CMS-PAS-EXO-17-022

CMS-PAS-EXO-17-022
A search for light pair-produced resonances decaying into at least four quarks
CMS Collaboration
March 2018

Abstract: Results are presented of a search for light pair-produced particles that each decay into at least four quarks, targeting particles with masses above 100 GeV. The representative signal model is a supersymmetric quark that decays into four quarks through an intermediate Higgsino with a hadronic $R$-parity-violating coupling. Using 38.2 fb$^{-1}$ of data collected by the CMS experiment at the LHC from 2015 to 2016 with proton-proton collisions at a center-of-mass energy $\sqrt{s}= $ 13 TeV, reconstructed particles are clustered into two jets with large radius and high transverse momentum, each consistent with four-parton substructure and with similar mass. A novel, data-driven technique is used to estimate the dominant QCD multijet event background. Background contributions from top-quark decays are also taken into account and additionally serve for the calibration of systematic uncertainties. No statistically significant excess is observed, and the production of supersymmetric quark pairs and supersymmetric gluon pairs with masses below 721 GeV and 1.0 TeV, respectively, are excluded at the 95% confidence level.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, PRL 121 (2018) 141802. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The background estimation results in the control region (left) and b-tagged control region (right). The relevant fit parameters are displayed on each plot.
png pdf	Figure 1-a: The background estimation results in the control region (left) and b-tagged control region (right). The relevant fit parameters are displayed on each plot.
png pdf	Figure 1-b: The background estimation results in the control region (left) and b-tagged control region (right). The relevant fit parameters are displayed on each plot.
png pdf	Figure 2: Left: the $m$ distribution of the tagged $ {p_{\mathrm {T}}} $-leading fatjets $P(m)$ in the signal region and the $ {\overline {m}} $ PDFs derived from these fatjets with and without $ {H_{\mathrm {T}}} $ re-weighting. Right: a comparison between the QCD multijet $ {\overline {m}} $ PDF and the tagged fatjet pair selection in simulated QCD multijet events that pass the signal selection.
png pdf	Figure 2-a: Left: the $m$ distribution of the tagged $ {p_{\mathrm {T}}} $-leading fatjets $P(m)$ in the signal region and the $ {\overline {m}} $ PDFs derived from these fatjets with and without $ {H_{\mathrm {T}}} $ re-weighting. Right: a comparison between the QCD multijet $ {\overline {m}} $ PDF and the tagged fatjet pair selection in simulated QCD multijet events that pass the signal selection.
png pdf	Figure 2-b: Left: the $m$ distribution of the tagged $ {p_{\mathrm {T}}} $-leading fatjets $P(m)$ in the signal region and the $ {\overline {m}} $ PDFs derived from these fatjets with and without $ {H_{\mathrm {T}}} $ re-weighting. Right: a comparison between the QCD multijet $ {\overline {m}} $ PDF and the tagged fatjet pair selection in simulated QCD multijet events that pass the signal selection.
png pdf	Figure 3: Distributions in $ {\overline {m}} $ and the predicted background contributions. Shown also are the signal expected from a squark with masses of 100 and 500 GeV.
png pdf	Figure 4: The expected and observed limits on the squark (left) and gluino (right) signal production.
png pdf	Figure 4-a: The expected and observed limits on the squark (left) and gluino (right) signal production.
png pdf	Figure 4-b: The expected and observed limits on the squark (left) and gluino (right) signal production.

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 statistical fit. Except for the QCD multijet $ {\overline {m}} $ PDF normalization, which is floating (and whose value is simply the event yield with statistical uncertainty), each nuisance parameter has a Gaussian PDF and is reported as its mean $\pm $ its standard deviation.

Summary

In summary, a search was conducted for light pair-produced resonances that decay into at least four quarks. No statistically significant excess over standard model expectations was observed. The data impose limits on RPV SUSY [13] pair production, excluding squark masses between 100 and 721 GeV and gluino masses between 0.10 and 1.0 TeV. This is the first time that constraints have been placed on pair-produced particles decaying into four or five quarks in this mass range, covering a significant gap in the parameter space of RPV SUSY. This analysis is sufficiently general that other models of strongly produced particles decaying into four or more detector-visible objects are also likely to be constrained.

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