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Search for long-lived particles with displaced vertices in multijet events in proton-proton collisions at $\sqrt{s}=$13 TeV

The collaboration
Phys.Rev. D98 (2018) 092011, 2018

Abstract (data abstract)
Results are reported from a search for long-lived particles in proton-proton collisions at $\sqrt{s}$ = 13 TeV delivered by the CERN LHC and collected by the CMS experiment. The data sample, which was recorded during 2015 and 2016, corresponds to an integrated luminosity of $38.5~\textrm{fb}^{-1}$. This search uses benchmark signal models in which long-lived particles are pair-produced and each decays into two or more quarks, leading to a signal with multiple jets and two displaced vertices composed of many tracks. No events with two well-separated high-track-multiplicity vertices are observed. Upper limits are placed on models of $R$-parity violating supersymmetry in which the long-lived particles are neutralinos or gluinos decaying solely into multijet final states or top squarks decaying solely into dijet final states. For neutralino, gluino, or top squark masses between 800 and 2600 GeV and mean proper decay lengths between 1 and 40 mm, the analysis excludes cross sections above 0.3 fb at 95% confidence level. Gluino and top squark masses are excluded below 2200 and 1400 GeV, respectively, for mean proper decay lengths between 0.6 and 80 mm. A method is provided for extending the results to other models with pair-produced long-lived particles.

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Figure 2

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Distribution of the distance between vertices in the $x$-$y$ plane, $d_{VV}$, for simulated multijet signals with $m$ = 800 GeV,...

• #### Figure 3a

Figure 3a (upper plot)

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Signal efficiency as a function of signal mass and lifetime for the multijet signal samples. All vertex and event selection...

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Figure 3b (lower plot)

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Signal efficiency as a function of signal mass and lifetime for the dijet signal samples. All vertex and event selection...

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Figure 4

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Distribution of $d_{BV}$ in $\geq$5-track one-vertex events for data and simulated multijet signals with $m$ = 800 GeV, production cross...

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Figure 5a (upper left plot)

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Distribution of the distance between vertices in the $x$-$y$ plane in events with two 3-track vertices. The points show the...

• #### Figure 5b

Figure 5b (upper right plot)

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Distribution of the distance between vertices in the $x$-$y$ plane in events with one 4-track vertex and one 3-track vertex....

• #### Figure 5c

Figure 5c (lower left plot)

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Distribution of the distance between vertices in the $x$-$y$ plane in events with two 4-track vertices. The points show the...

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Figure 5d (lower right plot)

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Distribution of the distance between vertices in the $x$-$y$ plane in events with two $\geq$5-track vertices. The points show the...

• #### Figure 6a (grid of limit values)

Figure 6a (left upper and lower plots, grid of limit values)

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Observed 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the multijet signals as a function of mass and mean proper decay...

• #### Figure 6b (grid of limit values)

Figure 6b (right upper and lower plots, grid of limit values)

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Observed 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the dijet signals as a function of mass and mean proper decay...

• #### Figure 6a (mass exclusion curves)

Figure 6a (left upper and lower plots, mass exclusion curves)

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Mass exclusion curves for the multijet signals, assuming gluino pair production cross sections and 100% branching fraction.

• #### Figure 6b (mass exclusion curves)

Figure 6b (right upper and lower plots, mass exclusion curves)

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Mass exclusion curves for the dijet signals, assuming top squark pair production cross sections and 100% branching fraction.

• #### Figure 7a

Figure 7a (upper left plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the multijet signals as a function of mass for a...

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Figure 7b (upper right plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the dijet signals as a function of mass for a...

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Figure 7c (middle left plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the multijet signals as a function of mass for a...

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Figure 7d (middle right plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the dijet signals as a function of mass for a...

• #### Figure 7e

Figure 7e (lower left plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the multijet signals as a function of mass for a...

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Figure 7f (lower right plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the dijet signals as a function of mass for a...

• #### Figure 8a

Figure 8a (upper left plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the multijet signals as a function of $c\tau$ for a...

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Figure 8b (upper right plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the dijet signals as a function of $c\tau$ for a...

• #### Figure 8c

Figure 8c (middle left plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the multijet signals as a function of $c\tau$ for a...

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Figure 8d (middle right plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the dijet signals as a function of $c\tau$ for a...

• #### Figure 8e

Figure 8e (lower left plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the multijet signals as a function of $c\tau$ for a...

• #### Figure 8f

Figure 8f (lower right plot)

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Observed and expected 95% C.L. upper limits on $\sigma\mathcal{B}^2$ for the dijet signals as a function of $c\tau$ for a...