Search for Z' bosons decaying into charginos in final states with two oppositely charged leptons and missing transverse momentum in pp collisions at $\sqrt{s}$ = 13 TeV

Abstract

Massive leptophobic Z' bosons decaying to a pair of charginos are searched for in proton-proton collisions at $\sqrt{s}$ = 13 TeV, using data samples collected by the CMS experiment in 2016, 2017, and 2018, corresponding to a total integrated luminosity of 138 fb$^{-1}$. The Z' bosons originate from an additional U(1)' gauge symmetry extended to the minimal supersymmetric standard model. The final state consists of two oppositely charged leptons and missing transverse momentum. The signal extraction is performed with a parametrized neural network. The measurements are found to be consistent with the standard model expectations. Upper limits are set on the Z' boson production cross sections as a function of the Z' and chargino masses. The analysis excludes Z' boson masses up to about 3.5 TeV for the specific case of Z' bosons decaying exclusively to charginos, with the charginos decaying to W bosons and neutralinos.

Figures (7)

• Figure 1: Diagram showing the signal process studied in this analysis: a leptophobic $\mathup{{{{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\prime}}}$ boson decaying into two charginos, each subsequently decaying into a lepton, a neutrino, and a neutralino.
• Figure 2: Distributions measured from the ${ \mathup{{{{ \mathup{{{e}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\pm}}} }\xspace{ \mathup{{{{ \mathup{{{\upmu}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\mp}}} }\xspace$ sample collected in 2018, for $p_{\mathrm{T}}\xspace({ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace_1)$ (upper left), $m_{{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace}$ (upper right), $m_{\mathrm{T}}\xspace$ (lower left), and $M_\mathrm{T2}$ (lower right). Several benchmark signal distributions are overlaid (colored lines), illustrating the separation power between signal and background. The panel under each plot shows the data-to-background ratio, along with the corresponding total uncertainty band (in cyan).
• Figure 3: Asimov significance, $Z_A$, vs. $m_{ \mathup{{{{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\prime}}} }\xspace$ for the PNN model (circles) and for a NN model trained on a specific signal point (triangles) for the 2017 simulated event sample, in the ${ \mathup{{{{ \mathup{{{e}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\pm}}} }\xspace{ \mathup{{{{ \mathup{{{\upmu}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\mp}}} }\xspace$ channel. Two chargino masses have been considered, as indicated.
• Figure 4: Measured and simulated SM PNN score distributions for a model with $m_{{ \mathup{{{{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\prime}}} }\xspace} = 2.5$$\,\text{Te\spaceV}$ and $m_{{ \mathup{{{{ \mathup{{ \widetilde{ {\upchi}}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {1}} ^{ {\pm}}} }\xspace} = 345$$\,\text{Ge\spaceV}$, for the $\mathup{{{t}}{} _{ {}} ^{ {}}}$$\mathup{{ \overline{ {{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}}$ (upper left) and ${ \mathup{{{W}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{W}}{} _{ {}} ^{ {}}} }\xspace$ (upper right) CRs in the ${ \mathup{{{{ \mathup{{{e}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\pm}}} }\xspace{ \mathup{{{{ \mathup{{{\upmu}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\mp}}} }\xspace$ channel and for the DY CR in the ${ \mathup{{{{ \mathup{{{e}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {+}}} }\xspace{ \mathup{{{{ \mathup{{{e}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {-}}} }\xspace\xspace+{ \mathup{{{{ \mathup{{{\upmu}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {+}}} }\xspace { \mathup{{{{ \mathup{{{\upmu}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {-}}} }\xspace\xspace$ channel (lower). The panel under each plot shows the data-to-background ratios using either a background-only fit (black circles and cyan band) or a pre-fit (magenta dashed line and band). The uncertainties are displayed around the unity line.
• Figure 5: Measured and estimated background PNN score distributions, in the SRs of the three search channels. Signal distributions for a model with $m_{{ \mathup{{{{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\prime}}} }\xspace} = 2.5$$\,\text{Te\spaceV}$ and $m_{{ \mathup{{{{ \mathup{{ \widetilde{ {\upchi}}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {1}} ^{ {\pm}}} }\xspace} = 345$$\,\text{Ge\spaceV}$ are superimposed on the plots. The panel under each plot shows the data-to-background ratios using either a background-only fit (black circles and cyan band) or a pre-fit (magenta dashed line and band). The uncertainties are displayed around the unity line.