The first observation of the decay <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msubsup><a:mi mathvariant="normal">Ξ</a:mi><a:mi>b</a:mi><a:mo>−</a:mo></a:msubsup><a:mo stretchy="false">→</a:mo><a:mrow><a:mi>ψ</a:mi><a:mrow><a:mo stretchy="false">(</a:mo><a:mn>2</a:mn><a:mi>S</a:mi><a:mo stretchy="false">)</a:mo></a:mrow></a:mrow><a:msup><a:mi mathvariant="normal">Ξ</a:mi><a:mo>−</a:mo></a:msup></a:math> and measurement of the branching ratio of <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:msubsup><h:mi mathvariant="normal">Ξ</h:mi><h:mi>b</h:mi><h:mo>−</h:mo></h:msubsup><h:mo stretchy="false">→</h:mo><h:mrow><h:mi>ψ</h:mi><h:mrow><h:mo stretchy="false">(</h:mo><h:mn>2</h:mn><h:mi>S</h:mi><h:mo stretchy="false">)</h:mo></h:mrow></h:mrow><h:msup><h:mi mathvariant="normal">Ξ</h:mi><h:mo>−</h:mo></h:msup></h:math> to <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:msubsup><o:mi mathvariant="normal">Ξ</o:mi><o:mi>b</o:mi><o:mo>−</o:mo></o:msubsup><o:mo stretchy="false">→</o:mo><o:mrow><o:mi>J</o:mi><o:mo>/</o:mo><o:mi>ψ</o:mi></o:mrow><o:msup><o:mi mathvariant="normal">Ξ</o:mi><o:mo>−</o:mo></o:msup></o:math> are presented. The <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:mi>J</t:mi><t:mo>/</t:mo><t:mi>ψ</t:mi></t:math> and <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"><v:mi>ψ</v:mi><v:mrow><v:mo stretchy="false">(</v:mo><v:mn>2</v:mn><v:mi>S</v:mi><v:mo stretchy="false">)</v:mo></v:mrow></v:math> mesons are reconstructed using their dimuon decay modes. The results are based on proton-proton colliding beam data from the LHC collected by the CMS experiment at <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline"><z:msqrt><z:mi>s</z:mi></z:msqrt><z:mo>=</z:mo><z:mn>13</z:mn><z:mtext> </z:mtext><z:mtext> </z:mtext><z:mi>TeV</z:mi></z:math> in 2016–2018, corresponding to an integrated luminosity of <bb:math xmlns:bb="http://www.w3.org/1998/Math/MathML" display="inline"><bb:mn>140</bb:mn><bb:mtext> </bb:mtext><bb:mtext> </bb:mtext><bb:msup><bb:mi>fb</bb:mi><bb:mrow><bb:mo>−</bb:mo><bb:mn>1</bb:mn></bb:mrow></bb:msup></bb:math>. The branching fraction ratio is measured to be <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"><db:mrow><db:mi mathvariant="script">B</db:mi><db:mo stretchy="false">(</db:mo><db:mrow><db:msubsup><db:mrow><db:mi mathvariant="normal">Ξ</db:mi></db:mrow><db:mrow><db:mi>b</db:mi></db:mrow><db:mrow><db:mo>−</db:mo></db:mrow></db:msubsup><db:mo stretchy="false">→</db:mo><db:mrow><db:mi>ψ</db:mi><db:mrow><db:mo stretchy="false">(</db:mo><db:mn>2</db:mn><db:mi>S</db:mi><db:mo stretchy="false">)</db:mo></db:mrow></db:mrow><db:msup><db:mrow><db:mi mathvariant="normal">Ξ</db:mi></db:mrow><db:mrow><db:mo>−</db:mo></db:mrow></db:msup></db:mrow><db:mo stretchy="false">)</db:mo><db:mo>/</db:mo><db:mi mathvariant="script">B</db:mi><db:mo stretchy="false">(</db:mo><db:mrow><db:msubsup><db:mrow><db:mi mathvariant="normal">Ξ</db:mi></db:mrow><db:mrow><db:mi>b</db:mi></db:mrow><db:mrow><db:mo>−</db:mo></db:mrow></db:msubsup><db:mo stretchy="false">→</db:mo><db:mrow><db:mi>J</db:mi><db:mo>/</db:mo><db:mi>ψ</db:mi></db:mrow><db:msup><db:mrow><db:mi mathvariant="normal">Ξ</db:mi></db:mrow><db:mrow><db:mo>−</db:mo></db:mrow></db:msup></db:mrow><db:mo stretchy="false">)</db:mo><db:mo>=</db:mo><db:mspace linebreak="goodbreak"/><db:mn>0.8</db:mn><db:msubsup><db:mrow><db:mn>4</db:mn></db:mrow><db:mrow><db:mo>−</db:mo><db:mn>0.19</db:mn></db:mrow><db:mrow><db:mo>+</db:mo><db:mn>0.21</db:mn></db:mrow></db:msubsup><db:mrow><db:mo stretchy="false">(</db:mo><db:mi>stat</db:mi><db:mo stretchy="false">)</db:mo></db:mrow><db:mo>±</db:mo><db:mn>0.10</db:mn><db:mrow><db:mo stretchy="false">(</db:mo><db:mi>syst</db:mi><db:mo stretchy="false">)</db:mo></db:mrow><db:mo>±</db:mo><db:mn>0.02</db:mn><db:mo stretchy="false">(</db:mo><db:mi mathvariant="script">B</db:mi><db:mo stretchy="false">)</db:mo></db:mrow></db:math>, where the last uncertainty comes from the uncertainties in the branching fractions of the charmonium states. New measurements of the <bc:math xmlns:bc="http://www.w3.org/1998/Math/MathML" display="inline"><bc:msub><bc:mi mathvariant="normal">Ξ</bc:mi><bc:mi>b</bc:mi></bc:msub><bc:mo stretchy="false">(</bc:mo><bc:mn>5945</bc:mn><bc:msup><bc:mo stretchy="false">)</bc:mo><bc:mn>0</bc:mn></bc:msup></bc:math> baryon mass and natural width are also presented, using the <gc:math xmlns:gc="http://www.w3.org/1998/Math/MathML" display="inline"><gc:msubsup><gc:mi mathvariant="normal">Ξ</gc:mi><gc:mi>b</gc:mi><gc:mo>−</gc:mo></gc:msubsup><gc:msup><gc:mi>π</gc:mi><gc:mo>+</gc:mo></gc:msup></gc:math> final state, where the <jc:math xmlns:jc="http://www.w3.org/1998/Math/MathML" display="inline"><jc:msubsup><jc:mi mathvariant="normal">Ξ</jc:mi><jc:mi>b</jc:mi><jc:mo>−</jc:mo></jc:msubsup></jc:math> baryon is reconstructed through the decays <mc:math xmlns:mc="http://www.w3.org/1998/Math/MathML" display="inline"><mc:mrow><mc:mi>J</mc:mi><mc:mo>/</mc:mo><mc:mi>ψ</mc:mi></mc:mrow><mc:msup><mc:mi mathvariant="normal">Ξ</mc:mi><mc:mo>−</mc:mo></mc:msup></mc:math>, <pc:math xmlns:pc="http://www.w3.org/1998/Math/MathML" display="inline"><pc:mrow><pc:mi>ψ</pc:mi><pc:mrow><pc:mo stretchy="false">(</pc:mo><pc:mn>2</pc:mn><pc:mi>S</pc:mi><pc:mo stretchy="false">)</pc:mo></pc:mrow></pc:mrow><pc:msup><pc:mi mathvariant="normal">Ξ</pc:mi><pc:mo>−</pc:mo></pc:msup></pc:math>, <uc:math xmlns:uc="http://www.w3.org/1998/Math/MathML" display="inline"><uc:mrow><uc:mi>J</uc:mi><uc:mo>/</uc:mo><uc:mi>ψ</uc:mi></uc:mrow><uc:mi mathvariant="normal">Λ</uc:mi><uc:msup><uc:mi>K</uc:mi><uc:mo>−</uc:mo></uc:msup></uc:math>, and <xc:math xmlns:xc="http://www.w3.org/1998/Math/MathML" display="inline"><xc:mrow><xc:mi>J</xc:mi><xc:mo>/</xc:mo><xc:mi>ψ</xc:mi></xc:mrow><xc:msup><xc:mi mathvariant="normal">Σ</xc:mi><xc:mn>0</xc:mn></xc:msup><xc:msup><xc:mi>K</xc:mi><xc:mo>−</xc:mo></xc:msup></xc:math>. Finally, the fraction of <ad:math xmlns:ad="http://www.w3.org/1998/Math/MathML" display="inline"><ad:msubsup><ad:mi mathvariant="normal">Ξ</ad:mi><ad:mi>b</ad:mi><ad:mo>−</ad:mo></ad:msubsup></ad:math> baryons produced from <dd:math xmlns:dd="http://www.w3.org/1998/Math/MathML" display="inline"><dd:msub><dd:mi mathvariant="normal">Ξ</dd:mi><dd:mi>b</dd:mi></dd:msub><dd:mo stretchy="false">(</dd:mo><dd:mn>5945</dd:mn><dd:msup><dd:mo stretchy="false">)</dd:mo><dd:mn>0</dd:mn></dd:msup></dd:math> decays is determined. © 2024 CERN, for the CMS Collaboration 2024 CERN