A search is presented for a new scalar resonance, X, decaying to a standard model Higgs boson and another new scalar particle, Y, in the final state where the Higgs boson decays to a $\mathrm{b\bar{b}}$ pair, while the Y particle decays to a pair of photons. The search is performed in the mass range 240$-$100 \GeV for the resonance X, and in the mass range 70$-$800 GeV for the particle Y, using proton-proton collision data collected by the CMS experiment at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 132 fb$^{-1}$. In general, the data are found to be compatible with the standard model expectation. Observed (expected) upper limits at 95% confidence level on the product of the production cross section and the relevant branching fraction are extracted for the X $\to$ YH process, and are found to be within the range of 0.05$-$2.69 (0.08$-$1.94) fb, depending on $m_\mathrm{X}$ and $m_\mathrm{Y}$. The most significant deviation from the background-only hypothesis is observed for X and Y masses of 300 and 77 GeV, respectively, with a local (global) significance of 3.33 (0.65) standard deviations.
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 making use of a discriminating variable that is agnostic to the signal hypothesis developed through machine learning. The analysis is based on proton-proton collision data at $\sqrt{s}$ = 13 TeV collected with the CMS detector from 2012$-$2018, corresponding to an integrated luminosity of 138 fb$^{-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.
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 \PW 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). 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).
A search for pseudoscalar or scalar bosons decaying to a top quark pair ($\mathrm{t\bar{t}}$) in final states with one or two charged leptons is presented. The analyzed proton-proton collision data was recorded at $\sqrt{s}$ = 13 TeV by the CMS experiment at the CERN LHC and corresponds to an integrated luminosity of 138 fb$^{-1}$. The invariant mass $m_\mathrm{t\bar{t}}$ of the reconstructed $\mathrm{t\bar{t}}$ system and variables sensitive to its spin and parity are used to discriminate against the standard model $\mathrm{t\bar{t}}$ background. Interference between pseudoscalar or scalar boson production and the standard model $\mathrm{t\bar{t}}$ continuum is included, leading to peak-dip structures in the $m_\mathrm{t\bar{t}}$ distribution. An excess of the data above the background prediction, based on perturbative quantum chromodynamics (QCD) calculations, is observed near the kinematic $\mathrm{t\bar{t}}$ production threshold, while good agreement is found for high $m_\mathrm{t\bar{t}}$. The data are consistent with the background prediction if the contribution from the production of a color-singlet ${}^1\mathrm{S}_0^{[1]}$$\mathrm{t\bar{t}}$ quasi-bound state $η_\mathrm{t}$, predicted by nonrelativistic QCD, is added. Upper limits at 95% confidence level are set on the coupling between the pseudoscalar or scalar bosons and the top quark for boson masses in the range 365$-$1000 GeV, relative widths between 0.5 and 25%, and two background scenarios with or without $η_\mathrm{t}$ contribution.
An analysis of the flavour structure of dimension-6 effective field theory (EFT) operators in multilepton final states is presented, focusing on the interactions involving 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$^{-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.
A reinterpretation of a prior narrow-resonance search is performed to investigate the resonant production of pairs of dijet resonances via broad mediators. This analysis targets events with four resolved jets, requiring dijet invariant masses greater than 0.2 TeV and four-jet invariant masses greater than 1.6 TeV. The search uses a data sample corresponding to an integrated luminosity of 138 fb$^{-1}$ collected by the CMS experiment in proton-proton collisions at $\sqrt{s}$ = 13 TeV. The reinterpretation considers the production of new heavy four-jet resonances, with widths ranging from 1.5 to 10% of their mass, which decay to a pair of dijet resonances. This analysis probes resonant production in the four-jet and dijet mass distributions. Upper limits at 95% confidence level and significances are reported on the production cross section of new resonances as functions of their widths and masses, between 2 and 10 TeV. In particular, at a four-jet resonance mass of 8.6 TeV, the local (global) significance ranges from 3.9 (1.6) to 3.6 (1.4) standard deviations (s.d.) as the resonance width is increased from 1.5 to 10%. This relative insensitivity to the choice of width indicates that a broad resonance is an equally valid interpretation of this excess. The broad resonance hypothesis at a resonance mass of 8.6 TeV is supported by the presence of an event with a four-jet mass of 5.8 TeV and an average dijet mass of 2.0 TeV. Also, we report the reinterpretation of a second effect, at a four-jet resonance mass of 3.6 TeV, which has a local (global) significance of up to 3.9 (2.2) s.d.
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 TeV collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. Each of the decays Z $\to$ e$μ$, Z $\to$ e$τ$, and Z $\to$$μτ$ is considered. The data are consistent with the backgrounds expected from standard model processes. For the Z $\to$ e$μ$ channel the observed (expected) 95% confidence level upper limit on the branching fraction is 1.9 (2.0) $\times$ 10$^{-7}$, which is the most stringent direct limit to date on this process; the corresponding limits for the Z $\to$ e$τ$ and Z $\to$ $μτ$ channels are 13.8 (11.4) $\times$ 10$^{-6}$ and 12.0 (5.3) $\times$ 10$^{-6}$, respectively. Additionally, the e$μ$ final state is used to search for lepton flavor violating decays of Z' resonances in the mass range from 110 to 500 GeV. No significant excess is observed above the predicted background levels.
The production of prompt charged particles in proton-lead collisions and in proton-proton collisions at the nucleon-nucleon centre-of-mass energy ${\sqrt{s_{\scriptscriptstyle\mathrm{NN}}}=5\,\mathrm{TeV}}$ is studied at LHCb as a function of pseudorapidity ($\eta$) and transverse momentum ($p_{\mathrm{T}}$) with respect to the proton beam direction. The nuclear modification factor for charged particles is determined as a function of $\eta$ between ${-4.8<\eta<-2.5}$ (backward region) and ${2.0<\eta<4.8}$ (forward region), and $p_{\mathrm{T}}$ between ${0.2<p_{\mathrm{T}}<8.0\,\mathrm{GeV}/c}$. The results show a suppression of charged particle production in proton-lead collisions relative to proton-proton collisions in the forward region and an enhancement in the backward region for $p_{\mathrm{T}}$ larger than $1.5\,\mathrm{GeV}/c$. This measurement constrains nuclear PDFs and saturation models at previously unexplored values of the parton momentum fraction down to $10^{-6}$.
The inclusive $b \bar{b}$- and $c \bar{c}$-dijet production cross-sections in the forward region of $pp$ collisions are measured using a data sample collected with the LHCb detector at a centre-of-mass energy of 13 TeV in 2016. The data sample corresponds to an integrated luminosity of 1.6 fb$^{-1}$. Differential cross-sections are measured as a function of the transverse momentum and of the pseudorapidity of the leading jet, of the rapidity difference between the jets, and of the dijet invariant mass. A fiducial region for the measurement is defined by requiring that the two jets originating from the two $b$ or $c$ quarks are emitted with transverse momentum greater than 20 GeV$/c$, pseudorapidity in the range $2.2 < \eta < 4.2$, and with a difference in the azimuthal angle between the two jets greater than 1.5. The integrated $b \bar{b}$-dijet cross-section is measured to be $53.0 \pm 9.7$ nb, and the total $c \bar{c}$-dijet cross-section is measured to be $73 \pm 16$ nb. The ratio between $c \bar{c}$- and $b \bar{b}$-dijet cross-sections is also measured and found to be $1.37 \pm 0.27$. The results are in agreement with theoretical predictions at next-to-leading order.
This article presents differential measurements of the asymmetry between $\Lambda_b^0$ and $\overline{\Lambda}_b^0$ baryon production rates in proton-proton collisions at centre-of-mass energies of $\sqrt{s}=7$ and $8\,\textrm{TeV}$ collected with the LHCb experiment, corresponding to an integrated luminosity of $3\,\textrm{fb}^{-1}$. The $\Lambda_b^0$ baryons are reconstructed through the inclusive semileptonic decay $\Lambda_b^0\rightarrow\Lambda_c^+\mu^-\overline{\nu}_{\mu}X$. The production asymmetry is measured both in intervals of rapidity in the range $2.15<y<4.10$ and transverse momentum in $2<p_T<27\,\textrm{GeV}/c$. The results are found to be incompatible with symmetric production with a significance of 5.8 standard deviations for both $\sqrt{s}=7$ and $8\,\textrm{TeV}$ data, assuming no $C\!P$ violation in the decay. There is evidence for a trend as a function of rapidity with a significance of 4 standard deviations. Comparisons to predictions from hadronisation models in PYTHIA and heavy-quark recombination are provided. This result constitutes the first observation of a particle-antiparticle asymmetry in $b$-hadron production at LHC energies.
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