Search for charged lepton flavor violating <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>Z</mml:mi> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msup> <mml:mi>Z</

A search for flavor violating decays of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>Z</a:mi> </a:math> boson to charged leptons is performed using data from proton-proton collisions at <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msqrt> <c:mi>s</c:mi> </c:msqrt> <c:mo>=</c:mo> <c:mn>13</c:mn> <c:mtext> </c:mtext> <c:mtext> </c:mtext> <c:mi>TeV</c:mi> </c:math> collected with the CMS detector at the LHC, corresponding to an integrated luminosity of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mn>138</e:mn> <e:mtext> </e:mtext> <e:mtext> </e:mtext> <e:msup> <e:mi>fb</e:mi> <e:mrow> <e:mo>−</e:mo> <e:mn>1</e:mn> </e:mrow> </e:msup> </e:math> . Each of the decays <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi>Z</g:mi> <g:mo stretchy="false">→</g:mo> <g:mi>e</g:mi> <g:mi>μ</g:mi> </g:math> , <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:mi>Z</j:mi> <j:mo stretchy="false">→</j:mo> <j:mi>e</j:mi> <j:mi>τ</j:mi> </j:math> , and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:mi>Z</m:mi> <m:mo stretchy="false">→</m:mo> <m:mi>μ</m:mi> <m:mi>τ</m:mi> </m:math> is considered. The data are consistent with the backgrounds expected from standard model processes. For the <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"> <p:mi>Z</p:mi> <p:mo stretchy="false">→</p:mo> <p:mi>e</p:mi> <p:mi>μ</p:mi> </p:math> channel the observed (expected) 95% confidence level upper limit on the branching fraction is <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:mn>1.9</s:mn> <s:mo stretchy="false">(</s:mo> <s:mn>2.0</s:mn> <s:mo stretchy="false">)</s:mo> <s:mo>×</s:mo> <s:msup> <s:mn>10</s:mn> <s:mrow> <s:mo>−</s:mo> <s:mn>7</s:mn> </s:mrow> </s:msup> </s:math> , which is the most stringent direct limit to date on this process; the corresponding limits for the <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"> <w:mi>Z</w:mi> <w:mo stretchy="false">→</w:mo> <w:mi>e</w:mi> <w:mi>τ</w:mi> </w:math> and <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline"> <z:mi>Z</z:mi> <z:mo stretchy="false">→</z:mo> <z:mi>μ</z:mi> <z:mi>τ</z:mi> </z:math> channels are <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML" display="inline"> <cb:mn>13.8</cb:mn> <cb:mo stretchy="false">(</cb:mo> <cb:mn>11.4</cb:mn> <cb:mo stretchy="false">)</cb:mo> <cb:mo>×</cb:mo> <cb:msup> <cb:mn>10</cb:mn> <cb:mrow> <cb:mo>−</cb:mo> <cb:mn>6</cb:mn> </cb:mrow> </cb:msup> </cb:math> and <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"> <gb:mn>12.0</gb:mn> <gb:mo stretchy="false">(</gb:mo> <gb:mn>5.3</gb:mn> <gb:mo stretchy="false">)</gb:mo> <gb:mo>×</gb:mo> <gb:msup> <gb:mn>10</gb:mn> <gb:mrow> <gb:mo>−</gb:mo> <gb:mn>6</gb:mn> </gb:mrow> </gb:msup> </gb:math> , respectively. Additionally, the <kb:math xmlns:kb="http://www.w3.org/1998/Math/MathML" display="inline"> <kb:mi>e</kb:mi> <kb:mi>μ</kb:mi> </kb:math> final state is used to search for lepton flavor violating decays of <mb:math xmlns:mb="http://www.w3.org/1998/Math/MathML" display="inline"> <mb:msup> <mb:mi>Z</mb:mi> <mb:mo>′</mb:mo> </mb:msup> </mb:math> resonances in the mass range from 110 to <ob:math xmlns:ob="http://www.w3.org/1998/Math/MathML" display="inline"> <ob:mrow> <ob:mn>500</ob:mn> <ob:mtext> </ob:mtext> <ob:mtext> </ob:mtext> <ob:mi>GeV</ob:mi> </ob:mrow> </ob:math> . No significant excess is observed above the predicted background levels.

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Publication Details

Journal
Physical review. D/Physical review. D.
Published
2025-10-16
DOI
https://doi.org/10.1103/8lw4-6lyk
Primary Topic
Particle physics theoretical and experimental studies
Type
article
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article

Search for charged lepton flavor violating <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>Z</mml:mi> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msup> <mml:mi>Z</

Karl J. Friston
Physical review. D/Physical review. D.
Particle physics theoretical and experimental studies
article

Search for charged lepton flavor violating <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>Z</mml:mi> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msup> <mml:mi>Z</

Karl J. Friston
article en

Abstract

A search for flavor violating decays of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>Z</a:mi> </a:math> boson to charged leptons is performed using data from proton-proton collisions at <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msqrt> <c:mi>s</c:mi> </c:msqrt> <c:mo>=</c:mo> <c:mn>13</c:mn> <c:mtext> </c:mtext> <c:mtext> </c:mtext> <c:mi>TeV</c:mi> </c:math> collected with the CMS detector at the LHC, corresponding to an integrated luminosity of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mn>138</e:mn> <e:mtext> </e:mtext> <e:mtext> </e:mtext> <e:msup> <e:mi>fb</e:mi> <e:mrow> <e:mo>−</e:mo> <e:mn>1</e:mn> </e:mrow> </e:msup> </e:math> . Each of the decays <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi>Z</g:mi> <g:mo stretchy="false">→</g:mo> <g:mi>e</g:mi> <g:mi>μ</g:mi> </g:math> , <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:mi>Z</j:mi> <j:mo stretchy="false">→</j:mo> <j:mi>e</j:mi> <j:mi>τ</j:mi> </j:math> , and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:mi>Z</m:mi> <m:mo stretchy="false">→</m:mo> <m:mi>μ</m:mi> <m:mi>τ</m:mi> </m:math> is considered. The data are consistent with the backgrounds expected from standard model processes. For the <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"> <p:mi>Z</p:mi> <p:mo stretchy="false">→</p:mo> <p:mi>e</p:mi> <p:mi>μ</p:mi> </p:math> channel the observed (expected) 95% confidence level upper limit on the branching fraction is <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:mn>1.9</s:mn> <s:mo stretchy="false">(</s:mo> <s:mn>2.0</s:mn> <s:mo stretchy="false">)</s:mo> <s:mo>×</s:mo> <s:msup> <s:mn>10</s:mn> <s:mrow> <s:mo>−</s:mo> <s:mn>7</s:mn> </s:mrow> </s:msup> </s:math> , which is the most stringent direct limit to date on this process; the corresponding limits for the <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"> <w:mi>Z</w:mi> <w:mo stretchy="false">→</w:mo> <w:mi>e</w:mi> <w:mi>τ</w:mi> </w:math> and <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline"> <z:mi>Z</z:mi> <z:mo stretchy="false">→</z:mo> <z:mi>μ</z:mi> <z:mi>τ</z:mi> </z:math> channels are <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML" display="inline"> <cb:mn>13.8</cb:mn> <cb:mo stretchy="false">(</cb:mo> <cb:mn>11.4</cb:mn> <cb:mo stretchy="false">)</cb:mo> <cb:mo>×</cb:mo> <cb:msup> <cb:mn>10</cb:mn> <cb:mrow> <cb:mo>−</cb:mo> <cb:mn>6</cb:mn> </cb:mrow> </cb:msup> </cb:math> and <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"> <gb:mn>12.0</gb:mn> <gb:mo stretchy="false">(</gb:mo> <gb:mn>5.3</gb:mn> <gb:mo stretchy="false">)</gb:mo> <gb:mo>×</gb:mo> <gb:msup> <gb:mn>10</gb:mn> <gb:mrow> <gb:mo>−</gb:mo> <gb:mn>6</gb:mn> </gb:mrow> </gb:msup> </gb:math> , respectively. Additionally, the <kb:math xmlns:kb="http://www.w3.org/1998/Math/MathML" display="inline"> <kb:mi>e</kb:mi> <kb:mi>μ</kb:mi> </kb:math> final state is used to search for lepton flavor violating decays of <mb:math xmlns:mb="http://www.w3.org/1998/Math/MathML" display="inline"> <mb:msup> <mb:mi>Z</mb:mi> <mb:mo>′</mb:mo> </mb:msup> </mb:math> resonances in the mass range from 110 to <ob:math xmlns:ob="http://www.w3.org/1998/Math/MathML" display="inline"> <ob:mrow> <ob:mn>500</ob:mn> <ob:mtext> </ob:mtext> <ob:mtext> </ob:mtext> <ob:mi>GeV</ob:mi> </ob:mrow> </ob:math> . No significant excess is observed above the predicted background levels.

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