Search for supersymmetry in pp collisions at √s = 8 TeV in events with three leptons and at least one b-tagged jet

Abstract

Results are reported from a search for new physics processes in events with three leptons and at least one b-tagged jet. The analysis is based on a sample of proton-proton collisions at a center-of-mass energy of 8 TeV with an integrated luminosity of , collected by the CMS detector at the LHC. The event selection focuses on signatures for supersymmetry (SUSY) that include multiple W or Z bosons and b-jets in the final state, and the b-jet multiplicity is used to define low-background search regions. The standard model background contributions are determined using well-established techniques that are based on control samples in the data. The observed yields in the data are consistent with the background predictions, and the results are used to obtain upper limits on the production cross sections for several SUSY event topologies defined in the framework of simplified models.

Detailed documentation

The documentation can be found at SUS-13-008.

Tables and Plots from SUS-13-008

( click on plot to get .pdf )

Introduction

Figures	Abbreviated Caption
	Figure 1a: Processes targeted by this analysis include gluino-pair production with subsequent decay to four top quarks and two lightest SUSY particles (LSP) () via off-shell top squark.
	Figure 1b: Processes targeted by this analysis include gluino-pair production with subsequent decay to four top quarks and two lightest SUSY particles (LSP) () via on-shell top squark.
	Figure 2a: Processes targeted by this analysis include direct sbottom-pair production with decay to two top quarks, two W and two LSP ().
	Figure 2b: Processes targeted by this analysis include gluino-pair production with decay to two bottom quarks, two top quarks, two W bosons, and two LSP via on-shell bottom squark ().
	Figure 3: Process targeted by this analysis includes direct sbottom-pair production with decay to two b-quarks, two Z and two LSP ().

Event Selection and Backgrounds

Tables and Figures	Abbreviated Caption
	Figure 4: Distribution of events after the baseline event selection in data in the MET vs. HT plane for On-Z (left) and Off-Z (right) category. The requirement has not been applied to illustrate the background population at low MET.
	Table 1: Binning defining the baseline selection and the search regions of the analysis. All the combinations of these requirements are used to create the 60 search regions (SR). For no extra jet multiplicity binning is added.
	Figure 5: Jet multiplicity distributions for diboson events in WZ (left) and ZZ (right) control regions in data and simulated event samples.

Results

Tables and Figures	Abbreviated Caption
	Table 2: Predicted total background and observed data yields as a function of MET for events with no Z candidate present (Off-Z). Upper limits (68% CL) are quoted when there is not enough events in data and simulation to derive an expected number of background events.
	Table 3: Predicted total background and observed data yields as a function of MET for events with a Z candidate present (On-Z). Upper limits (68% CL) are quoted when there is not enough events in data and simulation to derive an expected number of background events.
	Figure 6a: Observed data events and predicted SM background as a function of number of jets, MET, HT, and number of b-jets are shown for events that do not contain an opposite-sign-same-flavour pair that is a Z boson candidate. The last bin in the histograms includes overflow events. The shaded bands correspond to the estimated uncertainties on the background which are calculated on the per bin basis.
	Figure 6b: Observed data events and predicted SM background as a function of number of jets, MET, HT, and number of b-jets are shown for events that contain an opposite-sign-same-flavour pair that is a Z boson candidate. The last bin in the histograms includes overflow events. The shaded bands correspond to the estimated uncertainties on the background which are calculated on the per bin basis.
	Figure 7: Predicted total background and observed data yields as a function of MET for events that do not contain an opposite-sign-same-flavour pair that is a Z boson candidate (Off-Z): (a) and (b) . The shaded bands correspond to the estimated uncertainties on the background. The dashed histograms show an expected yield for the A1 model with particle masses and . The dotted histograms show an expected yield for the B1 model with particle masses and .
	Figure 8: Predicted total background and observed data yields as a function of MET for events that contain an opposite-sign-same-flavour pair that is a Z boson candidate (On-Z): (a) and (b) . The shaded bands correspond to the estimated uncertainties on the background. The dashed histograms show an expected yield for the A1 model with particle masses and . The dotted histograms show an expected yield for the B1 model with particle masses and .

Interpretation

Tables and Figures	Abbreviated Caption
	Table 4: Systematic uncertainties on the signal acceptance.

Figures		Abbreviated Caption
		Figure 9: The 95% CL upper limits on the (left) model A1 and (right) model A2 scenario cross sections (fb) derived using the CLs method. The solid (black) contours show the observed exclusions assuming the NLO+NLL cross sections, along with the one standard deviation theory uncertainties. The dashed (red) contours present the corresponding expected results, along with the one standard deviation experimental uncertainties.
		Figure 10: The 95% CL upper limits on the model B2 scenario cross sections (fb) derived using the CLs method. In the model B2, it is assumed that with (left) or (right) . The solid (black) contours show the observed exclusions assuming the NLO+NLL cross sections, along with the one standard deviation theory uncertainties.The dashed (red) contours present the corresponding expected results, along with the one standard deviation experimental uncertainties.
		Figure 11a: The 95% CL upper limits on the model B1 scenario cross sections (fb) derived using the CLs method. The limits are computed for the following scenarios within the model B1: . The solid (black) contours show the observed exclusions assuming the NLO+NLL cross sections, along with the one standard deviation theory uncertainties. The dashed (red) contours present the corresponding expected results, along with the one standard deviation experimental uncertainties.
		Figure 11bc: The 95% CL upper limits on the model B1 scenario cross sections (fb) derived using the CLs method. The limits are computed for the following scenarios within the model B1: (left) or (right) . The solid (black) contours show the observed exclusions assuming the NLO+NLL cross sections, along with the one standard deviation theory uncertainties. The dashed (red) contours present the corresponding expected results, along with the one standard deviation experimental uncertainties. The deviation of the observed limit from the expected one is evaluated to be at the level of two standard deviations experimental uncertainties. The exclusion plots with additional information in them can be found at the link.
		Figure 12: The 95% CL upper limits on the model C1 scenario cross sections (fb) derived using the CLs method. The solid (black) contours show the observed exclusions assuming the NLO+NLL cross sections, along with the one standard deviation theory uncertainties. The dashed (red) contours present the corresponding expected results, along with the one standard deviation experimental uncertainties.

Electronic version of interpretations and acceptance maps

The root files contain the efficiencies for the signal regions used in the limits for the given model (as well as the total efficiency for the sum of these SR), the cross section limits, and the 6 exclusion contours.

Model	Specification	Link to the file	LHE files
A1		T13lb.root	(900, 100) GeV
A2		T53lb.root
B1		T63lb.root	(500, 200) GeV
B1		T6x053lb.root
B1		T6x083lb.root
B2	,	T71503lb.root
B2	,	T73003lb.root
C1		T6bbZZ3lb.root

Additional Material

Figures and Tables	Abbreviated Caption
	Performance in MC of the method for non-prompt leptons background estimation: muons. Red line in the ratio plots corresponds to a fit with a constant.
	Performance in MC of the method for non-prompt leptons background estimation: electrons. Red line in the ratio plots corresponds to a fit with a constant.
	The complete list of search regions (SR) used in the analysis. Signal regions 30-59 are the same as 0-29 except that the off-Z dilepton mass requirement is inverted.

Distributions in data

	The kinematical distributions for the Off-Z data selected with and requirements. The last bin in the histograms includes overflow events. The shaded bands correspond to the estimated uncertainties on the background which are calculated on the per bin basis.
	The kinematical distributions for the data selected with and requirements. The last bin in the histograms includes overflow events. The shaded bands correspond to the estimated uncertainties on the background which are calculated on the per bin basis.
	The kinematical distributions for the data selected with and requirements. The last bin in the histograms includes overflow events. The shaded bands correspond to the estimated uncertainties on the background which are calculated on the per bin basis.
	The kinematical distributions for the On-Z data selected with and requirements. The last bin in the histograms includes overflow events. The shaded bands correspond to the estimated uncertainties on the background which are calculated on the per bin basis.

Additional plots for the model B1 exclusion

Figures		Abbreviated Caption
		The 95% CL upper limits on the model B1 scenario cross sections (fb) derived using the CLs method. The limits are computed for the following scenario within the model B1: . The solid (black) contours show the observed exclusions assuming the NLO+NLL cross sections, along with the one standard deviation theory uncertainties. The dashed (red) contours present the corresponding expected results, along with (left) the two standard deviations or (right) one and two standard deviations experimental uncertainties.

The most sensitive search regions

Figures		Abbreviated Caption
		The most sensitive search regions for (left) model A1 and (right) model A2.
		The most sensitive search regions for the model B2. In the model B2, it is assumed that with .
		The most sensitive search regions for the model B1: .
		The most sensitive search regions for the model B1: (left) or (right) .
		The most sensitive search regions for the model C1.

SR	SR	All SR	Abbreviated Caption
			Acceptance maps for two most sensitive search regions and for all used SR for model A1 (T1tttt).
			Acceptance maps for two most sensitive search regions and for all used SR for model A2 (T5tttt).
			Acceptance maps for two most sensitive search regions and for all used SR for model B2 (T7btW) with .
			Acceptance maps for two most sensitive search regions and for all used SR for model B2 (T7btW) with .
			Acceptance maps for two most sensitive search regions and for all used SR for model B1 (T6ttWW).
			Acceptance maps for two most sensitive search regions and for all used SR for model B1 (T6ttWW).
			Acceptance maps for two most sensitive search regions and for all used SR for model B1 (T6ttWW).
			Acceptance maps for two most sensitive search regions and for all used SR for model C1 (T6bbZZ).

Cut Flow plots

Tables and Figures		Abbreviated Caption
		B-tagged jet multiplicity for 3l off-Z events. At the left for the gluino pair production (T1tttt model), at the right for sbottom pair production (T6ttWW model).
		HT distribution for 3l off-Z events after applying a b-tagged jet multiplicity cut. At the left for the gluino pair production (T1tttt model) after asking for at least 2 b-jets, at the right for sbottom pair production (T6ttWW model) asking for at least 1 b-jet.
		Jet multiplicity for 3l off-Z events with at least 2 b-tags (left, for T1tttt model) or 1 b-tag (right, for sbottom pair production - T6ttWW model).
		MET distribution for 3l off-Z events with at least 4 jets in the event. At the left for the gluino pair production (T1tttt model) is shown with a requirement of at least 2 b-jets, at the right the sbottom pair production (T6ttWW model) with at least 1 b-jet.

Event displays

Event display of one event with 3 leptons and 3 b-tagged jets: