Search for anomalous production of prompt like-sign lepton pairs at $\sqrt{s}=7$ TeV with the ATLAS detector

An inclusive search for anomalous production of two prompt, isolated leptons with the same electric charge is presented. The search is performed in a data sample corresponding to 4.7 fb-1 of integrated luminosity collected in 2011 at $\sqrt{s}$ = 7 TeV with the ATLAS detector at the LHC. Pairs of leptons (ee, emu, and mumu) with large transverse momentum are selected, and the dilepton invariant mass distribution is examined for any deviation from the Standard Model expectation. No excess is found, and upper limits on the production cross section of like-sign lepton pairs from physics processes beyond the Standard Model are placed as a function of the dilepton invariant mass within a fiducial region close to the experimental selection criteria. The 95% confidence level upper limits on the cross section of anomalous ee, emu, or mumu production range between 1.7 fb and 64 fb depending on the dilepton mass and flavour combination.

17 October 2012

Contact: Exotics conveners internal

JHEP 12 (2012) 007

e-print arXiv:1210.4538 - pdf from arXiv

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Figures | Auxiliary Material

Figures

Figure 01a

Invariant mass distributions for (a) e±e±, (b) μ±μ±, and (c) e±μ± pairs passing the full event selection. The data are shown as closed circles. The stacked histograms represent the backgrounds composed of pairs of prompt leptons from SM processes, pairs with at least one non- prompt lepton, and for the electron channels, backgrounds arising from charge misidentification and photon conversions. Pairs in the ee channel with invariant masses between 70 GeV and 110 GeV are excluded because of the large background from charge misidentification in Z → e±e∓ decays. The last bin is an overflow bin.

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Figure 01b

Figure 01c

Figure 02a

Leading lepton pT distributions for (a) e±e±, (b) μ±μ±, and (c) e±μ± pairs passing the full event selection. The data are shown as closed circles. The stacked histograms represent the backgrounds composed of pairs of prompt leptons from SM processes, pairs with at least one non-prompt lepton, and for the electron channels, backgrounds arising from charge misidentification and photon conversions. The last bin is an overflow bin.

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Figure 02b

Figure 02c

Auxiliary material

Figure 03a

Subleading lepton pT distributions for (a) e±e±, (b) μ±μ±, and (c) e±μ± pairs passing the full event selection. The data are shown as closed circles, and the stacked histograms represent the background predictions. The last bin is an overflow bin.

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Figure 03b

Figure 03c

Figure 04a

Leading lepton η distributions for (a) e±e±, (b) μ±μ±, and (c) e±μ± pairs passing the full event selection. The data are shown as closed circles, and the stacked histograms represent the background predictions.

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Figure 04b

Figure 04c

Figure 05a

Subleading lepton η distributions for (a) e±e±, (b) μ±μ±, and (c) e±μ± pairs passing the full event selection. The data are shown as closed circles, and the stacked histograms represent the background predictions.

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Figure 05b

Figure 05c

Figure 06a

Invariant mass distributions for (a) e+e+, (b) μ+μ+, and (c) e+μ+ pairs passing the full event selection. The data are shown as closed circles, and the stacked histograms represent the background predictions. The last bin is an overflow bin.

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Figure 06b

Figure 06c

Figure 07a

Invariant mass distributions for (a) e−e−, (b) μ−μ−, and (c) e−μ− pairs passing the full event selection. The data are shown as closed circles, and the stacked histograms represent the background predictions. The last bin is an overflow bin.

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Figure 07b

Figure 07c

Figure 08a

Distributions of (a) leading electron pT, (b) subleading electron pT, (c) leading electron η, and (d) subleading electron η for the e+e+ signal region. The last bin in the plots of pT is an overflow bin.

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Figure 08b

Figure 08c

Figure 08d

Figure 09a

Distributions of (a) leading electron pT, (b) subleading electron pT, (c) leading electron η, and (d) subleading electron η for the e−e− signal region. The last bin shown in the plots of pT is an overflow bin.

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Figure 09b

Figure 09c

Figure 09d

Figure 10a

Distributions of (a) leading muon pT, (b) subleading muon pT, (c) leading muon η, and (d) subleading muon η for the μ+μ+ signal region. The last bin in the plots of pT is an overflow bin.

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Figure 10b

Figure 10c

Figure 10d

Figure 11a

Distributions of (a) leading muon pT, (b) subleading muon pT, (c) leading muon η, and (d) subleading muon η for the μ−μ− signal region. The last bin shown in the plots of pT is an overflow bin.

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Figure 11b

Figure 11c

Figure 11d

Figure 12a

Distributions of (a) leading lepton pT, (b) subleading lepton pT, (c) leading lepton η, and (d) subleading lepton η for the e+μ+ signal region. The last bin in the plots of pT is an overflow bin.

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Figure 12b

Figure 12c

Figure 12d

Figure 13a

Distributions of (a) leading lepton pT, (b) subleading lepton pT, (c) leading lepton η, and (d) subleading lepton η for the e−μ− signal region. The last bin shown in the plots of pT is an overflow bin.

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Figure 13b

Figure 13c

Figure 13d

Figure 14a

Invariant mass distributions for the control regions with isolated, opposite-sign (a) e+e−, (b) μ+μ−, and (c) e±μ∓ pairs. The data are shown as closed circles, and the stacked histograms represent the Standard Model predictions. The last bin is an overflow bin. The ratios between data and predictions are shown beneath the distributions. The grey bands represent the systematic uncertainties on the predictions.

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Figure 14b

Figure 14c

Figure 15a

Distributions of (a) leading electron η and (b) subleading electron η for the e±e∓ control region with two oppositely-charged isolated electrons. The ratios between data and predictions are shown beneath the distributions. The grey bands represent the systematic uncertainties on the predictions.

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Figure 15b

Figure 16a

Distributions of (a) leading muon η and (b) subleading muon η for the μ±μ∓ control region with two oppositely-charged isolated muons. The ratios between data and predictions are shown beneath the distributions. The grey bands represent the systematic uncertainties on the predictions.

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Figure 16b

Figure 17a

Distributions of (a) leading lepton η and (b) subleading lepton η for the e±μ∓ control region with two oppositely-charged isolated leptons. The ratios between data and predictions are shown beneath the distributions. The grey bands represent the systematic uncertainties on the predictions.

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Figure 17b

Figure 18a

Invariant mass distributions for different e±e± control regions enhanced in non-prompt lepton background. Figure (a) shows like-sign medium electron pairs where both electrons satisfy intermediate isolation criteria. Figure (b) shows like-sign tight electron pairs where the leading electron is fully isolated and the subleading electron satisfies intermediate isolation criteria. The last bin is an overflow bin.

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Figure 18b

Figure 19a

Invariant mass distributions for different μ±μ± control regions enhanced in non-prompt lepton background. Figure (a) shows like-sign muon pairs, requiring |d0|/σ(d0) > 3 for ≥ 1 muon. Figure (b) shows like-sign muon pairs where both muons satisfy intermediate isolation criteria. Figure (c) shows like-sign muon pairs where the leading muon is fully isolated and the subleading muon satisfies intermediate isolation criteria. The last bin is an overflow bin.

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Figure 19b

Figure 19c

Figure 20a

Invariant mass distributions for eμ control regions enhanced in non-prompt lepton background. Figure (a) shows like-sign eμ pairs where the electron is intermediately isolated and the muon is fully isolated. Figure (b) shows like-sign eμ pairs where the electron is fully isolated and the muon is intermediately isolated. The last bin is an overflow bin.

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Figure 20b

Figure 21a

Distributions of (a) leading electron η, (b) subleading electron η, (c) leading electron pT, (d) subleading electron pT, and (e) invariant mass in the like-sign Z → ee peak control region with two isolated electrons. The last bin in the plots of pT and invariant mass is an overflow bin.

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Figure 21b

Figure 21c

Figure 21d

Figure 21e

Figure 22a

95% C.L. upper limits on the fiducial cross section for new physics contributing to the fiducial region for (a) e±e±, (b) e±μ±, and (c) μ±μ± pairs.

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Figure 22b

95% C.L. upper limits on the fiducial cross section for new physics contributing to the fiducial region for (a) e±e±, (b) e±μ±, and (c) μ±μ± pairs.

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Figure 22c

95% C.L. upper limits on the fiducial cross section for new physics contributing to the fiducial region for (a) e±e±, (b) e±μ±, and (c) μ±μ± pairs.

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Figure 23a

95% C.L. upper limits on the fiducial cross section for new physics contributing to the fiducial region for (a) e+e+, (b) e+μ+, and (c) μ+μ+ pairs.

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Figure 23b

95% C.L. upper limits on the fiducial cross section for new physics contributing to the fiducial region for (a) e+e+, (b) e+μ+, and (c) μ+μ+ pairs.

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Figure 23c

95% C.L. upper limits on the fiducial cross section for new physics contributing to the fiducial region for (a) e+e+, (b) e+μ+, and (c) μ+μ+ pairs.

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Figure 24a

95% C.L. upper limits on the fiducial cross section for new physics contributing to the fiducial region for (a) e−e−, (b) e−μ−, and (c) μ−μ− pairs.

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Figure 24b

95% C.L. upper limits on the fiducial cross section for new physics contributing to the fiducial region for (a) e−e−, (b) e−μ−, and (c) μ−μ− pairs.

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Figure 24c

95% C.L. upper limits on the fiducial cross section for new physics contributing to the fiducial region for (a) e−e−, (b) e−μ−, and (c) μ−μ− pairs.

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Figure 25a

Ratio of the number of selected to anti-selected leptons, used to estimate the non-prompt lepton background, shown for (a) electrons and (b) muons as a function of lepton pT. The band reflects the statistical and systematic uncertainties.

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Figure 25b

Figure 26

Electron charge flip rate as function of electron η, measured in data and MC simulation. The errors shown are statistical only.

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Figure 27

Event display of the ee event with the highest invariant mass (589 GeV). The high-mass same-sign electron tracks are shown in red. The leading electron has an ET of 196 GeV, (η, φ) of (1.31, -1.86), and charge +1. The subleading electron has an ET of 50 GeV, (η, φ) of (-2.25, 2.73), and charge +1. There is a third electron (shown as a blue track) with an ET of 35 GeV, (η, φ) of (-0.54, 1.73), and charge -1. There are two reconstructed jets. The leading jet has a pT of 207 GeV and (η, φ) of (0.59, 1.49), and the subleading jet has a pT of 30 GeV and (η, φ) of (1.14, 1.45). The missing transverse energy (shown as a green arrow) is 9 GeV with φ of -1.05.

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Figure 28

Event display of the μμ event with the highest invariant mass (522 GeV). The muon tracks are shown in blue and red, with the high mass like-sign pair having red tracks. The leading muon has a pT of 486 GeV, (η, φ) of (0.13, -3.04), and charge +1. The subleading muon has a pT of 79 GeV, (η, φ) of (-1.73, -1.23), and charge +1. There is a third muon (shown as a blue track) with a pT of 32 GeV, (η, φ) of (-1.41, 2.70), and charge -1. There are two reconstructed jets. The leading jet has a pT of 394 GeV and (η, φ) of (-0.64, 0.17), and the subleading jet has a pT of 27 GeV and (η, φ) of (1.16, 0.15). The missing transverse energy, shown as a green arrow, is 93 GeV with φ of 0.22.

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Figure 29

Event display of the eμ event with the highest invariant mass (464 GeV). The muon and electron tracks of the high mass pair are shown in red. The muon has a pT of 212 GeV, (η, φ) of (0.68, -1.24), and charge +1. The electron has a pT of 161 GeV, (η, φ) of (2.11, 2.26), and charge +1. There is a second electron candidate shown in blue with pT of 86 GeV, (η, φ) of (1.87, 1.54) and a charge of -1. No high pT jets are reconstructed. The missing transverse energy, shown as a green arrow, is 16 GeV with φ of -0.26.

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