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CMS Collaboration

Publications and source records attributed to CMS Collaboration.

At least 37 records · Page 2Linked to original sources

arXiv2026

Full event interpretation with machine-learning-based particle-flow reconstruction in the CMS detector

The particle-flow (PF) algorithm constructs a global description of each particle collision by producing a comprehensive list of final-state particles, and is central to event reconstruction in the CMS experiment at the CERN LHC. The existing PF implementation relies on physics-motivated heuristics and assumptions that can be replaced by machine-learning (ML) models trained directly on simulated data and naturally suited to modern graphics processing units (GPUs). A state-of-the-art ML-based PF (MLPF) reconstruction algorithm, implemented within the CMS software framework, is presented. The MLPF algorithm performs a learnable full-event reconstruction on GPUs, generalizes across detector conditions and collision energies, and replaces multiple modular reconstruction steps with a single unified model. Physics performance comparable to standard PF reconstruction is achieved in both simulation and data, with improved jet energy resolution and inference time. In simulated top quark-antiquark events under LHC Run-3 (2023$-$2024) conditions, the jet energy resolution improves by 10$-$20% for jets with transverse momentum between 30$-$100 GeV. Inference time is evaluated using simulated multijet events, with a median of 20 ms per event on an Nvidia L4 GPU, compared to approximately 110 ms for the standard CMS PF reconstruction.

physics.ins-det↗

arXiv2026

Constraint on the Higgs boson width in the diphoton final state using signal-background interference in proton-proton collisions at $\sqrt{s}$ = 13 TeV

The standard model Higgs boson, with a mass of 125 GeV, has a predicted decay width, $Γ_\mathrm{H}$, of 4.1 MeV. This Letter presents the first constraint on $Γ_\mathrm{H}$ obtained through the interference between the resonant H $\to$ $γγ$ process and the continuum $γγ$ production, both produced via gluon-gluon fusion. The analysis is performed using proton-proton collision data at $\sqrt{s}$ = 13 TeV, collected by the CMS experiment between 2016 and 2018, corresponding to an integrated luminosity of 138 fb$^{-1}$. The observed (expected) limit on the Higgs boson width is $Γ_\mathrm{H}$ $\lt$ 92 (138) MeV at 95% confidence level. This is the most stringent constraint on $Γ_\mathrm{H}$ from on-shell Higgs boson measurements to date.

hep-ex↗

arXiv2026

Evidence for the dead-cone effect in bottom quark initiated jets produced in proton-proton collisions at $\sqrt{s}$ = 13 TeV

The suppression of collinear gluon emissions from a massive quark, or the ``dead-cone effect,'' is the primary manifestation of quark mass effects in parton showers. A proton-proton collision data set recorded by the CMS experiment at $\sqrt{s}$ = 13 TeV with an integrated luminosity of 59.8 fb$^{-1}$ is analyzed. A differential measurement is presented of the emission density of bottom quark jets, studied as a function of the angular separation between iteratively declustered subjets. The measurement is performed in bottom quark initiated jets with transverse momenta between 40 and 200 GeV originating from top quark pair production. Compared to data, a parton shower Monte Carlo model that includes the dead-cone effect is favored, while a model without the dead-cone effect is disfavored with a significance of 4.3 standard deviations.

hep-ex↗

arXiv2026

Search for scalar leptoquarks produced via muon-quark scattering in proton-proton collisions at $\sqrt{s}$ = 13 TeV

The first search for TeV-scale scalar leptoquarks (LQs) produced in muon-quark ($μ$q) interactions is presented. It is based on proton-proton collision data recorded at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. Quantum fluctuations inside the proton generate charged-lepton components, enabling the study of lepton-induced processes. In particular, the interaction of a muon from one colliding proton with a quark from the other proton enables the study of resonant production of a single LQ and its subsequent decay. The final state includes one or two muons and a jet that can come from the hadronization of either a light quark (u) or a b quark. The primary observable is the invariant mass of the muon-jet system, whose distribution peaks at the LQ mass. The data are found to be in agreement with the background predictions. Upper limits are set on the product of the LQ production cross section and its decay branching fraction to the $μ$q final state. The results exclude broad regions in the parameter plane of the LQ mass and the LQ-$μ$q coupling, improving upon previous CMS searches by extending the coverage for LQs with masses between 1.5 and 3.6 TeV, and couplings between 0.2 and 0.6 for the LQ(u$μ$) scenario; and masses above 1.8 TeV, and couplings above 1 for the LQ(b$μ$) scenario.

hep-ex↗

arXiv2026

A search for microscopic black holes, string balls, and sphalerons in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for microscopic black holes, string balls, and electroweak sphalerons using proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded with the CMS detector at the CERN LHC during the 2016$-$2018 data taking, and corresponding to an integrated luminosity of 138 fb$^{-1}$, is presented. Two search strategies based on control samples in data are used. Model-independent limits on the cross section of physics phenomena with multiple energetic jets, leptons, and photons are set using a method that relies on the shape invariance of the scalar sum of the transverse momenta of all objects in the event. Model-dependent limits on black hole and sphaleron production are set using a newly introduced method that has been developed for the identification of collider events with distinct kinematic features by separating them into classes based on phase space proximity. In the context of models with large extra dimensions, semiclassical black holes and string balls with masses below 8.4$-$11.4 TeV and 9.0$-$10.7 TeV, respectively, are excluded at 95% confidence level, significantly extending the reach beyond previous searches. Results of a dedicated search for electroweak sphalerons are used to derive an upper limit of 0.0034 at 95% confidence level on the fraction of quark-quark interactions, with a center-of-mass energy above the nominal sphaleron transition energy threshold of 9 TeV, that result in a sphalaron transition.

hep-ex↗

arXiv2026

Search for a narrow resonance with a mass between 10 and 70 GeV decaying to a pair of photons in proton-proton collisions at $\sqrt{s}$ = 13 TeV

The existence of a new spin-zero particle with a mass below the electroweak scale is predicted by several theoretical models. Searches for resonant production of photon pairs at the LHC are able to probe these models. We present a search for a narrow resonance produced through gluon fusion that decays into a pair of photons with an invariant mass between 10 and 70 GeV, using a proton-proton collision data set from the CMS experiment. This data set, corresponding to an integrated luminosity of 54.4 fb$^{-1}$, was recorded in 2018 at a center-of-mass energy of 13 TeV using a newly introduced diphoton trigger that enabled exploration of the low-mass diphoton spectrum. No significant excess above the expected background is observed. Upper limits are set on the product of the gluon fusion production cross section and the branching fraction of the diphoton decay of a narrow resonance. An interpretation of these limits within an effective field theory framework for axion-like particles is also provided.

hep-ex↗

arXiv2026

Observation of an excess at the top quark pair production threshold in the single-lepton channel

A search is presented for top quark-antiquark ($\mathrm{t\bar{t}}$) quasi-bound ``toponium'' states, near the kinematic $\mathrm{t\bar{t}}$ production threshold in final states with a single electron or muon and jets. The study uses proton-proton collision data at $\sqrt{s}$ = 13 TeV, collected by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis examines the relative velocity between the top quark and antiquark, along with two angular observables sensitive to the parity and spin of the $\mathrm{t\bar{t}}$ system. A significant excess of events is observed relative to the standard model prediction for $\mathrm{t\bar{t}}$ production calculated at next-to-next-to-leading order in perturbative quantum chromodynamics (QCD). The excess corresponds to an observed total cross section of 5.1$\pm$0.9 pb and is consistent with a simplified model of a color singlet pseudoscalar toponium motivated by nonrelativistic QCD, with a resulting observed significance of 6.1 standard deviations. The result provides an independent confirmation of the excess reported in the dilepton channel.

hep-ex↗

arXiv2026

Search for top quark flavor-changing neutral currents in multilepton final states using an effective field theory approach in proton--proton collisions at $\sqrt{s}$ = 13 TeV

We present a search for flavor-changing neutral current (FCNC) interactions involving the top quark in production and decay. This analysis establishes the first global search in the top quark FCNC sector within the standard model effective field theory where all relevant operators are constrained simultaneously in a single fit to data, providing a framework for future measurements and combinations at the LHC. The analysis uses proton$-$proton collision data collected at $\sqrt{s}$ = 13 TeV by the CMS detector, corresponding to an integrated luminosity of 138 fb$^{-1}$. Signal contributions are probed in final states with two same-sign charged leptons or three leptons. Multivariate discriminants are used to separate signal from background, and their distributions enter a likelihood fit to determine 95% confidence intervals for 24 Wilson coefficients. No evidence for FCNC interactions is observed. These results provide the first simultaneous constraints on the complete operator set and place the most stringent limits to date on FCNC top quark decay branching fractions via two-quark$-$two-lepton interactions.

hep-ex↗

arXiv2026

Search for a Higgs boson produced in association with a charm quark and decaying to a W boson pair in proton-proton collisions at $\sqrt{s}$ = 13 TeV

This paper presents a search for a Higgs boson produced in association with a charm quark (cH) which allows to probe the Higgs-charm Yukawa coupling strength modifier $κ_\mathrm{c}$. Higgs boson decays to a pair of W bosons are considered, where one W boson decays to an electron and a neutrino, and the other W boson decays to a muon and a neutrino. The data, corresponding to an integrated luminosity of 138 fb$^{-1}$, were collected between 2016 and 2018 with the CMS detector at the LHC at a center-of-mass energy of $\sqrt{s}$ = 13 TeV. Upper limits at the 95% confidence level (CL) are set on the ratio of the measured yield to the standard model expectation for cH production. The observed (expected) upper limit is 1065 (506), corresponding to an observed (expected) constraint of $\lvertκ_\mathrm{c}\rvert$ $\lt$ 211 (95). When combined with the previous search for cH in the diphoton decay channel of the Higgs boson, the limits are interpreted as observed (expected) constraints at 95% CL on the value of $κ_\mathrm{c}$, $\lvertκ_\mathrm{c}\rvert$ $\lt$ 47 (51).

hep-ex↗

arXiv2026

Search for a new heavy resonance decaying to a top quark and a neutral scalar boson in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A first search at the LHC for a new heavy resonance decaying to a top quark and a neutral scalar boson $ϕ$ in the fully hadronic final state is presented, where the $ϕ$ boson is identified by its decay into a bottom quark-antiquark pair. The search is focused on final states in which the decay products of the highly Lorentz boosted top quark and $ϕ$ boson are each reconstructed as a single, large-radius jet with distinct substructure. The analysis is performed using proton-proton collision data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$, recorded with the CMS detector at the LHC in 2016$-$2018. The single production of a vector-like top quark, $\mathrm{T}'$, is used as a benchmark model for the signal process. The results of this search are combined with those of a previous CMS search in which semileptonic decays of the top quark were used. No significant excess of data is observed with respect to the background prediction. For the case where the neutral scalar is a standard model Higgs boson and the $\mathrm{T}'$ quark width is 5% of its mass, $\mathrm{T}'$ quark masses between 0.85 and 1.3 TeV are excluded at 95% confidence level and the most stringent limits to date are set for masses above 2 TeV. For other $ϕ$ boson masses, upper limits as low as 0.1 fb are set on the product of the $\mathrm{T}'$ quark production cross section and branching fraction for its decay to a top quark and a $ϕ$ boson.

hep-ex↗

arXiv2026

Observation of long-range collective flow in OO and NeNe collisions and implications for nuclear structure studies

The long-range collective flow of particles produced in oxygen-oxygen (OO) and neon-neon (NeNe) collisions is measured with the CMS detector at the CERN LHC. The data samples were collected at a center-of-mass energy per nucleon pair of 5.36 TeV, with integrated luminosities of 7 nb$^{-1}$ and 0.8 nb$^{-1}$ for OO and NeNe collisions, respectively. Two- and four-particle azimuthal correlations are measured over nearly five units of pseudorapidity. Significant elliptic ($v_2$) and triangular ($v_3$) flow harmonics are observed in both systems. The ratios of $v_n$ coefficients between NeNe and OO collisions suggest sensitivity to the intrinsic nuclear structure of the respective Ne and O ions. Hydrodynamic models with $\textit{ab initio}$ nuclear structure inputs qualitatively reproduce the collision-overlap dependence of both the $v_n$ values and the NeNe to OO ratios. These measurements provide new constraints when modeling the interplay of nuclear structure and collective dynamics in collisions of $^{16}$O and $^{20}$Ne, respectively.

nucl-ex↗

arXiv2026

Search for anomalous couplings in WW and WZ production with single-lepton final states in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for deviations from the standard model using an effective field theory approach is carried out using the proton-proton collision data set recorded by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. In this study Wilson coefficients corresponding to dimension-six effective field theory operators that would lead to anomalous gauge boson self-couplings and modified couplings between vector bosons and quarks are constrained. Diboson (WW and WZ) production processes with one W boson decaying to a lepton plus antineutrino or charge conjugate and the second W or Z boson decaying hadronically are considered. Since the contribution from anomalous couplings is expected to be most visible at high energy scales, the focus is on final states where the hadronic decay products of a W or Z boson are merged into a single large-radius jet. A dedicated classifier based on machine learning is employed to separate hadronic W and Z boson decays from background processes. The most stringent constraints to date on the Wilson coefficients of operators corresponding to anomalous triple gauge boson couplings are reported. The bounds set on the couplings between vector bosons and quarks are competitive with those from previous inclusive jet measurements.

hep-ex↗

arXiv2026

Observation of enhanced baryon production using strange hadrons in oxygen-oxygen collisions

A hot deconfined medium known as the quark-gluon plasma (QGP) is created in collisions of ultrarelativistic heavy nuclei. In these systems, hadron production is strongly modified relative to proton-proton (pp) interactions. In the hadron transverse momentum region 2 $\lt$ $p_\mathrm{T}$ $\lt$ 5 GeV, collective radial flow and quark coalescence are important mechanisms that can produce such modifications. While these effects are well-established for collisions of large ions, such as lead, it is unknown if they are present in systems produced using smaller ions. To address this question, the $p_\mathrm{T}$ spectra of two strange hadrons, K$^0_\mathrm{S}$ and $Λ$, are measured in oxygen-oxygen (OO) and pp collisions at a center-of-mass energy per nucleon pair of 5.36 TeV. The measurements are performed using the CMS detector at the LHC, and the OO and pp datasets correspond to integrated luminosities of 6.8 nb$^{-1}$ and 1.1 pb$^{-1}$, respectively. The spectral modification of K$^0_\mathrm{S}$ mesons in OO collisions relative to pp collisions is found to be similar to that of inclusive charged hadrons. Conversely, the $Λ$-to-K$^0_\mathrm{S}$ cross section ratio exhibits a pronounced enhancement in OO collisions when compared to pp collisions. The results provide the first observation of a baryon-to-meson enhancement in OO collisions and suggest the formation of a deconfined medium, offering insight into the roles of strangeness, radial flow, and quark coalescence in QGP.

nucl-ex↗

arXiv2026

Performance of heavy-flavour jet identification in the CMS high-level trigger in proton-proton collisions at $\sqrt{s}$ = 13.6 TeV

The CMS trigger system plays a crucial role during data taking, reducing the large collision rate delivered by the LHC to a few kHz for data storage and subsequent offline analysis. The system aims to maintain a high selection efficiency for a wide range of processes, including those involving jets originating from heavy-flavour quarks (b and c), which provide a distinctive signature in many physics analyses. To achieve this while maintaining a sustainable trigger output rate, dedicated jet flavour identification methods are developed and optimized for use in the high-level trigger (HLT). This paper presents the design, commissioning, and performance of deep-learning-based jet identification algorithms deployed in the HLT during 2022$-$2024, for proton-proton collisions at $\sqrt{s}$ = 13.6 TeV. The new algorithms enabled significant improvements in signal efficiency for a variety of key physics processes, including the non-resonant production of Higgs boson pairs decaying to four b quarks, as well as Higgs boson production via both vector boson fusion and in association with a $\mathrm{t\bar{t}}$ pair, in the H $\to$ $\mathrm{b\bar{b}}$ and H $\to$ $\mathrm{c\bar{c}}$ decay channels.

hep-ex↗

arXiv2026

Observation of the jet diffusion wake using dijets in heavy ion collisions

Energetic quarks and gluons traversing a hot and dense quark-gluon plasma deposit energy and momentum into the medium before hadronizing to collimated sprays of particles, known as jets. This energy-momentum deposition is expected to produce medium responses, collectively known as jet wakes, with ``diffusion wake'' denoting a depletion of particles in the direction opposite to the propagating jet. The diffusion wake is studied by comparing dijet-hadron correlations measured in lead-lead (PbPb) and proton-proton (pp) collisions. The analysis uses PbPb and pp data recorded at a nucleon-nucleon (NN) center-of-mass energy $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV with the CMS detector at the CERN LHC. By exploring how the dijet-hadron correlation distributions differ for various pseudorapidity separations of the two jets in the dijet, the presence of a jet diffusion wake is firmly established. The diffusion wake signal has a significance greater than 5 standard deviations for charged particles in the transverse momentum range 1 $\lt$ $p_\mathrm{T}$ $\lt$ 2 GeV. The measurements are compared with various model predictions with and without jet wake effects, providing new insights into quark-gluon plasma properties and the formation of jet-induced wakes.

nucl-ex↗

arXiv2026

Search for Higgs boson pair production in the $\mathrm{b\bar{b}WW}$ decay channel with two leptons in the final state using proton-proton collision data at $\sqrt{s}$ = 13.6 TeV

A search for Higgs boson pair production is presented, targeting final states where one Higgs boson decays to a pair of bottom quarks and the other Higgs boson decays to two W bosons, both of which decay leptonically, to an electron or a muon, and a neutrino. For the first time, the search is conducted with proton-proton collision data from the LHC at $\sqrt{s}$ = 13.6 TeV, recorded with the CMS detector in 2022 and 2023 and corresponding to an integrated luminosity of 62 fb$^{-1}$. The results are consistent with the standard model predictions. An upper limit of 12.0 times the standard model prediction at 95% confidence level is set on the Higgs boson pair production cross section, with an expected limit of 18.5. The results are also used to constrain the strength of the trilinear self-coupling of the Higgs boson, as well as of the quartic coupling between two Higgs bosons and two vector bosons.

hep-ex↗

arXiv2026

Combined measurements and interpretations of Higgs boson production and decay in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Combined measurements of Higgs boson production and decay rates are reported, representing the most comprehensive study performed by the CMS Collaboration to date. The included analyses use proton-proton collision data recorded by the CMS experiment at $\sqrt{s}$ = 13 TeV from 2016 to 2018, corresponding to an integrated luminosity of 138 fb$^{-1}$. The statistical combination is based on analyses that measure the following decay channels: H $\to$ $γγ$, H $\to$ ZZ, H $\to$ WW, H $\to$ $ττ$, H $\to$ bb, H $\to$ $μμ$, and H $\to$ Z$γ$. Information in the events from each decay channel is used to target multiple Higgs boson production processes. Searches for invisible Higgs boson decays are also considered, as well as an analysis that measures off-shell Higgs boson production in the H $\to$ ZZ $\to$ 4$\ell$ ($\ell$ = e, $μ$) decay channel. The best fit inclusive signal yield is measured to be 1.014 $^{+0.055}_{-0.053}$ times the standard model expectation, for a Higgs boson mass of 125.38 GeV. Measurements in kinematic regions defined by the simplified template cross section framework are also provided, as well as interpretations in the coupling modifier and standard model effective field theory frameworks. The coupling modifier interpretation is further used to place constraints on various two-Higgs-doublet models. The results show good compatibility with the standard model predictions for the majority of the measured parameters.

hep-ex↗

arXiv2026

Search for a new resonance decaying to a Higgs boson and a scalar boson in events with two b jets and two Z bosons in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search is performed for a new resonance X decaying into a Higgs boson and a new scalar boson Y (HY) including the case where Y is assumed to be a second Higgs boson (HH), using proton-proton collision data collected at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. This study performs a comprehensive exploitation of the bbZZ events, encompassing the following decay topologies. One H candidate is identified through its decay into a bottom quark-antiquark pair, while the other H or the Y candidate is selected through its decay into a pair of Z bosons. One Z boson is required to decay leptonically and the other, to decay into a pair of quarks or neutrinos. Events of interest are categorized based on the Lorentz boosts of the hadronically decaying H and Z bosons. Machine-learning-based discriminants, together with the reconstructed resonance mass, are employed across the different categories to separate signal from backgrounds, and their corresponding distributions are included in a simultaneous fit. No significant deviations from the standard model predictions are observed. Upper limits at the 95% confidence level are set on the HY and HH production cross sections. For HY production, the upper limit on the cross section pp $\to$ X $\to$ HY $\to$ bbZZ ranges from 500 to 5 fb, with the most stringent constraints achieved for high-mass X resonances and Y masses near the threshold for decay into a pair of massive vector bosons. This is comparable to the sensitivity achieved in other analyses, which focus on H decays to $γγ$ or $ττ$ and Y decays into a pair of bottom quarks or massive vector bosons. For resonant HH production, the upper limit on the cross section of pp $\to$ X $\to$ HH production is 1 pb for a high-mass resonance.

hep-ex↗