Search for direct pair production of sleptons and charginos decaying to two leptons and neutralinos with mass splittings near the W-boson mass in $$ \sqrt{s} $$ = 13 TeV pp collisions with the ATLAS detector (2023)

A bstract A search for the electroweak production of pairs of charged sleptons or charginos decaying into two-lepton final states with missing transverse momentum is presented. Two simplified models of R -parity-conserving supersymmetry are considered: direct pair-production of sleptons $$ \left(\overset{\sim }{\ell}\overset{\sim }{\ell}\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mrow> <mml:mover> <mml:mi>ℓ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mover> <mml:mi>ℓ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> </mml:mrow> </mml:mfenced> </mml:math> , with each decaying into a charged lepton and a $$ {\overset{\sim }{\chi}}_1^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math> neutralino, and direct pair-production of the lightest charginos $$ \left({\overset{\sim }{\chi}}_1^{\pm }{\overset{\sim }{\chi}}_1^{\mp}\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mrow> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mo>±</mml:mo> </mml:msubsup> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mo>∓</mml:mo> </mml:msubsup> </mml:mrow> </mml:mfenced> </mml:math> , with each decaying into a W -boson and a $$ {\overset{\sim }{\chi}}_1^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math> . The lightest neutralino $$ \left({\overset{\sim }{\chi}}_1^0\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math> is assumed to be the lightest supersymmetric particle (LSP). The analyses target the experimentally challenging mass regions where $$ m\left(\overset{\sim }{\ell}\right)-m\left({\overset{\sim }{\chi}}_1^0\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>m</mml:mi> <mml:mfenced> <mml:mover> <mml:mi>ℓ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> </mml:mfenced> <mml:mo>−</mml:mo> <mml:mi>m</mml:mi> <mml:mfenced> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math> and $$ m\left({\overset{\sim }{\chi}}_1^{\pm}\right)-m\left({\overset{\sim }{\chi}}_1^0\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>m</mml:mi> <mml:mfenced> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mo>±</mml:mo> </mml:msubsup> </mml:mfenced> <mml:mo>−</mml:mo> <mml:mi>m</mml:mi> <mml:mfenced> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math> are close to the W -boson mass (‘moderately compressed’ regions). The search uses 139 fb − 1 of $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 TeV proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider. No significant excesses over the expected background are observed. Exclusion limits on the simplified models under study are reported in the $$ \left(\overset{\sim }{\ell },{\overset{\sim }{\chi}}_1^0\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mover> <mml:mi>ℓ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math> and $$ \left({\overset{\sim }{\chi}}_1^{\pm }{\overset{\sim }{\chi}}_1^0\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mrow> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mo>±</mml:mo> </mml:msubsup> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> </mml:mrow> </mml:mfenced> </mml:math> mass planes at 95% confidence level (CL). Sleptons with masses up to 150 GeV are excluded at 95% CL for the case of a mass-splitting between sleptons and the LSP of 50 GeV. Chargino masses up to 140 GeV are excluded at 95% CL for the case of a mass-splitting between the chargino and the LSP down to about 100 GeV.