CMS-EXO-21-003

CMS-EXO-21-003 ; CERN-EP-2022-105
Probing heavy Majorana neutrinos and the Weinberg operator through vector boson fusion processes in proton-proton collisions at $\sqrt{s} = $ 13 TeV
CMS Collaboration
17 June 2022
Phys. Rev. Lett. 131 (2023) 011803
Abstract: The first search exploiting the vector boson fusion process to probe heavy Majorana neutrinos and the Weinberg operator at the LHC is presented. The search is performed in the same-sign dimuon final state using a proton-proton collision data set recorded at $\sqrt{s} = $ 13 TeV, collected with the CMS detector and corresponding to a total integrated luminosity of 138 fb$^{-1}$. The results are found to agree with the predictions of the standard model. For heavy Majorana neutrinos, constraints on the squared mixing element between the muon and the heavy neutrino are derived in the heavy neutrino mass range 50 GeV-25 TeV; for masses above 650 GeV these are the most stringent constraints from searches at the LHC to date. A first test of the Weinberg operator at colliders provides an observed upper limit at 95% confidence level on the effective $\mu\mu$ Majorana neutrino mass of 10.8 GeV.
Links: e-print arXiv:2206.08956 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; Physics Briefing ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Example Feynman diagrams of VBF processes with heavy Majorana neutrino production (left) and processes mediated by the Weinberg operator (right) at the LHC.
png pdf	Figure 1-a: Example Feynman diagram of VBF processes with heavy Majorana neutrino production at the LHC.
png pdf	Figure 1-b: Example Feynman diagram of processes mediated by the Weinberg operator at the LHC.
png pdf	Figure 2: The $ {H_{\mathrm {T}}} / {p_{\mathrm {T}}} ^{\mu _{1}}$ distribution in the SRs and CRs. The horizontal axis indicates the bin width. The predicted yields of the backgrounds are shown with their best fit normalizations from the simultaneous fits for the background-only hypothesis. The lines indicate the scaled expected distributions of the heavy Majorana neutrino process with $m_{\mathrm {N}} = $ 750 GeV (solid red), 1.5 TeV (dashed red), 5.0 TeV (dotted red), and of the Weinberg operator process (dash-dotted green). The heavy Majorana neutrino processes are characterized by the azimuthal separation variable $ {\Delta \phi _{\ell \ell}} $, while the Weinberg operator process features in low missing transverse momentum.
png pdf	Figure 3: Upper limits on the heavy neutrino mixing element $ {\| V_{\mu \mathrm {N}} \|}^{2}$ at the 95% CL as a function of the heavy neutrino mass $m_{\mathrm {N}} $. The black dashed curve shows the expected upper limit, with the one and two standard deviation bands are indicated in lime green and light yellow, respectively. The solid black curve is the observed upper limit. The red dashed curve indicates observed upper limits from Ref. [17], while the blue dashed curve shows the observed upper limits from Ref. [20]. The result from Ref. [18] is not shown since it focuses on low $m_{\mathrm {N}} $. Starting from $m_{\mathrm {N}} $ around 650 GeV, the analysis presented in this Letter improves upon the upper limits from those references.

Tables
png pdf	Table 1: Signal region and WZ control region definitions. The signal region is binned differently for the heavy Majorana neutrino and Weinberg operator analyses. A b-tagged CR is defined by using the same selection as for the SR, however requiring the presence of a b-tagged jet. A WZb CR is defined by requiring the same selection as for the WZ CR, but requiring at least one b-tagged jet.

Summary

In summary, this Letter presents the first search for Majorana neutrinos at several TeV and a first probe of the Weinberg operator at the LHC. These achievements were made possible by considering for the first time vector boson fusion processes resulting in a same-sign dimuon final state. The results are consistent with the predictions from the standard model. For heavy Majorana neutrinos, upper limits on the mixing element $|{V_{\mu \mathrm{N}} }|^{2}$ are set for the mass range 50 GeV $ < m_{\mathrm{N}} < $ 25 TeV and the best sensitivity is reached for $m_{\mathrm{N}} \gtrsim $ 650 GeV. The phase space explored exceeds the center-of-mass energy of the LHC, improving previous limits for direct production of Majorana neutrinos. The highest mass for which $|{V_{\mu \mathrm{N}} }|^{2}=$ 1 is excluded is around 23 TeV. The observed (expected) 95% confidence level upper limit on the effective $\mu\mu$ Majorana mass associated with the Weinberg operator is 10.8 (12.8) GeV, exceeding the current best limit from high intensity Kaon experiments.

References
1	SNO Collaboration	Direct evidence for neutrino flavor transformation from neutral current interactions in the Sudbury Neutrino Observatory	PRL 89 (2002) 011301	nucl-ex/0204008
2	Super-Kamiokande Collaboration	A measurement of atmospheric neutrino oscillation parameters by Super-Kamiokande I	PRD 71 (2005) 112005	hep-ex/0501064
3	A. Loureiro et al.	Upper bound of neutrino masses from combined cosmological observations and particle physics experiments	PRL 123 (2019) 081301	1811.02578
4	eBOSS Collaboration	Completed SDSS-IV extended baryon oscillation spectroscopic survey: Cosmological implications from two decades of spectroscopic surveys at the apache point observatory	PRD 103 (2021) 083533	2007.08991
5	KATRIN Collaboration	Direct neutrino-mass measurement with sub-electronVolt sensitivity	NP 18 (2022) 160	2105.08533
6	P. Minkowski	$ \mu \to \mathrm{e} \gamma $ at a rate of one out of 1-billion muon decays?	PLB 67 (1977) 421
7	M. Gell-Mann, P. Ramond, and R. Slansky	Complex spinors and unified theories	in Supergravity, p. 315 North-Holland, 1979 Conf. Proc. C 790927 (1979) 315	1306.4669
8	O. Sawada and A. Sugamoto, eds.	Proceedings: Workshop on the Unified Theories and the Baryon Number in the Universe	Natl. Lab. HEP, Tsukuba, Japan, (1979)
9	R. N. Mohapatra and G. Senjanović	Neutrino mass and spontaneous parity violation	PRL 44 (1980) 912
10	S. Weinberg	Baryon- and lepton-nonconserving processes	PRL 43 (1979) 1566
11	A. Das and N. Okada	Improved bounds on the heavy neutrino productions at the LHC	PRD 93 (2016) 033003	1510.04790
12	A. Das, P. Konar, and S. Majhi	Production of heavy neutrino in next-to-leading order QCD at the LHC and beyond	JHEP 06 (2016) 019	1604.00608
13	A. Das and N. Okada	Bounds on heavy Majorana neutrinos in type-I seesaw and implications for collider searches	PLB 774 (2017) 32	1702.04668
14	KamLAND-Zen Collaboration	Search for majorana neutrinos near the inverted mass hierarchy region with KamLAND-Zen	PRL 117 (2016) 082503	1605.02889
15	GERDA Collaboration	Final results of GERDA on the search for neutrinoless double-$ \beta $ decay	PRL 125 (2020) 252502	2009.06079
16	B. Fuks et al.	Probing the Weinberg operator at colliders	PRD 103 (2021) 115014	2012.09882
17	NA62 Collaboration	Searches for lepton number violating $ {{K^+}} $ decays	PLB 797 (2019) 134794	1905.07770
18	CMS Collaboration	Search for heavy neutral leptons in events with three charged leptons in proton-proton collisions at $ \sqrt{s} = $ 13 TeV	PRL 120 (2018) 221801	CMS-EXO-17-012 1802.02965
19	ATLAS Collaboration	Search for heavy neutral leptons in decays of W bosons produced in 13 TeV pp collisions using prompt and displaced signatures with the ATLAS detector	JHEP 10 (2019) 265	1905.09787
20	CMS Collaboration	Search for physics beyond the standard model in multilepton final states in proton-proton collisions at $ \sqrt{s} = $ 13 TeV	JHEP 03 (2020) 051	CMS-EXO-19-002 1911.04968
21	CMS Collaboration	Search for heavy majorana neutrinos in same-sign dilepton channels in proton-proton collisions at $ \sqrt{s}= $ 13 TeV	JHEP 01 (2019) 122	CMS-EXO-17-028 1806.10905
22	ATLAS Collaboration	Search for heavy Majorana or Dirac neutrinos and right-handed W gauge bosons in final states with two charged leptons and two jets at $ \sqrt{s}= $ 13 TeV with the ATLAS detector	JHEP 01 (2019) 016	1809.11105
23	B. Fuks et al.	Majorana neutrinos in same-sign W$^\pm$ W$^\pm $ scattering at the LHC: Breaking the TeV barrier	PRD 103 (2021) 055005	2011.02547
24	CMS Collaboration	HEPData record for this analysis	link
25	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
26	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
27	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
28	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
29	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
30	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
31	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
32	CMS Collaboration	Performance of reconstruction and identification of $ \tau $ leptons decaying to hadrons and $ \nu_\tau $ in pp collisions at $ \sqrt{s}= $ 13 TeV	JINST 13 (2018) P10005	CMS-TAU-16-003 1809.02816
33	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
34	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
35	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
36	D. Alva, T. Han, and R. Ruiz	Heavy majorana neutrinos from W$ \gamma $ fusion at hadron colliders	JHEP 02 (2015) 072	1411.7305
37	C. Degrande, O. Mattelaer, R. Ruiz, and J. Turner	Fully-automated precision predictions for heavy neutrino production mechanisms at hadron colliders	PRD 94 (2016) 053002	1602.06957
38	P. Nason and G. Zanderighi	W$^+ $W$^- $ , WZ and ZZ production in the Powheg-box-V2	EPJC 74 (2014) 2702	1311.1365
39	J. M. Campbell, R. K. Ellis, and C. Williams	Vector boson pair production at the LHC	JHEP 07 (2011) 018	1105.0020
40	J. Alwall et al.	MadGraph 5: going beyond	JHEP 06 (2011) 128	1106.0522
41	R. Frederix and S. Frixione	Merging meets matching in MC@NLO	JHEP 12 (2012) 061	1209.6215
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	NNPDF Collaboration	Parton distributions from high-precision collider data	EPJC 77 (2017) 663	1706.00428
45	CMS Collaboration	Event generator tunes obtained from underlying event and multiparton scattering measurements	EPJC 76 (2016) 155	CMS-GEN-14-001 1512.00815
46	CMS Collaboration	Extraction and validation of a new set of CMS Pythia-8 tunes from underlying-event measurements	EPJC 80 (2020) 4	CMS-GEN-17-001 1903.12179
47	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
48	GEANT4 Collaboration	GEANT4--a simulation toolkit	NIMA 506 (2003) 250
49	CMS Collaboration	Technical proposal for the Phase-II upgrade of the Compact Muon Solenoid	CMS-PAS-TDR-15-002	CMS-PAS-TDR-15-002
50	M. Cacciari, G. P. Salam, and G. Soyez	FastJet user manual	EPJC 72 (2012) 1896	1111.6097
51	M. Cacciari, G. P. Salam, and G. Soyez	The anti-$ {k_{\mathrm{T}}} $ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
52	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
53	D. L. Rainwater, R. Szalapski, and D. Zeppenfeld	Probing color-singlet exchange in Z+2-jet events at the CERN LHC	PRD 54 (1996) 6680	hep-ph/9605444
54	CMS Collaboration	Performance of CMS muon reconstruction in cosmic-ray events	JINST 5 (2010) T03022	CMS-CFT-09-014 0911.4994
55	CMS Collaboration	Performance of the reconstruction and identification of high-momentum muons in proton-proton collisions at $ \sqrt{s} = $ 13 TeV	JINST 15 (2020) P02027	CMS-MUO-17-001 1912.03516
56	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
57	CMS Collaboration	Measurement of the inclusive and differential Higgs boson production cross sections in the leptonic WW decay mode at $ \sqrt{s} = $ 13 TeV	JHEP 03 (2021) 003	CMS-HIG-19-002 2007.01984
58	CMS Collaboration	Observation of electroweak production of same-sign W boson pairs in the two jet and two same-sign lepton final state in proton-proton collisions at $ \sqrt{s} = $ 13 TeV	PRL 120 (2018) 081801	CMS-SMP-17-004 1709.05822
59	CMS Collaboration	Measurements of production cross sections of WZ and same-sign WW boson pairs in association with two jets in proton-proton collisions at $ \sqrt{s} = $ 13 TeV	PLB 809 (2020) 135710	CMS-SMP-19-012 2005.01173
60	CMS Collaboration	Measurements of production cross sections of polarized same-sign W boson pairs in association with two jets in proton-proton collisions at $ \sqrt{s} = $ 13 TeV	PLB 812 (2021) 136018	CMS-SMP-20-006 2009.09429
61	T. Junk	Confidence level computation for combining searches with small statistics	NIMA 434 (1999) 435	hep-ex/9902006
62	A. L. Read	Presentation of search results: The CL$ _{\text{s}} $ technique	JPG 28 (2002) 2693
63	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC 71 (2011) 1554	1007.1727
64	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
65	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
66	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
67	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
68	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
69	CMS Collaboration	Jet energy scale and resolution performance with 13 TeV data collected by CMS in 2016-2018	CDS
70	B. Biedermann, A. Denner, and M. Pellen	Complete NLO corrections to W$ ^{+} $W$ ^{+} $ scattering and its irreducible background at the LHC	JHEP 10 (2017) 124	1708.00268
71	A. Ballestrero et al.	Precise predictions for same-sign W-boson scattering at the LHC	EPJC 78 (2018) 671	1803.07943
72	J. Butterworth et al.	PDF4LHC recommendations for LHC Run II	JPG 43 (2016) 023001	1510.03865
73	R. J. Barlow and C. Beeston	Fitting using finite monte carlo samples	CPC 77 (1993) 219