Improving sensitivity of trilinear R-parity violating SUSY searches using machine learning at the LHC

Abstract

In this work, we have explored the sensitivity of multilepton final states in probing the gaugino sector of a R-parity violating supersymmetric scenario with specific lepton number violating trilinear couplings (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msub><a:mi>λ</a:mi><a:mrow><a:mi>i</a:mi><a:mi>j</a:mi><a:mi>k</a:mi></a:mrow></a:msub></a:math>) being nonzero. The gaugino spectrum is such that the charged leptons in the final state can arise from the R-parity violating decays of the lightest supersymmetric particle (LSP) as well as R-parity conserving decays of the next-to-LSP (NLSP). Apart from a detailed cut-based analysis, we have also performed a machine learning-based analysis using a boosted decision tree algorithm, which provides much better sensitivity. In the scenarios with nonzero <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:msub><c:mi>λ</c:mi><c:mn>121</c:mn></c:msub></c:math> and/or <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:msub><e:mrow><e:mi>λ</e:mi></e:mrow><e:mrow><e:mn>122</e:mn></e:mrow></e:msub></e:mrow></e:math> couplings, the LSP pair in the final states decays to <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:mn>4</g:mn><g:mi>l</g:mi></g:mrow></g:math> <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mrow><i:mo stretchy="false">(</i:mo><i:mi>l</i:mi><i:mo>=</i:mo><i:mi>e</i:mi><i:mo>,</i:mo><i:mi>μ</i:mi><i:mo stretchy="false">)</i:mo><i:mo>+</i:mo><i:msub><i:mrow><i:menclose notation="updiagonalstrike"><i:mrow><i:mi mathvariant="normal">E</i:mi></i:mrow></i:menclose></i:mrow><i:mrow><i:mi mathvariant="normal">T</i:mi></i:mrow></i:msub></i:mrow></i:math> final states with a 100% branching ratio. We have shown that under this circumstance, a final state with <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:mo>≥</p:mo><p:mn>4</p:mn><p:mi>l</p:mi></p:math> has the highest sensitivity while probing for gaugino masses. We also discuss how the sensitivity can change in the presence of <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:mi>τ</r:mi></r:math> lepton(s) in the final state due to other choices of trilinear couplings. We present our results through the estimation of the discovery and exclusion contours in the gaugino mass plane for both the high luminosity LHC (HL-LHC with <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:msqrt><t:mi>s</t:mi></t:msqrt><t:mo>=</t:mo><t:mn>14</t:mn><t:mtext> </t:mtext><t:mtext> </t:mtext><t:mi>TeV</t:mi></t:math> and <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"><v:mrow><v:mi mathvariant="script">L</v:mi><v:mo>=</v:mo><v:mn>3000</v:mn><v:mtext> </v:mtext><v:mtext> </v:mtext><v:msup><v:mrow><v:mi>fb</v:mi></v:mrow><v:mrow><v:mo>−</v:mo><v:mn>1</v:mn></v:mrow></v:msup></v:mrow></v:math>) and high energy LHC (HE-LHC with <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"><y:msqrt><y:mi>s</y:mi></y:msqrt><y:mo>=</y:mo><y:mn>27</y:mn><y:mtext> </y:mtext><y:mtext> </y:mtext><y:mi>TeV</y:mi></y:math> and <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:mrow><ab:mi mathvariant="script">L</ab:mi><ab:mo>=</ab:mo><ab:mn>3000</ab:mn><ab:mtext> </ab:mtext><ab:mtext> </ab:mtext><ab:msup><ab:mrow><ab:mi>fb</ab:mi></ab:mrow><ab:mrow><ab:mo>−</ab:mo><ab:mn>1</ab:mn></ab:mrow></ab:msup></ab:mrow></ab:math>). For the <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"><db:msub><db:mi>λ</db:mi><db:mn>121</db:mn></db:msub></db:math> and/or <fb:math xmlns:fb="http://www.w3.org/1998/Math/MathML" display="inline"><fb:msub><fb:mi>λ</fb:mi><fb:mn>122</fb:mn></fb:msub></fb:math> nonzero scenario, the projected <hb:math xmlns:hb="http://www.w3.org/1998/Math/MathML" display="inline"><hb:mrow><hb:mn>2</hb:mn><hb:mi>σ</hb:mi></hb:mrow></hb:math> exclusion limit on NLSP masses reaches upto 2.37 TeV and 4 TeV for the HL-LHC and the HE-LHC, respectively, by using a machine learning based algorithm. We observe an enhancement of <jb:math xmlns:jb="http://www.w3.org/1998/Math/MathML" display="inline"><jb:mrow><jb:mo>∼</jb:mo><jb:mn>380</jb:mn><jb:mtext> </jb:mtext><jb:mo stretchy="false">(</jb:mo><jb:mn>190</jb:mn><jb:mo stretchy="false">)</jb:mo><jb:mtext> </jb:mtext><jb:mtext> </jb:mtext><jb:mi>GeV</jb:mi></jb:mrow></jb:math> in the projected <nb:math xmlns:nb="http://www.w3.org/1998/Math/MathML" display="inline"><nb:mrow><nb:mn>2</nb:mn><nb:mi>σ</nb:mi></nb:mrow></nb:math> exclusion limit on the NLSP masses at the 27 (14) TeV LHC. Considering the same final state (<pb:math xmlns:pb="http://www.w3.org/1998/Math/MathML" display="inline"><pb:msub><pb:mi>N</pb:mi><pb:mi>l</pb:mi></pb:msub><pb:mo>≥</pb:mo><pb:mn>4</pb:mn></pb:math>) for the <rb:math xmlns:rb="http://www.w3.org/1998/Math/MathML" display="inline"><rb:msub><rb:mi>λ</rb:mi><rb:mn>133</rb:mn></rb:msub></rb:math> and/or <tb:math xmlns:tb="http://www.w3.org/1998/Math/MathML" display="inline"><tb:msub><tb:mi>λ</tb:mi><tb:mn>233</tb:mn></tb:msub></tb:math> nonzero scenario, we find that the corresponding <vb:math xmlns:vb="http://www.w3.org/1998/Math/MathML" display="inline"><vb:mrow><vb:mn>2</vb:mn><vb:mi>σ</vb:mi></vb:mrow></vb:math> projected limits are <xb:math xmlns:xb="http://www.w3.org/1998/Math/MathML" display="inline"><xb:mo>∼</xb:mo><xb:mn>1.97</xb:mn><xb:mtext> </xb:mtext><xb:mtext> </xb:mtext><xb:mi>TeV</xb:mi></xb:math> and <zb:math xmlns:zb="http://www.w3.org/1998/Math/MathML" display="inline"><zb:mo>∼</zb:mo><zb:mn>3.25</zb:mn><zb:mtext> </zb:mtext><zb:mtext> </zb:mtext><zb:mi>TeV</zb:mi></zb:math> for the HL-LHC and HE-LHC, respectively. Published by the American Physical Society 2024

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