CMS-PAS-SUS-14-020

CMS-PAS-SUS-14-020
Search for $R$-parity violating supersymmetry with displaced vertices
CMS Collaboration
June 2016

Abstract: A search for $R$-parity violating supersymmetry has been performed using proton-proton collision data collected by the CMS experiment at a center-of-mass energy of $\sqrt{s}= $ 8 TeV. The data analyzed correspond to an integrated luminosity of 17.6 fb$^{-1}$. This search assumes a minimal flavor violating model where the lightest supersymmetric particle is a long-lived neutralino or gluino, leading to a signal with jets emanating from displaced vertices. Based on a sample of events with two displaced vertices, the pair production cross section is bounded as a function of mass and lifetime of the neutralino or gluino. For a mass of 400 GeV and mean proper decay length of 10 mm, the analysis excludes cross sections above 0.6 fb at 95% confidence level.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PRD 95 (2017) 012009. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: This search uses as a benchmark a model in which neutralino or gluino LSPs are pair-produced, and then decay as shown.
png pdf	Figure 2: In events with exactly one vertex, the $x$-$y$ distance from the beam axis to the vertex, $ {d_{\textrm {BV}}}$, for data, simulated background normalized to data, and a simulated signal with $ {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. These events are used to construct the two-vertex background template as explained in the text.
png pdf	Figure 3: The $x$-$y$ distance between vertices, $ {d_{\textrm {VV}}}$, for simulated background normalized to data, and a simulated signal with $ {c\tau }= $ 1 mm, $M = $ 400 GeV, and production cross section 1 fb. All vertex and event selection criteria have been applied. The last bin includes the overflow events.
png pdf	Figure 4: Signal efficiency as a function of neutralino/gluino mass and lifetime, requiring two quality vertices and $ {d_{\textrm {VV}}}> $ 600 $ \mu$m.
png pdf	Figure 5: The $x$-$y$ distance between vertices, $ {d_{\textrm {VV}}}$, for simulated background events (blue crosses), compared with the best fit construction $ {d_{\textrm {VV}}^{\textrm { C}}}$ (red crosshatches). The distributions are normalized to the number of two-vertex events in the data. The error bars for the simulated events represent only the statistical uncertainty, while the shaded region for the constructed distribution is the result of varying $ {\mu _{\textrm {clear}}}$ and $ {\sigma _{\textrm {clear}}}$ within one standard deviation of the values from the fit.
png pdf	Figure 6: Fit to the data using the $ {c\tau }=$ 1 mm, $ {M}=$ 400 GeV signal hypothesis, with the background-only and signal+background fits shown with blue dotted and red dashed lines, respectively. The last bin contains events with 1 $ < {d_{\textrm {VV}}}< $ 50 mm, but is shortened for visualization.
png pdf	Figure 7-a: Observed 95% CL upper limits on cross section times branching fraction, 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-b: Observed 95% CL upper limits on cross section times branching fraction, 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.

Tables
png pdf	Table 1: Summary of systematic uncertainties in the signal efficiency.
png pdf	Table 2: Uncertainties in the predicted event yield in each $ {d_{\textrm {VV}}^{\textrm { C}}}$ bin, arising from the correlations between vertex distances, the modeling of $ {\Delta \phi _{\textrm {VV}}}$, the $ {d_{\textrm {BV}}}$ sample size, and the choice of $ {d_{\textrm {BV}}}$ binning. In the first two cases, shifts are given with their statistical uncertainty. The last row gives the overall systematic uncertainties, assuming no correlations. All yields are normalized to the total number of two-vertex events in the data.
png pdf	Table 3: Observed and mean expected background-only counts in each bin. The uncertainty is the sum in quadrature of the statistical and systematic uncertainties.

Summary

A search has been performed using data corresponding to an integrated luminosity of 17.6 fb$^{-1}$ collected with the CMS detector at $\sqrt{s} =$ 8 TeV in 2012. The data were collected with a trigger requiring the presence of at least four jets. No evidence has been found for events in which pairs of massive particles with intermediate lifetimes decay into multijet final states. At 95% confidence level, the data exclude $\sigma\mathcal{B}^2$ above approximately 1 fb for pairs of particles with masses between 400 and 1500 GeV and $\tau\nu$ between 1 and 30 mm. While the search specifically addresses the production and decay of neutralino or gluino LSPs in $R$-parity violating SUSY, the results are relevant to other massive particles that decay to two or more jets. These are the best bounds to date on the production and decay of pairs of such massive particles with intermediate lifetimes.

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