Stau pairs from natural SUSY at high luminosity LHC

Natural supersymmetry (SUSY) with light Higgsinos is perhaps the most plausible of all weak scale SUSY models while a variety of motivations point to (right) tau sleptons as the lightest of all the sleptons. We examine a SUSY model line with rather light right staus embedded within natural SUSY. For light <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msub><a:mover accent="true"><a:mi>τ</a:mi><a:mo stretchy="false">˜</a:mo></a:mover><a:mn>1</a:mn></a:msub></a:math> of a few hundred GeV, the decays <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msub><e:mover accent="true"><e:mi>τ</e:mi><e:mo stretchy="false">˜</e:mo></e:mover><e:mn>1</e:mn></e:msub><e:mo stretchy="false">→</e:mo><e:mi>τ</e:mi><e:msubsup><e:mover accent="true"><e:mi>χ</e:mi><e:mo stretchy="false">˜</e:mo></e:mover><e:mrow><e:mn>1</e:mn><e:mo>,</e:mo><e:mn>2</e:mn></e:mrow><e:mn>0</e:mn></e:msubsup></e:math> and <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:msub><l:mi>ν</l:mi><l:mi>τ</l:mi></l:msub><l:msubsup><l:mover accent="true"><l:mi>χ</l:mi><l:mo stretchy="false">˜</l:mo></l:mover><l:mn>1</l:mn><l:mo>−</l:mo></l:msubsup></l:math> occur at comparable rates where the (Higgsino-like) <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:msubsup><p:mover accent="true"><p:mi>χ</p:mi><p:mo stretchy="false">˜</p:mo></p:mover><p:mn>1</p:mn><p:mo>±</p:mo></p:msubsup></p:math> and <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:msubsup><t:mover accent="true"><t:mi>χ</t:mi><t:mo stretchy="false">˜</t:mo></t:mover><t:mn>2</t:mn><t:mn>0</t:mn></t:msubsup></t:math> release only small visible energy: in this case, the expected <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"><x:msup><x:mi>τ</x:mi><x:mo>+</x:mo></x:msup><x:msup><x:mi>τ</x:mi><x:mo>−</x:mo></x:msup><x:mo>+</x:mo><x:msub><x:menclose notation="updiagonalstrike" other="updiag1"><x:mi>E</x:mi></x:menclose><x:mi>T</x:mi></x:msub></x:math> signature is diminished from the usual expectations due to the presence of the nearly invisible decay mode <bb:math xmlns:bb="http://www.w3.org/1998/Math/MathML" display="inline"><bb:msub><bb:mover accent="true"><bb:mi>τ</bb:mi><bb:mo stretchy="false">˜</bb:mo></bb:mover><bb:mn>1</bb:mn></bb:msub><bb:mo stretchy="false">→</bb:mo><bb:msub><bb:mi>ν</bb:mi><bb:mi>τ</bb:mi></bb:msub><bb:msubsup><bb:mover accent="true"><bb:mi>χ</bb:mi><bb:mo stretchy="false">˜</bb:mo></bb:mover><bb:mn>1</bb:mn><bb:mo>−</bb:mo></bb:msubsup></bb:math>. However, once <ib:math xmlns:ib="http://www.w3.org/1998/Math/MathML" display="inline"><ib:msub><ib:mi>m</ib:mi><ib:msub><ib:mover accent="true"><ib:mi>τ</ib:mi><ib:mo stretchy="false">˜</ib:mo></ib:mover><ib:mn>1</ib:mn></ib:msub></ib:msub><ib:mo>≳</ib:mo><ib:mi>m</ib:mi><ib:mo stretchy="false">(</ib:mo><ib:mi>b</ib:mi><ib:mi>i</ib:mi><ib:mi>n</ib:mi><ib:mi>o</ib:mi><ib:mo stretchy="false">)</ib:mo></ib:math>, decays to binos such as <ob:math xmlns:ob="http://www.w3.org/1998/Math/MathML" display="inline"><ob:msub><ob:mover accent="true"><ob:mi>τ</ob:mi><ob:mo stretchy="false">˜</ob:mo></ob:mover><ob:mn>1</ob:mn></ob:msub><ob:mo stretchy="false">→</ob:mo><ob:mi>τ</ob:mi><ob:msubsup><ob:mover accent="true"><ob:mi>χ</ob:mi><ob:mo stretchy="false">˜</ob:mo></ob:mover><ob:mn>3</ob:mn><ob:mn>0</ob:mn></ob:msubsup></ob:math> open up where <vb:math xmlns:vb="http://www.w3.org/1998/Math/MathML" display="inline"><vb:msubsup><vb:mover accent="true"><vb:mi>χ</vb:mi><vb:mo stretchy="false">˜</vb:mo></vb:mover><vb:mn>3</vb:mn><vb:mn>0</vb:mn></vb:msubsup></vb:math> decays to Higgsinos plus <zb:math xmlns:zb="http://www.w3.org/1998/Math/MathML" display="inline"><zb:msup><zb:mi>W</zb:mi><zb:mo>±</zb:mo></zb:msup></zb:math>, <bc:math xmlns:bc="http://www.w3.org/1998/Math/MathML" display="inline"><bc:msup><bc:mi>Z</bc:mi><bc:mn>0</bc:mn></bc:msup></bc:math>, and <dc:math xmlns:dc="http://www.w3.org/1998/Math/MathML" display="inline"><dc:mi>h</dc:mi></dc:math> at comparable rates. For these heavier staus, the stau pair production gives rise to <fc:math xmlns:fc="http://www.w3.org/1998/Math/MathML" display="inline"><fc:mrow><fc:mtext>diboson</fc:mtext><fc:mo>+</fc:mo><fc:msub><fc:mrow><fc:menclose notation="updiagonalstrike" other="updiag1"><fc:mrow><fc:mi>E</fc:mi></fc:mrow></fc:menclose></fc:mrow><fc:mrow><fc:mi>T</fc:mi></fc:mrow></fc:msub></fc:mrow></fc:math> events, which may contain 0, 1, or 2 additional hard <jc:math xmlns:jc="http://www.w3.org/1998/Math/MathML" display="inline"><jc:mi>τ</jc:mi></jc:math> leptons. From these considerations, we examine the potential for future discovery of tau-slepton pair production at a high-luminosity LHC. While we do not find a <lc:math xmlns:lc="http://www.w3.org/1998/Math/MathML" display="inline"><lc:mn>5</lc:mn><lc:mi>σ</lc:mi></lc:math> HL-LHC discovery reach for <nc:math xmlns:nc="http://www.w3.org/1998/Math/MathML" display="inline"><nc:mn>3000</nc:mn><nc:mtext> </nc:mtext><nc:mtext> </nc:mtext><nc:msup><nc:mi>fb</nc:mi><nc:mrow><nc:mo>−</nc:mo><nc:mn>1</nc:mn></nc:mrow></nc:msup></nc:math>, we do find a 95% CL exclusion reach, ranging between <pc:math xmlns:pc="http://www.w3.org/1998/Math/MathML" display="inline"><pc:msub><pc:mi>m</pc:mi><pc:msub><pc:mover accent="true"><pc:mi>τ</pc:mi><pc:mo stretchy="false">˜</pc:mo></pc:mover><pc:mn>1</pc:mn></pc:msub></pc:msub><pc:mo>:</pc:mo><pc:mtext> </pc:mtext><pc:mtext> </pc:mtext><pc:mn>100</pc:mn><pc:mi>–</pc:mi><pc:mn>450</pc:mn><pc:mtext> </pc:mtext><pc:mtext> </pc:mtext><pc:mi>GeV</pc:mi></pc:math> for <tc:math xmlns:tc="http://www.w3.org/1998/Math/MathML" display="inline"><tc:msub><tc:mi>m</tc:mi><tc:msubsup><tc:mover accent="true"><tc:mi>χ</tc:mi><tc:mo stretchy="false">˜</tc:mo></tc:mover><tc:mn>1</tc:mn><tc:mn>0</tc:mn></tc:msubsup></tc:msub><tc:mo>∼</tc:mo><tc:mn>100</tc:mn><tc:mtext> </tc:mtext><tc:mtext> </tc:mtext><tc:mi>GeV</tc:mi></tc:math>. This latter reach disappears for <xc:math xmlns:xc="http://www.w3.org/1998/Math/MathML" display="inline"><xc:msub><xc:mi>m</xc:mi><xc:msubsup><xc:mover accent="true"><xc:mi>χ</xc:mi><xc:mo stretchy="false">˜</xc:mo></xc:mover><xc:mn>1</xc:mn><xc:mn>0</xc:mn></xc:msubsup></xc:msub><xc:mo>≳</xc:mo><xc:mn>200</xc:mn><xc:mtext> </xc:mtext><xc:mtext> </xc:mtext><xc:mi>GeV</xc:mi></xc:math>. Published by the American Physical Society 2024