CMS-SUS-14-020

CMS-SUS-14-020 ; CERN-EP-2016-224
Search for $R$-parity violating supersymmetry with displaced vertices in proton-proton collisions at $\sqrt{s}= $ 8 TeV
CMS Collaboration
17 October 2016
Phys. Rev. D 95 (2017) 012009
Abstract: Results are reported from a search for $R$-parity violating supersymmetry in proton-proton collision events collected by the CMS experiment at a center-of-mass energy of $\sqrt{s}=$ 8 TeV. The data sample corresponds to an integrated luminosity of 17.6 fb$^{-1}$. This search assumes a minimal flavor violating model in which the lightest supersymmetric particle is a long-lived neutralino or gluino, leading to a signal with jets emanating from displaced vertices. In a sample of events with two displaced vertices, no excess yield above the expectation from standard model processes is observed, and limits are placed on the pair production cross section as a function of mass and lifetime of the neutralino or gluino. At 95% confidence level, the analysis excludes cross sections above approximately 1 fb for neutralinos or gluinos with mass between 400 and 1500 GeV and mean proper decay length between 1 and 30 mm. Assuming gluino pair production cross sections, gluino masses are excluded below 1 and 1.3 TeV for mean proper decay lengths of 300 $\mu$m and 1 mm, respectively, and below 1.4 TeV for the range 2-30 mm. The results are also applicable to other models in which long-lived particles decay into multijet final states.
Links: e-print arXiv:1610.05133 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Decay diagram for the pair-produced neutralino ($ \tilde{\chi}^0 $) or gluino ($ \tilde{\mathrm{g}}$) LSP in the assumed signal model. In both cases, the LSP decays into a top antiquark plus a virtual top squark ($\tilde{ \mathrm{ t } } $); the top squark then decays via a baryon-number violating process into strange and bottom antiquarks.
png pdf	Figure 2: Distribution of the $x$-$y$ distance between vertices, $ {d_{\mathrm {VV}}}$, for a simulated signal with LSP $ {c\tau }=$ 1 mm, $M = $ 400 GeV, and production cross section 1 fb, overlaid on simulated background normalized to the observed number of events. All vertex and event selection criteria have been applied.
png pdf	Figure 3: Signal efficiency as a function of neutralino or gluino mass and lifetime. All vertex and event selection criteria have been applied, as well as the requirement $ {d_{\mathrm {VV}}}> $ 600 $\mu$m.
png pdf	Figure 4: One-vertex events: distribution of the $x$-$y$ distance from the beam axis to the vertex, $ {d_{\mathrm {BV}}} $, for data, simulated background normalized to data, and a simulated signal with LSP $ {c\tau }=$ 1 mm, $M = $ 400 GeV, and production cross section 1 fb. Event preselection and vertex selection criteria have been applied. The last bin includes the overflow events.
png pdf	Figure 5: Distribution of the $x$-$y$ distance between vertices, $ {d_{\mathrm {VV}}}$, for simulated background events (blue crosses), overlaid on the template $ {d_{\mathrm {VV}}^{\mathrm {C}}} $ (red line and crosshatches) constructed from simulated one-vertex events. The distributions are normalized to the observed number of two-vertex events. The error bars for the simulated events represent only the statistical uncertainty, while the shaded region for the template is the result of varying $ {\mu _{\text {clear}}} $ and $ {\sigma _{\text {clear}}} $ within one standard deviation of the values from the fit.
png pdf	Figure 6: The observed distribution of the $x$-$y$ distance between the vertices, $ {d_{\mathrm {VV}}}$, shown as points with error bars. Superimposed are the results of the fits with the background-only (blue dotted lines) and signal+background (red dashed lines) hypotheses, using the signal template corresponding to LSP $ {c\tau }=$ 1 mm, $ {M} = $ 400 GeV.
png pdf	Figure 7: Observed 95% CL upper limits on cross section times branching fraction squared, with overlaid curves assuming gluino pair production cross section, for both observed (solid), with $\pm $1 standard deviation theoretical uncertainties, and expected (dashed) limits. The search excludes masses to the left of the curve. The left plot spans $ {c\tau }$ from 300 through 900 $ \mu$m, while the right plot ranges from 1 to 30 mm.
png pdf	Figure 7-a: Observed 95% CL upper limits on cross section times branching fraction squared, with overlaid curves assuming gluino pair production cross section, for both observed (solid), with $\pm $1 standard deviation theoretical uncertainties, and expected (dashed) limits. The search excludes masses to the left of the curve. The plot spans $ {c\tau }$ from 300 through 900 $ \mu$m.
png pdf	Figure 7-b: Observed 95% CL upper limits on cross section times branching fraction squared, with overlaid curves assuming gluino pair production cross section, for both observed (solid), with $\pm $1 standard deviation theoretical uncertainties, and expected (dashed) limits. The search excludes masses to the left of the curve. The plot spans $ {c\tau }$ from 1 to 30 mm.

Tables
png pdf	Table 1: Summary of systematic uncertainties in the signal efficiency.
png pdf	Table 2: Systematic uncertainties in the background yield in each $ {d_{\mathrm {VV}}}$ bin arising from construction of the $ {d_{\mathrm {VV}}^{\mathrm {C}}} $ template. In the first two rows, shifts are given with their statistical uncertainty. The last row gives the overall systematic uncertainties, assuming no correlations. All yields are normalized to the observed total number of two-vertex events.
png pdf	Table 3: Observed and expected background event yields in each bin. The uncertainty is the sum in quadrature of the statistical and systematic uncertainties.

Summary

A search for $R$-parity violating SUSY in which long-lived neutralinos or gluinos decay into multijet final states has been performed using proton-proton collision events collected with the CMS detector at $ \sqrt{s} = $ 8 TeV in 2012. The data sample corresponds to an integrated luminosity of 17.6 fb$^{-1}$, and was collected requiring the presence of at least four jets. No excess above the prediction from standard model processes is observed, and at 95% confidence level, the data exclude cross section times branching fraction squared above approximately 1 fb for neutralinos or gluinos with mass between 400 and 1500 GeV and $c\tau$ between 1 and 30 mm. Assuming gluino pair production cross sections, gluino masses below 1 and 1.3 TeV are excluded for mean proper decay lengths of 300 $\mu$m and 1 mm, respectively, and below 1.4 TeV for the range 2-30 mm. While the search specifically addresses $R$-parity violating SUSY, the results are relevant to other massive particles that decay to two or more jets. These are the most restrictive bounds to date on the production and decay of pairs of such massive particles with intermediate lifetimes.

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