CMS-EXO-17-022

CMS-EXO-17-022 ; CERN-EP-2018-094
Search for pair-produced resonances each decaying into at least four quarks in proton-proton collisions at $\sqrt{s} = $ 13 TeV
CMS Collaboration
4 June 2018
Phys. Rev. Lett. 121 (2018) 141802
Abstract: This letter presents the results of a search for pair-produced particles of masses above 100 GeV that each decay into at least four quarks. Using data collected by the CMS experiment at the LHC in 2015-2016, corresponding to an integrated luminosity of 38.2 fb$^{-1}$, reconstructed particles are clustered into two large jets of similar mass, each consistent with four-parton substructure. No statistically significant excess of data over the background prediction is observed in the distribution of average jet mass. Pair-produced squarks with dominant hadronic $R$-parity-violating decays into four quarks and with masses between 0.10 and 0.72 TeV are excluded at 95% confidence level. Similarly, pair-produced gluinos that decay into five quarks are also excluded with masses between 0.10 and 1.41 TeV at 95% confidence level. These are the first constraints that have been placed on pair-produced particles with masses below 400 GeV that decay into four or five quarks, bridging a significant gap in the coverage of $R$-parity-violating supersymmetry parameter space.
Links: e-print arXiv:1806.01058 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1: Leading order Feynman diagrams for a squark decaying into four quarks via an intermediate higgsino and a three-body decay involving an off-shell squark with an RPV coupling (left) and for a gluino decaying into five quarks via a three-body decay into two quarks and a higgsino, which decays into three quarks as in the squark case (right). This analysis assumes that the initial squarks (or gluinos) are pair-produced and that they each decay as presented.
png pdf	Figure 1-a: Leading order Feynman diagram for a squark decaying into four quarks via an intermediate higgsino and a three-body decay involving an off-shell squark with an RPV coupling. This analysis assumes that the initial squarks are pair-produced and that they each decay as presented.
png pdf	Figure 1-b: Leading order Feynman diagram for a gluino decaying into five quarks via a three-body decay into two quarks and a higgsino, which decays into three quarks as in the squark case. This analysis assumes that the initial gluinos are pair-produced and that they each decay as presented.
png pdf	Figure 2: The background estimation results in the inclusive CR (left) and b-tagged CR (right). The relevant fit parameters are displayed on each plot. The pull of each $ {\overline {m}} $ bin is the difference of the value of the data $ {\overline {m}} $ distribution and the value of the combined background post-fit $ {\overline {m}} $ PDF, divided by the statistical uncertainty.
png pdf	Figure 2-a: The background estimation results in the inclusive CR. The relevant fit parameters are displayed. The pull of each $ {\overline {m}} $ bin is the difference of the value of the data $ {\overline {m}} $ distribution and the value of the combined background post-fit $ {\overline {m}} $ PDF, divided by the statistical uncertainty.
png pdf	Figure 2-b: The background estimation results in the b-tagged CR. The relevant fit parameters are displayed. The pull of each $ {\overline {m}} $ bin is the difference of the value of the data $ {\overline {m}} $ distribution and the value of the combined background post-fit $ {\overline {m}} $ PDF, divided by the statistical uncertainty.
png pdf	Figure 3: Left: a comparison between the QCD multijet $ {\overline {m}} $ PDF and the tagged fat-jet pair selection in simulated QCD multijet events that pass the signal selection. The pull of each $ {\overline {m}} $ bin is the difference of the value of the fat-jet pair $ {\overline {m}} $ distribution and the value of the post-fit $ {\overline {m}} $ PDF, divided by the statistical uncertainty. Right: distributions in $ {\overline {m}} $, including the predicted (post-fit) background contributions. Shown also are the signals from squarks with masses of 100 GeV and 500 GeV. The pull of each $ {\overline {m}} $ bin is the difference of the value of the data $ {\overline {m}} $ distribution and the value of the background prediction, divided by the statistical uncertainty.
png pdf	Figure 3-a: A comparison between the QCD multijet $ {\overline {m}} $ PDF and the tagged fat-jet pair selection in simulated QCD multijet events that pass the signal selection. The pull of each $ {\overline {m}} $ bin is the difference of the value of the fat-jet pair $ {\overline {m}} $ distribution and the value of the post-fit $ {\overline {m}} $ PDF, divided by the statistical uncertainty.
png pdf	Figure 3-b: Distributions in $ {\overline {m}} $, including the predicted (post-fit) background contributions. Shown also are the signals from squarks with masses of 100 GeV and 500 GeV. The pull of each $ {\overline {m}} $ bin is the difference of the value of the data $ {\overline {m}} $ distribution and the value of the background prediction, divided by the statistical uncertainty.
png pdf	Figure 4: The expected and observed limits on the product of the pair-production cross section and branching fraction squared for a quark decaying to four quarks (left) and for a gluino decaying to five quarks (right).
png pdf	Figure 4-a: The expected and observed limits on the product of the pair-production cross section and branching fraction squared for a quark decaying to four quarks.
png pdf	Figure 4-b: The expected and observed limits on the product of the pair-production cross section and branching fraction squared for a gluino decaying to five quarks.

Tables

png pdf

Table 1:
The nuisance parameters corresponding to each rate and shape parameter of the background and signal distributions, before and after the maximum-likelihood fit. Except for the QCD multijet $ {\overline {m}} $ PDF normalization, which is floating (and the value of which is simply the event yield with its statistical uncertainty), each nuisance parameter has a Gaussian prior PDF and is reported with the given mean and standard deviation.

Summary

In summary, a search has been conducted at the LHC for light pair-produced resonances that each decay into at least four quarks. No statistically significant excess over the expectation is observed. The data impose limits on $R$-parity-violating supersymmetry pair production [15], excluding squark masses between 0.10 and 0.72 TeV and gluino masses between 0.10 and 1.41 TeV. These are the first constraints that have been placed on pair-produced particles with masses below 400 GeV that decay into four or five quarks, bridging a significant gap in the coverage of $R$-parity-violating supersymmetry parameter space. This analysis is sufficiently general that it can be applied to other models describing pair-produced particles decaying into four or more detectable objects.

Additional Figures
png pdf	Additional Figure 1: Acceptance and acceptance times efficiency in the SR for the simulated squark and gluino signal samples.
png pdf	Additional Figure 2: Distributions in ${\overline {m}}$ in the SR for a selection of simulated squark signal samples.
png pdf	Additional Figure 3: Distributions in ${\overline {m}}$ in the SR for a selection of simulated gluino signal samples.
png pdf	Additional Figure 4: Distributions in ${\overline {m}}$ for the tagged ${p_{\mathrm {T}}}$ -leading fat jets $P(m)$ in the SR and the ${\overline {m}}$ PDFs derived from these fat jets with and without ${H_{\mathrm {T}}}$ reweighting.

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