Measurement of the Z -Boson Mass

The first dedicated <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>Z</a:mi></a:math>-boson mass measurement at the LHC with <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>Z</c:mi><c:mo stretchy="false">→</c:mo><c:msup><c:mi>μ</c:mi><c:mo>+</c:mo></c:msup><c:msup><c:mi>μ</c:mi><c:mo>−</c:mo></c:msup></c:math> decays is reported. The dataset uses proton-proton collisions at a center-of-mass energy of 13 TeV, recorded in 2016 by the LHCb experiment, and corresponds to an integrated luminosity of <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"><f:mn>1.7</f:mn><f:mtext> </f:mtext><f:mtext> </f:mtext><f:msup><f:mi>fb</f:mi><f:mrow><f:mo>−</f:mo><f:mn>1</f:mn></f:mrow></f:msup></f:math>. A template fit to the <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:msup><h:mi>μ</h:mi><h:mo>+</h:mo></h:msup><h:msup><h:mi>μ</h:mi><h:mo>−</h:mo></h:msup></h:math> mass distribution yields the following result for the <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:mi>Z</j:mi></j:math>-boson mass: <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:mrow><l:msub><l:mrow><l:mi>m</l:mi></l:mrow><l:mrow><l:mi>Z</l:mi></l:mrow></l:msub><l:mo>=</l:mo><l:mn>91</l:mn><l:mo>,</l:mo><l:mn>185.7</l:mn><l:mo>±</l:mo><l:mn>8.3</l:mn><l:mo>±</l:mo><l:mn>3.9</l:mn><l:mtext> </l:mtext><l:mtext> </l:mtext><l:mi>MeV</l:mi></l:mrow></l:math>, where the first uncertainty is statistical and the second systematic. This result is consistent with previous measurements and predictions from global electroweak fits.