A Model for the Schottky Anomaly in Metallic Nd2−yCeyCuO4Nd_{2-y}Ce_{y}CuO_{4}

We present a simple model for the doped compound $Nd_{2-y}Ce_{y}CuO_{4}$, in order to explain some recent experimental results on the latter. Within a Hartree-Fock context, we start from an impurity Anderson-like model and consider the magnetic splitting of the $Nd$-$4f$ ground state Kramers doublet due to exchange interactions with the ordered $Cu$ moments. Our results are in very good agreement with the experimental data, yielding a Schottky anomaly peak for the specific heat that reduces its amplitude, broadens and shifts to lower temperatures, upon $Ce$ doping. For overdoped compounds at low temperatures, the specific heat behaves linearly and the magnetic susceptibility is constant. A smooth transition from this Fermi liquid like behavior ocurrs as temperature is increased and at high temperatures the susceptibility exhibits a Curie-like behavior. Finally, we discuss some improvements our model is amenable to incorporate.Comment: 7 pages, 5 figures, and 13 reference

Search for heavy neutral resonances decaying to tau lepton pairs in proton-proton collisions at (Formula presented)

A search for heavy neutral gauge bosons ((Formula presented)) decaying into a pair of tau leptons is performed in proton-proton collisions at (Formula presented) at the CERN LHC. The data were collected with the CMS detector and correspond to an integrated luminosity of (Formula presented). The observations are found to be in agreement with the expectation from standard model processes. Limits at 95% confidence level are set on the product of the (Formula presented) production cross section and its branching fraction to tau lepton pairs for a range of (Formula presented) boson masses. For a narrow resonance in the sequential standard model scenario, a (Formula presented) boson with a mass below 3.5 TeV is excluded. This is the most stringent limit to date from this type of search

Measurement of inclusive and differential cross sections of single top quark production in association with a W boson in proton-proton collisions at s = 13.6 TeV

The first measurement of the inclusive and normalised differential cross sections of single top quark production in association with a W boson in proton-proton collisions at a centre-of-mass energy of 13.6 TeV is presented. The data were recorded with the CMS detector at the LHC in 2022, and correspond to an integrated luminosity of 34.7 fb−1. The analysed events contain one muon and one electron in the final state. For the inclusive measurement, multivariate discriminants exploiting the kinematic properties of the events are used to separate the signal from the dominant top quark-antiquark production background. A cross section of 82.3±2.1stat−9.7+9.9syst±3.3lumi pb is obtained, consistent with the predictions of the standard model. A fiducial region is defined according to the detector acceptance to perform the differential measurements. The resulting differential distributions are unfolded to particle level and show good agreement with the predictions at next-to-leading order in perturbative quantum chromodynamics

Search for rare decays of the Z and Higgs bosons to a J/ψ or ψ(2S) meson and a photon in proton-proton collisions at s=13TeV

A search is presented for rare decays of the Image 1 and Higgs bosons to a photon and a Image 2 or a Image 3 meson, with the charmonium state subsequentially decaying to a pair of muons. The data set corresponds to an integrated luminosity of 123fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV collected with the CMS detector at the LHC. No evidence for branching fractions of these rare decay channels larger than predicted in the standard model is observed. Upper limits at 95% confidence level are set: Image 4, Image 5, Image 6, and Image 7. The ratio of the Higgs boson coupling modifiers Image 8 is constrained to be in the interval (−157,+199) at 95% confidence level. Assuming Image 9, this interval becomes (−166,+208)

Girth and groomed radius of jets recoiling against isolated photons in lead-lead and proton-proton collisions at sNN=5.02 TeV

This Letter presents the first measurements of the groomed jet radius Rg and the jet girth g in events with an isolated photon recoiling against a jet in lead-lead (PbPb) and proton-proton (pp) collisions at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The observables Rg and g provide a quantitative measure of how narrow or broad a jet is. The analysis uses PbPb and pp data samples with integrated luminosities of 1.7 nb−1 and 301 pb−1, respectively, collected with the CMS experiment in 2018 and 2017. Events are required to have a photon with transverse momentum pTγ>100 GeV and at least one jet back-to-back in azimuth with respect to the photon and with transverse momentum pTjet such that pTjet/pTγ>0.4. The measured Rg and g distributions are unfolded to the particle level, which facilitates the comparison between the PbPb and pp results and with theoretical predictions. It is found that jets with pTjet/pTγ>0.8, i.e., those that closely balance the photon pTγ, are narrower in PbPb than in pp collisions. Relaxing the selection to include jets with pTjet/pTγ>0.4 reduces the narrowing of the angular structure of jets in PbPb relative to the pp reference. This shows that selection bias effects associated with jet energy loss play an important role in the interpretation of jet substructure measurements

Identification of low-momentum muons in the CMS detector using multivariate techniques in proton-proton collisions at √s = 13.6 TeV

"Soft"muons with a transverse momentum below 10 GeV are featured in many processes studied by the CMS experiment, such as decays of heavy-flavor hadrons or rare tau lepton decays. Maximizing the selection efficiency for these muons, while simultaneously suppressing backgrounds from long-lived light-flavor hadron decays, is therefore important for the success of the CMS physics program. Multivariate techniques have been shown to deliver better muon identification performance than traditional selection techniques. To take full advantage of the large data set currently being collected during Run 3 of the CERN LHC, a new multivariate classifier based on a gradient-boosted decision tree has been developed. It offers a significantly improved separation of signal and background muons compared to a similar classifier used for the analysis of the Run 2 data. The performance of the new classifier is evaluated on a data set collected with the CMS detector in 2022 and 2023, corresponding to an integrated luminosity of 62 fb-

Search for the Higgs boson decays to a ρ0, ϕ, or K⁎0 meson and a photon in proton-proton collisions at s=13TeV

Three rare decay processes of the Higgs boson to a ρ(770)0, ϕ(1020), or K⁎(892)0 meson and a photon are searched for using s=13TeV proton-proton collision data collected by the CMS experiment at the LHC. Events are selected assuming the mesons decay into a pair of charged pions, a pair of charged kaons, or a charged kaon and pion, respectively. Depending on the Higgs boson production mode, different triggering and reconstruction techniques are adopted. The analyzed data sets correspond to integrated luminosities up to 138fb−1, depending on the reconstructed final state. After combining various data sets and categories, no significant excess above the background expectations is observed. Upper limits at 95% confidence level on the Higgs boson branching fractions into ρ(770)0γ, ϕ(1020)γ, and K⁎(892)0γ are determined to be 3.7×10−4, 3.0×10−4, and 3.0×10−4, respectively. In case of the ρ(770)0γ and ϕ(1020)γ channels, these are the most stringent experimental limits to date

Observation of nuclear modification of energy-energy correlators inside jets in heavy ion collisions

Energy-energy correlators are constructed by averaging the number of charged particle pairs within jets, weighted by the product of their transverse momenta, as a function of the angular separation of the particles within a pair. They are sensitive to a multitude of perturbative and nonperturbative quantum chromodynamics phenomena in high-energy particle collisions. Using lead-lead data recorded with the CMS detector, energy-energy correlators inside high transverse momentum jets are measured in heavy ion collisions for the first time. The data are obtained at a nucleon-nucleon center-of-mass energy of 5.02 TeV and correspond to an integrated luminosity of 1.70nb−1. A similar analysis is done for proton-proton collisions at the same center-of-mass energy to establish a reference. The ratio of lead-lead to proton-proton energy-energy correlators reveals significant jet substructure modifications in the quark-gluon plasma. The results are compared to different models that incorporate either color coherence or medium response effects, where the two effects predict similar substructure modifications

Search for Nuclear Modifications of (Formula presented) Meson Production in (Formula presented)-Pb Collisions at (Formula presented)

Nuclear medium effects on (Formula presented) meson production are studied using the binary-collision scaled cross section ratio between events of different charged-particle multiplicities from proton-lead collisions. Data, collected by the CMS experiment in 2016 at a nucleon-nucleon center-of-mass energy of (Formula presented), corresponding to an integrated luminosity of (Formula presented), were used. The scaling factors in the ratio are determined using a novel approach based on the (Formula presented) cross sections measured in the same events. The scaled ratio for (Formula presented) is consistent with unity for all event multiplicities, putting stringent constraints on nuclear modification for heavy flavor. © 2025 CERN, for the CMS Collaboration

Search for heavy neutral Higgs bosons A and H in the tt¯Z channel in proton-proton collisions at 13 TeV

A direct search for new heavy neutral Higgs bosons Image 1 and Image 2 in the Image 3 channel is presented, targeting the process Image 4 with Image 5. For the first time, the channel with decays of the Image 6 boson to muons or electrons in association with all-hadronic decays of the Image 7 system is targeted. The analysis uses proton-proton collision data collected at the CERN LHC with the CMS experiment at s=13TeV, which correspond to an integrated luminosity of 138fb−1. No signal is observed. Upper limits on the product of the cross section and branching fractions are derived for narrow resonances Image 8 and Image 9 with masses up to 2100 and 2000 GeV, respectively, assuming Image 10 boson production through gluon fusion. The results are also interpreted within two-Higgs-doublet models, where Image 11 and Image 12 are CP-odd and CP-even states, respectively, complementing and substantially extending the reach of previous searches