CMS-HIG-23-010

CMS-HIG-23-010 ; CERN-EP-2025-010
Search for the associated production of a Higgs boson with a charm quark in the diphoton decay channel in pp collisions at $\sqrt{s}=$ 13 TeV
CMS Collaboration
11 March 2025
Submitted to J. High Energy Phys.
Abstract: This paper presents the first search for the associated production of a Higgs boson with a charm quark ( $\mathrm{c}\mathrm{H}$ ), with the Higgs boson decaying to two photons. Associated $\mathrm{c}\mathrm{H}$ production provides an opportunity to probe the coupling of the Higgs boson to charm quarks. The results are based on a data set of proton-proton collisions at a center-of-mass energy of 13 TeV collected with the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 fb $^{-1}$ . Assuming the standard model (SM) rates for all other Higgs boson production processes, the observed (expected) upper limit at 95% confidence level on the $\mathrm{c}\mathrm{H}$ signal strength is 243 (355) times the SM prediction. Under the same assumption, the observed (expected) allowed interval on the Higgs boson to charm quark coupling modifier, $\kappa_\mathrm{c}$ , is $\|\kappa_\mathrm{c}\| <$ 38.1 ( $\|\kappa_\mathrm{c}\| <$ 72.5) at 95% confidence level.
Links: e-print arXiv:2503.08797 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Leading order Feynman diagrams that contribute to the $\mathrm{p}\mathrm{p} \to \mathrm{c}\mathrm{H}$ process. Red dots correspond to vertices where the charm Yukawa coupling modifier $\kappa_\mathrm{c}$ enters.
png pdf	Figure 1-a: Leading order Feynman diagrams that contribute to the $\mathrm{p}\mathrm{p} \to \mathrm{c}\mathrm{H}$ process. Red dots correspond to vertices where the charm Yukawa coupling modifier $\kappa_\mathrm{c}$ enters.
png pdf	Figure 1-b: Leading order Feynman diagrams that contribute to the $\mathrm{p}\mathrm{p} \to \mathrm{c}\mathrm{H}$ process. Red dots correspond to vertices where the charm Yukawa coupling modifier $\kappa_\mathrm{c}$ enters.
png pdf	Figure 2: Distributions of the CvsL score for the leading jet in simulated $\mathrm{c}\mathrm{H}$ signal and resonant background events and sideband data events. Error bars representing the statistical uncertainties in the data are too small to be displayed. Events with CvsL score values below the dashed vertical line are not included in the signal region.
png pdf	Figure 3: Distributions of BDT1 (left) and BDT2 outputs (right) for simulated $\mathrm{c}\mathrm{H}$ signal and resonant background events, as well as sideband data (representing the continuous background) events. The BDT1 score discriminates the $\mathrm{c}\mathrm{H}$ signal from the resonant background. The BDT2 score discriminates the $\mathrm{c}\mathrm{H}$ signal from the continuous background. The plots are indicative of the shapes of the distributions and should not be interpreted as a comparison of their magnitudes. The error bars correspond to the statistical uncertainties.
png pdf	Figure 3-a: Distributions of BDT1 (left) and BDT2 outputs (right) for simulated $\mathrm{c}\mathrm{H}$ signal and resonant background events, as well as sideband data (representing the continuous background) events. The BDT1 score discriminates the $\mathrm{c}\mathrm{H}$ signal from the resonant background. The BDT2 score discriminates the $\mathrm{c}\mathrm{H}$ signal from the continuous background. The plots are indicative of the shapes of the distributions and should not be interpreted as a comparison of their magnitudes. The error bars correspond to the statistical uncertainties.
png pdf	Figure 3-b: Distributions of BDT1 (left) and BDT2 outputs (right) for simulated $\mathrm{c}\mathrm{H}$ signal and resonant background events, as well as sideband data (representing the continuous background) events. The BDT1 score discriminates the $\mathrm{c}\mathrm{H}$ signal from the resonant background. The BDT2 score discriminates the $\mathrm{c}\mathrm{H}$ signal from the continuous background. The plots are indicative of the shapes of the distributions and should not be interpreted as a comparison of their magnitudes. The error bars correspond to the statistical uncertainties.
png pdf	Figure 4: The shape of the parametric signal model for an analysis category targeting $\mathrm{c}\mathrm{H}$ signal (left) and for the sum of all analysis categories (right). The open squares represent simulated events and the blue line represents the corresponding model. Also shown is the $\sigma_{\text{eff}}$ value (half the width of the narrowest interval containing 68.3% of the diphoton mass distribution) in the grey shaded area.
png pdf	Figure 4-a: The shape of the parametric signal model for an analysis category targeting $\mathrm{c}\mathrm{H}$ signal (left) and for the sum of all analysis categories (right). The open squares represent simulated events and the blue line represents the corresponding model. Also shown is the $\sigma_{\text{eff}}$ value (half the width of the narrowest interval containing 68.3% of the diphoton mass distribution) in the grey shaded area.
png pdf	Figure 4-b: The shape of the parametric signal model for an analysis category targeting $\mathrm{c}\mathrm{H}$ signal (left) and for the sum of all analysis categories (right). The open squares represent simulated events and the blue line represents the corresponding model. Also shown is the $\sigma_{\text{eff}}$ value (half the width of the narrowest interval containing 68.3% of the diphoton mass distribution) in the grey shaded area.
png pdf	Figure 5: Invariant mass distribution of the selected events in all categories scaled by $\mathrm{S}/(\mathrm{S}+\mathrm{B})$ , where S (B) is the number of expected signal (background) events in the smallest mass window containing 68.3% of the expected signal events. Curves for the signal + background fit (red), separately showing the resonant (black) and continuous (blue) backgrounds, as well as bands representing the 68.3% and 95.5% CL intervals in the background estimation, are overlaid. The middle (lower) panel shows the $m_{\gamma\gamma}$ distribution after subtracting only the continuous background (subtracting all background components) and overlaying the curve for the fitted signal (purple).

Tables
png pdf	Table 1: Number of expected signal $\mathrm{c}\mathrm{H}$ ( $\mathrm{H} \to \gamma\gamma$ ), resonant background and continuous background events, as well as the resulting signal-over-background ratio (S/B) in the diphoton mass window [122.88, 127.88] GeV for all categories. For each category, the event yields for the three years are summed. The fraction of different production processes contributing to the resonant background ( $\mathrm{g}\mathrm{g}\mathrm{H}$ , ${\mathrm{t}\overline{\mathrm{t}}} \mathrm{H}$ , VBF, VH, and $\mathrm{b}\mathrm{H}$ ) is also reported.
png pdf	Table 2: Impacts of several uncertainty groups divided by the total uncertainty in the signal strength measurement.

Summary

We have presented the first search for associated production of a charm quark (c) and a Higgs boson (H). Assuming the signal strengths of non-

$\mathrm{c}\mathrm{H}$ Higgs production processes in the diphoton decay channel to be as predicted by the standard model (SM), the observed and expected upper limits at 95% confidence level on the

$\mathrm{c}\mathrm{H}$ signal strength are 243 and 355 times the SM predictions, respectively. This search also provides sensitivity to the Yukawa coupling between the Higgs boson and the charm quark. Under the same assumption, the observed (expected) allowed interval on the Higgs boson to charm quark coupling modifier

$\kappa_\mathrm{c}$ is

$|\kappa_\mathrm{c}| <$ 38.1 (

$|\kappa_\mathrm{c}| <$ 72.5) at 95% confidence level. The analysis is presently limited by statistical uncertainties. Improvements can be achieved by incorporating complementary decay channels and, as larger datasets become available, implementing more refined selection criteria and categorization strategies.

References
1	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
2	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
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 Collaboration	Measurements of the Higgs boson production and decay rates and coupling strengths using pp collision data at $\sqrt{s}=$ 7 and 8 TeV in the ATLAS experiment	EPJC 76 (2016) 6	1507.04548
5	CMS Collaboration	Precise determination of the mass of the Higgs boson and tests of compatibility of its couplings with the standard model predictions using proton collisions at 7 and 8 $\,\text {TeV}$	EPJC 75 (2015) 212	CMS-HIG-14-009 1412.8662
6	CMS Collaboration	Study of the mass and spin-parity of the Higgs boson candidate via its decays to Z boson pairs	PRL 110 (2013) 081803	CMS-HIG-12-041 1212.6639
7	ATLAS Collaboration	Evidence for the spin-0 nature of the Higgs boson using ATLAS data	PLB 726 (2013) 120	1307.1432
8	ATLAS and CMS Collaborations	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
9	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
10	ATLAS Collaboration	Combined measurement of differential and total cross sections in the $H \rightarrow \gamma \gamma$ and the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channels at $\sqrt{s} =$ 13 TeV with the ATLAS detector	PLB 786 (2018) 114	1805.10197
11	CMS Collaboration	A measurement of the Higgs boson mass in the diphoton decay channel	PLB 805 (2020) 135425	CMS-HIG-19-004 2002.06398
12	CMS Collaboration	Measurement of the Higgs boson mass and width using the four-lepton final state in proton-proton collisions at $\sqrt{s}$ = 13 TeV	Submitted to Phys. Rev. D, 2024	CMS-HIG-21-019 2409.13663
13	P. W. Higgs	Broken symmetries and the masses of gauge bosons	PRL 13 (1964) 508
14	P. W. Higgs	Broken symmetries, massless particles and gauge fields	PL 12 (1964) 132
15	F. Englert and R. Brout	Broken symmetry and the mass of gauge vector mesons	PRL 13 (1964) 321
16	P. W. Higgs	Spontaneous symmetry breakdown without massless bosons	PR 145 (1966) 1156
17	ATLAS Collaboration	Measurement of Higgs boson production in the diphoton decay channel in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector	PRD 90 (2014) 112015	1408.7084
18	CMS Collaboration	Observation of the diphoton decay of the Higgs boson and measurement of its properties	EPJC 74 (2014) 3076	CMS-HIG-13-001 1407.0558
19	ATLAS Collaboration	Measurements of Higgs boson production and couplings in the four-lepton channel in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector	PRD 91 (2015) 012006	1408.5191
20	CMS Collaboration	Measurement of the properties of a Higgs boson in the four-lepton final state	PRD 89 (2014) 092007	CMS-HIG-13-002 1312.5353
21	ATLAS Collaboration	Observation and measurement of Higgs boson decays to WW $^*$ with the ATLAS detector	PRD 92 (2015) 012006	1412.2641
22	ATLAS Collaboration	Study of (W/Z)H production and Higgs boson couplings using $H \rightarrow WW^{\ast}$ decays with the ATLAS detector	JHEP 08 (2015) 137	1506.06641
23	CMS Collaboration	Measurement of Higgs boson production and properties in the WW decay channel with leptonic final states	JHEP 01 (2014) 096	CMS-HIG-13-023 1312.1129
24	ATLAS Collaboration	Evidence for the Higgs-boson Yukawa coupling to tau leptons with the ATLAS detector	JHEP 04 (2015) 117	1501.04943
25	CMS Collaboration	Evidence for the 125 GeV Higgs boson decaying to a pair of $\tau$ leptons	JHEP 05 (2014) 104	CMS-HIG-13-004 1401.5041
26	CMS Collaboration	Search for Higgs boson pair production in events with two bottom quarks and two tau leptons in proton-proton collisions at $\sqrt{s}=$ 13 TeV	PLB 778 (2018) 101	CMS-HIG-17-002 1707.02909
27	CMS Collaboration	Measurements of properties of the Higgs boson decaying to a W boson pair in pp collisions at $\sqrt{s}=$ 13 TeV	PLB 791 (2019) 96	CMS-HIG-16-042 1806.05246
28	ATLAS Collaboration	A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery	[Corrigendum: \DOI10./s41586-022-05581-5], 2022 Nature 607 (2022) 52	2207.00092
29	CMS Collaboration	A portrait of the Higgs boson by the CMS experiment ten years after the discovery	[Corrigendum: \DOI10./s41586-023-06164-8], 2022 Nature 607 (2022) 60	CMS-HIG-22-001 2207.00043
30	CMS Collaboration	Evidence for Higgs boson decay to a pair of muons	JHEP 01 (2021) 148	CMS-HIG-19-006 2009.04363
31	ATLAS Collaboration	Direct constraint on the Higgs-charm coupling from a search for Higgs boson decays into charm quarks with the ATLAS detector	EPJC 82 (2022) 717	2201.11428
32	CMS Collaboration	Search for Higgs boson decay to a charm quark-antiquark pair in proton-proton collisions at $\sqrt{s} =$ 13 TeV	PRL 131 (2023) 061801	CMS-HIG-21-008 2205.05550
33	ATLAS Collaboration	Searches for exclusive Higgs and Z boson decays into a vector quarkonium state and a photon using 139 fb $^{-1}$ of ATLAS $\sqrt{s}=$ 13 TeV proton-proton collision data	EPJC 83 (2023) 781	2208.03122
34	CMS Collaboration	Search for rare decays of Z and Higgs bosons to J $/\psi$ and a photon in proton-proton collisions at $\sqrt{s} =$ 13 TeV	EPJC 79 (2019) 94	CMS-SMP-17-012 1810.10056
35	I. Brivio, F. Goertz, and G. Isidori	Probing the charm quark Yukawa coupling in Higgs+charm production	PRL 115 (2015) 211801	1507.02916
36	N. M. Coyle, C. E. M. Wagner, and V. Wei	Bounding the charm Yukawa coupling	PRD 100 (2019) 073013	1905.09360
37	ATLAS Collaboration	Search for the associated production of charm quarks and a Higgs boson decaying into a photon pair with the ATLAS detector	JHEP 02 (2025) 045	2407.15550
38	CMS Collaboration	Precision luminosity measurement in proton-proton collisions at $\sqrt{s} =$ 13 TeV in 2015 and 2016 at CMS	EPJC 81 (2021) 800	CMS-LUM-17-003 2104.01927
39	CMS Collaboration	CMS luminosity measurement for the 2017 data-taking period at $\sqrt{s}$ = 13 TeV	CMS Physics Analysis Summary, 2018 link	CMS-PAS-LUM-17-004
40	CMS Collaboration	CMS luminosity measurement for the 2018 data-taking period at $\sqrt{s}$ = 13 TeV	CMS Physics Analysis Summary, 2019 link	CMS-PAS-LUM-18-002
41	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004
42	CMS Collaboration	Development of the CMS detector for the CERN LHC Run 3	JINST 19 (2024) P05064	CMS-PRF-21-001 2309.05466
43	CMS Collaboration	Performance of the CMS Level-1 trigger in proton-proton collisions at $\sqrt{s} =$ 13\,TeV	JINST 15 (2020) P10017	CMS-TRG-17-001 2006.10165
44	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
45	CMS Collaboration	Performance of the CMS high-level trigger during LHC Run 2	JINST 19 (2024) P11021	CMS-TRG-19-001 2410.17038
46	P. Nason	A new method for combining NLO QCD with shower Monte Carlo algorithms	JHEP 11 (2004) 040	hep-ph/0409146
47	S. Frixione, P. Nason, and C. Oleari	Matching NLO QCD computations with parton shower simulations: the POWHEG method	JHEP 11 (2007) 070	0709.2092
48	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
49	E. Bagnaschi, G. Degrassi, P. Slavich, and A. Vicini	Higgs production via gluon fusion in the POWHEG approach in the SM and in the MSSM	JHEP 02 (2012) 088	1111.2854
50	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
51	R. Frederix and S. Frixione	Merging meets matching in MC@NLO	JHEP 12 (2012) 061	1209.6215
52	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
53	LHC Higgs Cross Section Working Group	Handbook of LHC Higgs cross sections: 4. Deciphering the nature of the Higgs sector	CERN Report CERN-2017-002-M, 2016 link	1610.07922
54	M. Wiesemann et al.	Higgs production in association with bottom quarks	JHEP 02 (2015) 132	1409.5301
55	T. Sjöstrand et al.	An introduction to PYTHIA 8.2	Comput. Phys. Commun. 191 (2015) 159	1410.3012
56	CMS Collaboration	Event generator tunes obtained from underlying event and multiparton scattering measurements	EPJC 76 (2016) 155	CMS-GEN-14-001 1512.00815
57	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
58	NNPDF Collaboration	Parton distributions for the LHC run II	JHEP 04 (2015) 040	1410.8849
59	NNPDF Collaboration	Parton distributions from high-precision collider data	EPJC 77 (2017) 663	1706.00428
60	E. Bothmann et al.	Event generation with SHERPA 2.2	SciPost Phys. 7 (2019) 34	1905.09127
61	\GEANTfour Collaboration	GEANT 4---a simulation toolkit	NIM A 506 (2003) 250
62	CMS Collaboration	Measurements of Higgs boson properties in the diphoton decay channel in proton-proton collisions at $\sqrt{s} =$ 13 TeV	JHEP 11 (2018) 185	CMS-HIG-16-040 1804.02716
63	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
64	M. Cacciari, G. P. Salam, and G. Soyez	The anti- $k_{\mathrm{T}}$ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
65	M. Cacciari, G. P. Salam, and G. Soyez	FastJet user manual	EPJC 72 (2012) 1896	1111.6097
66	CMS Collaboration	Pileup mitigation at CMS in 13 TeV data	JINST 15 (2020) P09018	CMS-JME-18-001 2003.00503
67	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
68	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
69	E. Spyromitros-Xioufis, W. Groves, G. Tsoumakas, and I. Vlahavas	Multi-target regression via input space expansion: treating targets as inputs	Mach. Learn. 104 (2016) 55	1211.6581
70	E. Bols et al.	Jet flavour classification using DeepJet	JINST 15 (2020) P12012	2008.10519
71	CMS Collaboration	Performance of the DeepJet b tagging algorithm using 41.9/fb of data from proton-proton collisions at 13 TeV with Phase 1 CMS detector	CMS Detector Performance Note CMS-DP-2018-058, 2018 CDS
72	CMS Collaboration	Identification of heavy-flavor jets with the CMS detector in pp collisions at 13 TeV	JINST 13 (2018) P05011	CMS-BTV-16-002 1712.07158
73	T. Chen and C. Guestrin	XGBoost: A scalable tree boosting system	in \it nd Int. Conf. on Knowledge Discovery and Data Mining\/, 2016 Proc. 2 (2016) 785	1603.02754
74	R. A. Fisher	On the interpretation of $\chi^2$ from contingency tables, and the calculation of p	J. R. Stat. Soc. 85 (1922) 87
75	P. D. Dauncey, M. Kenzie, N. Wardle, and G. J. Davies	Handling uncertainties in background shapes	JINST 10 (2015) P04015	1408.6865
76	S. Manzoni et al.	Taming a leading theoretical uncertainty in HH measurements via accurate simulations for $\textrm{b}\overline{\textrm{b}}\textrm{H}$ production	JHEP 09 (2023) 179	2307.09992
77	CMS Collaboration	The CMS Statistical Analysis and Combination Tool: Combine	Comput. Softw. Big Sci. 8 (2024) 19	CMS-CAT-23-001 2404.06614
78	ATLAS and CMS Collaborations and the LHC Higgs Combination Group	Procedure for the LHC Higgs boson search combination in Summer 2011	Technical Report CMS-NOTE-2011-005, ATL-PHYS-PUB-2011-11, 2011
79	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC 71 (2011) 1554	1007.1727
80	CMS Collaboration	HEPData record for this analysis	link