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| CMS-EXO-25-001 ; CERN-EP-2026-259 | ||
| Search for Higgs boson compositeness effects in high-mass dilepton final states in proton-proton collisions at $ \sqrt{s} = $ 13 and 13.6 TeV | ||
| CMS Collaboration | ||
| 3 October 2026 | ||
| Submitted to the Journal of High Energy Physics | ||
| Abstract: A search for beyond the standard model effects in high-mass dielectron and dimuon final states with the CMS detector is performed, with a specific focus on Higgs boson compositeness. The search uses data collected at the LHC at 13 and 13.6 TeV center-of-mass energies, corresponding to a total integrated luminosity of 207 fb$ ^{-1} $. Compositeness would manifest as distortions in the observed dilepton mass spectrum and the presence of bound states, such as the Higgs boson and new massive vector boson resonances. Assuming the existence of new boson states with masses well above the TeV scale, an effective field theory approach provides stringent bounds on the oblique parameters $ \mathcal{W} $ and $ \mathcal{Y} $, which are zero in the standard model. One-dimensional fits, in which only one of the oblique parameters is allowed to deviate from zero, provide the following limits: $ -3.9 \times 10^{-4} < \mathcal{Y} < 3.5 \times 10^{-4} $ and $ -2.1 \times 10^{-4} < \mathcal{W} < 1.6 \times 10^{-4} $ at 95% confidence level. More stringent compositeness limits at the TeV scale are set in several new physics scenarios under the assumption that a new $ \mathrm{Z}^{'} $ resonance is physically present within or slightly above the visible dilepton mass spectrum. In this context, cases with large resonance decay widths are explored for the first time. | ||
| Links: e-print arXiv:2610.04782 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Run 2 (left) and Run 3 (right) reconstructed dilepton invariant mass distribution after selection for (upper) electrons and (lower) muons. The uncertainty bands from the simulation include statistical uncertainties and systematic effects that modify the overall differential shape but not the normalization. The ratios between data and predictions are also displayed. |
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Figure 1-a:
Run 2 (left) and Run 3 (right) reconstructed dilepton invariant mass distribution after selection for (upper) electrons and (lower) muons. The uncertainty bands from the simulation include statistical uncertainties and systematic effects that modify the overall differential shape but not the normalization. The ratios between data and predictions are also displayed. |
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Figure 1-b:
Run 2 (left) and Run 3 (right) reconstructed dilepton invariant mass distribution after selection for (upper) electrons and (lower) muons. The uncertainty bands from the simulation include statistical uncertainties and systematic effects that modify the overall differential shape but not the normalization. The ratios between data and predictions are also displayed. |
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Figure 1-c:
Run 2 (left) and Run 3 (right) reconstructed dilepton invariant mass distribution after selection for (upper) electrons and (lower) muons. The uncertainty bands from the simulation include statistical uncertainties and systematic effects that modify the overall differential shape but not the normalization. The ratios between data and predictions are also displayed. |
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Figure 1-d:
Run 2 (left) and Run 3 (right) reconstructed dilepton invariant mass distribution after selection for (upper) electrons and (lower) muons. The uncertainty bands from the simulation include statistical uncertainties and systematic effects that modify the overall differential shape but not the normalization. The ratios between data and predictions are also displayed. |
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Figure 2:
Distribution of the product of the simulated invariant mass and the sign of $ \cos\theta_\mathrm{CS} $ for DY dielectron production in Run 2, after the application of selection criteria. The expectations in the SM and in several BSM scenarios, corresponding to different values of $ \mathcal{W} $ and $ \mathcal{Y} $, are shown. The ratios between data and predictions are also displayed. The uncertainty band from the simulation includes the estimated statistical uncertainties and systematic effects. |
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Figure 3:
Allowed regions in the 2-dimensional $ (\mathcal{W},\mathcal{Y}) $ parameter plane, from a fit to the full data sample considered in the analysis. The fit minimum corresponds to $ (\mathcal{W},\mathcal{Y})\approx (+6.6\times10^{-4}, -7.0\times10^{-4}) $. There is consistency with the SM at the two-standard deviation level. This deviation is largely driven by the presence of a dielectron event observed in 2022 data with an invariant mass above 5 TeV. |
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Figure 4:
Two-dimensional EFT fit results superimposed on the observed data and SM predictions, for Run 2 dimuons (upper plot) and dielectrons (lower plot). The ratios between data and predictions are also displayed. |
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Figure 4-a:
Two-dimensional EFT fit results superimposed on the observed data and SM predictions, for Run 2 dimuons (upper plot) and dielectrons (lower plot). The ratios between data and predictions are also displayed. |
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Figure 4-b:
Two-dimensional EFT fit results superimposed on the observed data and SM predictions, for Run 2 dimuons (upper plot) and dielectrons (lower plot). The ratios between data and predictions are also displayed. |
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Figure 5:
Two-dimensional EFT fit results superimposed on the observed data and SM predictions for Run 3 dimuons (upper plot) and dielectrons (lower plot). The ratios between data and predictions are also displayed. |
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Figure 5-a:
Two-dimensional EFT fit results superimposed on the observed data and SM predictions for Run 3 dimuons (upper plot) and dielectrons (lower plot). The ratios between data and predictions are also displayed. |
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Figure 5-b:
Two-dimensional EFT fit results superimposed on the observed data and SM predictions for Run 3 dimuons (upper plot) and dielectrons (lower plot). The ratios between data and predictions are also displayed. |
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Figure 6:
Allowed region in the $ (\mathcal{W},\mathcal{Y}) $ parameter plane, using the full data sample, when the $ \mathcal{W} $ constraint [9], $ \mathcal{W} = (- $ 1.2 $ ^{+0.5}_{-0.6} $) \times 10^-4 is included in the fit. The fit minimum corresponds to $ (\mathcal{W},\mathcal{Y})\approx (-1.9\times10^{-4}, +8.9\times10^{-4}) $. The SM is consistent with the observations at the two-standard deviation level. The figure also shows the region constrained by LEP electroweak measurements [48]. |
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Figure 7:
Allowed regions as a function of $ \mathcal{W} $ and $ \mathcal{Y} $ under a universality assumption, which requires $ \mathcal{W}\ge $ 0 and $ \mathcal{Y}\ge $ 0. The likelihood is derived from the analysis of the full Run 2+2022+2023 data sample of dielectrons and dimuons. The green and yellow areas correspond to the allowed 68% and 95% Bayesian credible intervals (CI) [8], under the positivity constraint and a flat prior assumption for the parameters. |
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Figure 8:
Excluded regions at the 95% CL in the $ (m^*,g^*) $ plane in a Y-universal scenario [50], assuming the presence of a neutral gauge boson $ \mathrm{Z}^{'} $ of mass $ m^* $. Decays into WW and ZH final states are assumed to increase the width of the new resonance, which is explicitly defined as a function of the strong coupling constant $ g^* $ of the SILH model (see text). These bounds are compared with those deduced from a non-resonant, EFT fit and from the current CMS global fits of the Higgs boson signal strength modifier for $ c_{H}= $ 1 ($ g^* < 1.4 m^*[\text{Te\hspace{-.08em}V}] $ at 95% CL) [56]. |
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Figure 9:
Excluded regions at the 95% CL in the $ (m^*,g^*) $ plane in a Little Higgs scenario with custodial symmetry [52], assuming the presence of a neutral gauge boson $ \mathrm{Z}^{'} $ of mass $ m^* $. Decays into WW and ZH final states are assumed to increase the width of the new resonance, which is explicitly defined as a function of the strong coupling constant $ g^* $ of the SILH model (see text). These bounds are compared with those deduced from a non-resonant, EFT fit and from the current CMS global fits of the Higgs boson signal strength modifier for $ c_{H}= $ 0.5 ($ g^* < 2 m^*[\text{Te\hspace{-.08em}V}] $ at 95% CL) [56]. |
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Figure 10:
Allowed regions at the 95% CL in the 2-dimensional $ (\mathcal{W},\mathcal{Y}) $ parameter plane, assuming a nearby BSM energy scale. The presence of neutral gauge boson resonances of 6 TeV (left) and 10 TeV (right) is assumed, with a medium (10%) or large (40%) relative decay width, due to the potential presence of a significant decay rate into WW or ZH final states. |
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Figure 10-a:
Allowed regions at the 95% CL in the 2-dimensional $ (\mathcal{W},\mathcal{Y}) $ parameter plane, assuming a nearby BSM energy scale. The presence of neutral gauge boson resonances of 6 TeV (left) and 10 TeV (right) is assumed, with a medium (10%) or large (40%) relative decay width, due to the potential presence of a significant decay rate into WW or ZH final states. |
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Figure 10-b:
Allowed regions at the 95% CL in the 2-dimensional $ (\mathcal{W},\mathcal{Y}) $ parameter plane, assuming a nearby BSM energy scale. The presence of neutral gauge boson resonances of 6 TeV (left) and 10 TeV (right) is assumed, with a medium (10%) or large (40%) relative decay width, due to the potential presence of a significant decay rate into WW or ZH final states. |
| Tables | |
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Table 1:
Systematic uncertainty sources considered in the analysis that have a non-negligible impact on the shape of the reconstructed invariant mass distribution in the 0.3 $ < M < $ 6 TeV mass interval. Their typical sizes, used as input for the likelihood fits, are also shown. |
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Table 2:
Confidence intervals of the one-dimensional fits to the mass to extract $ \mathcal{Y} $ and $ \mathcal{W} $. The value of the non-fitted parameter is fixed to be zero during minimization. The expected boundaries at the 95% CL under the SM assumption are also given. |
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Table 3:
EFT constraints on the oblique parameters $ \mathcal{W} $ and $ \mathcal{Y} $ for several universal scenarios: Y-universal [Y-none], Little Higgs [51,5], Little Higgs with custodial symmetry [52,5], and holographic composite Higgs with equal bulk gauge couplings [53,5]). The quoted bounds on $ m^*g^* $ correspond to the 95% Bayesian credible intervals [8]. |
| Summary |
| A search for new physics effects due to Higgs boson compositeness in high-mass dielectron and dimuon final states has been performed with the CMS detector, using LHC data collected at center-of-mass energies of 13 and 13.6 TeV corresponding to a total integrated luminosity of 207 fb$ ^{-1} $. The presence of such effects could imply the existence of new massive boson resonances with couplings to difermions and dibosons. Assuming new boson states with masses well above the TeV scale, stringent bounds are set on the oblique parameters $ \mathcal{W} $ and $ \mathcal{Y} $, which are zero in the standard model. These results are also combined with previous CMS constraints on $ \mathcal{W} $ from $ \mathrm{W}^{'} $ searches to derive the most stringent limits to date. One-dimensional fits, in which only one of the oblique parameters is permitted to deviate from zero, yield the following limits: $-3.9\times 10^{-4} < \mathcal{Y} <3.5\times 10^{-4}$, and $-2.1\times 10^{-4} < \mathcal{W} <1.6\times 10^{-4}$ at 95% confidence level. Universal coupling scenarios with $ \mathcal{W} , \mathcal{Y} > 0$, such as Strongly Interacting Light Higgs models, are excluded for $ \mathcal{W} > 7.8 \times 10^{-5}$ or $ \mathcal{Y} > 7.6 \times 10^{-4}$ at a credibility level above $95%$. Taking into account the current CMS bounds on the Higgs boson signal strength modifier [56], Higgs boson compositeness scale limits at the TeV scale are set in Y-universal and Little Higgs scenarios, independently of the value of the compositeness coupling strength $ g^{\star} $. Limits are also set for $ \mathrm{Z}^{'} $ resonances in scenarios with large decay widths that would result from significant decay branching fractions into diboson final states. In this context, cases with large resonance decay widths are explored for the first time. |
| References | ||||
| 1 | S. L. Glashow | Partial symmetries of weak interactions | NP 22 (1961) 579 | |
| 2 | S. Weinberg | A model of leptons | PRL 19 (1967) 1264 | |
| 3 | A. Salam | Weak and electromagnetic interactions | Conf. Proc. C 680519 (1968) 367 | |
| 4 | M. J. G. Veltman | The infrared --- ultraviolet connection | Acta Phys. Polon. B 12 (1981) 437 | |
| 5 | G. F. Giudice, C. Grojean, A. Pomarol, and R. Rattazzi | The strongly-interacting light Higgs | JHEP 06 (2007) 045 | hep-ph/0703164 |
| 6 | L. Evans and P. Bryant | LHC machine | JINST 3 (2008) S08001 | |
| 7 | R. Barbieri, A. Pomarol, R. Rattazzi, and A. Strumia | Electroweak symmetry breaking after LEP-1 and LEP-2 | NPB 703 (2004) 127 | hep-ph/0405040 |
| 8 | Particle Data Group , S. Navas et al. | Review of particle physics | PRD 110 (2024) 030001 | |
| 9 | CMS Collaboration | Search for new physics in the lepton plus missing transverse momentum final state in proton-proton collisions at $ \sqrt{s} = $ 13 TeV | JHEP 07 (2022) 067 | CMS-EXO-19-017 2202.06075 |
| 10 | MS Collaboration | none | HEPData record for this analysis link |
|
| 11 | CMS Collaboration | The CMS experiment at the CERN LHC | JINST 3 (2008) S08004 | |
| 12 | CMS Collaboration | Development of the CMS detector for the CERN LHC Run 3 | JINST 19 (2024) P05064 | |
| 13 | 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 |
| 14 | CMS Collaboration | The cms trigger system | JINST 12 (2017) P01020 | CMS-TRG-12-001 1609.02366 |
| 15 | CMS Collaboration | Performance of the CMS high-level trigger during LHC run 2 | JINST 19 (2024) P11021 | CMS-TRG-19-001 2410.17038 |
| 16 | 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 |
| 17 | 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 |
| 18 | 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 |
| 19 | CMS Collaboration | Technical proposal for the Phase-II upgrade of the Compact Muon Solenoid | CMS Technical Proposal CERN-LHCC-2015-010, CMS-TDR-15-02, 2015 CDS |
|
| 20 | CMS Collaboration | Particle-flow reconstruction and global event description with the CMS detector | JINST 12 (2017) P10003 | CMS-PRF-14-001 1706.04965 |
| 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 | R. Torre, L. Ricci, and A. Wulzer | On the W\&Y interpretation of high-energy Drell-Yan measurements | JHEP 02 (2021) 144 | 2008.12978 |
| 24 | M. Farina et al. | Energy helps accuracy: electroweak precision tests at hadron colliders | PLB 772 (2017) 210 | 1609.08157 |
| 25 | S. Alioli, P. Nason, C. Oleari, and E. Re | NLO vector-boson production matched with shower in POWHEG | JHEP 07 (2008) 060 | 0805.4802 |
| 26 | M. Chaichian, M. Hayashi, and K. Yamagishi | Angular distributions of high mass dileptons with finite transverse momentum in high-energy hadronic collisions | erratum: Phys. Rev. D26 () 2534, 1982 PRD 25 (1982) 130 |
|
| 27 | J. C. Collins and D. E. Soper | Angular distribution of dileptons in high-energy hadron collisions | PRD 16 (1977) 2219 | |
| 28 | J. Alcaraz Maestre and O. M. Carretero | An optimal strategy for experimental searches in high-mass dilepton production at the LHC | link | 2610.01965 |
| 29 | P. Nason | A new method for combining NLO QCD with shower Monte Carlo algorithms | JHEP 11 (2004) 040 | hep-ph/0409146 |
| 30 | S. Frixione, P. Nason, and C. Oleari | Matching NLO QCD computations with Parton Shower simulations: the POWHEG method | JHEP 11 (2007) 070 | 0709.2092 |
| 31 | 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 |
| 32 | T. Sjöstrand et al. | An introduction to PYTHIA 8.2 | Comput. Phys. Commun. 191 (2015) 159 | 1410.3012 |
| 33 | M. Czakon and A. Mitov | Top++: a program for the calculation of the top-pair cross-cection at hadron colliders | Comput. Phys. Commun. 185 (2014) 2930 | 1112.5675 |
| 34 | M. Grazzini, S. Kallweit, and M. Wiesemann | Fully differential NNLO computations with MATRIX | EPJC 78 (2018) 537 | 1711.06631 |
| 35 | R. Gavin, Y. Li, F. Petriello, and S. Quackenbush | FEWZ 2.0: A code for hadronic Z production at next-to-next-to-leading order | Comput. Phys. Commun. 182 (2011) 2388 | 1011.3540 |
| 36 | J. Butterworth et al. | PDF4LHC recommendations for LHC Run II | JPG 43 (2016) 023001 | 1510.03865 |
| 37 | PDF4LHC Working Group Collaboration | The PDF4LHC21 combination of global PDF fits for the LHC Run III | JPG 49 (2022) 080501 | 2203.05506 |
| 38 | C. Bierlich et al. | A comprehensive guide to the physics and usage of PYTHIA 8.3 | SciPost Phys. Codeb. 2022 (2022) | 2203.11601 |
| 39 | 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 |
| 40 | GEANT4 Collaboration | GEANT 4---a simulation toolkit | NIM A 506 (2003) 250 | |
| 41 | CMS Collaboration | Search for resonant and nonresonant new phenomena in high-mass dilepton final states at $ \sqrt{s} = $ 13 TeV | JHEP 07 (2021) 208 | CMS-EXO-19-019 2103.02708 |
| 42 | 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 |
| 43 | 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 |
| 44 | E. Bols et al. | Jet flavour classification using DeepJet | JINST 15 (2020) P12012 | 2008.10519 |
| 45 | A. Manohar, P. Nason, G. P. Salam, and G. Zanderighi | How bright is the proton? A precise determination of the photon parton distribution function | PRL 117 (2016) 242002 | 1607.04266 |
| 46 | CMS Collaboration | The CMS statistical analysis and combination tool: Combine | Comput. Softw. Big Sci. 8 (2024) 19 | CMS-CAT-23-001 2404.06614 |
| 47 | 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 |
| 48 | A. Falkowski and K. Mimouni | Model independent constraints on four-lepton operators | JHEP 02 (2016) 086 | 1511.07434 |
| 49 | M. McCullough, M. Riembau, and L. Ricci | Boundaries of universal theories | PRD 111 (2025) 015031 | 2312.03834 |
| 50 | T. Appelquist, B. A. Dobrescu, and A. R. Hopper | Nonexotic neutral gauge bosons | PRD 68 (2003) 035012 | hep-ph/0212073 |
| 51 | N. Arkani-Hamed, A. G. Cohen, E. Katz, and A. E. Nelson | The littlest Higgs | JHEP 07 (2002) 034 | hep-ph/0206021 |
| 52 | S. Chang | A 'Littlest Higgs' model with custodial SU(2) symmetry | JHEP 12 (2003) 057 | hep-ph/0306034 |
| 53 | K. Agashe, R. Contino, and A. Pomarol | The minimal composite Higgs model | NPB 719 (2005) 165 | hep-ph/0412089 |
| 54 | D. Pappadopulo, A. Thamm, R. Torre, and A. Wulzer | Heavy vector triplets: bridging theory and data | JHEP 09 (2014) 060 | 1402.4431 |
| 55 | M. J. Baker, T. Martonhelyi, A. Thamm, and R. Torre | A simplified model of Heavy Vector Singlets for the LHC and future colliders | JHEP 06 (2025) 187 | 2407.11117 |
| 56 | CMS Collaboration | Combined measurements and interpretations of Higgs boson production and decay in proton-proton collisions at $ \sqrt{s} = 13 \textrm{TeV} $ | Rept. Prog. Phys. 89 (2026) 087801 | CMS-HIG-21-018 2602.18611 |
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