements of the tt¯ t t ¯ production cross-section in the ee, eμ e μ and μμ μ μ dilepton final states. To reduce systematic uncertainties, it is normalised by the square root of the corresponding ratio RZμμ/ee R Z μ μ / e e for the Z boson measured in inclusive Zee Z → e e and Zμμ Z → μ μ events. By using the precise value of RZμμ/ee R Z μ μ / e e determined from e+e e + e - colliders, the ratio RWμ/e R W μ / e is determined to be RWμ/e=0.9995±0.0022(stat)±0.0036(syst)±0.0014(ext). R W μ / e = 0.9995 ± 0.0022 ( stat ) ± 0.0036 ( syst ) ± 0.0014 ( ext ) . The three uncertainties correspond to data statistics, experimental systematics and the external measurement of RZμμ/ee R Z μ μ / e e , giving a total uncertainty of 0.0045, and confirming the Standard Model assumption of lepton flavour universality in W-boson decays at the 0.5% level.

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