Search for long-lived particles using out-of-time trackless jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV

The collaboration
CMS-EXO-21-014, 2022.

Abstract (data abstract)
A search for long-lived particles decaying in the outer regions of the CMS silicon tracker or in the calorimeters is presented. The search is based on a data sample of proton-proton collisions at $\sqrt{s} = 13$ TeV recorded with the CMS detector at the LHC in 2016-2018, corresponding to an integrated luminosity of 138 $\text{fb}^{-1}$. A novel technique, using trackless and out-of-time jet information combined in a deep neural network discriminator, is employed to identify decays of long-lived particles. The results are interpreted in a simplified model of chargino-neutralino production, where the neutralino is the next-to-lightest supersymmetric particle, is long-lived, and decays to a gravitino and either a Higgs or $Z$ boson.This search is most sensitive to neutralino proper decay lengths of approximately 0.5 m, for which masses up to 1.18 TeV are excluded at 95% confidence level. The current search is the best result to date in the mass range from the kinematic limit imposed by the Higgs mass up to 1.8 TeV.

• #### Table 1

Data from Table 1

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Summary of combined statistical and systematic uncertainties, the size of their effect, and whether it applies to the signal or...

• #### Figure 1a

Figure 1 (left), located on page 2.

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Feynman diagrams of the effective neutralino pair production in the GMSB simplified model in which the two neutralinos decay into...

• #### Figure 1b

Figure 1 (center), located on page 2.

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Feynman diagrams of the effective neutralino pair production in the GMSB simplified model in which the two neutralinos decay into...

• #### Figure 1c

Figure 1 (right), located on page 2.

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Feynman diagrams of the effective neutralino pair production in the GMSB simplified model in which the two neutralinos decay into...

• #### Figure 2a

Figure 2 (upper left), located on page 8.

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The distributions of the most impactful input variables to the TD jet tagger for signal (red, lighter) and collision background...

• #### Figure 2b

Figure 2 (upper right), located on page 8.

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The distributions of the most impactful input variables to the TD jet tagger for signal (red, lighter) and collision background...

• #### Figure 2c

Figure 2 (middle left), located on page 8.

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The distributions of the most impactful input variables to the TD jet tagger for signal (red, lighter) and collision background...

• #### Figure 2d

Figure 2 (middle right), located on page 8.

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The distributions of the most impactful input variables to the TD jet tagger for signal (red, lighter) and collision background...

• #### Figure 2e

Figure 2 (lower), located on page 8.

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The distributions of the most impactful input variables to the TD jet tagger for signal (red, lighter) and collision background...

• #### Figure 3a

Figure 3 (left), located on page 9.

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TD jet tagger score distributions (left) for signal (red, lighter) and collision background (blue, darker). Identification probability for the signal...

• #### Figure 3b

Figure 3 (right), located on page 9.

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TD jet tagger score distributions (left) for signal (red, lighter) and collision background (blue, darker). Identification probability for the signal...

• #### Figure 4

Figure 4, located on page 10.

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The TD jet tagger score distributions for simulation (shaded histogram) and data (black markers) when using electrons from $W\to e\nu_e$...

• #### Figure 5a

Figure 5 (left), located on page 11.

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The TD jet tagger misidentification probability measured using the nominal $W$+jets MR is shown along with the systematic uncertainty, quantifying...

• #### Figure 5b

Figure 5 (right), located on page 11.

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The TD jet tagger misidentification probability measured using the nominal $W$+jets MR is shown along with the systematic uncertainty, quantifying...

• #### Figure 6

Figure 6, located on page 14.

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Distribution of the number of TD tagged jets for the $m_{\chi} = 400$ GeVsimulated signal samples with $c\tau_{\chi} = 0.5$...

• #### Figure 7a

Figure 7 (left), located on page 14.

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• #### Figure 8a

Figure 8 (left), located on page 15.

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• #### Figure 9

Figure 9, located on page 15.

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The observed 95% CL upper limit on $\sigma_{\chi\chi}$ as a function of $m_{\chi}$ and $c\tau_{\chi}$ in a scenario with \$\mathcal{B}(\chi\to...