CMS-PAS-TOP-19-002

CMS-PAS-TOP-19-002
Search for flavor-changing neutral current interactions of the top quark and the Higgs boson decaying to a bottom quark-antiquark pair at $\sqrt{s}=$ 13 TeV
CMS Collaboration
July 2021

Abstract: A search for flavor-changing neutral current interactions between the top quark and the Higgs boson is presented. The search is based on a data sample corresponding to an integrated luminosity of 137 fb$^{-1}$ recorded by the CMS experiment at the LHC in proton-proton collisions at $\sqrt{s}=$ 13 TeV. Events containing exactly one lepton (electron or muon) and at least three jets, among which at least two are identified as coming from the hadronization of a b quark, are analyzed. Selected events are separated into five categories based on the jet and b jet multiplicity. A deep neural network is used to associate the reconstructed objects to the matrix-element partonic final state, while boosted decision trees are used to distinguish the signal from the background events. No significant excess over the background predictions is observed, and upper limits on the signal production cross sections are set. These limits are interpreted in terms of top quark decay branching fractions. Assuming one nonvanishing extra coupling at a time, the observed (expected) upper limits at the 95% confidence level are $\mathcal{B}(\mathrm{t}\to\mathrm{Hu}) < $ 7.9 $\times$ 10$^{-4}$ (1.1 $\times$ 10$^{-3}$) and $\mathcal{B}(\mathrm{t}\to\mathrm{Hc}) < $ 9.4 $\times$ 10$^{-4}$ (8.6 $\times$ 10$^{-4}$).
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, JHEP 02 (2022) 169. The superseded preliminary plots can be found here.

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1-a: The reconstructed Higgs boson mass in the b3j3 category for the ST signal scenario (left), the distribution of the subleading DeepCSV value for the b-tagged jet from the Higgs boson decay in the b4j4 category for the TT signal scenario (middle), and the mass of the hadronically decaying top quark in the b2j4 category for the SM ${{\mathrm {t}\overline {\mathrm {t}}}}$ background scenario (right) for the combined 2017 and 2018 data.
png pdf	Figure 1-b: The reconstructed Higgs boson mass in the b3j3 category for the ST signal scenario (left), the distribution of the subleading DeepCSV value for the b-tagged jet from the Higgs boson decay in the b4j4 category for the TT signal scenario (middle), and the mass of the hadronically decaying top quark in the b2j4 category for the SM ${{\mathrm {t}\overline {\mathrm {t}}}}$ background scenario (right) for the combined 2017 and 2018 data.
png pdf	Figure 1-c: The reconstructed Higgs boson mass in the b3j3 category for the ST signal scenario (left), the distribution of the subleading DeepCSV value for the b-tagged jet from the Higgs boson decay in the b4j4 category for the TT signal scenario (middle), and the mass of the hadronically decaying top quark in the b2j4 category for the SM ${{\mathrm {t}\overline {\mathrm {t}}}}$ background scenario (right) for the combined 2017 and 2018 data.
png pdf	Figure 2-a: BDT output distributions for the combined 2017 and 2018 data and simulation for the Hut coupling and for the different jet categories. The signal contributions are normalized to the data.
png pdf	Figure 2-b: BDT output distributions for the combined 2017 and 2018 data and simulation for the Hut coupling and for the different jet categories. The signal contributions are normalized to the data.
png pdf	Figure 2-c: BDT output distributions for the combined 2017 and 2018 data and simulation for the Hut coupling and for the different jet categories. The signal contributions are normalized to the data.
png pdf	Figure 2-d: BDT output distributions for the combined 2017 and 2018 data and simulation for the Hut coupling and for the different jet categories. The signal contributions are normalized to the data.
png pdf	Figure 2-e: BDT output distributions for the combined 2017 and 2018 data and simulation for the Hut coupling and for the different jet categories. The signal contributions are normalized to the data.
png pdf	Figure 3-a: BDT output distributions for the combined 2017 and 2018 data and simulation for the Hct coupling and for the different jet categories. The signal contributions are normalized to the data.
png pdf	Figure 3-b: BDT output distributions for the combined 2017 and 2018 data and simulation for the Hct coupling and for the different jet categories. The signal contributions are normalized to the data.
png pdf	Figure 3-c: BDT output distributions for the combined 2017 and 2018 data and simulation for the Hct coupling and for the different jet categories. The signal contributions are normalized to the data.
png pdf	Figure 3-d: BDT output distributions for the combined 2017 and 2018 data and simulation for the Hct coupling and for the different jet categories. The signal contributions are normalized to the data.
png pdf	Figure 3-e: BDT output distributions for the combined 2017 and 2018 data and simulation for the Hct coupling and for the different jet categories. The signal contributions are normalized to the data.
png pdf	Figure 4-a: Excluded signal cross sections at 95% CL in units of pb for the Hut (left) and Hct (right) couplings obtained using the BDT distributions. Each jet category and their combination are shown separately.
png pdf	Figure 4-b: Excluded signal cross sections at 95% CL in units of pb for the Hut (left) and Hct (right) couplings obtained using the BDT distributions. Each jet category and their combination are shown separately.
png pdf	Figure 5-a: Upper limits on the couplings $\kappa _{Hut}$ and $\kappa _{Hct}$ (left) and the branching fractions $\mathcal {B}({\mathrm {t}}\to \mathrm{H} {\mathrm {u}})$ and $\mathcal {B}({\mathrm {t}}\to \mathrm{H} {\mathrm {c}})$ (right) at 95% CL.
png pdf	Figure 5-b: Upper limits on the couplings $\kappa _{Hut}$ and $\kappa _{Hct}$ (left) and the branching fractions $\mathcal {B}({\mathrm {t}}\to \mathrm{H} {\mathrm {u}})$ and $\mathcal {B}({\mathrm {t}}\to \mathrm{H} {\mathrm {c}})$ (right) at 95% CL.

Summary

A search for flavor-changing neutral current interactions in events with a top quark decaying leptonically and a Higgs boson decaying to two b quarks has been presented. The search uses the full CMS Run 2 data set, collected at $\sqrt s = $ 13 TeV in 2016--2018 and corresponding to 137 fb$^{-1}$ of proton-proton collisions. No significant deviation from the SM prediction has been observed and upper limits on the branching ratios $\mathcal{B}(\mathrm{t} \to \mathrm{Hq})$ have been set. The observed (expected) excluded branching ratios at 95% CL are $\mathcal{B}(\mathrm{ t \to H u }) < $ 7.9 $\times$ 10$^{-4}$ (1.1 $\times$ 10$^{-3}$) and $\mathcal{B}(\mathrm{ t \to H c }) < $ 9.4 $\times$ 10$^{-4}$ (8.6 $\times$ 10$^{-4}$). This search significantly improves upon the CMS search presented in Ref.[X] by exploiting the full Run 2 luminosity of 137 fb$^{-1}$ and by using advanced multivariate analysis techniques to perform the event reconstruction.

References
1	CMS Collaboration	Observation of a New Boson at a Mass of 125 GeV with the CMS Experiment at the LHC	PLB 716 (2012) 30	CMS-HIG-12-028 1207.7235
2	ATLAS Collaboration	Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC	PLB 716 (2012) 1	1207.7214
3	CMS Collaboration	Observation of a New Boson with Mass Near 125 GeV in $ pp $ Collisions at $ \sqrt{s} = $ 7 and 8 TeV	JHEP 06 (2013) 081	CMS-HIG-12-036 1303.4571
4	ATLAS, CMS Collaboration	Measurements of the Higgs boson production and decay rates and constraints on its couplings from a combined ATLAS and CMS analysis of the LHC pp collision data at $ \sqrt{s}= $ 7 and 8 TeV	JHEP 08 (2016) 045	1606.02266
5	CMS Collaboration	Measurement of the top quark Yukawa coupling from $ \mathrm{t\bar{t}} $ kinematic distributions in the dilepton final state in proton-proton collisions at $ \sqrt{s}= $ 13 TeV	PRD 102 (2020) 092013	CMS-TOP-19-008 2009.07123
6	B. A. Dobrescu and C. T. Hill	Electroweak symmetry breaking via top condensation seesaw	PRL 81 (1998) 2634	hep-ph/9712319
7	R. S. Chivukula, B. A. Dobrescu, H. Georgi, and C. T. Hill	Top Quark Seesaw Theory of Electroweak Symmetry Breaking	PRD 59 (1999) 075003	hep-ph/9809470
8	D. Delepine, J. M. Gerard, and R. Gonzalez Felipe	Is the standard Higgs scalar elementary?	PLB 372 (1996) 271	hep-ph/9512339
9	S. L. Glashow, J. Iliopoulos, and L. Maiani	Weak Interactions with Lepton-Hadron Symmetry	PRD 2 (1970) 1285
10	J. A. Aguilar-Saavedra	Top flavor-changing neutral interactions: Theoretical expectations and experimental detection	Acta Phys. Polon. B 35 (2004) 2695	hep-ph/0409342
11	B. Mele, S. Petrarca, and A. Soddu	A New evaluation of the t ---$ > $ cH decay width in the standard model	PLB 435 (1998) 401	hep-ph/9805498
12	G. Eilam, J. L. Hewett, and A. Soni	Rare decays of the top quark in the standard and two Higgs doublet models	PRD 44 (1991) 1473, . [Erratum: Phys.Rev.D 59, 039901 (1999)]
13	G. Eilam, J. L. Hewett, and A. Soni	Erratum: Rare decays of the top quark in the standard and two-Higgs-doublet models [Phys. Rev. D 44, 1473 (1991)]	PRD 59 (1998) 039901
14	T. P. Cheng and M. Sher	Mass Matrix Ansatz and Flavor Nonconservation in Models with Multiple Higgs Doublets	PRD 35 (1987) 3484
15	D. Atwood, L. Reina, and A. Soni	Phenomenology of two Higgs doublet models with flavor changing neutral currents	PRD 55 (1997) 3156	hep-ph/9609279
16	S. Bejar, J. Guasch, and J. Sola	Loop induced flavor changing neutral decays of the top quark in a general two Higgs doublet model	NPB 600 (2001) 21	hep-ph/0011091
17	J. Guasch and J. Sola	FCNC top quark decay in the MSSM: A Door to SUSY physics in high luminosity colliders?	NPB 562 (1999) 3	hep-ph/9906268
18	G. Eilam et al.	Top quark rare decay t ---$ > $ ch in R-parity violating SUSY	PLB 510 (2001) 227	hep-ph/0102037
19	J. A. Aguilar-Saavedra	Effects of mixing with quark singlets	PRD 67 (2003) 035003	hep-ph/0210112
20	A. Azatov, M. Toharia, and L. Zhu	Higgs Mediated FCNC's in Warped Extra Dimensions	PRD 80 (2009) 035016	0906.1990
21	A. Crivellin, J. Heeck, and P. Stoffer	A perturbed lepton-specific two-Higgs-doublet model facing experimental hints for physics beyond the Standard Model	PRL 116 (2016), no. 8, 081801	1507.07567
22	ATLAS Collaboration	Search for top quark decays $ t\rightarrow qH $, with $ H\to\gamma\gamma $, in $ \sqrt{s}=13 TeV pp $ collisions using the ATLAS detector	JHEP 10 (2017) 129	1707.01404
23	ATLAS Collaboration	Search for flavor-changing neutral currents in top quark decays $ t\to Hc $ and $ t \to Hu $ in multilepton final states in proton-proton collisions at $ \sqrt{s}= $ 13 TeV with the ATLAS detector	PRD 98 (2018), no. 3, 032002	1805.03483
24	ATLAS Collaboration	Search for top-quark decays $ t \to Hq $ with 36 fb$ ^{-1} $ of $ pp $ collision data at $ \sqrt{s}= $ 13 TeV with the ATLAS detector	JHEP 05 (2019) 123	1812.11568
25	CMS Collaboration	Search for the flavor-changing neutral current interactions of the top quark and the Higgs boson which decays into a pair of b quarks at $ \sqrt{s}= $ 13 TeV	JHEP 06 (2018) 102	CMS-TOP-17-003 1712.02399
26	CMS Collaboration	Search for flavor-changing neutral current interactions of the top quark and the Higgs boson in the diphoton decay channel in proton-proton collisions at $ \sqrt{s}= $ 13 TeV	CMS-PAS-TOP-20-007	CMS-PAS-TOP-20-007
27	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
28	A. Alloul et al.	FeynRules 2.0 - A complete toolbox for tree-level phenomenology	CPC 185 (2014) 2250	1310.1921
29	C. Degrande et al.	UFO - The Universal FeynRules Output	CPC 183 (2012) 1201	1108.2040
30	J. Alwall et al.	Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions	EPJC 53 (2008) 473	0706.2569
31	M. Czakon and A. Mitov	Top++: A Program for the Calculation of the Top-Pair Cross-Section at Hadron Colliders	CPC 185 (2014) 2930	1112.5675
32	M. Czakon et al.	Top-pair production at the LHC through NNLO QCD and NLO EW	JHEP 10 (2017) 186	1705.04105
33	CMS Collaboration	Measurement of differential $ \mathrm{t}\bar{\mathrm{t}} $ production cross sections in the full kinematic range using lepton+jets events from pp collisions at $ \sqrt{s}= $ 13 TeV	CMS-PAS-TOP-20-001	CMS-PAS-TOP-20-001
34	P. Nason	A New method for combining NLO QCD with shower Monte Carlo algorithms	JHEP 11 (2004) 040	hep-ph/0409146
35	S. Frixione, P. Nason, and C. Oleari	Matching NLO QCD computations with Parton Shower simulations: the POWHEG method	JHEP 11 (2007) 070	0709.2092
36	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
37	CMS Collaboration	Measurement of the cross section for $ \text{t}\bar{\text{t}} $ production with additional jets and b jets in pp collisions at $ \sqrt{s}= $ 13 TeV	JHEP 07 (2020) 125	CMS-TOP-18-002 2003.06467
38	M. Aliev et al.	HATHOR: HAdronic Top and Heavy quarks crOss section calculatoR	CPC 182 (2011) 1034	1007.1327
39	P. Kant et al.	HatHor for single top-quark production: Updated predictions and uncertainty estimates for single top-quark production in hadronic collisions	CPC 191 (2015) 74	1406.4403
40	N. Kidonakis	Two-loop soft anomalous dimensions for single top quark associated production with a $ W^- $ or $ H^- $	PRD 82 (2010) 054018	1005.4451
41	N. Kidonakis	Top Quark Production	in Proceedings, Helmholtz International Summer School on Physics of Heavy Quarks and Hadrons (HQ 2013): JINR, Dubna, Russia, July 15-28, 2013, p. 139 2014	1311.0283
42	T. Sjostrand et al.	An introduction to PYTHIA 8.2	CPC 191 (2015) 159	1410.3012
43	NNPDF Collaboration	Parton distributions for the LHC Run II	JHEP 04 (2015) 040	1410.8849
44	CMS Collaboration	Extraction and validation of a new set of CMS PYTHIA8 tunes from underlying-event measurements	EPJC 80 (2020) 4	CMS-GEN-17-001 1903.12179
45	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
46	CMS Collaboration	Measurement of the inelastic proton-proton cross section at $ \sqrt{s}= $ 13 TeV	JHEP 07 (2018) 161	CMS-FSQ-15-005 1802.02613
47	GEANT4 Collaboration	GEANT4--a simulation toolkit	NIMA 506 (2003) 250
48	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
49	CMS Collaboration	Performance of missing transverse momentum reconstruction in proton-proton collisions at $ \sqrt{s} = $ 13 TeV using the CMS detector	JINST 14 (2019) P07004	CMS-JME-17-001 1903.06078
50	M. Cacciari, G. P. Salam, and G. Soyez	The anti-$ kt $ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
51	M. Cacciari, G. P. Salam, and G. Soyez	FastJet User Manual	EPJC 72 (2012) 1896	1111.6097
52	CMS Collaboration	Determination of Jet Energy Calibration and Transverse Momentum Resolution in CMS	JINST 6 (2011) P11002	CMS-JME-10-011 1107.4277
53	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
54	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
55	CMS Collaboration	Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $ \sqrt{s}= $ 13 TeV	JINST 13 (2018), no. 06, P06015	CMS-MUO-16-001 1804.04528
56	CMS Collaboration	Electron and photon reconstruction and identification with the CMS experiment at the CERN LHC	JINST 16 (2021) P05014	CMS-EGM-17-001 2012.06888
57	K. He, X. Zhang, S. Ren, and J. Sun	Deep Residual Learning for Image Recognition		1512.03385
58	M. Erdmann, B. Fischer, and M. Rieger	Jet-parton assignment in $ t\bar t $H events using deep learning	JINST 12 (2017) P08020	1706.01117
59	CMS Collaboration	CMS luminosity measurement for the 2017 data-taking period at $ \sqrt{s} = $ 13 TeV	CMS-PAS-LUM-17-004	CMS-PAS-LUM-17-004
60	CMS Collaboration	CMS luminosity measurement for the 2018 data-taking period at $ \sqrt{s} = $ 13 TeV	CMS-PAS-LUM-18-002	CMS-PAS-LUM-18-002
61	M. Cacciari et al.	The t anti-t cross-section at 1.8-TeV and 1.96-TeV: A Study of the systematics due to parton densities and scale dependence	JHEP 04 (2004) 068	hep-ph/0303085
62	S. Catani, D. de Florian, M. Grazzini, and P. Nason	Soft gluon resummation for Higgs boson production at hadron colliders	JHEP 07 (2003) 028	hep-ph/0306211
63	J. Butterworth et al.	PDF4LHC recommendations for LHC Run II	JPG 43 (2016) 023001	1510.03865
64	R. J. Barlow and C. Beeston	Fitting using finite Monte Carlo samples	CPC 77 (1993) 219
65	J. S. Conway	Incorporating Nuisance Parameters in Likelihoods for Multisource Spectra	in PHYSTAT 2011 3	1103.0354
66	T. Junk	Confidence level computation for combining searches with small statistics	NIMA 434 (1999) 435	hep-ex/9902006
67	A. L. Read	Presentation of search results: The CL(s) technique	JPG 28 (2002) 2693
68	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC 71 (2011) 1554	1007.1727
69	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Erratum to: Asymptotic formulae for likelihood-based tests of new physics	The European Physical Journal C 73 (2013) 2501
70	J. Gao, C. S. Li, and H. X. Zhu	Top Quark Decay at Next-to-Next-to Leading Order in QCD	PRL 110 (2013), no. 4, 042001	1210.2808