A search for the production of a top quark in association with a photon and additional jets via flavor changing neutral current interactions is presented. The analysis uses proton-proton collision data recorded by the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. The search is performed by looking for processes where a single top quark is produced in association with a photon, or a pair of top quarks where one of the top quarks decays into a photon and an up or charm quark. Events with an electron or a muon, a photon, one or more jets, and missing transverse momentum are selected. Multivariate analysis techniques are used to discriminate signal and standard model background processes. No significant deviation is observed over the predicted background. Observed (expected) upper limits are set on the branching fractions of top quark decays: $\mathcal{B}$(t $\to$ u$\gamma$) $\lt$ 0.95 $\times$ 10$^{-5}$ (1.20 $\times$ 10$^{-5}$) and $\mathcal{B}$(t $\to$ c$\gamma$) $\lt$ 1.51 $\times$ 10$^{-5}$ (1.54 $\times$ 10$^{-5}$) at 95% confidence level, assuming a single nonzero coupling at a time. The obtained limit for $\mathcal{B}$(t $\to$ u$\gamma$) is similar to the current best limit, while the limit for $\mathcal{B}$(t $\to$ c$\gamma$) is significantly tighter than previous results.
Expected and observed 95\% CL upper limits on the branching fraction as well as FCNC couplings of the top quark decaying to the photon and a light-flavor quark (either an up or a charm quark)
The observation of forward proton scattering in association with lepton pairs ($e^+e^-+p$ or $\mu^+\mu^-+p$) produced via photon fusion is presented. The scattered proton is detected by the ATLAS Forward Proton spectrometer while the leptons are reconstructed by the central ATLAS detector. Proton-proton collision data recorded in 2017 at a center-of-mass energy of $\sqrt{s} = 13$ TeV are analyzed, corresponding to an integrated luminosity of 14.6 fb$^{-1}$. A total of 57 (123) candidates in the $ee+p$ ($\mu\mu+p$) final state are selected, allowing the background-only hypothesis to be rejected with a significance exceeding five standard deviations in each channel. Proton-tagging techniques are introduced for cross-section measurements in the fiducial detector acceptance, corresponding to $\sigma_{ee+p}$ = 11.0 $\pm$ 2.6 (stat.) $\pm$ 1.2 (syst.) $\pm$ 0.3 (lumi.) fb and $\sigma_{\mu\mu+p}$ = 7.2 $\pm$ 1.6 (stat.) $\pm$ 0.9 (syst.) $\pm$ 0.2 (lumi.) fb in the dielectron and dimuon channel, respectively.
The measured fiducial cross sections. The first systematic uncertainty is the combined systematic uncertainty excluding luminosity, the second is the luminosity
A search is reported for heavy resonances and quantum black holes decaying into e$\mu$, e$\tau$, and $\mu\tau$ final states in proton-proton collision data recorded by the CMS experiment at the CERN LHC during 2016-2018 at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. The e$\mu$, e$\tau$, and $\mu\tau$ invariant mass spectra are reconstructed, and no evidence is found for physics beyond the standard model. Upper limits are set at 95% confidence level on the product of the cross section and branching fraction for lepton flavor violating signals. Three benchmark signals are studied: resonant $\tau$ sneutrino production in $R$ parity violating supersymmetric models, heavy Z' gauge bosons with lepton flavor violating decays, and nonresonant quantum black hole production in models with extra spatial dimensions. Resonant $\tau$ sneutrinos are excluded for masses up to 4.2 TeV in the e$\mu$ channel, 3.7 TeV in the e$\tau$ channel, and 3.6 TeV in the $\mu\tau$ channel. A Z' boson with lepton flavor violating couplings is excluded up to a mass of 5.0 TeV in the e$\mu$ channel, up to 4.3 TeV in the e$\tau$ channel, and up to 4.1 TeV in the $\mu\tau$ channel. Quantum black holes in the benchmark model are excluded up to the threshold mass of 5.6 TeV in the e$\mu$ channel, 5.2 TeV in the e$\tau$ channel, and 5.0 TeV in the $\mu\tau$ channel. In addition, model-independent limits are extracted to allow comparisons with other models for the same final states and similar event selection requirements. The results of these searches provide the most stringent limits available from collider experiments for heavy particles that undergo lepton flavor violating decays.
Mass distributions for the e$\mu$ channel. In addition to the observed data (black points) and SM prediction (filled histograms), expected signal distributions for three models are shown: the RPV SUSY model with $\lambda = \lambda' = 0.01$ and $\tau$ sneutrino mass of 1.6 TeV, a Z′ boson ($\mathcal{B}=0.1$) with a mass of 1.6 TeV , and the QBH signal expectation for $n=4$ and a threshold mass of 1.6 TeV. The bin width gradually increases with mass.
Mass distributions for the e$\tau$ channel. In addition to the observed data (black points) and SM prediction (filled histograms), expected signal distributions for three models are shown: the RPV SUSY model with $\lambda = \lambda' = 0.01$ and $\tau$ sneutrino mass of 1.6 TeV, a Z′ boson ($\mathcal{B}=0.1$) with a mass of 1.6 TeV , and the QBH signal expectation for $n=4$ and a threshold mass of 1.6 TeV. The bin width gradually increases with mass.
Mass distributions for the $\mu\tau$ channel. In addition to the observed data (black points) and SM prediction (filled histograms), expected signal distributions for three models are shown: the RPV SUSY model with $\lambda = \lambda' = 0.01$ and $\tau$ sneutrino mass of 1.6 TeV, a Z′ boson ($\mathcal{B}=0.1$) with a mass of 1.6 TeV , and the QBH signal expectation for $n=4$ and a threshold mass of 1.6 TeV. The bin width gradually increases with mass.
A search for the central exclusive production of top quark-antiquark pairs ($\mathrm{t\bar{t}}$) is performed for the first time using proton-tagged events in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 29.4 fb$^{-1}$. The $\mathrm{t\bar{t}}$ decay products are reconstructed using the central CMS detector, while forward protons are measured in the CMS-TOTEM precision proton spectrometer. An observed (expected) upper bound on the production cross section of 0.59 (1.14) pb is set at 95% confidence level, for collisions of protons with fractional momentum losses between 2 and 20%.
Expected and observed 95% confidence level (CL) upper limits for the cross section of $\mathrm{pp} \rightarrow \mathrm{p t \bar{t} p}$, for the dilepton and $\ell+$jets channels separately and combined. The green and yellow bands show the 68 and 95% intervals, respectively, for the expected upper limit.
A search is reported for high-mass hadronic resonances that decay to a parton and a Lorentz-boosted resonance, which in turn decays into a pair of partons. The search is based on data collected with the CMS detector at the LHC in proton-proton collisions at $\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. The boosted resonance is reconstructed as a single wide jet with substructure consistent with a two-body decay. The high-mass resonance is thus considered as a dijet system. The jet substructure information and the kinematic properties of cascade resonance decays are exploited to disentangle the signal from the large quantum chromodynamics multijet background. The dijet mass spectrum is analyzed for the presence of new high-mass resonances, and is found to be consistent with the standard model background predictions. Results are interpreted in a warped extra dimension model where the high-mass resonance is a Kaluza-Klein gluon, the boosted resonance is a radion, and the final state partons are all gluons. Limits on the production cross section are set as a function of the Kaluza-Klein gluon and radion masses. These limits exclude at 95% confidence level models with Kaluza-Klein gluon masses in the range from 2.0 to 4.3 TeV and radion masses in the range from 0.20 to 0.74 TeV. By exploring a novel experimental signature, the observed limits on the Kaluza-Klein gluon mass are extended by up to about 1 TeV compared to previous searches.
Observed upper limits on the product of signal cross section and branching fraction, as a function of the mass ratio $m(\mathrm{R}_{2}) / m(\mathrm{R}_{1})$ vs. $m(\mathrm{R}_{1})$, for a resonance model with three gluons in the final state. The excluded regions from this search (black hatched) are optimized for the decay of a Kaluza--Klein gluon ($\mathrm{G}_{\mathrm{KK}}$) to a gluon ($\mathrm{g}$) and a radion ($\phi$), which in turns decays to two gluons, leading to a final state with three gluons ($\mathrm{ggg}$). The couplings of the model are set to the values $g_{\mathrm{grav}} = 6.0$ and $g_{\mathrm{GKK}} = 3.0$. These excluded regions are compared with those obtained from a reinterpretation of the inclusive CMS dijet resonance search (JHEP 05 (2020) 033), which is more sensitive to the decay channel of $\mathrm{G}_{\mathrm{KK}}$ to a quark-antiquark pair (red hatched). The vertical band between the $m(\mathrm{R}_{1})$ values of $\sim$3.0 and $\sim$3.1 TeV, for $m(\mathrm{R}_{2}) / m(\mathrm{R}_{1}) \lesssim 0.19$, is not excluded by the dijet search because of an upward statistical fluctuation in the observed limit. The white, dashed lines represent a sample of curves corresponding to fixed $m(\mathrm{R}_{2})$ values.
Observed upper limits on the product of signal cross section and branching fraction, as a function of the mass ratio $m(\mathrm{R}_{2}) / m(\mathrm{R}_{1})$ vs. $m(\mathrm{R}_{1})$, for a resonance model with three gluons in the final state. The excluded regions from this search (black hatched) are optimized for the decay of a Kaluza--Klein gluon ($\mathrm{G}_{\mathrm{KK}}$) to a gluon ($\mathrm{g}$) and a radion ($\phi$), which in turns decays to two gluons, leading to a final state with three gluons ($\mathrm{ggg}$). The couplings of the model are set to the values $g_{\mathrm{grav}} = 6.0$ and $g_{\mathrm{GKK}} = 3.0$. These excluded regions are compared with those obtained from a reinterpretation of the inclusive CMS dijet resonance search (JHEP 05 (2020) 033), which is more sensitive to the decay channel of $\mathrm{G}_{\mathrm{KK}}$ to a quark-antiquark pair (red hatched). The vertical band between the $m(\mathrm{R}_{1})$ values of $\sim$3.0 and $\sim$3.1 TeV, for $m(\mathrm{R}_{2}) / m(\mathrm{R}_{1}) \lesssim 0.19$, is not excluded by the dijet search because of an upward statistical fluctuation in the observed limit. The white, dashed lines represent a sample of curves corresponding to fixed $m(\mathrm{R}_{2})$ values.
Expected 95% CL upper limits on signal cross section times branching fraction, as a function of the ratio $m(\mathrm{R}_{2})/m(\mathrm{R}_{1})$ vs. $m(\mathrm{R}_{1})$, for a trijet resonance model with 3 gluons in the final state. The limits are optimized for the decay of a Kaluza-Klein gluon ($\mathrm{G}_{\mathrm{KK}}$) to a radion ($\phi$) and a gluon ($\mathrm{g}$) where the radion itself decays to 2 gluons, leading to a final state with 3 gluons ($\mathrm{ggg}$).
The production of J/$\psi$ is measured as a function of charged-particle multiplicity at forward rapidity in proton$-$proton (pp) collisions at center-of-mass energies $\sqrt{s} =$ 5.02 and 13 TeV. The J/$\psi$ mesons are reconstructed via their decay into dimuons in the rapidity interval (2.5 $< y <$ 4.0), whereas the charged-particle multiplicity density (${\rm d}N_{\rm{ch}}/{\rm d}\eta$) is measured at midrapidity $(|\eta| < 1)$. The production rate as a function of multiplicity is reported as the ratio of the yield in a given multiplicity interval to the multiplicity-integrated one. This observable shows a linear increase with charged-particle multiplicity normalized to the corresponding average value for inelastic events (${{\rm d}N_{\rm ch}/{\rm d}\eta}/{\langle {\rm d}N_{\rm ch}/{\rm d}\eta \rangle}$), at both the colliding energies. Measurements are compared with available ALICE results at midrapidity and theoretical model calculations. First measurement of the mean transverse momentum ($\langle p_{\mathrm{T}}\rangle$) of J/$\psi$ in pp collisions exhibits an increasing trend as a function of ${{\rm d}N_{\rm ch}/{\rm d}\eta}/{\langle {\rm d}N_{\rm ch}/{\rm d}\eta \rangle}$ showing a saturation towards high charged-particle multiplicities.
Results are presented from a search for the Higgs boson decay H $\to$ Z$\gamma$, where Z $\to$$\ell^+\ell^-$ with $\ell$ = e or $\mu$. The search is performed using a sample of proton-proton (pp) collision data at a center-of-mass energy of 13 TeV, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. Events are assigned to mutually exclusive categories, which exploit differences in both event topology and kinematics of distinct Higgs production mechanisms to enhance signal sensitivity. The signal strength $\mu$, defined as the product of the cross section and the branching fraction [$\sigma($pp $\to$ H$)\mathcal{B}($H $\to$ Z$\gamma)$] relative to the standard model prediction, is extracted from a simultaneous fit to the $\ell^+\ell^-\gamma$ invariant mass distributions in all categories and is found to be $\mu$ = 2.4 $\pm$ 0.9 for a Higgs boson mass of 125.38 GeV. The statistical significance of the observed excess of events is 2.7 standard deviations. This measurement corresponds to $\sigma($pp $\to$ H$)\mathcal{B}($H $\to$ Z$\gamma)$ = 0.21 $\pm$ 0.08 pb. The observed (expected) upper limit at 95% confidence level on $\mu$ is 4.1 (1.8). The ratio of branching fractions $\mathcal{B}($H $\to$ Z$\gamma) / \mathcal{B}($H $\to$ $\gamma\gamma)$ is measured to be 1.5 $^{+0.7}_{-0.6}$, which agrees with the standard model prediction of 0.69 $\pm$ 0.04 at the 1.5 standard deviation level.
The $\mathcal{D}_{\mathrm{VBF}}$ distributions for signal, simulated background, and data. The $\mathcal{D}_{\mathrm{VBF}}$ distribution includes only dijet-tagged events. The sum of contributions from all signal production mechanisms is shown by the blue line, while the contribution from only the VBF mechanism is shown by the red line. The uncertainty band incorporates all statistical and systematic uncertainties in the expected background. The dashed lines indicate the boundaries for dijet-tagged categories.
The $\mathcal{D}_{\mathrm{kin}}$ distributions for signal, simulated background, and data. The $\mathcal{D}_{\mathrm{kin}}$ distribution includes only untagged events. The sum of contributions from all signal production mechanisms is shown by the blue line. The uncertainty band incorporates all statistical and systematic uncertainties in the expected background. The dashed lines indicate the boundaries for untagged categories. The gray shaded region in the $\mathcal{D}_{\mathrm{kin}}$ distribution is excluded from the analysis.
Fits to the $m_{\ell^+\ell^-\gamma}$ data distribution in the lepton-tagged categories. In the upper panel, the red solid line shows the result of a signal-plus-background fit to the given category. The red dashed line shows the background component of the fit. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit. Also plotted is the expected SM signal, scaled by a factor of 10. In the lower panel, the data minus the background component of the fit is shown.
A search for an extended Higgs sector, characterized by a massive resonance X decaying to a pair of spin-0 bosons $\phi$ that themselves decay to pairs of bottom quarks, is presented. The analysis is restricted to the mass ranges $m_\phi$ from 25 to 100 GeV and $m_\mathrm{X}$ from 1 to 3 TeV. For these mass ranges, the decay products of each $\phi$ boson are expected to merge into a single large-radius jet. Jet substructure and flavor identification techniques are used to identify these jets. The search is based on CERN LHC proton-proton collision data at $\sqrt{s} =$ 13 TeV, collected with the CMS detector in 2016-2018, corresponding to an integrated luminosity of 138 fb$^{-1}$. Model-specific limits are set on the product of the production cross section and branching fraction for X $\to$$\phi\phi$$\to$$(\mathrm{b\bar{b}})(\mathrm{b\bar{b}})$ as a function of mass, where both the X $\to$$\phi\phi$ and $\phi$$\to$$\mathrm{b\bar{b}}$ branching fractions are assumed to be 100%. These limits are the first of their kind on this process, ranging between 30 and 1 fb at 95% confidence level for the considered mass ranges.
The observed 95% CL upper limits on the product of the cross section, and branching fraction for the production of X$\to\phi\phi\to$4b, with $m_\phi$ = 25 GeV. The corresponding expected limits and their variations at the 1 and 2 standard deviation levels are also shown. Limits are compared to various extended higgs sector model cross sections as a function of the parameter $m_XN/f$.
The observed 95% CL upper limits on the product of the cross section, and branching fraction for the production of X$\to\phi\phi\to$4b, with $m_\phi$ = 30 GeV. The corresponding expected limits and their variations at the 1 and 2 standard deviation levels are also shown. Limits are compared to various extended higgs sector model cross sections as a function of the parameter $m_XN/f$.
The observed 95% CL upper limits on the product of the cross section, and branching fraction for the production of X$\to\phi\phi\to$4b, with $m_\phi$ = 35 GeV. The corresponding expected limits and their variations at the 1 and 2 standard deviation levels are also shown. Limits are compared to various extended higgs sector model cross sections as a function of the parameter $m_XN/f$.
The first results on K$^{*}$(892)$^{\mathrm{\pm}}$ resonance production in inelastic pp collisions at LHC energies of $\sqrt{s} = 5.02$, 8, and 13 TeV are presented. The K$^{*}$(892)$^{\mathrm{\pm}}$ has been reconstructed via its hadronic decay channel K$^{*}$(892)$^{\mathrm{\pm}}$$\rightarrow$$\mathrm {K^0_S}$$~+~\pi^{\pm}$ with the ALICE detector. Measurements of transverse momentum distributions, $p_{\mathrm{T}}$-integrated yields, and mean transverse momenta for charged K$^{*}$(892) are found to be consistent with previous ALICE measurements for neutral K$^{*}$(892) within uncertainties. For $p_{\mathrm{T}} > 1$ GeV/$c$ the K$^{*}$(892)$^{\mathrm{\pm}}$ transverse momentum spectra become harder with increasing centre-of-mass energy from 5.02 to 13 TeV, similar to what previously observed for charged kaons and pions. For $p_{\mathrm{T}} < 1$ GeV/$c$ the K$^{*}$(892)$^{\mathrm{\pm}}$ yield does not evolve significantly and the abundance of K$^{*}$(892)$^{\mathrm{\pm}}$ relative to K is rather independent of the collision energy. The transverse momentum spectra, measured for K$^{*}$(892)$^{\mathrm{\pm}}$ at midrapidity in the interval $0 < p_{\mathrm{T}} < 15$ GeV/$c$, are not well described by predictions of different versions of PYTHIA 6, PYTHIA 8 and EPOS-LHC event generators. These generators reproduce the measured $p_{\mathrm{T}}$-integrated K$^{*\mathrm{\pm}}$/K ratios and describe well the momentum dependence for $p_{\mathrm{T}} < 2$ GeV/$c$.
The p$_{T}$ distribution of K*(892)$^{\pm}$ in inelastic pp collisions at $\sqrt{s} = 13$ TeV. The data were collected in 2015 with an integrated luminosity of 0.92 nb$^{-1}$.
The p$_{T}$ distribution of K*(892)$^{\pm}$ in inelastic pp collisions at $\sqrt{s} = 8$ TeV. The data were collected in 2012 with an integrated luminosity of 1.25 nb$^{-1}$.
The p$_{T}$ distribution of K*(892)$^{\pm}$ in inelastic pp collisions at $\sqrt{s} = 5$ TeV. The data were collected in 2015 with an integrated luminosity of 2.12 nb$^{-1}$.
Two-particle azimuthal correlations are measured with the ALICE apparatus in pp collisions at $\sqrt{s} = 13$ TeV to explore strangeness- and multiplicity-related effects in the fragmentation of jets and the transition regime between bulk and hard production, probed with the condition that a strange meson (K$^{0}_{\rm S}$) or baryon ($\Lambda$) with transverse momentum $p_{\rm T} > 3$ GeV/c is produced. Azimuthal correlations between kaons or $\Lambda$ hyperons with other hadrons are presented at midrapidity for a broad range of the trigger ($3 < p_{\rm T}^{\rm trigg} < 20$ GeV/$c$) and associated particle $p_{\rm T}$ (1 GeV/$c$$< p_{\rm T}^{\rm assoc} < p_{\rm T}^{\rm trigg}$), for minimum-bias events and as a function of the event multiplicity. The near- and away-side peak yields are compared for the case of either K$^{0}_{\rm S}$ or $\Lambda$($\overline{\Lambda}$) being the trigger particle with that of inclusive hadrons (a sample dominated by pions). In addition, the measurements are compared with predictions from PYTHIA 8 and EPOS LHC event generators.
$\Delta\varphi$ projection of ($\Lambda+\overline{\Lambda}$)-h correlation function with $3<p_{\mathrm{T}}^{\mathrm{trigg}}< 4 \mathrm{GeV}/c$ and $1 \mathrm{GeV}/c<p_{\mathrm{T}}^{\mathrm{assoc}}< p_{\mathrm{T}}^{\mathrm{trigg}} $
$\Delta\varphi$ projection of ($\Lambda+\overline{\Lambda}$)-h correlation function with $3<p_{\mathrm{T}}^{\mathrm{trigg}}< 4 \mathrm{GeV}/c$ and $1 \mathrm{GeV}/c<p_{\mathrm{T}}^{\mathrm{assoc}}< p_{\mathrm{T}}^{\mathrm{trigg}} $
Forum