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Search for pair-produced third-generation squarks decaying via charm quarks or in compressed supersymmetric scenarios in $pp$ collisions at $\sqrt{s}=8~$TeV with the ATLAS detector

The collaboration
Phys.Rev. D90 (2014) 052008, 2014

Abstract (data abstract)
CERN-LHC. Results of a search for supersymmetry via direct production of third-generation squarks are reported, using $20.3$ fb$^{-1}$ of proton-proton collision data at $\sqrt{s} = 8$ TeV recorded by the ATLAS experiment at the LHC in 2012. Two different analysis strategies based on monojet-like and $c$-tagged event selections are carried out to optimize the sensitivity for direct top squark pair production in the decay channel to a charm quark and the lightest neutralino ($\tilde{t}_1 \to c + \tilde{\chi}_{1}^{0}$) across the top squark--neutralino mass parameter space. No excess above the Standard Model background expectation is observed. The results are interpreted in the context of direct pair production of top squarks and presented in terms of exclusion limits in the $(m_{\tilde{t}_1}$, $m_{\tilde{\chi}_{1}^{0}})$ parameter space. A top squark of mass up to about 240 GeV is excluded at 95$\%$ confidence level for arbitrary neutralino masses, within the kinematic boundaries. Top squark masses up to 270 GeV are excluded for a neutralino mass of 200 GeV. In a scenario where the top squark and the lightest neutralino are nearly degenerate in mass, top squark masses up to 260 GeV are excluded. The results from the monojet-like analysis are also interpreted in terms of compressed scenarios for top squark pair production in the decay channel $\tilde{t}_1 \to b + ff^{'} + \tilde{\chi}^{0}_{1}$ and sbottom pair production with $\tilde{b}_1 \to b + \tilde{\chi}^{0}_{1}$, leading to a similar exclusion for nearly mass-degenerate third-generation squarks and the lightest neutralino. The results in this paper significantly extend previous results at colliders.

• #### Table 1

Data from Figure 2a

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Distribution of the discriminator against b-jets, log(Pcharm/Pb), for the first-leading jet. For illustration purposes, the distributions of two different SUSY...

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Data from Figure 2b

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Distribution of the discriminator against b-jets, log(Pcharm/Pu), for the third-leading jet. For illustration purposes, the distributions of two different SUSY...

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Data from Figure 3a

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The measured $E_T^{miss}$ distribution in the $W \rightarrow \mu \nu$ control region, for the M1 selection, compared to the background...

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Data from Figure 3b

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The measured leading jet $p_T$ distribution in the $W \rightarrow \mu \nu$ control region, for the M1 selection, compared to...

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Data from Figure 3c

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The measured $E_T^{miss}$ distribution in the $W \rightarrow e \nu$ control region, for the M1 selection, compared to the background...

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Data from Figure 3d

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The measured leading jet $p_T$ distribution in the $W \rightarrow e \nu$ control region, for the M1 selection, compared to...

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Data from Figure 3e

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The measured $E_T^{miss}$ distribution in the $Z \rightarrow \mu \mu$ control region, for the M1 selection, compared to the background...

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Data from Figure 3f

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The measured leading jet $p_T$ distribution in the $Z \rightarrow \mu \mu$ control region, for the M1 selection, compared to...

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Data from Figure 4a

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The measured $E_T^{miss}$ distribution in the $W\rightarrow \mu \nu$ control region, for the c-tagged selection, compared to the background predictions....

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Data from Figure 4b

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The measured leading jet $p_T$ distribution in the $W\rightarrow \mu \nu$ control region, for the c-tagged selection, compared to the...

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Data from Figure 4c

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The measured $E_T^{miss}$ distribution in the $W\rightarrow e \nu$ control region, for the c-tagged selection, compared to the background predictions....

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Data from Figure 4d

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The measured leading jet $p_T$ distribution in the $W\rightarrow e \nu$ control region, for the c-tagged selection, compared to the...

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Data from Figure 4e

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The measured $E_T^{miss}$ distribution in the $Z\rightarrow ll$ control region, for the c-tagged selection, compared to the background predictions. The...

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Data from Figure 4f

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The measured leading jet $p_T$ distribution in the $Z\rightarrow ll$ control region, for the c-tagged selection, compared to the background...

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Data from Figure 5a

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The measured $E_T^{miss}$ distribution in the t-(anti)-t control region, for the c-tagged selection, compared to the background predictions. The latter...

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Data from Figure 5b

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The measured leading jet $p_T$ distribution in the t-(anti)-t control region, for the c-tagged selection, compared to the background predictions....

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Data from Figure 6a

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Measured leading jet $p_T$ distribution for the V3 selections compared to the SM predictions.

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Data from Figure 6b

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Measured $E_T^{miss}$ distribution for the V4 selections compared to the SM predictions.

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Data from Figure 6c

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Measured leading jet $p_T$ distribution for the V5 selections compared to the SM predictions.

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Data from Figure 6d

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Measured $E_T^{miss}$ distribution for the V5 selections compared to the SM predictions.

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Data from Figure 7a

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Measured $E_T^{miss}$ distribution for the M1 selection compared to the SM predictions. For illustration purposes, the distribution of two different...

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Data from Figure 7b

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Measured leading jet $p_T$ distribution for the M1 selection compared to the SM predictions. For illustration purposes, the distribution of...

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Data from Figure 7c

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Measured $E_T^{miss}$ distribution for the M2 selection compared to the SM predictions. For illustration purposes, the distribution of two different...

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Data from Figure 7d

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Measured leading jet $p_T$ distribution for the M2 selection compared to the SM predictions. For illustration purposes, the distribution of...

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Data from Figure 7e

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Measured $E_T^{miss}$ distribution for the M3 selection compared to the SM predictions. For illustration purposes, the distribution of two different...

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Data from Figure 7f

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Measured leading jet $p_T$ distribution for the M3 selection compared to the SM predictions. For illustration purposes, the distribution of...

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Data from Figure 8a

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Measured $E_T^{miss}$ distribution for the C1 selection before the cut in the variable shown is applied. The data are compared...

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Data from Figure 8b

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Measured leading jet $p_T$ distribution for the C1 selection before the cut in the variable shown is applied. The data...

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Data from Figure 8c

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Measured leading jet $p_T$ for the C2 selection. The data are compared to the SM predictions. For illustration purposes, the...

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Data from Figure 8d

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Measured jet multiplicity for the C2 selection. The data are compared to the SM predictions. For illustration purposes, the distribution...

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Data from Auxiliary Figure 2

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The measured $W$ transverse mass distribution in the $W \rightarrow \mu \nu$ control region for the M1 monojet-like selection, compared...

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Data from Auxiliary Figure 3

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The measured $W$ transverse mass distribution in the $W \rightarrow e \nu$ control region for the M1 monojet-like selection, compared...

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Data from Auxiliary Figure 4

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The measured dimuon invariant mass distribution in the $Z \rightarrow \mu \mu$ control region for the M1 monojet-like selection, compared...

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Data from Auxiliary Figure 5

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The measured $E_T^{miss}$ distribution in a multijet control sample for the monojet-like analysis. This region is defined with similar $E_T^{miss}$...

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Data from Auxiliary Figure 6a

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Measured jet multiplicity in the $W \rightarrow e \nu$ control region for the c-tagged analysis, compared to background predictions. The...

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Data from Auxiliary Figure 6b

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Measured jet multiplicity in the $W \rightarrow \mu \nu$ control region for the c-tagged analysis, compared to background predictions. The...

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Data from Auxiliary Figure 6c

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Measured jet multiplicity in the $Z \rightarrow ll$ control region for the c-tagged analysis, compared to background predictions. The latter...

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Data from Auxiliary Figure 6d

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Measured jet multiplicity in the t-(anti)-t control region for the c-tagged analysis, compared to background predictions. The latter include the...

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Data from Auxiliary Figure 7

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Measured dilepton invariant mass in the $Z \rightarrow ll$ control region for the c-tagged analysis. The predictions include the global...

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Data from Auxiliary Figure 8a

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Measured jet multiplicity distribution for the M1 selection compared to the SM predictions. For illustration purposes, the impact of two...

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Data from Auxiliary Figure 8b

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Measured leading jet $\eta$ distribution for the M1 selection compared to the SM predictions. For illustration purposes, the impact of...

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Data from Auxiliary Figure 8c

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Measured $\Delta \phi (jet, p_T^{miss})$ distribution for the M1 selection compared to the SM predictions. For illustration purposes, the impact...

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Data from Auxiliary Figure 9

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Measured $E_T^{miss}$ distribution after preselection cuts compared to background predictions.

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Data from Auxiliary Figure 10a

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Measured jet multiplicity distribution in the C1 c-tagged selection compared to background predictions.

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Data from Auxiliary Figure 10b

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Multiplicity of jets with loose heavy-flavor tags in the C1 selection.

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Data from Auxiliary Figure 10c

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Multiplicity of jets with medium heavy-flavor tags in the C1 selection.

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Data from Auxiliary Figure 18, 19a, 19b, 19c, 19d, 22a, 23a, 24a

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Expected and observed CLs, number of events, acceptance and efficiency for M1 SR for $\tilde{t}_1 \rightarrow c + \tilde{\chi}^0_1$. The...

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Data from Auxiliary Figure 18, 20a, 20b, 20c, 20d, 22b, 23b, 24b

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Expected and observed CLs, number of events, acceptance and efficiency for M2 SR for $\tilde{t}_1 \rightarrow c + \tilde{\chi}^0_1$. The...

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Data from Auxiliary Figure 18, 21a, 21b, 21c, 21d, 22c, 23c, 24c

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Expected and observed CLs, number of events, acceptance and efficiency for M3 SR for $\tilde{t}_1 \rightarrow c + \tilde{\chi}^0_1$. The...

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Data from Auxiliary Figure 18, 25a, 25b, 25c, 25d, 27a, 28a, 29a

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Expected and observed CLs, number of events, acceptance and efficiency for C1 SR for $\tilde{t}_1 \rightarrow c + \tilde{\chi}^0_1$. The...

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Data from Auxiliary Figure 18, 26a, 26b, 26c, 26d, 27b, 28b, 29b

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Expected and observed CLs, number of events, acceptance and efficiency for C2 SR for $\tilde{t}_1 \rightarrow c + \tilde{\chi}^0_1$. The...

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Data from Auxiliary Figure 30, 32a, 32b, 32c, 32d, 35a, 36a, 37a

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Expected and observed CLs, number of events, acceptance and efficiency for M1 SR for $\tilde{b}_1 \rightarrow b + \tilde{\chi}^0_1$. The...

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Data from Auxiliary Figure 30, 33a, 33b, 33c, 33d, 35b, 36b, 37b

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Expected and observed CLs, number of events, acceptance and efficiency for M2 SR for $\tilde{b}_1 \rightarrow b + \tilde{\chi}^0_1$. The...

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Data from Auxiliary Figure 30, 34a, 34b, 34c, 34d, 35c, 35c, 37c

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Expected and observed CLs, number of events, acceptance and efficiency for M3 SR for $\tilde{b}_1 \rightarrow b + \tilde{\chi}^0_1$. The...

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Data from Auxiliary Figure 38, 40a, 40b, 40c, 40d, 43a, 44a, 45a

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Data from Auxiliary Figure 38, 42a, 42b, 42c, 42d, 43c, 44c, 45c

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Expected and observed CLs, number of events, acceptance and efficiency for M3 SR for \$\tilde{t}_1 \rightarrow b + ff' +...