CMS-HIG-23-002 ; ATLAS-CONF-2023-025

CMS-HIG-23-002 ; ATLAS-CONF-2023-025 ; CERN-EP-2023-114
Evidence for the Higgs boson decay to a Z boson and a photon at the LHC
ATLAS and CMS Collaborations
7 September 2023
Phys. Rev. Lett. 132 (2024) 021803
Abstract: The first evidence for the Higgs boson decay to a Z boson and a photon is presented, with a statistical significance of 3.4 standard deviations. The result is derived from a combined analysis of the searches performed by the ATLAS and CMS Collaborations with proton--proton collision data sets collected at the CERN Large Hadron Collider (LHC) from 2015 to 2018. These correspond to integrated luminosities of around 140 fb$ ^{-1} $ for each experiment, at a center-of-mass energy of 13 TeV. The measured signal yield is 2.2 $ \pm $ 0.7 times the Standard Model prediction, and agrees with the theoretical expectation within 1.9 standard deviations.
Links: e-print arXiv:2309.03501 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; Physics Briefing ; CADI line (restricted) ;

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Examples of Feynman diagrams for H ${\rightarrow}$ Z$\gamma $ decay.
png pdf	Figure 2: The Z$\gamma $ invariant mass distribution. Events from all categories in the ATLAS and CMS analyses are shown. As different ranges in $ m_{\mathrm{Z}\gamma} $ are used in the two analyses, only the common subrange is visualized here. The data (points with error bars) in each category are weighted by $ \ln(1 + S/B) $, where $ S $ and $ B $ are the observed signal and background yields in that category, in the 120--130 GeV interval. The $ S $ and $ B $ values are derived from the fit to data. The error bars are invisible because of their small values. The fitted signal-plus-background (background) probability density functions (pdfs) in each category are also weighted in the same way and summed, and represented by a red solid (blue dashed) line. The lower panel shows the background-subtracted results with the same data and pdfs.
png pdf	Figure 3: The negative profile log-likelihood test statistic, where $ \Lambda $ represents the likelihood ratio, as a function of the signal strength $ \mu $ derived from the ATLAS data (blue line), the CMS data (red line), and the combined result (black line). The different Higgs boson masses assumed by ATLAS and CMS have a negligible impact on the results.

Summary

In summary, a combined analysis of ATLAS and CMS searches for the Higgs boson decay to a Z boson and a photon, where the Z boson decays into an electron or muon pair, is presented. The results are based on the 13 TeV proton--proton collision data recorded by the ATLAS and CMS experiments at the CERN LHC, amounting to integrated luminosities of 139 fb$ ^{-1} $ and 138 fb$ ^{-1} $ respectively. Evidence for H ${\rightarrow}$ Z$\gamma $ decay is established, with an observed significance of 3.4 standard deviations. The observed signal yield is 2.2 $ \pm $ 0.7 times the Standard Model prediction. The measured H ${\rightarrow}$ Z$\gamma $ branching fraction is ( 3.4 $ \pm $ 1.1 ) $\times$ 10$^{-3} $. The result agrees with the Standard Model prediction within 1.9 standard deviations.

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	The ATLAS Experiment at the CERN Large Hadron Collider	JINST 3 (2008) S08003
5	CMS Collaboration	The CMS Experiment at the CERN LHC	JINST 3 (2008) S08004
6	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
7	ATLAS Collaboration	A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery	Nature 607 (2022) 52--59	2207.00092
8	CMS Collaboration	A portrait of the Higgs boson by the CMS experiment ten years after the discovery	Nature 607 (2022) 60--68	CMS-HIG-22-001 2207.00043
9	R. Cahn, M. Chanowitz, and N. Fleishon	Higgs particle production by $ Z\rightarrow H\gamma $	PLB 82 (1979) 113
10	L. Bergstrom and G. Hulth	Induced Higgs couplings to neutral bosons in $ e^{+}e^{-} $ collisions	NPB 259 (1985) 137
11	M. Spira, A. Djouadi, and P. Zerwas	QCD corrections to the $ HZ\gamma $ coupling	PLB 276 (1992) 350
12	A. Djouadi, J. Kalinowski, and M. Spira	HDECAY: A program for Higgs boson decays in the Standard Model and its supersymmetric extension	Comput. Phys. Commun. 108 (1998) 56	hep-ph/9704448
13	LHC Higgs Cross Section Working Group Collaboration	Handbook of LHC Higgs Cross Sections: 4. Deciphering the Nature of the Higgs Sector		1610.07922
14	A. Azatov, R. Contino, A. Di Iura, and J. Galloway	New Prospects for Higgs Compositeness in $ h\to Z \gamma $	PRD 88 (2013) 075019	1308.2676
15	Q.-H. Cao, L.-X. Xu, B. Yan, and S.-h. Zhu	Signature of pseudo Nambu–Goldstone Higgs boson in its decay	PLB 789 (2019) 233	1810.07661
16	I. Low, J. Lykken, and G. Shaughnessy	Singlet scalars as Higgs imposters at the Large Hadron Collider	PRD 84 (2011) 035027	1105.4587
17	I. Low, J. Lykken, and G. Shaughnessy	Have we observed the Higgs (imposter)?	PRD 86 (2012) 093012	1207.1093
18	M. Carena, I. Low, and C. E. Wagner	Implications of a modified Higgs to diphoton decay width	JHEP 08 (2012) 060	1206.1082
19	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
20	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
21	ATLAS Collaboration	A search for the Z$\gamma$ decay mode of the Higgs boson in pp collisions at $\sqrt{s} =$ 13 TeV with the ATLAS detector	PLB 809 (2020) 135754	2005.05382
22	CMS Collaboration	Search for Higgs boson decays to a Z boson and a photon in proton--proton collisions at $\sqrt{s} =$ 13 TeV	JHEP 05 (2022) 233	CMS-HIG-19-014 2204.12945
23	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
24	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
25	CMS Collaboration	Search for the decay of a Higgs boson in the $\ell\ell\gamma$ channel in proton--proton collisions at $\sqrt{s} =$ 13 TeV	JHEP 11 (2018) 152	CMS-HIG-17-007 1806.05996
26	P. Nason and C. Oleari	NLO Higgs boson production via vector-boson fusion matched with shower in POWHEG	JHEP 02 (2010) 037	0911.5299
27	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
28	P. Nason	A new method for combining NLO QCD with shower Monte Carlo algorithms	JHEP 11 (2004) 040	hep-ph/0409146
29	S. Frixione, P. Nason, and C. Oleari	Matching NLO QCD computations with parton shower simulations: the POWHEG method	JHEP 11 (2007) 070	0709.2092
30	H. B. Hartanto, B. J ä ger, L. Reina, and D. Wackeroth	Higgs boson production in association with top quarks in the POWHEG BOX	PRD 91 (2015) 094003	1501.04498
31	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
32	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
33	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
34	M. Vesterinen	A novel technique for studying the Z boson transverse momentum distribution at hadron colliders	NIMA 602 (2009) 432
35	W. Verkerke and D. Kirkby	The RooFit toolkit for data modeling	2003
36	L. Moneta et al.	The RooStats Project	link	1009.1003
37	K. Cranmer and G. Lewis and L. Moneta and A. Shibata and W. Verkerke	HistFactory: A tool for creating statistical models for use with RooFit and RooStats	CERN-OPEN-2012-016, 2012
38	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC 71 (2011) 1554	1007.1727
39	P. Dauncey, M. Kenzie, N. Wardle, and G. Davies	Handling uncertainties in background shapes: the discrete profiling method	JINST 10 (2015) P04015
40	I. W. Stewart and F. J. Tackmann	Theory uncertainties for Higgs and other searches using jet bins	PRD 85 (2012) 034011	1107.2117
41	S. Gangal and F. J. Tackmann	Next-to-leading-order uncertainties in Higgs+2 jets from gluon fusion	PRD 87 (2013) 093008	1302.5437
42	M. Grazzini and H. Sargsyan	Heavy-quark mass effects in Higgs boson production at the LHC	JHEP 09 (2013) 129	1306.4581
43	A. Martin, W. Stirling, R. Thorne, and G. Watt	Parton distributions for the LHC	JHEP 63 (2009) 189	0901.0002
44	J. Butterworth et al.	PDF4LHC recommendations for LHC Run II	JPG 43 (2016) 023001	1510.03865
45	ATLAS Collaboration	Luminosity determination in pp collisions at $\sqrt{s} =$ 13 TeV using the ATLAS detector at the LHC	ATLAS-CONF-2019-021, 2019
46	G. Avoni et al.	The new lucid-2 detector for luminosity measurement and monitoring in atlas	JINST 13 (2018) P07017
47	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
48	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
49	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
50	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
51	CMS Collaboration	A measurement of the Higgs boson mass in the diphoton decay channel	PLB 805 (2020) 135425	CMS-HIG-19-004 2002.06398
52	S. Baker and R. D. Cousins	Clarification of the use of chi square and likelihood functions in fits to histograms	NIM 221 (1984) 437
53	CMS Collaboration	HEPData record for this analysis	link