Search for: All records

A<sc>bstract</sc> A search for Higgs boson (H) production at high transverse momentum (p_T) in the WW decay channel is presented. The analysis uses proton-proton collisions at$$ \sqrt{s}=13 $$ $\sqrt{s}=13$ TeV recorded by the CMS experiment in 2016–2018, corresponding to an integrated luminosity of 138 fb⁻¹. The visible decay products of the Higgs boson are reconstructed as a single large-radius jet with one isolated lepton or none (1ℓand 0ℓ, respectively;ℓ= e,μ). The H-candidate jets are identified using an advanced transformer-based algorithm and are calibrated with the Lund jet plane reweighting technique. The 1ℓchannel is further split into gluon fusion, vector boson fusion, and associated production with hadronically decaying vector boson categories, while the 0ℓchannel considers all production processes inclusively. The measured cross section times the H→WW branching fraction relative to the standard model expectation is$$ \mu =-{0.19}_{-0.46}^{+0.48} $$ $\mu =-{0.19}_{-0.46}^{+0.48}$ , indicating no evidence of a signal above the background. This measurement represents the first dedicated study of highly Lorentz-boosted H→WW decays, complementing earlier searches for high-p_THiggs boson in other decay channels. 

A search for the pair production of heavy spin- $1/2$ or spin- $3/2$ resonances ( $t^{*}$ ) in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ is presented. Data collected with the CMS detector at the CERN LHC from 2016 to 2018 corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ are used. The analysis targets benchmark signal scenarios where one $t^{*}$ decays into a top quark ( $t$ ) and a photon ( $\gamma$ ), and the other into a $t$ quark and a gluon ( $g$ ), i.e., $pp\to t^{*}\overline{t^{*}}\to tt\gamma g$ . All-hadronic final states from the $t$ pair decay chain are selected using jet substructure techniques. The signal is probed as a function of the $t^{*}$ 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- $1/2$ $t^{*}$ particles below 930 (930) GeV and spin- $3/2$ $t^{*}$ particles below 1330 (1390) GeV. This analysis marks the first search for heavy resonances in the $t\overline{t}\gamma g$ channel. Exploiting the high-energy photon to reduce the backgrounds, this search achieves sensitivity competitive with $pp\to t^{*}\overline{t^{*}}\to t\overline{t}gg$ searches for spin- $1/2$ $t^{*}$ despite the small expected $t^{*}\to t\gamma$ branching fraction. 

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 $\sqrt{s_{\mathrm{NN}}}=5.36\mathrm{TeV}$ correspond to integrated luminosities of $6.1{\mathrm{nb}}^{-1}$ and $1.02{\mathrm{pb}}^{-1}$ , respectively. The $R_{\mathrm{AA}}$ is below unity with a minimum of $0.69\pm 0.04$ around $p_{\mathrm{T}}=6\mathrm{GeV}$ . The data exhibit better agreement with theoretical models incorporating parton energy loss as compared to baseline models without energy loss. 

Abstract This paper presents a search for new physics through the process where a massive particle, X, decays into a Higgs boson and a second particle, Y. The Higgs boson subsequently decays into a bottom quark–antiquark pair, which is reconstructed as a single large-radius jet. The decay products of Yare also assumed to produce a single large-radius jet. The identification of the Yparticle is enhanced by computing the anomaly score of its candidate jet using an autoencoder, which measures deviations from typical quark- or gluon-induced jets. This allows a simultaneous search for multiple Ydecay scenarios within a single analysis. In the main benchmark process, Yis a scalar particle that decays into a Wboson pair. Two other scalar Ydecay processes are also considered as benchmarks: decays to a light quark–antiquark pair, and decays to a top quark–antiquark pair. A fourth benchmark process considers Yas a hadronically decaying top quark, arising from the decay of a vector-like quark into a top quark and a Higgs boson. Data recorded by the CMS experiment at a center-of-mass energy of 13$$\,\text {Te}\hspace{-.08em}\text {V}$$ $\text{Te}\text{V}$ in 2016–2018, corresponding to an integrated luminosity of 138$$\,\text {fb}^{-1}$$ ${\text{fb}}^{-1}$ , are analyzed. The search covers Xmasses between 1.4 and 3.0$$\,\text {Te}\hspace{-.08em}\text {V}$$ $\text{Te}\text{V}$ and Ymasses between 90 and 400$$\,\text {Ge}\hspace{-.08em}\text {V}$$ $\text{Ge}\text{V}$ , with all simulated signals produced in the narrow-width approximation. No significant excess above the standard model background expectation is observed. The most stringent upper limits to date are placed on benchmark signal cross sections for various masses of X and Y particles 

A search for flavor violating decays of the $Z$ boson to charged leptons is performed using data from proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ collected with the CMS detector at the LHC, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . Each of the decays $Z\to e\mu$ , $Z\to e\tau$ , and $Z\to \mu \tau$ is considered. The data are consistent with the backgrounds expected from standard model processes. For the $Z\to e\mu$ channel the observed (expected) 95% confidence level upper limit on the branching fraction is $1.9\left(2.0\right)\times {10}^{-7}$ , which is the most stringent direct limit to date on this process; the corresponding limits for the $Z\to e\tau$ and $Z\to \mu \tau$ channels are $13.8\left(11.4\right)\times {10}^{-6}$ and $12.0\left(5.3\right)\times {10}^{-6}$ , respectively. Additionally, the $e\mu$ final state is used to search for lepton flavor violating decays of $Z^{\prime }$ resonances in the mass range from 110 to $500\mathrm{GeV}$ . No significant excess is observed above the predicted background levels. 

A<sc>bstract</sc> Many analyses at the CERN LHC exploit the substructure of jets to identify heavy resonances produced with high momenta that decay into multiple quarks and/or gluons. This paper presents a new technique for correcting the substructure of simulated large-radius jets from multiprong decays. The technique is based on reclustering the jet constituents into several subjets such that each subjet represents a single prong, and separately correcting the radiation pattern in the Lund jet plane of each subjet using a correction derived from data. The data presented here correspond to an integrated luminosity of 138 fb⁻¹collected by the CMS experiment between 2016–2018 at a center-of-mass energy of 13 TeV. The correction procedure improves the agreement between data and simulation for several different substructure observables of multiprong jets. This technique establishes, for the first time, a robust calibration for the substructure of jets with four or more prongs, enabling future measurements and searches for new phenomena containing these signatures. 

A search for flavor-changing neutral current interactions of the top quark ( $t$ ) and the Higgs boson ( $H$ ) is presented. The search is based on proton-proton collision data collected in 2016–2018 at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, and corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . Events containing a pair of leptons with the same-sign electric charge and at least one jet are considered. The results are used to constrain the branching fraction ( $\mathcal{B}$ ) of the top quark decaying to a Higgs boson and an up ( $u$ ) or charm ( $c$ ) quark. No significant excess above the estimated background was found. The observed (expected) upper limits at a 95% confidence level are found to be 0.072% (0.059%) for $\mathcal{B}(t\to Hu)$ and 0.043% (0.062%) for $\mathcal{B}(t\to Hc)$ . These results are combined with two other searches performed by the CMS Collaboration for flavor-changing neutral current interactions of top quarks and Higgs bosons in final states where the Higgs boson decays to either a pair of photons or a pair of bottom quarks. The resulting observed (expected) upper limits at the 95% confidence level are 0.019% (0.027%) for $\mathcal{B}(t\to Hu)$ and 0.037% (0.035%) for $\mathcal{B}(t\to Hc)$ . 

A measurement is presented of the cross section in proton-proton collisions for the production of two $W$ bosons and one $Z$ boson. It is based on data recorded by the CMS experiment at the CERN LHC at center-of-mass energies $\sqrt{s}=13$ and 13.6 TeV, corresponding to an integrated luminosity of $200{\mathrm{fb}}^{-1}$ . Events with four charged leptons (electrons or muons) in the final state are selected. Both nonresonant $WWZ$ production and $ZH$ production, with the Higgs boson decaying into two $W$ bosons, are reported. For the first time, the two processes are measured separately in a simultaneous fit. Combining the two modes, signal strengths relative to the standard model (SM) predictions of ${0.75}_{-0.29}^{+0.34}$ and ${1.74}_{-0.60}^{+0.71}$ are measured for $\sqrt{s}=13$ and 13.6 TeV, respectively. The observed (expected) significance for the triboson signal is 3.8 (2.5) standard deviations for $\sqrt{s}=13.6\mathrm{TeV}$ , thus providing the first evidence for triboson production at this center-of-mass energy. Combining the two modes and the two center-of-mass energies, the inclusive signal strength relative to the SM prediction is measured to be ${1.03}_{-0.28}^{+0.31}$ , with an observed (expected) significance of 4.5 (5.0) standard deviations.