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CMS Collaboration

Publications and source records attributed to CMS Collaboration.

At least 127 records · Page 7Linked to original sources

arXiv2026

Measurement of the Z $\to$ $μ^+μ^-$ angular coefficients in pp collisions at $\sqrt{s}$ = 13 TeV as functions of transverse momentum and rapidity

A measurement of the eight angular polarization coefficients, $A_0$ to $A_7$, in the cross section for the Drell$-$Yan production of two muons is presented. The analysis is based on proton-proton (pp) collision data recorded with the CMS detector at the LHC at a center-of-mass energy of $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 140 fb$^{-1}$. The coefficients are determined double differentially in eight intervals of transverse momentum and two intervals of rapidity of the muon pair $μ^+μ^-$. The results are presented for the $μ^+μ^-$ invariant mass range 81$-$101 GeV and are compared with theoretical predictions calculated at next-to-next-to-leading order in perturbative quantum chromodynamics. The measurement provides relevant information about the underlying partonic dynamics and the Z boson production mechanisms.

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arXiv2026

Search for light pseudoscalar boson pairs produced from Higgs boson decays using the 4$τ$ and 2$μ$2$τ$ final states in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for a pair of light pseudoscalar bosons (a$_1$) produced in the decay of the 125 GeV Higgs boson is presented. The analysis examines decay modes where one a$_1$ decays into a pair of tau leptons and the other decays into either another pair of tau leptons or a pair of muons. The a$_1$ boson mass probed in this study ranges from 4 to 15 GeV. The data sample was recorded by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponds to an integrated luminosity of 138 fb$^{-1}$. No excess above standard model (SM) expectations is observed. The study combines the 4$τ$ and 2$μ$2$τ$ channels to set upper limits at 95% confidence level (CL) on the product of the Higgs boson production cross section and the branching fraction to the 4$τ$ final state, relative to the Higgs boson production cross section predicted by the SM. In this interpretation, the a$_1$ boson is assumed to have Yukawa-like couplings to fermions, with coupling strengths proportional to the respective fermion masses. The observed (expected) upper limits range between 0.007 (0.011) and 0.079 (0.066) across the mass range considered. The results are also interpreted in the context of models with two Higgs doublets and an additional complex singlet field (2HD+S). The tightest constraints are obtained for the Type III 2HD+S model. In this case, assuming the Higgs boson production cross section equals the SM prediction, values of the branching ratio for the Higgs boson decay into a pair of a$_1$ bosons exceeding 16% are excluded at 95% CL for a$_1$ boson masses between 5 and 15 GeV and $\tanβ$ $\gt$ 2, with the exception of scenarios in which the a$_1$ boson mixes with charm or bottom quark-antiquark bound states.

hep-ex↗

arXiv2026

Jet fragmentation function and groomed substructure of bottom quark jets in proton-proton collisions at 5.02 TeV

A measurement of the substructure of bottom quark jets (b jets) in proton-proton (pp) collisions is presented. The measurement uses data collected in pp collisions at $\sqrt{s}$ = 5.02 TeV, with a low number of simultaneous interactions per bunch crossing, recorded by the CMS experiment in 2017, corresponding to an integrated luminosity of 301 pb$^{-1}$. An algorithm to identify and cluster the charged decay daughters of b hadrons is developed for this analysis, which facilitates the exposure of the gluon radiation pattern of b jets using iterative Cambridge$-$Aachen declustering. The soft-drop-groomed jet radius, $R_\mathrm{g}$, and momentum balance, $z_\mathrm{g}$, of b quark jets are presented. These observables can be used to test perturbative quantum chromodynamics predictions that account for mass effects. Because the b hadron is partially reconstructed from its charged decay daughters, only charged particles are used for the jet substructure studies. In addition, a jet fragmentation function, $z_\text{b,ch}$, is measured, which is defined as the distribution of the ratio of the transverse momentum ($p_\mathrm{T}$) of the partially reconstructed b hadron with respect to the charged-particle component of the jet $p_\mathrm{T}$. The substructure variable distributions are unfolded to the charged-particle level. The b jet substructure is compared to the substructure of jets in an inclusive jet sample that is dominated by light-quark and gluon jets in order to assess the role of the b quark mass. A strong suppression of emissions at small $R_\mathrm{g}$ values is observed for b jets when compared to inclusive jets, consistent with the dead-cone effect. The measurement is also compared with theoretical predictions from Monte Carlo event generators. This is the first substructure measurement of b jets that clusters together the b hadron decay daughters.

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arXiv2026

Measurement of D$^0$ meson photoproduction in ultraperipheral heavy ion collisions

This Letter reports the first measurement of photonuclear D$^0$ meson production in ultraperipheral heavy ion collisions. The study is performed using lead-lead collision data, with an integrated luminosity of 1.34 nb$^{-1}$, collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.36 TeV. Photonuclear events, where one of the colliding nuclei breaks up and the other remains intact, are selected based on breakup neutron emissions and by requiring no particle activity in a large rapidity interval in the direction of the photon-emitting nucleus. The D$^0$ mesons are reconstructed via the D$^0$ $\to$ K$^-$$π^+$ decay channel, with the cross section measured as a function of D$^0$ meson transverse momentum and rapidity. The results are compared with next-to-leading-order perturbative QCD calculations that employ recent parametrizations of the lead nuclear parton distribution functions, as well as with predictions based on the color glass condensate framework. This measurement is the first photonuclear collision study characterizing parton distribution functions of lead nuclei for parton fractional momenta $x$ (relative to the nucleon) ranging approximately from a few 10$^{-4}$ to 10$^{-2}$ for different hard energy scale $Q^2$ selections.

nucl-ex↗

arXiv2026

Observation of suppressed charged-particle production in ultrarelativistic oxygen-oxygen collisions

A hot and dense state of nuclear matter, known as the quark-gluon plasma, is created in collisions of ultrarelativistic heavy nuclei. Highly energetic quarks and gluons, collectively referred to as partons, lose energy as they travel through this matter, leading to suppressed production of particles with large transverse momenta ($p_\mathrm{T}$). Conversely, high-$p_\mathrm{T}$ particle suppression has not been seen in proton-lead collisions, raising questions regarding the minimum system size required to observe parton energy loss. Oxygen-oxygen (OO) collisions examine a region of effective system size that lies between these two extreme cases. The CMS detector at the CERN LHC has been used to quantify charged-particle production in inclusive OO collisions for the first time via measurements of the nuclear modification factor ($R_\mathrm{AA}$). The $R_\mathrm{AA}$ is derived by comparing particle production to expectations based on proton-proton (pp) data and has a value of unity in the absence of nuclear effects. The data for OO and pp collisions at a nucleon-nucleon center-of-mass energy $\sqrt{s_\mathrm{NN}}$ = 5.36 TeV correspond to integrated luminosities of 6.1 nb$^{-1}$ and 1.02 pb$^{-1}$, respectively. The $R_\mathrm{AA}$ is below unity with a minimum of 0.69 $\pm$ 0.04 around $p_\mathrm{T}$ = 6 GeV. The data exhibit better agreement with theoretical models incorporating parton energy loss as compared to baseline models without energy loss.

nucl-ex↗

arXiv2026

DeepMET: Improving missing transverse momentum estimation with a deep neural network

At hadron colliders, the net transverse momentum of particles that do not interact with the detector (missing transverse momentum, $\vec{p}_\mathrm{T}^\text{miss}$) is a crucial observable in many analyses. In the standard model, $\vec{p}_\mathrm{T}^\text{miss}$ originates from neutrinos. Many beyond-the-standard-model particles, such as dark matter candidates, are also expected to leave the experimental apparatus undetected. This paper presents a novel $\vec{p}_\mathrm{T}^\text{miss}$ estimator, DeepMET, which is based on deep neural networks that were developed by the CMS Collaboration at the LHC. The DeepMET algorithm produces a weight for each reconstructed particle based on its properties. The estimator is based on the negative vector sum of the weighted transverse momenta of all reconstructed particles in an event. Compared with other estimators currently employed by CMS, DeepMET improves the $\vec{p}_\mathrm{T}^\text{miss}$ resolution by 10$-$30%, shows improvement for a wide range of final states, is easier to train, and is more resilient against the effects of additional proton-proton interactions accompanying the collision of interest.

hep-ex↗

arXiv2026

Search for dark matter produced in association with a dark Higgs boson decaying into a bottom quark-antiquark pair in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for dark matter produced in association with a dark Higgs boson decaying into a bottom quark-antiquark pair has been performed using proton-proton collision data at a center-of-mass energy of 13 TeV. The search uses data collected with the CMS detector at the CERN LHC during the 2016$-$2018 data-taking period, corresponding to an integrated luminosity of 138 fb$^{-1}$. The results are interpreted in terms of a theoretical model of dark matter production that, together with a spin-1 gauge boson mediator, predicts the existence of a Higgs-boson-like particle in the dark sector (i.e., a dark Higgs boson). This search focuses on an experimental signature with large missing transverse momentum from dark matter production and a resonant structure in the invariant mass of the bottom quark-antiquark pair from the dark Higgs boson decay. Upper limits at 95% confidence level on the signal strength for dark Higgs boson mass hypotheses below 160 GeV are set. Values of the mediator mass up to 4.5 (2.5) TeV are excluded at 95% confidence level for a dark Higgs boson mass of 50 (150) GeV. This represents the most stringent limits set to date for the dark Higgs boson masses considered in this study.

hep-ex↗

arXiv2026

Inclusive and differential measurements of the $\mathrm{t\bar{t}}γ$ cross section and the $\mathrm{t\bar{t}}γ$ / $\mathrm{t\bar{t}}$ cross section ratio in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Inclusive and differential cross section measurements of top quark pair ($\mathrm{t\bar{t}}$) production in association with a photon ($γ$) are performed as a function of lepton, photon, top quark, and $\mathrm{t\bar{t}}$ kinematic observables, using data from proton-proton collisions at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$, collected at the CERN LHC with the CMS detector. Events containing two leptons (electrons or muons) and a photon in the final state are considered. The fiducial cross section of $\mathrm{t\bar{t}}γ$ is measured to be 137 $\pm$ 8 fb, in a phase space including events with a high momentum, isolated photon. The fiducial cross section of $\mathrm{t\bar{t}}γ$ is also measured to be 56 $\pm$ 5 fb when considering only events where the photon is emitted in the production part of the process. Both measurements are in agreement with the theoretical predictions, of 126 $\pm$ 19 fb and 57 $\pm$ 5 fb, respectively. Differential measurements are performed at the particle and parton levels. Additionally, inclusive and differential ratios between the cross sections of $\mathrm{t\bar{t}}γ$ and $\mathrm{t\bar{t}}$ production are measured. The inclusive ratio is found to be 0.0133 $\pm$ 0.0005, in agreement with the standard model prediction of 0.0127 $\pm$ 0.0008. The top quark charge asymmetry in $\mathrm{t\bar{t}}γ$ production is also measured to be $-$0.012 $\pm$ 0.042, compatible with both the standard model prediction and with no asymmetry.

hep-ex↗

arXiv2026

Search for the single production of vector-like quarks decaying into a W boson and a b quark using single-lepton final states in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search is performed for the single production of a heavy vector-like quark (VLQ), decaying into a W boson and a b quark. The analysis uses proton-proton collision data collected by the CMS experiment at the CERN LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb$^{-1}$. The search targets events with leptonic W boson decays. The event signature consists of one electron or muon, large transverse momentum imbalance, at least one jet consistent with coming from the fragmentation of a b quark and having large transverse momentum, and at least one jet in the forward region of the detector. No significant excess over the standard model prediction is observed. Upper limits are set at the 95% confidence level on the production cross section of a VLQ and its coupling $κ_\mathrm{W}$ to the standard model sector. For a VLQ decaying exclusively into Wb, the upper limit on $κ_\mathrm{W}$ depends on the VLQ mass and reaches values as low as 0.086 for masses around 1.4 TeV. For $κ_\mathrm{W}$ = 0.2 the lower limit on the VLQ mass is 2.4 TeV. These are the most stringent limits to date on the single production of VLQs decaying into Wb.

hep-ex↗

arXiv2026

Search for heavy resonances decaying into four-lepton final states via light bosons in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for a resonance heavier than 250 GeV decaying into four leptons via two intermediate bosons is presented. The search uses proton-proton collision data at $\sqrt{s}$ = 13 TeV collected by the CMS experiment, corresponding to an integrated luminosity of 138 fb$^{-1}$. Novel techniques are used to enhance the sensitivity to a collimated pair of dileptons reconstructed as a single merged object, resulting from the decay of an intermediate light boson. No significant excess of data over the background predictions is observed. Upper limits are set on the production cross section for a four-lepton resonance, including the previously unexplored phase space at the LHC with a dilepton mass of 0.4$-$15 GeV.

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arXiv2026

Particle transformers for identifying Lorentz-boosted Higgs bosons decaying to a pair of W bosons

A novel deep neural network classifier, a ``Particle transformer'' (PaRT), is introduced for the identification of highly Lorentz-boosted resonances reconstructed as single, multipronged jets in measurements and searches performed by the CMS Collaboration at the CERN LHC. Based on a self-attention mechanism that allows the model to weigh the importance of different particles, PaRT is trained on a wide variety of topologies, notably demonstrating strong performance for the first time on jets originating from boosted Higgs boson decays to W bosons. The PaRT algorithm achieves a tagging efficiency of more than 50\% for such jets at a background efficiency of 1%, while maintaining decorrelation from the jet mass. A calibration is performed in proton-proton collision data collected by CMS at a center-of-mass energy of 13 TeV, with a data set corresponding to a total luminosity of 138 fb$^{-1}$. Data-to-simulation selection efficiency scale factors are measured to be in the 0.9$-$1.0 range, with relative uncertainties between 7 and 23%. The tagging capability of PaRT enhances the sensitivity of standard model measurements and searches for beyond-the-standard-model resonances decaying to hadronic diboson systems.

hep-ex↗

arXiv2026

High-precision measurement of the W boson mass with the CMS experiment

In the standard model of particle physics, the masses of the W and Z bosons, the carriers of the weak interaction, are uniquely related. A precise determination of their masses is important because quantum loops of heavy, undiscovered particles could modify this relationship. Although the Z mass is known to the remarkable precision of 22 parts per million (2.0 MeV), the W mass is known much less precisely. A global fit to measured electroweak observables predicts the W mass with 6 MeV uncertainty [1$-$3]. Reaching a comparable experimental precision would be a sensitive and fundamental test of the standard model, made even more urgent by a recent challenge to the global fit prediction by a measurement from the CDF Collaboration at the Fermilab Tevatron collider [4]. Here we report the measurement of the W mass by the CMS Collaboration at the CERN LHC, based on a large data sample of W $\to$ $μν$ events collected in 2016 at the proton-proton collision energy of 13 TeV. The measurement exploits a high-granularity maximum likelihood fit to the kinematic properties of muons produced in W decays. By combining an accurate determination of experimental effects with marked in situ constraints of theoretical inputs, we reach a precise measurement of the W mass, of 80 360.2 $\pm$ 9.9 MeV, in agreement with the standard model prediction.

hep-ex↗

arXiv2026

Observation of nuclear suppression in coherent $Υ$(1S) photoproduction off heavy nuclei at the LHC

The first measurement of coherent $Υ$(1S) meson photoproduction off heavy nuclei is performed using ultraperipheral lead-lead collisions collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The nuclear gluonic structure is probed at a nucleon momentum fraction of order $x$ $\sim$ 10$^{-3}$, determined by the kinematics of the process. Owing to the large $Υ$(1S) mass, the measurement reaches the highest scale accessible so far through coherent vector-meson photoproduction, $μ^2$ = 22.4 GeV$^2$, where nonlinear quantum chromodynamics effects are expected to be minimal. In the $Υ$(1S) rapidity range $\lvert y\rvert$ $\lt$ 1, the ratio of the measured photoproduction cross section to a baseline model prediction that neglects nuclear effects is $S_{Υ\text{(1S)}}$ = 0.25 $\pm$ 0.06 (stat) $\pm$ 0.02 (syst), thereby demonstrating nuclear suppression in this process. Expressed in terms of a nuclear gluon suppression factor, the result yields $R_\text{g}^\text{Pb}$($x$ $\approx$ 10$^{-3}$, $μ^2$ = 22.4 GeV$^2$) = 0.55 $\pm$ 0.12 (stat) $\pm$ 0.02 (syst). The measured $R_\text{g}^\text{Pb}$ is only slightly larger than the values previously reported for coherent $ϕ$ photoproduction, despite the probed $μ^2$ differing by approximately two orders of magnitude.

nucl-ex↗

arXiv2026

Characterizing the initial state and dynamical evolution in XeXe and PbPb collisions using multiparticle cumulants

For the first time, correlations among mixed-order moments of two or three flow harmonics$-$($v_{n}^{k},v_{m}^{l}$) and ($v_{n}^{k},v_{m}^{l}, v_{p}^{q}$), with $k$, $l$, and $q$ denoting the respective orders$-$are measured in xenon-xenon (XeXe) collisions and compared with lead-lead (PbPb) results, providing a novel probe of collective behavior in heavy ion collisions. These measurements compare a nearly spherical, doubly-magic ${}^{208}$Pb nucleus to a triaxially deformed ${}^{129}$Xe nucleus, emphasizing the sensitivity to initial-state geometry fluctuations arising from nuclear deformation. The dependence of these results ($v_{n}$, $n$ = 2, 3, 4) on the shape and size of the nuclear overlap region is studied. Comparisons between $v_{2}$, $v_{3}$, and $v_{4}$ demonstrate the importance of $v_{3}$ and $v_{4}$ in exploring the nonlinear hydrodynamic response of the quark-gluon plasma (QGP) to the initial spatial anisotropy. The results constrain initial-state model parameters that influence the evolution of the QGP. The CMS detector was used to collect XeXe and PbPb data at nucleon-nucleon center-of-mass energies of $\sqrt{s_\mathrm{NN}}$ = 5.44 and 5.36 TeV, respectively. Correlations are extracted using multiparticle mixed-harmonic cumulants (up to eight-particle cumulants) with charged particles in the pseudorapidity range $\lvertη\rvert$ $\lt$ 2.4 and transverse momentum range 0.5 $\lt$ $p_\mathrm{T}$ $\lt$ 3 GeV/$c$.

nucl-ex↗

arXiv2026

High-level hadronic tau lepton triggers of the CMS experiment in proton-proton collisions at $\sqrt{s}$ = 13.6 TeV

The trigger system of the CMS detector is pivotal in the acquisition of data for physics measurements and searches. Studies of final states characterized by hadronic decays of tau leptons require the reconstruction and the identification of genuine tau leptons against quark- and gluon-initiated jets at the trigger level. This is a difficult task, particularly as improvements to the LHC have resulted in an increased number of interactions per bunch crossing in recent years. To address this challenge, a series of machine-learning algorithms with high identification efficiency and low computational cost have been incorporated into the high-level trigger for hadronically decaying tau leptons. In this paper, these developments and the trigger performance are summarized using data collected by the CMS experiment in proton-proton collisions at $\sqrt{s}$ = 13.6 TeV in 2022$-$2023, corresponding to an integrated luminosity of 62 fb$^{-1}$.

physics.ins-det↗

arXiv2026

Combined effective field theory interpretation of Higgs boson, electroweak vector boson, top quark, and multi-jet measurements

Constraints on Wilson coefficients (WCs) corresponding to dimension-six operators of the standard model effective field theory (SMEFT) are determined from a simultaneous fit to seven sets of CMS measurements probing Higgs boson, electroweak vector boson, top quark, and multijet production. Masurements of electroweak precision observables are also included and provide complementary constraints to those from CMS experiment. The CMS measurements, using LHC proton-proton collision data at $\sqrt{s}$ = 13 TeV, corresponding to integrated luminosities of 36.3 or 138 fb$^{-1}$, are chosen to provide sensitivity to a broad set of operators, for which consistent SMEFT predictions can be derived. These are primarily measurements of differential cross sections which are parameterized as functions of the WCs. In measurements targeting $\text{t}(\bar{\text{t}})\text{X}$ production, SMEFT effects are modelled at the detector level. Individual constraints on 64 WCs, and constraints on 43 linear combinations of WCs, are obtained.

hep-ex↗

arXiv2026

Measurement of dijet angular distributions and search for beyond the standard model physics in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A measurement is presented of dijet angular distributions in proton-proton collisions at $\sqrt{s}$ = 13 TeV, using data collected with the CMS detector at the CERN LHC and corresponding to an integrated luminosity of 138 fb$^{-1}$. For the first time, the dijet angular distributions, corrected for detector effects, are compared with the predictions of perturbative quantum chromodynamics at next-to-next-to-leading order, including next-to-leading-order electroweak corrections. While data are generally found to be in agreement with predictions, a small difference in shape of the normalized distributions is seen for dijet masses ranging from 2.4 to 4.8 TeV and above 6 TeV. The distributions are used to search for proposed signatures of quark compositeness, extra spatial dimensions, quantum black holes, dark-matter mediators, axion-like particles, and anomalous gluon couplings. The most stringent limits to date are set for most of these scenarios. Quark contact interactions are excluded at 95% confidence level (CL) up to a scale of 17 (37) TeV for destructive (constructive) interference in a benchmark scenario, valid to next-to-leading order in quantum chromodynamics, and in which only left-handed quarks participate. The coupling of axion-like particles to the gluon, $c_{\text{g}}/f_{\text{a}}$, is constrained to be lower than 0.42 TeV$^{-1}$ at 95% CL. The anomalous triple-gluon coupling, $C_{\text{G}}/Λ^2$, in a standard model effective field theory is constrained to be lower than 0.0076 TeV$^{-2}$ at 95% CL.

hep-ex↗

arXiv2026

Search for low-mass hidden-valley dark showers with non-prompt muon pairs in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for signatures of a dark analog to quantum chromodynamics is performed. The analysis targets long-lived dark mesons that decay into standard-model particles, with a high branching fraction of the dark mesons decaying into muons. The dark mesons are formed by the hadronisation of dark partons, which are produced by a decay of the Higgs boson. The search is performed using a data set corresponding to an integrated luminosity of 41.6 fb$^{-1}$, which was collected in proton-proton collisions at $\sqrt{s}$ = 13 TeV by the CMS experiment at the CERN LHC in 2018 using non-prompt muon triggers. The search is based on resonant muon pair signatures. Machine-learning techniques are employed in the analysis, utilising boosted decision trees to discriminate between signal and background. No significant excess is observed above the standard model expectation. Upper limits on the branching fraction of the Higgs boson decaying to dark partons are determined to be as low as 10$^{-4}$ at 95% confidence level, surpassing and extending the existing limits on models with dark $\tildeω$ mesons for mean proper decay lengths of less than 500 mm and for $\tildeω$ masses down to 0.3 GeV. First limits are set for extended dark-shower models with two dark flavours that contain dark photons, probing their masses down to 0.33 GeV.

hep-ex↗