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| CMS-PAS-EXO-16-022 | ||
| Search for displaced leptons in the e-$\mu$ channel | ||
| CMS Collaboration | ||
| August 2016 | ||
| Abstract: A search for new long-lived particles decaying to electrons and muons is presented using data from proton-proton collisions produced in 2015 by the LHC at $ \sqrt{s} = $ 13 TeV. Data used for the analysis were collected by the CMS detector and correspond to an integrated luminosity of 2.6 fb$^{-1}$. Events are selected with an electron and muon that both have transverse impact parameter values between 200 $\mu$m and 10 cm. Since no significant excess is observed, limits are set on the Displaced Supersymmetry model, with pair production of top squarks decaying into an e-$\mu$ final state via R-parity-violating interactions. The results are the most restrictive to date on this model. For a top squark mean proper decay length of cm$, masses below 870 GeV are excluded at 95% confidence level. | ||
| Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Diagram of control and search regions based on lepton impact parameter. CR I corresponds to the prompt control region, CR II corresponds to the displaced control region, and CR III (IV) corresponds to the region with a displaced electron (muon). Note that CR II is a subset of both CR III and CR IV. SR I, SR II, and SR III correspond to the three search regions. |
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Figure 2-a:
Lepton $|d_{0}|$ spectra in the HF+$e$ (a) and HF+$\mu $ (b) control regions with corresponding dedicated lepton-flavor-specific HF simulation used in each case. The rightmost bin of each plot contains the overflow entries. |
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Figure 2-b:
Lepton $|d_{0}|$ spectra in the HF+$e$ (a) and HF+$\mu $ (b) control regions with corresponding dedicated lepton-flavor-specific HF simulation used in each case. The rightmost bin of each plot contains the overflow entries. |
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Figure 3-a:
Lepton $| d_{0} |$ spectra in the HF+lepton (black) and anti-isolated preselection (red) regions for electrons (a) and muons (b). Event yields per bin have been divided by the bin width. The rightmost bin of each plot contains the overflow entries. The lower frame shows the difference between the HF+$\ell$ control data and the $\mathrm{e}$-$\mu$ control data, normalized to the $\mathrm{e}$-$\mu$ control data. |
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Figure 3-b:
Lepton $| d_{0} |$ spectra in the HF+lepton (black) and anti-isolated preselection (red) regions for electrons (a) and muons (b). Event yields per bin have been divided by the bin width. The rightmost bin of each plot contains the overflow entries. The lower frame shows the difference between the HF+$\ell$ control data and the $\mathrm{e}$-$\mu$ control data, normalized to the $\mathrm{e}$-$\mu$ control data. |
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Figure 4:
Expected and observed 95% exclusion contours for top squark pair production in the plane of top squark $c \tau $ and mass. The region to the left of the contours is excluded by this search. |
| Tables | |
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Table 1:
Names, purposes, and selection criteria of regions based on $|d_0|$ ranges. Preselection criteria are applied to all listed regions. |
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Table 2:
Yields in the displaced control region. Background and signal expectations are quoted as $\mathrm {N}_{\mathrm {exp}}$ $\pm$1$ \sigma $ (stat) $\pm$ 1$ \sigma $ (syst). |
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Table 3:
Sources of systematic uncertainty on simulation-based estimates in this search, in percent. The rightmost column includes all the relevant systematic uncertainties, not only those explicitly mentioned in the table. For simulated signal processes, the minimum and maximum uncertainty for any value of top squark mass and lifetime are shown. |
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Table 4:
Numbers of expected and observed events in the three search regions. Systematic and statistical uncertainties are added quadratically and the sum is quoted. |
| Summary |
| A search has been performed for new physics with an electron and muon in the final state which are displaced transversely from the LHC luminous region, with no requirements made on jets or missing energy. The data sample corresponds to 2.6 fb$^{-1}$ of proton-proton collisions recorded by the CMS detector at the LHC during the 2015 run at $ \sqrt{s} = $ 13 TeV. No excess is observed above the estimated number of background events for displacements up to 10 cm. The results are interpreted in the context of the displaced supersymmetry model with a top squark LSP having a lifetime up to 100 cm/$c$. We place limits at 95% CL on this model as a function of top squark mass and top squark lifetime. For a lifetime hypothesis of 2 cm/$c$, we exclude top squarks up to 870 GeV in mass. |
| References | ||||
| 1 | CMS Collaboration | Searches for Long-lived Charged Particles in Proton-Proton Collisions at $ \sqrt{s}=13 $ TeV | CMS-PAS-EXO-15-010 | CMS-PAS-EXO-15-010 |
| 2 | ATLAS Collaboration | Searches for heavy long-lived charged particles with the ATLAS detector in proton-proton collisions at $ \sqrt{s}=8 $ TeV | Journal of High Energy Physics 2015 (2015), no. 1, 1--51 | |
| 3 | CMS Collaboration | Search for disappearing tracks in proton-proton collisions at $ \sqrt{s}=8 $ TeV | JHEP 01 (2015) 096 | CMS-EXO-12-034 1411.6006 |
| 4 | ATLAS Collaboration | Search for charginos nearly mass degenerate with the lightest neutralino based on a disappearing-track signature in $ pp $ collisions at $ \sqrt{(}s)\mathbf{=}8\text{ }\text{ }\mathrm{TeV} $ with the ATLAS detector | PRD 88 (Dec, 2013) 112006 | |
| 5 | CMS Collaboration | Search for long-lived neutral particles decaying to quark-antiquark pairs in proton-proton collisions at $ \sqrt{s}=8\text{ }\text{ }\mathrm{TeV} $ | PRD 91 (Jan, 2015) 012007 | |
| 6 | CMS Collaboration | Search for long-lived neutral particles in the final state of delayed photons and missing energy in proton-proton collisions at $ \sqrt s $ = 8 TeV | CMS-PAS-EXO-12-035 | CMS-PAS-EXO-12-035 |
| 7 | CMS Collaboration | Search for displaced photons using conversions at 8 TeV | CMS-PAS-EXO-14-017 | CMS-PAS-EXO-14-017 |
| 8 | ATLAS Collaboration | Search for nonpointing and delayed photons in the diphoton and missing transverse momentum final state in 8 TeV $ pp $ collisions at the LHC using the ATLAS detector | PRD 90 (Dec, 2014) 112005 | |
| 9 | CMS Collaboration | Search for long-lived particles that decay into final states containing two electrons or two muons in proton-proton collisions at $ \sqrt{s}=8\text{ }\text{ }\mathrm{TeV} $ | PRD 91 (Mar, 2015) 052012 | |
| 10 | CMS Collaboration | Search for Displaced Supersymmetry in events with an electron and a muon with large impact parameters | PRL 114 (2015), no. 6, 061801 | CMS-B2G-12-024 1409.4789 |
| 11 | ATLAS Collaboration | Search for massive, long-lived particles using multitrack displaced vertices or displaced lepton pairs in $ pp $ collisions at $ \sqrt{s}=8\text{ }\text{ }\mathrm{TeV} $ with the ATLAS detector | PRD 92 (Oct, 2015) 072004 | |
| 12 | P. Graham, D. Kaplan, S. Rajendran, and P. Sarawat | Displaced Supersymmetry | Journal of High Energy Physics 149 (2012) | 1204.6038 |
| 13 | T. Sjostrand, S. Mrenna, and P. Z. Skands | A brief introduction to PYTHIA 8.1 | CPC 178 (2008) 852--867 | 0710.3820 |
| 14 | J. Alwall et al. | A Standard format for Les Houches event files | Computer Physics Communications 176 (2007), no. 4, 300 -- 304 | |
| 15 | B. Allanach et al. | The Snowmass points and slopes: Benchmarks for SUSY searches | Eur.Phys.J. C25 (2002) 113--123 | hep-ph/0202233 |
| 16 | CMS Collaboration | Particle-Flow Event Reconstruction in CMS and Performance for Jets, Taus, and MET | CDS | |
| 17 | CMS Collaboration | Performance of CMS muon reconstruction in pp collision events at $ \sqrt{s} $=7 TeV | Journal of Instrumentation 7 (2012) | CMS-MUO-10-004 1206.4071 |
| 18 | CMS Collaboration | Commissioning of the Particle-Flow reconstruction in Minimum-Bias and Jet Events from pp Collisions at 7 TeV | CDS | |
| 19 | CMS Collaboration | Performance of electron reconstruction and selection with the CMS detector in proton-proton collisions at $\sqrt{s} =$ 8 TeV | JINST 10 (2015) P06005 | |
| 20 | M. Cacciari and G. P. Salam | Pileup subtraction using jet areas | Phys.Lett. B659 (2008) 119--126 | 0707.1378 |
| 21 | CMS Collaboration | Identification of b quark jets at the CMS Experiment in the LHC Run 2 | CMS-PAS-BTV-15-001 | CMS-PAS-BTV-15-001 |
| 22 | M. Kramer et al. | Supersymmetry production cross sections in pp collisions at $ \sqrt{s} = $ 7 TeV | 1206.2892 | |
| 23 | J. Alwall, P. Schuster, and N. Toro | Simplified models for a first characterization of new physics at the LHC | PRD 79 (2009) 075020 | 0810.3921 |
| 24 | CMS Collaboration | Interpretation of searches for supersymmetry with simplified models | PRD 88 (2013) 052017 | CMS-SUS-11-016 1301.2175 |
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