Searching for new physics at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>μ</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>e</mml:mi></mml:math> facilities with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>μ</mml:mi><mml:mo>+</mml:mo></mml:msup></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>π</mml:mi><mml:mo>+</mml:mo></mml:msup></mml:math> decays at rest

Abstract

We investigate the ability of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>μ</a:mi><a:mo stretchy="false">→</a:mo><a:mi>e</a:mi></a:math> facilities, Mu2e and COMET, to probe, or discover, new physics with their detector validation datasets. The validation of the detector response may be performed using a dedicated run with <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"><d:msup><d:mi>μ</d:mi><d:mo>+</d:mo></d:msup></d:math>, collecting data below the Michel edge, <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"><f:mrow><f:msub><f:mrow><f:mi>E</f:mi></f:mrow><f:mrow><f:mi>e</f:mi></f:mrow></f:msub><f:mo>≲</f:mo><f:mn>52</f:mn><f:mtext> </f:mtext><f:mtext> </f:mtext><f:mi>MeV</f:mi></f:mrow></f:math>; an alternative strategy using <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mrow><h:msup><h:mrow><h:mi>π</h:mi></h:mrow><h:mrow><h:mo>+</h:mo></h:mrow></h:msup><h:mo stretchy="false">→</h:mo><h:msup><h:mrow><h:mi>e</h:mi></h:mrow><h:mrow><h:mo>+</h:mo></h:mrow></h:msup><h:msub><h:mrow><h:mi>ν</h:mi></h:mrow><h:mrow><h:mi>e</h:mi></h:mrow></h:msub></h:mrow></h:math> may also be considered. We focus primarily on a search for a monoenergetic <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:msup><k:mi>e</k:mi><k:mo>+</k:mo></k:msup></k:math> produced via two-body decays <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mrow><m:msup><m:mrow><m:mi>μ</m:mi></m:mrow><m:mrow><m:mo>+</m:mo></m:mrow></m:msup><m:mo stretchy="false">→</m:mo><m:msup><m:mrow><m:mi>e</m:mi></m:mrow><m:mrow><m:mo>+</m:mo></m:mrow></m:msup><m:mi>X</m:mi></m:mrow></m:math> or <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:mrow><p:msup><p:mrow><p:mi>π</p:mi></p:mrow><p:mrow><p:mo>+</p:mo></p:mrow></p:msup><p:mo stretchy="false">→</p:mo><p:msup><p:mrow><p:mi>e</p:mi></p:mrow><p:mrow><p:mo>+</p:mo></p:mrow></p:msup><p:mi>X</p:mi></p:mrow></p:math>, with <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"><s:mi>X</s:mi></s:math> a light new physics particle. Mu2e can potentially explore new parameter space beyond present astrophysical and laboratory constraints for a set of well motivated models including axionlike particles with flavor violating couplings (<u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:mrow><u:msup><u:mrow><u:mi>μ</u:mi></u:mrow><u:mrow><u:mo>+</u:mo></u:mrow></u:msup><u:mo stretchy="false">→</u:mo><u:msup><u:mrow><u:mi>e</u:mi></u:mrow><u:mrow><u:mo>+</u:mo></u:mrow></u:msup><u:mi>a</u:mi></u:mrow></u:math>), massive <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"><x:msup><x:mi>Z</x:mi><x:mo>′</x:mo></x:msup></x:math> bosons (<z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline"><z:mrow><z:msup><z:mrow><z:mi>μ</z:mi></z:mrow><z:mrow><z:mo>+</z:mo></z:mrow></z:msup><z:mo stretchy="false">→</z:mo><z:msup><z:mrow><z:mi>Z</z:mi></z:mrow><z:mrow><z:mo>′</z:mo></z:mrow></z:msup><z:msup><z:mrow><z:mi>e</z:mi></z:mrow><z:mrow><z:mo>+</z:mo></z:mrow></z:msup></z:mrow></z:math>), and heavy neutral leptons (<cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML" display="inline"><cb:mrow><cb:msup><cb:mrow><cb:mi>π</cb:mi></cb:mrow><cb:mrow><cb:mo>+</cb:mo></cb:mrow></cb:msup><cb:mo stretchy="false">→</cb:mo><cb:msup><cb:mrow><cb:mi>e</cb:mi></cb:mrow><cb:mrow><cb:mo>+</cb:mo></cb:mrow></cb:msup><cb:mi>N</cb:mi></cb:mrow></cb:math>). The projected sensitivities presented herein can be achieved in a matter of days. Published by the American Physical Society 2024

Topics & Concepts