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| CMS-HIG-17-007 ; CERN-EP-2018-092 | ||
| Search for the decay of a Higgs boson in the $\ell\ell\gamma$ channel in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 15 June 2018 | ||
| JHEP 11 (2018) 152 | ||
| Abstract: A search for a Higgs boson decaying into a pair of electrons or muons and a photon is described. Higgs boson decays to a Z boson and a photon ($\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$,$\ell=\mathrm{e}$ or $\mu$), or to two photons, one of which has an internal conversion into a muon pair ($\mathrm{H}\to\gamma^{*}\gamma\to\mu\mu\gamma$) were considered. The analysis is performed using a data set recorded by the CMS experiment at the LHC from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. No significant excess above the background prediction has been found. Limits are set on the cross section for a standard model Higgs boson decaying to opposite-sign electron or muon pairs and a photon. The observed limits on cross section times the corresponding branching fractions vary between 1.4 and 4.0 (6.1 and 11.4) times the standard model cross section for $\mathrm{H}\to\gamma^{*}\gamma\to\mu\mu\gamma$ ($\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$) in the 120-130 GeV mass range of the $\ell\ell\gamma$ system. The $\mathrm{H}\to\gamma^*\gamma\to\mu\mu\gamma$ and $\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$ analyses are combined for $m_\mathrm{H} = $ 125 GeV, obtaining an observed (expected) 95% confidence level upper limit of 3.9 (2.0) times the standard model cross section. | ||
| Links: e-print arXiv:1806.05996 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Dominant Feynman diagrams contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. |
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Figure 1-a:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. |
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Figure 1-b:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. |
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Figure 1-c:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. |
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Figure 1-d:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. |
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Figure 1-e:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. |
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Figure 1-f:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. |
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Figure 1-g:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. |
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Figure 2:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for EB-high $ {R_\mathrm {9}}$ (upper left), EB-low $ {R_\mathrm {9}}$ (upper right), EE (lower left) and dijet tag (lower right) for the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 2-a:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for EB-high $ {R_\mathrm {9}}$ for the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 2-b:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for EB-low $ {R_\mathrm {9}}$ for the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 2-c:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for EE for the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 2-d:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag for the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 3:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for dijet tag (upper left), boosted (upper right), untagged 1 (middle left), untagged 2 (middle right), untagged 3 (bottom left), and untagged 4 (bottom right) for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 3-a:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for dijet tag for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 3-b:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for boosted for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 3-c:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for untagged 1 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 3-d:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for untagged 2 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 3-e:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for untagged 3 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 3-f:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for untagged 4 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 4:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag (upper left), boosted (upper right), untagged 1 (middle left), untagged 2 (middle right), untagged 3 (bottom left), and untagged 4 (bottom right) for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 4-a:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 4-b:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for boosted for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
png pdf |
Figure 4-c:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag boosted untagged 1 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
png pdf |
Figure 4-d:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag boosted untagged 2 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
png pdf |
Figure 4-e:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag boosted untagged 3 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
png pdf |
Figure 4-f:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag boosted untagged 4 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 5:
Background model fit to the $m_{\ell \ell \gamma}$ distribution for $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ lepton tag category. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. |
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Figure 6:
Exclusion limit, at 95% CL, on the cross section of the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ process (upper plot) and the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ process (lower plot) relative to the SM prediction, as a function of the Higgs boson mass. |
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Figure 6-a:
Exclusion limit, at 95% CL, on the cross section of the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ process relative to the SM prediction, as a function of the Higgs boson mass. |
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Figure 6-b:
Exclusion limit, at 95% CL, on the cross section of the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ process relative to the SM prediction, as a function of the Higgs boson mass. |
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Figure 7:
Exclusion limit, at 95% CL, on the cross section of $ {\mathrm {H}} \to \ell \ell \gamma $ relative to the SM prediction, for an SM Higgs boson of $m_ {\mathrm {H}} = $ 125 GeV. The upper limits of each analysis category, as well as their combinations, are shown. Black full (empty) circles show the observed (background only expected) limit. Red circles show the expected upper limit assuming an SM Higgs boson decaying to $\ell \ell \gamma $ decay channel. |
| Tables | |
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Table 1:
Categories in $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ search. The electron and muon channels are considered separately in all classes except for the lepton-tag class. |
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Table 2:
Expected signal yields for a 125 GeV SM Higgs boson, corresponding to an integrated luminosity of 35.9 fb$^{-1}$, for all categories in the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ and $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ processes in the narrowest $\ell \ell \gamma $ invariant mass window around 125 GeV containing 68.3% of the expected signal distribution. |
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Table 3:
Fit functions chosen as a result of the bias study used in the analysis. |
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Table 4:
Sources of systematic uncertainties considered in the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ and $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ analyses. The pre-fit values of the nuisance parameters are shown averaged over all the categories in the analysis which either affect the normalization of the simulated signal event yields or the mean and resolution of $m_{\ell \ell \gamma}$. The "--'' indicates that the uncertainty is not applicable. |
| Summary |
| A search is performed for a standard model (SM) Higgs boson decaying into a lepton pair and a photon. This final state has contributions from Higgs boson decays to a Z boson and a photon ($\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$,$\ell=\mathrm{e}$ or $\mu$), or to two photons, one of which has an internal conversion into a muon pair ($\mathrm{H}\to\gamma^{*}\gamma\to\mu\mu\gamma$). The analysis is performed using a data set from pp collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. No significant excess above the expected background is found. Limits on the Higgs boson production cross section times the corresponding branching fractions are set. The expected exclusion limits at 95% confidence level are about 2.1-2.3 (3.9-9.1) times the SM cross section in the $\mathrm{H}\to\gamma^*\gamma\to\mu\mu\gamma$ ($\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$) channel in the mass range from 120 to 130 GeV, and the observed limit varies between about 1.4 and 4.0 (6.1 and 11.4) times the SM cross section. Finally, the $\mathrm{H}\to\gamma^*\gamma\to\mu\mu\gamma$ and $\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$ analyses are combined for $m_\mathrm{H} = $ 125 GeV, obtaining an observed (expected) 95% confidence level upper limit of 3.9 (2.0) times the SM cross section. |
| References | ||||
| 1 | A. Abbasabadi, D. Bowser-Chao, D. A. Dicus, and W. W. Repko | Radiative Higgs boson decays $ \mathrm{H}\to ff\gamma $ | PRD 55 (1997) 5647 | hep-ph/9611209 |
| 2 | L. B. Chen, C. F. Qiao, and R. L. Zhu | Reconstructing the 125 GeV SM Higgs boson through $ \ell\bar{\ell}\gamma $ | PLB 726 (2013) 306 | 1211.6058 |
| 3 | Y. Sun, H. Chang, and D. Gao | Higgs decays to $ \gamma \ell^+\ell^- $ in the standard model | JHEP 05 (2013) 061 | 1303.2230 |
| 4 | G. Passarino | Higgs boson production and decay: Dalitz sector | PLB 727 (2013) 424 | 1308.0422 |
| 5 | M. Carena, I. Low, and C. E. M. Wagner | Implications of a modified Higgs to diphoton decay width | JHEP 08 (2012) 060 | 1206.1082 |
| 6 | C.-S. Chen, C.-Q. Geng, D. Huang, and L.-H. Tsai | New scalar contributions to $ H\to Z\gamma $ | PRD 87 (2013) 075019 | 1301.4694 |
| 7 | I. Low, J. Lykken, and G. Shaughnessy | Singlet scalars as Higgs imposters at the Large Hadron Collider | PRD 84 (2011) 035027 | 1105.4587 |
| 8 | M. Bauer, M. Neubert, and A. Thamm | LHC as an axion factory: Probing an axion explanation for $ (g-2)_\mu $ with exotic Higgs decays | PRL 119 (2017) 031802 | 1704.08207 |
| 9 | A. Korchin and V. Kovalchuk | Angular distribution and forward-backward asymmetry of the Higgs-boson decay to photon and lepton pair | EPJC 74 (2014) 3141 | 1408.0342 |
| 10 | C.-W. Chiang and K. Yagyu | Higgs boson decays to $ \gamma\gamma $ and Z$ \gamma $ in models with Higgs extensions | PRD 87 (2013) 033003 | 1207.1065 |
| 11 | S. Dawson and P. P. Giardino | Higgs decays to $ ZZ $ and $ Z\gamma $ in the standard model effective field theory: An NLO analysis | PRD 97 (2018), no. 9, 093003 | 1801.01136 |
| 12 | ATLAS and CMS Collaborations | Combined measurement of the Higgs boson mass in $ pp $ collisions at $ \sqrt{s}= $ 7 and 8 TeV with the ATLAS and CMS experiments | PRL 114 (2015) 191803 | 1503.07589 |
| 13 | CMS Collaboration | Measurements of properties of the Higgs boson decaying into the four-lepton final state in pp collisions at $ \sqrt{s}= $ 13 TeV | JHEP 11 (2017) 047 | CMS-HIG-16-041 1706.09936 |
| 14 | LHC Higgs Cross Section Working Group Collaboration | Handbook of LHC Higgs cross sections: 4. deciphering the nature of the higgs sector | 1610.07922 | |
| 15 | J. M. Campbell and R. Ellis | MCFM for the Tevatron and the LHC | NPPS 205 (2010) 10 | 1007.3492 |
| 16 | D. A. Dicus and W. W. Repko | Calculation of the decay $ \mathrm{H} \to \mathrm{e}\bar{\mathrm{e}}\gamma $ | PRD 87 (2013) 077301 | 1302.2159 |
| 17 | D. A. Dicus and W. W. Repko | Dalitz decay $ \mathrm{H}\to f\bar{f}\gamma $ as a background for $ \mathrm{H}\to\gamma\gamma $ | PRD 89 (2014) 093013 | 1402.5317 |
| 18 | A. Firan and R. Stroynowski | Internal conversions in Higgs decays to two photons | PRD 76 (2007) 057301 | 0704.3987 |
| 19 | ATLAS Collaboration | Search for Higgs boson decays to a photon and a Z boson in pp collisions at $ \sqrt{s} = $ 7 and 8 TeV with the ATLAS detector | PLB 732 (2014) 8 | 1402.3051 |
| 20 | CMS Collaboration | Search for a Higgs boson decaying into a Z and a photon in pp collisions at $ \sqrt{s} = $ 7 and 8 TeV | PLB 726 (2013) 587 | CMS-HIG-13-006 1307.5515 |
| 21 | CMS Collaboration | Search for a Higgs boson decaying into $ \gamma^* \gamma \to \ell \ell \gamma $ with low dilepton mass in pp collisions at $ \sqrt s = $ 8 TeV | PLB 753 (2016) 341 | CMS-HIG-14-003 1507.03031 |
| 22 | ATLAS Collaboration | Searches for the $ Z\gamma $ decay mode of the Higgs boson and for new high-mass resonances in $ pp $ collisions at $ \sqrt{s} = $ 13 TeV with the ATLAS detector | JHEP 10 (2017) 112 | 1708.00212 |
| 23 | CMS Collaboration | The CMS experiment at the CERN LHC | JINST 3 (2008) S08004 | CMS-00-001 |
| 24 | CMS Collaboration | The CMS trigger system | JINST 12 (2017) P01020 | CMS-TRG-12-001 1609.02366 |
| 25 | CMS Collaboration | Particle-flow reconstruction and global event description with the CMS detector | JINST 12 (2017) P10003 | CMS-PRF-14-001 1706.04965 |
| 26 | CMS Collaboration | Performance of photon reconstruction and identification with the CMS detector in proton-proton collisions at $ \sqrt{s} = $ 8 TeV | JINST 10 (2015) P08010 | CMS-EGM-14-001 1502.02702 |
| 27 | CMS Collaboration | Measurement of the inclusive $ W $ and $ Z $ production cross sections in $ pp $ collisions at $ \sqrt{s}= $ 7 TeV | JHEP 10 (2011) 132 | CMS-EWK-10-005 1107.4789 |
| 28 | M. Cacciari, G. P. Salam, and G. Soyez | Fastjet user manual | EPJC 72 (2012) 1896 | 1111.6097 |
| 29 | M. Cacciari and G. P. Salam | Pileup subtraction using jet areas | PLB 659 (2008) 119 | 0707.1378 |
| 30 | M. Cacciari, G. P. Salam, and G. Soyez | The catchment area of jets | JHEP 04 (2008) 005 | 0802.1188 |
| 31 | D. L. Rainwater, R. Szalapski, and D. Zeppenfeld | Probing color singlet exchange in $ z $ + two jet events at the CERN LHC | PRD 54 (1996) 6680 | hep-ph/9605444 |
| 32 | Particle Data Group Collaboration | Review of particle physics | CPC 40 (2016), no. 10, 100001 | |
| 33 | 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 |
| 34 | NNPDF Collaboration | Parton distributions for the LHC run II | JHEP 04 (2015) 040 | 1410.8849 |
| 35 | CMS Collaboration | Event generator tunes obtained from underlying event and multiparton scattering measurements | EPJC 76 (2016) 155 | CMS-GEN-14-001 1512.00815 |
| 36 | T. Sjostrand, S. Mrenna, and P. Z. Skands | A brief introduction to PYTHIA 8.1 | CPC 178 (2008) 852 | 0710.3820 |
| 37 | T. Sjostrand et al. | An introduction to PYTHIA 8.2 | CPC 191 (2015) 159 | 1410.3012 |
| 38 | P. Artoisenet et al. | A framework for Higgs characterisation | JHEP 11 (2013) 043 | 1306.6464 |
| 39 | P. de Aquino and K. Mawatari | Characterising a Higgs-like resonance at the LHC | in Proceedings, 1st Toyama International Workshop on Higgs as a Probe of New Physics 2013 (HPNP2013): Toyama, Japan, February 13-16, 2013 2013 | 1307.5607 |
| 40 | S. Alioli, P. Nason, C. Oleari, and E. Re | NLO Higgs boson production via gluon fusion matched with shower in POWHEG | JHEP 04 (2009) 002 | 0812.0578 |
| 41 | P. Nason and C. Oleari | NLO Higgs boson production via vector-boson fusion matched with shower in POWHEG | JHEP 02 (2010) 037 | 0911.5299 |
| 42 | M. J. Oreglia | A study of the reactions $\psi' \to \gamma\gamma \psi$ | PhD thesis, Stanford University, 1980 SLAC Report SLAC-R-236, see A | |
| 43 | A. L. Read | Presentation of search results: The CL$ _{s} $ technique | JPG 28 (2002) 2693 | |
| 44 | T. Junk | Confidence level computation for combining searches with small statistics | NIMA 434 (1999) 435 | hep-ex/9902006 |
| 45 | ATLAS and CMS Collaborations, The LHC Higgs combination group | Procedure for the LHC Higgs boson search combination in summer 2011 | CMS-NOTE-2011-005 | |
| 46 | G. Cowan, K. Cranmer, E. Gross, and O. Vitells | Asymptotic formulae for likelihood-based tests of new physics | EPJC 71 (2011) 1554 | 1007.1727 |
| 47 | CMS Collaboration | CMS luminosity measurements for the 2016 data taking period | CMS-PAS-LUM-17-001 | CMS-PAS-LUM-17-001 |
| 48 | CMS Collaboration | Measurement of the inelastic proton-proton cross section at $ \sqrt{s}= $ 13 TeV | CMS-FSQ-15-005 1802.02613 |
|
| 49 | A. D. Martin, W. J. Stirling, R. S. Thorne, and G. Watt | Parton distributions for the LHC | EPJC 63 (2009) 189 | 0901.0002 |
| 50 | H. Lai et al. | New parton distributions for collider physics | PRD 82 (2010) 74024 | 1007.2241 |
| 51 | J. Butterworth et al. | PDF4LHC recommendations for LHC run II | JPG 43 (2016) 023001 | 1510.03865 |
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