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| CMS-PAS-EXO-18-004 | ||
| Search for excited leptons in the $\ell\ell\gamma$ final state in proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| July 2018 | ||
| Abstract: A search is presented for excited electrons and muons using a data sample of proton-proton collisions at a center-of-mass energy of $\sqrt{s}= $ 13 TeV, collected with the CMS detector in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. This is the first search in the $\ell\ell\gamma$ final state in proton-proton collisions at $\sqrt{s}= $ 13 TeV. The observed data are consistent with the standard model prediction, and exclusion limits on the excited lepton mass and the compositeness scale are set. Excited electrons (muons) with a mass below 3.9 (3.8) TeV are excluded under the assumption that the excited lepton mass equals the compositeness scale. The best observed limit on the compositeness scale is obtained in the mass range between 0.5 and 1.0 TeV, excluding a compositeness scale below 25 TeV for both excited electrons and muons. These are the most stringent limits to date in the $\ell\ell\gamma$ final state. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 04 (2019) 015. The superseded preliminary plots can be found here. |
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| Figures | |
png pdf |
Figure 1:
The distributions of ${M_{\ell \gamma}^\text {min}}$ (left panel) and ${M_{\ell \gamma}^\text {max}}$ (right panel) in the $ {\mathrm {e}} {\mathrm {e}}\gamma $ channel (upper panel) and the $ {{\mu}} {{\mu}}\gamma $ channel (lower panel). The black dots denote the data points. The green, yellow, red and blue histograms correspond to the prediction of Z$\gamma $, the jet background, $ {{\mathrm {t}\overline {\mathrm {t}}}} \gamma $, and triboson processes, respectively. The dotted lines represents ${\ell ^*}$ signal events for $ {M_{\ell ^*}} = $ 1 TeV at $\lambda = $ 10 TeV. |
png pdf |
Figure 1-a:
The distributions of ${M_{\ell \gamma}^\text {min}}$ (left panel) and ${M_{\ell \gamma}^\text {max}}$ (right panel) in the $ {\mathrm {e}} {\mathrm {e}}\gamma $ channel (upper panel) and the $ {{\mu}} {{\mu}}\gamma $ channel (lower panel). The black dots denote the data points. The green, yellow, red and blue histograms correspond to the prediction of Z$\gamma $, the jet background, $ {{\mathrm {t}\overline {\mathrm {t}}}} \gamma $, and triboson processes, respectively. The dotted lines represents ${\ell ^*}$ signal events for $ {M_{\ell ^*}} = $ 1 TeV at $\lambda = $ 10 TeV. |
png pdf |
Figure 1-b:
The distributions of ${M_{\ell \gamma}^\text {min}}$ (left panel) and ${M_{\ell \gamma}^\text {max}}$ (right panel) in the $ {\mathrm {e}} {\mathrm {e}}\gamma $ channel (upper panel) and the $ {{\mu}} {{\mu}}\gamma $ channel (lower panel). The black dots denote the data points. The green, yellow, red and blue histograms correspond to the prediction of Z$\gamma $, the jet background, $ {{\mathrm {t}\overline {\mathrm {t}}}} \gamma $, and triboson processes, respectively. The dotted lines represents ${\ell ^*}$ signal events for $ {M_{\ell ^*}} = $ 1 TeV at $\lambda = $ 10 TeV. |
png pdf |
Figure 1-c:
The distributions of ${M_{\ell \gamma}^\text {min}}$ (left panel) and ${M_{\ell \gamma}^\text {max}}$ (right panel) in the $ {\mathrm {e}} {\mathrm {e}}\gamma $ channel (upper panel) and the $ {{\mu}} {{\mu}}\gamma $ channel (lower panel). The black dots denote the data points. The green, yellow, red and blue histograms correspond to the prediction of Z$\gamma $, the jet background, $ {{\mathrm {t}\overline {\mathrm {t}}}} \gamma $, and triboson processes, respectively. The dotted lines represents ${\ell ^*}$ signal events for $ {M_{\ell ^*}} = $ 1 TeV at $\lambda = $ 10 TeV. |
png pdf |
Figure 1-d:
The distributions of ${M_{\ell \gamma}^\text {min}}$ (left panel) and ${M_{\ell \gamma}^\text {max}}$ (right panel) in the $ {\mathrm {e}} {\mathrm {e}}\gamma $ channel (upper panel) and the $ {{\mu}} {{\mu}}\gamma $ channel (lower panel). The black dots denote the data points. The green, yellow, red and blue histograms correspond to the prediction of Z$\gamma $, the jet background, $ {{\mathrm {t}\overline {\mathrm {t}}}} \gamma $, and triboson processes, respectively. The dotted lines represents ${\ell ^*}$ signal events for $ {M_{\ell ^*}} = $ 1 TeV at $\lambda = $ 10 TeV. |
png pdf |
Figure 2:
The two dimensional distributions of ${M_{\ell \gamma}^\text {min}}$ versus ${M_{\ell \gamma}^\text {max}}$ of excited electrons with a mass of 500 GeV (left) and of excited muons with a mass of 750 GeV (right), respectively, after event selection. The red dashed lines denote the boundary of the L-shaped search window for each mass point. |
png pdf |
Figure 2-a:
The two dimensional distributions of ${M_{\ell \gamma}^\text {min}}$ versus ${M_{\ell \gamma}^\text {max}}$ of excited electrons with a mass of 500 GeV (left) and of excited muons with a mass of 750 GeV (right), respectively, after event selection. The red dashed lines denote the boundary of the L-shaped search window for each mass point. |
png pdf |
Figure 2-b:
The two dimensional distributions of ${M_{\ell \gamma}^\text {min}}$ versus ${M_{\ell \gamma}^\text {max}}$ of excited electrons with a mass of 500 GeV (left) and of excited muons with a mass of 750 GeV (right), respectively, after event selection. The red dashed lines denote the boundary of the L-shaped search window for each mass point. |
png pdf |
Figure 3:
The two dimensional distributions of ${M_{\ell \gamma}^\text {min}}$ versus ${M_{\ell \gamma}^\text {max}}$ of Z$\gamma $ background events in the $ {\mathrm {e}} {\mathrm {e}}\gamma $ channel (left) and in the $ {{\mu}} {{\mu}}\gamma $ channel (right), respectively, after event selection. |
png pdf |
Figure 3-a:
The two dimensional distributions of ${M_{\ell \gamma}^\text {min}}$ versus ${M_{\ell \gamma}^\text {max}}$ of Z$\gamma $ background events in the $ {\mathrm {e}} {\mathrm {e}}\gamma $ channel (left) and in the $ {{\mu}} {{\mu}}\gamma $ channel (right), respectively, after event selection. |
png pdf |
Figure 3-b:
The two dimensional distributions of ${M_{\ell \gamma}^\text {min}}$ versus ${M_{\ell \gamma}^\text {max}}$ of Z$\gamma $ background events in the $ {\mathrm {e}} {\mathrm {e}}\gamma $ channel (left) and in the $ {{\mu}} {{\mu}}\gamma $ channel (right), respectively, after event selection. |
png pdf |
Figure 4:
Observed (solid) and expected (dashed) 95% CL upper limits on the product of the production cross section and branching fraction (left panel) and lower limits on the compositeness scale (right panel) as a function of signal mass ${M_{\ell ^*}}$, together with the 68% (green) and 95% (yellow) CL ranges of the expected limit for the background-only hypothesis, for ${{\mathrm {e}}^*}$ (upper panel) and ${{{\mu}}^*}$ (lower panel). |
png pdf |
Figure 4-a:
Observed (solid) and expected (dashed) 95% CL upper limits on the product of the production cross section and branching fraction (left panel) and lower limits on the compositeness scale (right panel) as a function of signal mass ${M_{\ell ^*}}$, together with the 68% (green) and 95% (yellow) CL ranges of the expected limit for the background-only hypothesis, for ${{\mathrm {e}}^*}$ (upper panel) and ${{{\mu}}^*}$ (lower panel). |
png pdf |
Figure 4-b:
Observed (solid) and expected (dashed) 95% CL upper limits on the product of the production cross section and branching fraction (left panel) and lower limits on the compositeness scale (right panel) as a function of signal mass ${M_{\ell ^*}}$, together with the 68% (green) and 95% (yellow) CL ranges of the expected limit for the background-only hypothesis, for ${{\mathrm {e}}^*}$ (upper panel) and ${{{\mu}}^*}$ (lower panel). |
png pdf |
Figure 4-c:
Observed (solid) and expected (dashed) 95% CL upper limits on the product of the production cross section and branching fraction (left panel) and lower limits on the compositeness scale (right panel) as a function of signal mass ${M_{\ell ^*}}$, together with the 68% (green) and 95% (yellow) CL ranges of the expected limit for the background-only hypothesis, for ${{\mathrm {e}}^*}$ (upper panel) and ${{{\mu}}^*}$ (lower panel). |
png pdf |
Figure 4-d:
Observed (solid) and expected (dashed) 95% CL upper limits on the product of the production cross section and branching fraction (left panel) and lower limits on the compositeness scale (right panel) as a function of signal mass ${M_{\ell ^*}}$, together with the 68% (green) and 95% (yellow) CL ranges of the expected limit for the background-only hypothesis, for ${{\mathrm {e}}^*}$ (upper panel) and ${{{\mu}}^*}$ (lower panel). |
| Tables | |
png pdf |
Table 1:
Summary of the systematic uncertainties (in %) in the signal yield, the prompt photon background prediction, and the jet background prediction. |
png pdf |
Table 2:
Summary of the observed (expected) lower limits on ${M_{\ell ^*}}$, assuming ${M_{\ell ^*}} = \lambda $, and the best observed (expected) lower limits on $\lambda $ in the mass range 0.5-1.0 TeV. |
| Summary |
| A search is presented for excited electrons and muons using a data sample of proton-proton collisions at a center-of-mass energy of $\sqrt{s}= $ 13 TeV, collected with the CMS detector in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. This is the first search in the $\ell\ell\gamma$ final state in proton-proton collisions at $\sqrt{s}= $ 13 TeV. The observed data are consistent with the standard model prediction, and exclusion limits on the excited lepton mass and the compositeness scale are set. Excited electrons (muons) with a mass below 3.9 (3.8) TeV are excluded under the assumption that the excited lepton mass equals the compositeness scale. The best observed limit on the compositeness scale is obtained in the mass range between 0.5 and 1.0 TeV, excluding a compositeness scale below 25 TeV for both excited electrons and muons. These are the most stringent limits to date in the $\ell\ell\gamma$ final state. |
| References | ||||
| 1 | J. C. Pati, A. Salam, and J. A. Strathdee | Are quarks composite? | PLB 59 (1975) 265 | |
| 2 | H. Terazawa, M. Yasu\`e, K. Akama, and M. Hayshi | Observable effects of the possible substructure of leptons and quarks | PLB 112 (1982) 387 | |
| 3 | M. Abolins et al. | Testing the Compositeness of Quarks and Leptons | in Elementary Particles and Future Facilities (Snowmass 1982), p. 274 1982eConf C8206282 | |
| 4 | E. Eichten, K. D. Lane, and M. E. Peskin | New Tests for Quark and Lepton Substructure | PRL 50 (1983) 811 | |
| 5 | H. Harari | Composite models for quarks and leptons | Physics Reports 104 (1984) 159 | |
| 6 | K. D. Lane, F. E. Paige, T. Skwarnicki, and W. J. Womersley | Simulations of supercollider physics | PR 278 (1997) 291 | hep-ph/9412280 |
| 7 | U. Baur, M. Spira, and P. M. Zerwas | Excited quark and lepton production at hadron colliders | PRD 42 (1990) 815 | |
| 8 | O. W. Greenberg and C. A. Nelson | Composite models of leptons | PRD 10 (1974) 2567 | |
| 9 | O. W. Greenberg and J. Sucher | A quantum structure dynamic model of quarks, leptons, weak vector bosons, and Higgs mesons | PLB 99 (1981) 339 | |
| 10 | S. Bhattacharya, S. S. Chauhan, B. C. Choudhary, and D. Choudhury | Search for excited quarks in $ q\overline{q} {\rightarrow} {\gamma} {\gamma} $ at the cern lhc | PRD 76 (2007) 115017 | |
| 11 | S. Bhattacharya, S. S. Chauhan, B. C. Choudhary, and D. Choudhury | Quark Excitations Through the Prism of Direct Photon Plus Jet at the LHC | PRD 80 (2009) 015014 | 0901.3927 |
| 12 | CMS Collaboration | Search for excited leptons in $ pp $ collisions at $ \sqrt{s}= $ 7 TeV | Phys.Lett. B720 (2013) 309--329 | CMS-EXO-11-034 1210.2422 |
| 13 | CMS Collaboration | Search for excited leptons in proton-proton collisions at $ \sqrt{s} = $ 8~TeV | JHEP 03 (2016) 125 | CMS-EXO-14-015 1511.01407 |
| 14 | ALEPH Collaboration | Search for excited leptons at 130--140 GeV | PLB 385 (1996) 445 | |
| 15 | DELPHI Collaboration | Search for composite and exotic fermions at LEP 2 | EPJC 8 (1999) 41 | hep-ex/9811005 |
| 16 | OPAL Collaboration | Search for unstable heavy and excited leptons at LEP 2 | EPJC 14 (2000) 73 | hep-ex/0001056 |
| 17 | L3 Collaboration | Search for excited leptons at LEP | PLB 568 (2003) 23 | hep-ex/0306016 |
| 18 | H1 Collaboration | Search for excited electrons in $ ep $ collisions at HERA | PLB 666 (2008) 131 | 0805.4530 |
| 19 | CDF Collaboration | Search for Excited and Exotic Electrons in the $ e\gamma $ Decay Channel in $ \rm {p}\overline{\rm p} $ Collisions at $ \sqrt{s} = $ 1.96 TeV | PRL 94 (2005) 101802 | hep-ex/0410013 |
| 20 | CDF Collaboration | Search for Excited and Exotic Muons in the $ \mu\gamma $ Decay Channel in $ \rm {p}\overline{\rm p} $ Collisions at $ \sqrt{s} = $ 1.96 TeV | PRL 97 (2006) 191802 | hep-ex/0606043 |
| 21 | D0 Collaboration | Search for excited muons in $ {p}\overline{p} $ collisions at $ \sqrt{s} = $ 1.96 TeV | PRD 73 (2006) 111102 | hep-ex/0604040 |
| 22 | D0 Collaboration | Search for excited electrons in $ {p}\overline{p} $ collisions at $ \sqrt{s} = $ 1.96 TeV | PRD 77 (2008) 091102 | 0801.0877 |
| 23 | ATLAS Collaboration | Search for excited leptons in proton-proton collisions at $ \sqrt{s} = $ 7~TeV with the ATLAS detector | PRD 85 (2012) 072003 | 1201.3293 |
| 24 | ATLAS Collaboration | Search for excited electrons and muons in $ \sqrt{s} = $ 8~TeV proton-proton collisions with the ATLAS detector | New J. Phys. 15 (2013) 093011 | 1308.1364 |
| 25 | CMS Collaboration | The CMS experiment at the CERN LHC | JINST 3 (2008) S08004 | CMS-00-001 |
| 26 | CMS Collaboration | The CMS trigger system | JINST 12 (2017) P01020 | CMS-TRG-12-001 1609.02366 |
| 27 | T. Sjostrand, S. Mrenna, and P. Skands | A Brief Introduction to PYTHIA 8.1 | CPC 178 (2008) 852 | 0710.3820 |
| 28 | P. Skands, S. Carrazza, and J. Rojo | Tuning PYTHIA 8.1: the Monash 2013 tune | EPJC 74 (2014) 3024 | 1404.5630 |
| 29 | CMS Collaboration | Event generator tunes obtained from underlying event and multiparton scattering measurements | EPJC 76 (2016) 155 | CMS-GEN-14-001 1512.00815 |
| 30 | S. Majhi | QCD corrections to excited lepton (pair) production at the LHC | PRD 88 (2013), no. 7, 074028 | 1210.8307 |
| 31 | J. Alwall et al. | The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations | JHEP 07 (2014) 079 | 1405.0301 |
| 32 | CMS Collaboration | Particle-flow reconstruction and global event description with the cms detector | JINST 12 (2017) P10003 | CMS-PRF-14-001 1706.04965 |
| 33 | M. Cacciari, G. P. Salam, and G. Soyez | The anti-$ k_t $ jet clustering algorithm | JHEP 04 (2008) 063 | 0802.1189 |
| 34 | M. Cacciari, G. P. Salam, and G. Soyez | FastJet user manual | EPJC 72 (2012) 1896 | 1111.6097 |
| 35 | CMS Collaboration | Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $ \sqrt{s} = $ 13 TeV | Submitted to JINST | CMS-MUO-16-001 1804.04528 |
| 36 | CMS Collaboration | Electron and Photon performance using data collected by CMS at $ \sqrt{s} = $ 13 TeV and 25ns | CDS | |
| 37 | CMS Collaboration | Performance of Photon Reconstruction and Identification with the CMS Detector in Proton-Proton Collisions at $ \sqrt{s} = $ 8 TeV | JINST 10 (2015), no. 08, P08010 | CMS-EGM-14-001 1502.02702 |
| 38 | CMS Collaboration | Search for high-mass resonances in dilepton final states in proton-proton collisions at $ \sqrt{s} = $ 13 TeV | JHEP 06 (2018) 120 | CMS-EXO-16-047 1803.06292 |
| 39 | CMS Collaboration | CMS luminosity measurements for the 2016 data-taking period | CMS-PAS-LUM-17-001 | CMS-PAS-LUM-17-001 |
| 40 | J. Butterworth et al. | PDF4LHC recommendations for LHC Run II | JPG 43 (2016) 023001 | 1510.03865 |
| 41 | ATLAS and CMS Collaborations | Procedure for the LHC higgs boson search combination in Summer 2011 | CMS-NOTE-2011-005 | |
| 42 | T. Junk | Confidence level computation for combining searches with small statistics | NIMA 434 (1999) 435 | hep-ex/9902006 |
| 43 | A. L. Read | Presentation of search results: the $ CL_s $ technique | JPG 28 (2002), no. 10 | |
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