Search for pair-produced three-jet resonances in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$

A search has been performed for pair-produced resonances decaying into three jets. The proton-proton collision data used for this analysis were collected with the CMS detector in 2016 at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of $35.9{\mathrm{fb}}^{-1}$. The mass range from 200 to 2000 GeV is explored in four separate mass regions. The observations show agreement with standard model expectations. The results are interpreted within the framework of $R$-parity violating SUSY, where pair-produced gluinos decay to a six quark final state. Gluino masses below 1500 GeV are excluded at 95% confidence level. An analysis based on data with multijet events reconstructed at the trigger level extends the reach to masses as low as 200 GeV. Improved analysis techniques have led to enhanced sensitivity, allowing the most stringent limits to date to be set on gluino pair production.

Figure 1

Pair masses within the triplet as described in Eq. (1) plotting superimposed $\widehat{m}(3,2{)}_{\mathrm{high}}^2$ vs $\widehat{m}(3,2{)}_{\mathrm{low}}^2$, $\widehat{m}(3,2{)}_{\mathrm{high}}^2$ vs $\widehat{m}(3,2{)}_{\mathrm{mid}}^2$ and $\widehat{m}(3,2{)}_{\mathrm{mid}}^2$ vs $\widehat{m}(3,2{)}_{\mathrm{low}}^2$. QCD multijet triplets (left) cluster at the edge, while triplets from signal events ($m_{\tilde{g}}=800\mathrm{GeV}$, right) fill the center.

Figure 2

right: The $D_{[3,2]}^2$ variable as described in Eq. (2) for signal (gluino of mass 400 GeV) and QCD multijet triplets. left: The $D_{[(6,3)+(3,2)]}^2$ distribution as described in Eq. (4), for signal (gluino of mass 400 GeV) and QCD multijet triplets. The distributions are made after nominal selection criteria.

Figure 3

Expected distribution of triplet invariant mass versus the scalar sum of jet $p_{\mathrm{T}}$ in the triplet for a gluino of mass 400 GeV decaying into jets. The filled color represents correctly reconstructed signal triplets, while the gray points and contour lines represent the QCD multijet background and combinatorial background from signal events. The red dashed line illustrates the $\mathrm{\Delta }$ cut: triplets to the right of the line are accepted by the selection criterion.

Figure 4

Mass distributions and background-only fits for each of the mass regions. Region 1 (top left) is fit to a function that combines the blackbodylike term described in Eq. (7) with a simulated $t\overline{t}$ distribution, while region 2 and 3 (top right and bottom left) are fit to the four parameter function from Eq. (8), and region 4 (bottom right) is fit to three parameter function from Eq. (8) with $p_3$ set to zero. The vertical gray lines indicate the mass regions. The gluino signal normalized to the cross section expected from [33] is shown in magenta.

Figure 5

Observed and expected frequentist ${\mathrm{CL}}_{\mathrm{s}}$ limits on cross section times branching fraction are calculated in the asymptotic approximation. The solid red curve shows the prediction for the gluino pair productions from [33]. The band around the theory curve indicates the uncertainty associated with PDF and scale choices. The gray vertical lines indicate the boundaries between the mass regions.