Compact Muon Solenoid
LHC, CERN
Visit us: CMS Public Website, CMS Physics ;
Contact us: CMS Publications Committee
| CMS-TOP-17-016 ; CERN-EP-2018-206 | ||
| Evidence for the associated production of a single top quark and a photon in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 8 August 2018 | ||
| Phys. Rev. Lett. 121 (2018) 221802 | ||
| Abstract: The first evidence of events consistent with the production of a single top quark in association with a photon is reported. The analysis is based on proton-proton collisions at $\sqrt{s} = $ 13 TeV and recorded by the CMS experiment in 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Events are selected by requiring the presence of a muon ($\mu$), a photon ($\gamma$), an imbalance in transverse momentum from an undetected neutrino ($\nu$), and at least two jets (j) of which exactly one is identified as associated to the hadronization of a b quark. A multivariate discriminant based on topological and kinematic event properties is employed to separate signal from background processes. An excess above the background-only hypothesis is observed, with a significance of 4.4 standard deviations. A fiducial cross section is measured for isolated photons with transverse momentum greater than 25 GeV in the central region of the detector. The measured product of the cross section and branching fraction is $\sigma({\mathrm{p}}{\mathrm{p}}\to\mathrm{t}\gamma\mathrm{j})\mathcal{B}(\mathrm{t}\to\mu\nu\mathrm{b}) = $ 115 $\pm$ 17 (stat) $\pm$ 30 (syst) fb, which is consistent with the standard model prediction. | ||
| Links: e-print arXiv:1808.02913 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
png pdf |
Figure 1:
Representative $t$-channel Feynman diagrams for single top quark production in association with a photon, including the leptonic decay of the W boson produced in the top quark decay. |
png pdf |
Figure 1-a:
Representative $t$-channel Feynman diagram for single top quark production in association with a photon, including the leptonic decay of the W boson produced in the top quark decay. |
png pdf |
Figure 1-b:
Representative $t$-channel Feynman diagram for single top quark production in association with a photon, including the leptonic decay of the W boson produced in the top quark decay. |
png pdf |
Figure 1-c:
Representative $t$-channel Feynman diagram for single top quark production in association with a photon, including the leptonic decay of the W boson produced in the top quark decay. |
png pdf |
Figure 2:
Distributions of some of the input variables to the BDT: $ {\Delta R}(\text {light jet},\gamma)$ (upper left), $\cos\theta $ (upper right), $\eta $ of the light-flavor jet (lower left), and $m_{{{\mu}}\nu {\mathrm {b}}}$ (lower right) after the final event selection in data (points), and the SM prediction (filled histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields, and the vertical bars on the points represent the statistical uncertainties of the data. The ratios of the data to the SM predictions are shown in the bottom panels. |
png pdf |
Figure 2-a:
Distribution of $ {\Delta R}(\text {light jet},\gamma)$, after the final event selection in data (points), and the SM prediction (filled histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields, and the vertical bars on the points represent the statistical uncertainties of the data. The ratios of the data to the SM predictions are shown in the bottom panel. |
png pdf |
Figure 2-b:
Distribution of $\cos\theta $, after the final event selection in data (points), and the SM prediction (filled histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields, and the vertical bars on the points represent the statistical uncertainties of the data. The ratios of the data to the SM predictions are shown in the bottom panel. |
png pdf |
Figure 2-c:
Distribution of $\eta $ of the light-flavor jet, after the final event selection in data (points), and the SM prediction (filled histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields, and the vertical bars on the points represent the statistical uncertainties of the data. The ratios of the data to the SM predictions are shown in the bottom panel. |
png pdf |
Figure 2-d:
Distribution of $m_{{{\mu}}\nu {\mathrm {b}}}$, after the final event selection in data (points), and the SM prediction (filled histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields, and the vertical bars on the points represent the statistical uncertainties of the data. The ratios of the data to the SM predictions are shown in the bottom panel. |
png pdf |
Figure 3:
The BDT output distribution for data and SM predictions after performing the fit. The inset presents a zoom of the last three bins plotted on log scale. The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields, and the vertical bars on the points represent the statistical uncertainties of the data. The ratio of the data to the SM prediction is shown in the bottom panel. |
| Tables | |
png pdf |
Table 1:
Event yields after the event selection in data and for each SM contribution. The expected yields are presented with their statistical and systematic uncertainties combined. |
| Summary |
| An excess of events above the expected background is observed at a $p$-value of 4.27x$10^{-6}$, which corresponds to a significance of 4.4 standard deviations. The median expected significance is 3.0, and the 68 and 95% confidence level ranges for the expected significance are [1.5, 4.0] and [0, 8.7], respectively. A fiducial product of the cross section and branching fraction of $\sigma(\mathrm{pp \to t \gamma j })\mathcal{B}(\mathrm{ t \to \mu \nu b }) = $ 115 $\pm$ 17 (stat) $\pm$ 30 (syst) fb is measured in the phase space defined by the photon transverse momentum $p_{{\mathrm {T}},\gamma} > $ 25 GeV, $| \eta_{\gamma} | < $1.44, and $\Delta R(X,\gamma) > $ 0.5, where $X$ stands for $\mu$, b jet, light-flavor jet. The expected SM product of the cross section and branching fraction within this fiducial phase space is 81$\pm $ 4 fb, in agreement with the measurement. This is the first experimental evidence for single top quark production in association with a photon. |
| References | ||||
| 1 | M. Fael and T. Gehrmann | Probing top quark electromagnetic dipole moments in single-top-plus-photon production | PRD 88 (2013) 033003 | 1307.1349 |
| 2 | S. M. Etesami, S. Khatibi, and M. Mohammadi Najafabadi | Measuring anomalous WW $ \gamma $ and t$ \bar{\text {t}}\gamma $ couplings using top+$ \gamma $ production at the LHC | EPJC 76 (2016) 533 | 1606.02178 |
| 3 | CDF Collaboration | Evidence for $ t\bar{t}\gamma $ production and measurement of $ \sigma_{t\bar{t}\gamma} / \sigma_{t\bar{t}} $ | PRD 84 (2011) 031104 | 1106.3970 |
| 4 | ATLAS Collaboration | Measurement of the $ t\bar{t}\gamma $ production cross section in proton-proton collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector | JHEP 11 (2017) 086 | 1706.03046 |
| 5 | CMS Collaboration | Measurement of the semileptonic $ \mathrm{t}\overline{\mathrm{t}}+\gamma $ production cross section in pp collisions at $ \sqrt{s}= $ 8 TeV | JHEP 10 (2017) 006 | CMS-TOP-14-008 1706.08128 |
| 6 | CMS Collaboration | The CMS trigger system | JINST 12 (2017) P01020 | CMS-TRG-12-001 1609.02366 |
| 7 | CMS Collaboration | The CMS experiment at the CERN LHC | JINST 3 (2008) S08004 | CMS-00-001 |
| 8 | 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 |
| 9 | NNPDF Collaboration | Parton distributions for the LHC Run II | JHEP 04 (2015) 040 | 1410.8849 |
| 10 | A. Kalogeropoulos and J. Alwall | The SysCalc code: A tool to derive theoretical systematic uncertainties | 1801.08401 | |
| 11 | P. Nason | A new method for combining NLO QCD with shower Monte Carlo algorithms | JHEP 11 (2004) 040 | hep-ph/0409146 |
| 12 | S. Frixione, P. Nason, and C. Oleari | Matching NLO QCD computations with parton shower simulations: the POWHEG method | JHEP 11 (2007) 070 | 0709.2092 |
| 13 | S. Alioli, P. Nason, C. Oleari, and E. Re | A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX | JHEP 06 (2010) 043 | 1002.2581 |
| 14 | J. M. Campbell, R. K. Ellis, P. Nason, and E. Re | Top-pair production and decay at NLO matched with parton showers | JHEP 04 (2015) 114 | 1412.1828 |
| 15 | T. Sjostrand, S. Mrenna, and P. Z. Skands | PYTHIA 6.4 Physics and Manual | JHEP 05 (2006) 026 | hep-ph/0603175 |
| 16 | T. Sjostrand, S. Mrenna, and P. Z. Skands | A Brief Introduction to PYTHIA 8.1 | CPC 178 (2008) 852 | 0710.3820 |
| 17 | CMS Collaboration | Event generator tunes obtained from underlying event and multiparton scattering measurements | EPJC 76 (2016) 155 | CMS-GEN-14-001 1512.00815 |
| 18 | GEANT4 Collaboration | GEANT4---a simulation toolkit | NIMA 506 (2003) 250 | |
| 19 | CMS Collaboration | Particle-flow reconstruction and global event description with the CMS detector | JINST 12 (2017) P10003 | CMS-PRF-14-001 1706.04965 |
| 20 | CMS Collaboration | Description and performance of track and primary-vertex reconstruction with the CMS tracker | JINST 9 (2014) P10009 | CMS-TRK-11-001 1405.6569 |
| 21 | M. Cacciari, G. P. Salam, and G. Soyez | The anti-$ {k_{\mathrm{T}}} $ jet clustering algorithm | JHEP 04 (2008) 063 | 0802.1189 |
| 22 | M. Cacciari, G. P. Salam, and G. Soyez | FastJet user manual | EPJC 72 (2012) 1896 | 1111.6097 |
| 23 | CMS Collaboration | Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV | JINST 13 (2018) P05011 | CMS-BTV-16-002 1712.07158 |
| 24 | CMS Collaboration | Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $ \sqrt{s}= $ 13 TeV | JINST 13 (2018) P06015 | CMS-MUO-16-001 1804.04528 |
| 25 | 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 |
| 26 | M. Cacciari and G. P. Salam | Pileup subtraction using jet areas | PLB 659 (2008) 119 | 0707.1378 |
| 27 | CMS Collaboration | Measurement of the $ t $-channel single top quark production cross section in pp collisions at $ \sqrt{s}= $ 7 TeV | PRL 107 (2011) 091802 | CMS-TOP-10-008 1106.3052 |
| 28 | CMS Collaboration | Measurement of $ W\gamma $ and $ Z\gamma $ production in pp collisions at $ \sqrt{s} = $ 7 TeV | PLB 701 (2011) 535 | CMS-EWK-10-008 1105.2758 |
| 29 | CMS Collaboration | Measurement of electroweak-induced production of W$ \gamma $ with two jets in pp collisions at $ \sqrt{s}= $ 8 TeV and constraints on anomalous quartic gauge couplings | JHEP 06 (2017) 106 | CMS-SMP-14-011 1612.09256 |
| 30 | CMS Collaboration | Jet algorithms performance in 13 TeV data | CDS | |
| 31 | CMS Collaboration | Jet energy scale and resolution in the CMS experiment in pp collisions at 8 TeV | JINST 12 (2017) P02014 | CMS-JME-13-004 1607.03663 |
| 32 | CMS Collaboration | Measurement of inclusive W and Z boson production cross sections in pp collisions at $ \sqrt{s} = $ 8 TeV | PRL 112 (2014) 191802 | CMS-SMP-12-011 1402.0923 |
| 33 | 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 | CMS-EGM-13-001 1502.02701 |
| 34 | CMS Collaboration | Measurement of the $ W\gamma $ and $ Z\gamma $ inclusive cross sections in pp collisions at $ \sqrt{s}= $ 7 TeV and limits on anomalous triple gauge boson couplings | PRD 89 (2014) 092005 | CMS-EWK-11-009 1308.6832 |
| 35 | ATLAS Collaboration | Measurement of the inelastic proton-proton cross section at $ \sqrt{s} = $ 13 TeV with the ATLAS detector at the LHC | PRL 117 (2016) 182002 | 1606.02625 |
| 36 | CMS Collaboration | CMS luminosity measurements for the 2016 data taking period | CDS | |
| 37 | CMS Collaboration | Measurement of the cross section for electroweak production of Z$ \gamma $ in association with two jets and constraints on anomalous quartic gauge couplings in proton-proton collisions at $ \sqrt{s} = $ 8 TeV | PLB 770 (2017) 380 | CMS-SMP-14-018 1702.03025 |
| 38 | CMS Collaboration | Measurement of the $ {{\mathrm{W}}^{+}}\mathrm{W}^{-} $ cross section in pp collisions at $ \sqrt{s} = $ 8 TeV and limits on anomalous gauge couplings | EPJC 76 (2016) 401 | CMS-SMP-14-016 1507.03268 |
| 39 | CMS Collaboration | Cross section measurement of $ t $-channel single top quark production in pp collisions at $ \sqrt{s} = $ 13 TeV | PLB 772 (2017) 752 | CMS-TOP-16-003 1610.00678 |
| 40 | M. Bahr et al. | $ HERWIG++ $ physics and manual | EPJC 58 (2008) 639 | 0803.0883 |
| 41 | H.-J. Yang, B. P. Roe, and J. Zhu | Studies of boosted decision trees for MiniBooNE particle identification | NIMA 555 (2005) 370 | physics/0508045 |
| 42 | H. Voss, A. Hocker, J. Stelzer, and F. Tegenfeldt | TMVA, the toolkit for multivariate data analysis with ROOT | in XIth International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT), p. 40 2007 | physics/0703039 |
| 43 | L. Lyons, P. Harrison, and A de Roeck, editors | Statistical issues for LHC physics | Proceedings, Workshop, PHYSTAT-LHC, CERN, 2007 | |
|
|
Compact Muon Solenoid LHC, CERN |
|
|
|
|
|
|