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Lambrecht, L. [Ghent University] (ORCID:0000000191081560)

Publications and source records attributed to Lambrecht, L. [Ghent University] (ORCID:0000000191081560).

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Measurement of 𝐡 meson production fraction ratios in proton-proton collisions at βˆšπ‘  = 13 TeV using open-charm and charmonium decays

Production fraction ratios of 𝐡 + , 𝐡 0 , and 𝐡$^{0}_{𝑠}$ mesons are measured in proton-proton collisions at βˆšπ‘  = 13 TeV using a special dataset recorded in 2018 with high-rate triggers designed to collect an unbiased sample of 1⁒010 𝑏 hadrons with the CMS experiment at the LHC. These data allow the study of the open-charm decays of 𝐡 mesons (𝐡 (𝑠) β†’ πœ‹β’π· (𝑠) ) where the 𝐷 meson decays into fully hadronic final states. By utilizing known branching fractions and precise theoretical calculations, production fraction ratios as functions of 𝐡 meson transverse momentum (𝑝 T ) and rapidity (𝑦) are measured using open-charm decays in the kinematic range of 8 < 𝑝 T < 60 GeV and |𝑦| <2.25. In addition, the same dataset is used to measure the relative production fraction ratios with the charmonium decay channels [𝐡 (𝑠) →𝑋⁒𝐽/πœ“ with 𝑋 indicating a 𝐾 + , 𝐾*(892) 0 , or πœ™β‘(1020) meson] where the 𝐽/πœ“ meson decays into a pair of muons. The open-charm results are used to normalize the relative production fraction ratios obtained from the charmonium samples. Measurements of the ratios of branching fractions of 𝐡 meson decays to charmonium and open-charm final states are also reported, which will improve the world-average values of these ratios. Finally, we test isospin invariance in 𝐡 meson production in proton-proton collisions and observe that it holds within the experimental precision.

Bottom mesons↗
DOE OSTI2026

Search for a new neutral gauge boson produced in association with one or two b jets and decaying into a pair of muons in proton-proton collisions at $\sqrt{s}=13$ TeV

A search for a new neutral gauge boson, Zβ€², produced in association with one or two jets, including at least one b jet, and decaying into a pair of muons is presented. The analysis uses proton-proton collision data collected with the CMS detector at $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of 138 fb βˆ’1 . No significant deviation from background expectations is observed. Upper limits at 95% confidence level on the product of cross section, branching fraction to dimuons, acceptance, and efficiency, from 0.2 to 2 fb, are set for Zβ€² boson masses between 125 and 350 GeV. Process-dependent products of acceptance and efficiency, and model-independent limits on the signal yield are provided. These are the only results to date in the 125–200 GeV mass range and the most stringent for b quark fusion production modes in the 200–350 GeV range, complementing inclusive Zβ€² boson searches.

beyond Standard Model↗
DOE OSTI2026

Search for pair production of heavy resonances in final states with a photon and large-radius jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for the pair production of heavy spin-1/2 or spin-3/2 resonances (𝑑*) in proton-proton collisions at $\sqrt{s}$ =13 TeV is presented. Data collected with the CMS detector at the CERN LHC from 2016 to 2018 corresponding to an integrated luminosity of 138 fb βˆ’1 are used. The analysis targets benchmark signal scenarios where one 𝑑* decays into a top quark (𝑑) and a photon (𝛾), and the other into a 𝑑 quark and a gluon (𝑔), i.e., 𝑝⁒𝑝 β†’ $𝑑^*\overline{⁒𝑑^*}$ β†’ 𝑑⁒𝑑⁒𝛾⁒𝑔. All-hadronic final states from the 𝑑 pair decay chain are selected using jet substructure techniques. The signal is probed as a function of the 𝑑* candidate mass, which is reconstructed using the photon and a top quark candidate jet. No significant deviation from the background-only hypothesis is found. Observed (expected) upper limits on the signal cross section at 95% confidence level are set, excluding masses of spin-1/2 𝑑* particles below 930 (930) GeV and spin-3/2 𝑑* particles below 1330 (1390) GeV. This analysis marks the first search for heavy resonances in the $𝑑\bar{⁒𝑑}𝛾⁒𝑔$ channel. Exploiting the high-energy photon to reduce the backgrounds, this search achieves sensitivity competitive with 𝑝⁒𝑝 β†’ $𝑑^*\overline{⁒𝑑^*}$ β†’ $𝑑\bar{⁒𝑑}⁒𝑔⁑𝑔$ searches for spin-1/2 𝑑* despite the small expected 𝑑* β†’ 𝑑⁒𝛾 branching fraction.

hadron colliders↗
DOE OSTI2026

Measurement of the ratio of the $𝐡^+_𝑐 β†’ 𝐽/πœ“β’πœ^+⁒𝜈_𝜏$ and $𝐡^+_𝑐 β†’ 𝐽/πœ“β’πœ‡^+⁒𝜈_πœ‡$ branching fractions using three-prong 𝜏 lepton decays

The ratio between the $𝐡^+_𝑐 β†’ 𝐽/πœ“β’πœ^+⁒𝜈_𝜏$ and $𝐡^+_𝑐 β†’ 𝐽/πœ“β’πœ‡^+⁒𝜈_πœ‡$ branching fractions is measured using a data sample of proton-proton collisions collected by CMS at a center-of-mass energy of 13 TeV in the years 2016–2018 and corresponding to an integrated luminosity of 138 fb βˆ’1 . The 𝐽/πœ“ meson is identified through its 𝐽/πœ“ β†’ πœ‡ + β’πœ‡ βˆ’ decay and the tau lepton is reconstructed in the hadronic three-prong final state. The measured ratio of branching fractions in this tau decay mode, β„› had 𝐽/πœ“ = $1.0⁒4^{+0.50}_{βˆ’0.44}$, is combined with the previous analysis based on the 𝜏 + $β†’ πœ‡^+⁒𝜈_πœ‡\bar{𝜈}_𝜏$ leptonic decay channel, leading to β„› 𝐽/πœ“ = 0.49 Β± 0.26. As this result is consistent with the standard model prediction of 0.258 Β± 0.004, no evidence of lepton flavor universality violation is found.

Chekhovsky, V. [Yerevan Physics Institute]β†—
DOE OSTI2026

Search for dark matter production in association with bottom quarks and a lepton pair in proton-proton collisions at $\sqrt{s}=13$ TeV

A search is performed for dark matter produced in association with bottom quarks and a pair of electrons or muons in data collected with the CMS detector at the LHC, corresponding to 138 fb βˆ’1 of integrated luminosity of proton-proton collisions at a center-of-mass energy of 13 TeV. For the first time at the LHC, the associated production of a bottom quark-antiquark pair and a new heavy neutral Higgs boson (H) that subsequently decays into a leptonically decaying Z boson and a pseudoscalar (a) is explored. The latter acts as a dark matter mediator in the context of the two Higgs doublet model plus a pseudoscalar (2HDM+a). Multivariate techniques that target a wide range of mass configurations for the H and a particles are used. The observations are consistent with the expectations from standard model processes. Upper limits at 95% confidence level are set on the product of cross section and branching fraction of the new particles, ranging from 10 βˆ’2 pb for an H mass of 400 GeV to 10 βˆ’3 pb for an H mass of 2000 GeV. Constraints on the parameter space of a benchmark 2HDM+a model are derived and compared with expectations in the context of cosmological predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Measurement of the dineutrino system kinematic variables in dileptonic top quark pair production in proton-proton collisions at $\sqrt{s}=13$ TeV

Differential top quark pair production cross sections are measured in the dilepton final states e + e βˆ’ , ΞΌ + ΞΌ βˆ’ , and e Β± ΞΌ βˆ“ , as a function of kinematic variables of the two-neutrino system: the transverse momentum $p^{vv}_{\textrm{T}}$ of the dineutrino system, the minimum distance in azimuthal angle between $\vec{p}^{vv}_{\textrm{T}}$ and leptons, and in two dimensions in bins of both observables. The measurements are performed using CERN LHC proton-proton collisions at $\sqrt{s}=13$ TeV, recorded by the CMS detector between 2016 and 2018, corresponding to an integrated luminosity of 138 fb βˆ’1 . The measured cross sections are unfolded to the particle level using an unregularized least squares method. Results are compared with predictions by the standard model of particle physics, and found to be in agreement with theoretical calculations as well as Monte Carlo simulations.

Hadron-Hadron Scattering↗
DOE OSTI2026

Exploring small-angle emissions in charm quark jets in proton-proton collisions at $\sqrt{s}=5.02$ TeV

A measurement of the angular structure of inclusive jets and those containing a prompt D 0 meson in proton-proton collisions at the LHC at a center-of-mass energy of 5.02 TeV is presented. The data corresponding to an integrated luminosity of 301 pb βˆ’1 were collected by the CMS experiment in 2017. Two jet grooming algorithms, late-k T and soft drop, are used to study the intrajet radiation pattern using iterative Cambridge-Aachen declustering. The splitting-angle distributions of jets with transverse momentum (p T ) of around 100 GeV, obtained with these two algorithms, show that there is a shift of the distribution for jets containing a prompt D 0 meson with respect to inclusive jets. The suppression of emissions at small angles observed in the late-k T grooming approach is consistent with the dead-cone effect, whereas the similar suppression for splittings selected with the soft-drop algorithm appears to be induced by gluon splitting to charm quark-antiquark pairs at large angles. The measured distributions are corrected to the particle level and can be used to constrain model predictions for the substructure of high-p T charm quark jets.

Charm Physics↗
DOE OSTI2026

Search for the nonresonant and resonant production of a Higgs boson in association with an additional scalar boson in the $γγττ$ final state in proton-proton collisions at $\sqrt{s}=13$ TeV

The results of a search for the production of two scalar bosons in final states with two photons and two tau leptons are presented. The search considers both nonresonant production of a Higgs boson pair, HH, and resonant production via a new boson X which decays either to HH or to H and a new scalar Y. The analysis uses up to 138 fb βˆ’1 of proton-proton collision data, recorded between 2016 and 2018 by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV. No evidence for signal is found in the data. For the nonresonant production, the observed (expected) upper limit at 95% confidence level (CL) on the HH production cross section is set at 930 (740) fb, corresponding to 33 (26) times the standard model prediction. At 95% CL, HH production is observed (expected) to be excluded for values of ΞΊ Ξ» outside the range between βˆ’12 (βˆ’9.4) and 17 (15). Observed (expected) upper limits at 95% CL for the X β†’ HH cross section are found to be within 160 to 2200 (200 to 1800) fb, depending on the mass of X. In the X β†’ Y(ττ)H(Ξ³Ξ³) search, the observed (expected) upper limits on the product of the production cross section and decay branching fractions vary between 0.059–1.2 fb (0.087–0.68 fb). For the X β†’ Y(Ξ³Ξ³)H(ττ) search the observed (expected) upper limits on the product of the production cross section and Y β†’ Ξ³Ξ³ branching fraction vary between 0.69–15 fb (0.73–8.3 fb) in the low Y mass search, tightening constraints on the next-to-minimal supersymmetric standard model, and between 0.64–10 fb (0.70–7.6 fb) in the high Y mass search.

Beyond Standard Model↗
DOE OSTI2026

Search for new physics in the final state with a single photon and large missing transverse momentum in proton-proton collisions at βˆšπ‘  =13 TeV

A search for new physics in events featuring a single photon and missing transverse momentum is presented, using proton-proton βˆšπ‘  =13 TeV collision data corresponding to an integrated luminosity of 101 fb βˆ’1 collected by the CMS experiment at the CERN LHC between 2017 and 2018. This analysis, combined with a previous study of 36 fb βˆ’1 of 2016 data (totaling 137 fb βˆ’1 ), reveals no significant deviations from standard model expectations. The results are then used to establish 95% confidence level limits on parameters in theoretical models involving dark matter and large extra dimensions. Compared to the 2016-only analysis, this search achieves up to a 14% improvement in exclusion reach for mediator masses in simplified dark matter models, along with 11% and 10% enhancements in the limits on the effective field theory suppression scale and the fundamental Planck scale, respectively. These results are the most stringent constraints on these parameters to date.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

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 βˆ’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 g , and momentum balance, z 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 b,ch , is measured, which is defined as the distribution of the ratio of the transverse momentum (p T ) of the partially reconstructed b hadron with respect to the charged-particle component of the jet p 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 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 independent of the b hadron species and decay channel.

boosted jets↗
DOE OSTI2026

Search for light pseudoscalar boson pairs produced from Higgs boson decays using the 4Ο„ and 2ΞΌ2Ο„ 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 a1 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 βˆ’1 . No excess above standard model (SM) expectations is observed. The study combines the 4Ο„ and 2ΞΌ2Ο„ 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 4Ο„ 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 a1 bosons exceeding 16% are excluded at 95% CL for a1 boson masses between 5 and 15 GeV and tan Ξ² > 2, with the exception of scenarios in which the a1 boson mixes with charm or bottom quark-antiquark bound states.

Higgs physics↗
DOE OSTI2026

Search for dijet resonances with data scouting in proton-proton collisions at $\sqrt{s}=13$ TeV

A search is presented for narrow resonances, with a mass between 0.6 and 1.8 TeV, decaying to pairs of jets, in proton-proton collisions at $\sqrt{s}=13$ TeV. The search is performed using dijets that are reconstructed, selected, and recorded in a compact form by the high-level trigger in a technique referred to as β€œdata scouting”, from data collected in 2016–2018 corresponding to an integrated luminosity of 117 fb βˆ’1 . The dijet mass spectra are well described by a smooth parameterization, and no significant evidence for the production of new particles is observed. Model-independent upper limits are presented on the product of the cross section, branching fraction, and acceptance for the individual cases of narrow quark-quark, quark-gluon, and gluon-gluon resonances, and are compared to the predictions from a variety of models of narrow dijet resonance production. The upper limit on the coupling of a dark matter mediator to quarks is presented as a function of the mediator mass. The sensitivity of this search goes beyond what is expected from statistical scaling with the integrated luminosity alone, as a consequence of the use of fewer parameters in the background function within a more robust statistical procedure.

beyond Standard Model↗
DOE OSTI2026

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 βˆ’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 β†’ 𝐾 βˆ’β’ πœ‹ + 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 π‘₯ (relative to the nucleon) ranging approximately from a few 10 βˆ’4 to 10 βˆ’2 for different hard energy scale 𝑄 2 selections.

charm quark↗
DOE OSTI2026

Probing the flavour structure of dimension-6 EFT operators in multilepton final states in proton-proton collisions at $\sqrt{s}=13$ TeV

An analysis of the flavour structure of dimension-6 effective field theory (EFT) operators in multilepton final states is presented, focusing on the interactions of quarks with Z bosons. For the first time, the flavour structure of these operators is disentangled by simultaneously probing the interactions with different quark generations. The analysis targets the associated production of a top quark pair and a Z boson, as well as diboson processes in final states with at least three leptons, which can be electrons or muons. The data were recorded by the CMS experiment in the years 2016–2018 in proton-proton collisions at a centre-of-mass energy of 13 TeV and correspond to an integrated luminosity of 138 fb βˆ’1 . Consistency with the standard model of particle physics is observed and limits are set on the selected Wilson coefficients, split into couplings to light- and heavy-quark generations.

Flavour Physics↗
DOE OSTI2026

Measurements of $\textrm{t}\overline{\textrm{t}}\textrm{W}$ differential cross sections and the leptonic charge asymmetry at $\sqrt{s}=13$ TeV

Measurements of properties of top quark-antiquark pair production in association with a W boson in proton-proton collisions at a center-of-mass energy of 13 TeV are presented, using a data sample corresponding to an integrated luminosity of 138 fb βˆ’1 , recorded by the CMS experiment at the CERN LHC. Events are selected based on the presence of either two leptons with the same electric charge or three leptons, and multiple jets and b-tagged jets. We present measurements of differential production cross sections as a function of kinematic variables sensitive to different aspects of the process modeling, using a multivariate discriminator in the two-lepton selection region and a simple selection-based method in the three-lepton region. The normalized cross section measurements are generally consistent with the standard model expectations, while we observe larger values compared to the expectations in the absolute cross section measurements, consistent with previous inclusive cross section measurements. In addition, we measure the leptonic charge asymmetry of this process, obtaining an observed value of ${A}_c^{\ell }=-{0.19}_{-0.18}^{+0.16}$, consistent with the expectation of βˆ’0.085 Β± 0.006 predicted by next-to-leading order simulations.

Hadron-Hadron Scattering↗
DOE OSTI2026

Model-independent measurement of the Higgs boson associated production with two jets and decaying to a pair of W bosons in proton-proton collisions at $\sqrt{s}=13$ TeV

A model-independent measurement of the differential production cross section of the Higgs boson decaying into a pair of W bosons, with a final state including two jets produced in association, is presented. In the analysis, events are selected in which the decay products of the two W bosons consist of an electron, a muon, and missing transverse momentum. The model independence of the measurement is maximized by employing a discriminating variable, developed through machine learning, that is agnostic to the signal hypothesis. The analysis is based on proton-proton collision data at $\sqrt{s}=13$ TeV collected with the CMS detector from 2016–2018, corresponding to an integrated luminosity of 138 fb βˆ’1 . The production cross section is measured as a function of the difference in azimuthal angle between the two jets. The differential cross section measurements are used to constrain Higgs boson couplings within the standard model effective field theory framework.

Hadron-Hadron Scattering↗
DOE OSTI2026

Vector boson scattering and anomalous quartic couplings in final states with β„“Ξ½qq or β„“β„“qq plus jets using proton-proton collisions at $\sqrt{s}=13$ TeV

A measurement is presented of the electroweak vector boson scattering production of ZV (V = W, Z) boson pairs associated with two jets in proton-proton collisions at a center-of-mass energy of 13 TeV. The data, corresponding to an integrated luminosity of 138 fb βˆ’1 , were collected at the CERN LHC with the CMS detector during the 2016–2018 data-taking period. The analysis targets final states with a pair of isolated electrons or muons from Z boson decays and three or four jets, depending on the momentum of the vector boson that decays into quarks. Signal strength is measured for events characterized by a large invariant mass of two forward jets with a wide pseudorapidity gap between them. The electroweak production of ZV in association with two jets is measured with an observed (expected) significance of 1.3 (1.8) standard deviations. A combination of the analyses of ZV channel and the previously published WV channel in the lepton plus jets final state places constraints on effective field theory parameters that describe anomalous electroweak production of WW, WZ, and ZZ boson pairs in association with two jets. Several world best limits are set on anomalous quartic gauge couplings in terms of dimension-8 standard model effective field theory operators.

Hadron-Hadron Scattering↗
DOE OSTI2026

Search for nonresonant new physics signals in high-mass dilepton events produced in association with b-tagged jets in proton-proton collisions at $\sqrt{s}=13$ TeV

A search for nonresonant new physics phenomena in high-mass dilepton events produced in association with b-tagged jets is performed using proton-proton collision data collected in 2016–2018 by the CMS experiment at the CERN LHC, at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb βˆ’1 . The analysis considers two effective field theory models with dimension-six operators; involving four-fermion contact interactions between two leptons (β„“β„“, electrons or muons) and b or s quarks (bbβ„“β„“ and bsβ„“β„“). Two lepton flavor combinations (ee and ΞΌΞΌ) are required and events are classified as having 0, 1, or β‰₯2 b-tagged jets in the final state. No significant excess is observed over the standard model backgrounds. Upper limits are set on the production cross section of the new physics signals. These translate into lower limits on the energy scale Ξ› of 6.9 to 9.0 TeV in the bbβ„“β„“ model, depending on model parameters, and on the ratio of energy scale and effective coupling, Ξ›/g*, of 2.0 to 2.6 TeV in the bsβ„“β„“ model. Lepton flavor universality is also tested by comparing the dielectron (ee) and dimuon (ΞΌΞΌ) mass spectra for different b-tagged jet multiplicities. No significant deviation from the standard model expectation of unity is observed.

Beyond Standard Model↗