A search for the rare $\eta$$\to$$\mu^+\mu^-\mu^+\mu^-$ double-Dalitz decay is performed using a sample of proton-proton collisions, collected by the CMS experiment at the CERN LHC with high-rate muon triggers in 2017-2018 and corresponding to an integrated luminosity of 101 fb$^{-1}$. A signal having a statistical significance well in excess of 5 standard deviations is observed. Using the $\eta$$\to$$\mu^+ \mu^-$ decay as normalization, the branching fraction $\mathcal{B}(\eta$$\to$$\mu^+\mu^-\mu^+\mu^-)$ = [5.0 $\pm$ 0.8 (stat) $\pm$ 0.7 (syst) $\pm$ 0.7 ($\mathcal{B}_{2\mu}$)] $\times$ 10$^{-9}$ is measured, where the last term is the uncertainty in the normalization channel branching fraction. This work achieves an improved precision of over five orders of magnitude compared to previous results, leading to the first measurement of this branching fraction, which is found to agree with theoretical predictions.
The total efficiencies for the four-muon ($A_{4\mu}^{i,j}$, red and blue points) and two-muon ($A_{2\mu}^{i,j}$, orange and green points) decay channels, as functions of the generated meson's $p_{\mathrm{T}}$ and $y$, evaluated through MC simulation.
Measured ratio of $\mathcal{B}_{4\mu}/\mathcal{B}_{2\mu}$
Measured branching fraction $\mathcal{B}_{4\mu}$
The production of $\Upsilon$(2S) and $\Upsilon$(3S) mesons in lead-lead (PbPb) and proton-proton (pp) collisions is studied in their dimuon decay channel using the CMS detector at the LHC. The $\Upsilon$(3S) meson is observed for the first time in PbPb collisions, with a significance above five standard deviations. The ratios of yields measured in PbPb and pp collisions are reported for both the $\Upsilon$(2S) and $\Upsilon$(3S) mesons, as functions of transverse momentum and PbPb collision centrality. These ratios, when appropriately scaled, are significantly less than unity, indicating a suppression of $\Upsilon$ yields in PbPb collisions. This suppression increases from peripheral to central PbPb collisions. Furthermore, the suppression is stronger for $\Upsilon$(3S) mesons compared to $\Upsilon$(2S) mesons, extending the pattern of sequential suppression of quarkonium states in nuclear collisions previously seen for the $\psi$/J, $\psi$(2S), $\Upsilon$(1S), and $\Upsilon$(2S) mesons.
Measured $R_\text{AA}$ for the $\Upsilon(2S)$ state as functions of PbPb collision centrality, integrated over the full kinematic range $p_\text{T}$ < 30 GeV/c and |y| < 2.4. The global uncertainty "PP MB" represents the pp luminosity and PbPb $N_\text{MB}$ combined uncertainties, whereas the global uncertainty "PP 2S" corresponds to the uncertainty on the $\Upsilon(2S)$ pp yields.
Measured $R_\text{AA}$ for the $\Upsilon(2S)$ state as functions of PbPb collision centrality, integrated over the full kinematic range $p_\text{T}$ < 30 GeV/c and |y| < 2.4. The global uncertainty "PP MB" represents the pp luminosity and PbPb $N_\text{MB}$ combined uncertainties, whereas the global uncertainty "PP 2S" corresponds to the uncertainty on the $\Upsilon(2S)$ pp yields.
Measured $R_\text{AA}$ for the $\Upsilon(3S)$ state as functions of PbPb collision centrality, integrated over the full kinematic range $p_\text{T}$ < 30 GeV/c and |y| < 2.4. The global uncertainty "PP MB" represents the pp luminosity and PbPb $N_\text{MB}$ combined uncertainties, whereas the global uncertainty "PP 3S" corresponds to the uncertainty on the $\Upsilon(3S)$ pp yields.
Quasireal photons exchanged in relativistic heavy ion interactions are powerful probes of the gluonic structure of nuclei. The coherent J/$\psi$ photoproduction cross section in ultraperipheral lead-lead collisions is measured as a function of photon-nucleus center-of-mass energies per nucleon (W$^\text{Pb}_{\gamma\text{N}}$), over a wide range of 40 $\lt$ W$^\text{Pb}_{\gamma\text{N}}$$\lt$ 400 GeV. Results are obtained using data at the nucleon-nucleon center-of-mass energy of 5.02 TeV collected by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 1.52 nb$^{-1}$. The cross section is observed to rise rapidly at low W$^\text{Pb}_{\gamma\text{N}}$, and plateau above W$^\text{Pb}_{\gamma\text{N}}$$\approx$ 40 GeV, up to 400 GeV, a new regime of small Bjorken-$x$ ($\approx$ 6 $\times$ 10$^{-5}$) gluons being probed in a heavy nucleus. The observed energy dependence is not predicted by current quantum chromodynamic models.
The differential coherent $\mathrm{J}/\psi$ photoproduction cross section as a function of rapidity, in different neutron multiplicity classes: 0n0n, 0nXn, XnXn , and AnAn.
The differential coherent $\mathrm{J}/\psi$ photoproduction cross section as a function of rapidity, in different neutron multiplicity classes: 0n0n, 0nXn, XnXn , and AnAn.
The total coherent $\mathrm{J}/\psi$ photoproduction cross section as a function of photon-nuclear center-of-mass energy per nucleon $W_{\gamma \mathrm{N}}^{\mathrm{Pb}}$, measured in PbPb ultra-peripheral collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. The $W_{\gamma \mathrm{N}}^{\mathrm{Pb}}$ values used correspond to the center of each rapidity range. The theoretical uncertainties is due to the uncertainties in the photon flux.
PHENIX presents a simultaneous measurement of the production of direct $\gamma$ and $\pi^0$ in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV over a $p_T$ range of 7.5 to 18 GeV/$c$ for different event samples selected by event activity, i.e. charged-particle multiplicity detected at forward rapidity. Direct-photon yields are used to empirically estimate the contribution of hard-scattering processes in the different event samples. Using this estimate, the average nuclear-modification factor $R_{d\rm Au,EXP}^{\gamma^{\rm dir}}$ is $0.925{\pm}0.023({\rm stat}){\pm}0.15^{\rm (scale)}$, consistent with unity for minimum-bias (MB) $d$$+$Au events. For event classes with moderate event activity, $R_{d\rm Au,EXP}^{\gamma^{\rm dir}}$ is consistent with the MB value within 5% uncertainty. These results confirm that the previously observed enhancement of high-$p_T$$\pi^0$ production found in small-system collisions with low event activity is a result of a bias in interpreting event activity within the Glauber framework. In contrast, for the top 5% of events with the highest event activity, $R_{d\rm Au,EXP}^{\gamma^{\rm dir}}$ is suppressed by 20% relative to the MB value with a significance of $4.5\sigma$, which may be due to final-state effects.
The $p_{T}$ distribution at high $p_{T}$ of neutral pions (panel (a)) for different d+Au event activity classes compared to those from p+p collisions (Phys. Rev. C 105, 064902).
The $p_{T}$ distribution at high $p_{T}$ of direct photons (panel (b)) for different d+Au event activity classes compared to those from p+p collisions (Phys. Rev. D 86, 072008).
Panel (c) shows the ratio $\gamma^{dir}/\pi^{0}$. For better visibility the points are slightly shifted in $p_{T}$ .
The first measurement of the top quark pair ($\mathrm{t\bar{t}}$) production cross section in proton-proton collisions at $\sqrt{s}$ = 13.6 TeV is presented. Data recorded with the CMS detector at the CERN LHC in Summer 2022, corresponding to an integrated luminosity of 1.21 fb$^{-1}$, are analyzed. Events are selected with one or two charged leptons (electrons or muons) and additional jets. A maximum likelihood fit is performed in event categories defined by the number and flavors of the leptons, the number of jets, and the number of jets identified as originating from b quarks. An inclusive $\mathrm{t\bar{t}}$ production cross section of 881 $\pm$ 23 (stat+syst) $\pm$ 20 (lumi) pb is measured, in agreement with the standard model prediction of 924 $^{+32}_{-40}$ pb.
Comparison of the number of observed (points) and predicted (filled histograms) events in the final analysis binning. The predictions are shown before fitting the model to the data. The lower panel of the plot displays the ratio of the event yields in data to the sum of predicted signal and background yields. The vertical bars on the points represent the statistical uncertainties in the data, while the hatched bands represent systematic uncertainty in the predictions, excluding the integrated luminosity. No b jet efficiency scale factors are applied in the plot, and no systematic uncertainty entering into the hatched bands is intended to cover thesefactors, which are free parameters in the fit.
Comparison of the number of observed (points) and predicted (filled histograms) events in the final analysis binning. The predictions are shown after fitting the model to the data. The lower panel of each plot displays the ratio of the event yields in data to the sum of predicted signal and background yields. The vertical bars on the points represent the statistical uncertainties in the data, while the hatched bands represent systematic uncertainty in the predictions, excluding the integrated luminosity. The hatched bands are greatly reduced due to additional constraint of the nuisances parameters as well as correlations between them.
Result for the inclusive ttbar production cross section
Presented are the first measurements of the transverse single-spin asymmetries ($A_N$) for neutral pions and eta mesons in $p$+Au and $p$+Al collisions at $\sqrt{s_{_{NN}}}=200$ GeV in the pseudorapidity range $|\eta|<$0.35 with the PHENIX detector at the Relativistic Heavy Ion Collider. The asymmetries are consistent with zero, similar to those for midrapidity neutral pions and eta mesons produced in $p$+$p$ collisions. These measurements show no evidence of additional effects that could potentially arise from the more complex partonic environment present in proton-nucleus collisions.
Data from Figure 2 (a) of the $\pi^{0}$ transverse single-spin asymmetry in $\sqrt{s_{NN}}=200$ GeV $p^{\uparrow}+$Au and $p^{\uparrow}+$Al collisions as a function of $p_{T}$.
Data from Figure 2 (b) of the $\eta$ transverse single-spin asymmetry in $\sqrt{s_{NN}}=200$ GeV $p^{\uparrow}+$Au and $p^{\uparrow}+$Al collisions as a function of $p_{T}$.
A generic search is presented for the associated production of a Z boson or a photon with an additional unspecified massive particle X, pp $\to$ pp + Z/$\gamma$ + X, in proton-tagged events from proton-proton collisions at $\sqrt{s}$ = 13 TeV, recorded in 2017 with the CMS detector and the CMS-TOTEM precision proton spectrometer. The missing mass spectrum is analysed in the 600-1600 GeV range and a fit is performed to search for possible deviations from the background expectation. No significant excess in data with respect to the background predictions has been observed. Model-independent upper limits on the visible production cross section of pp $\to$ pp + Z/$\gamma$ + X are set.
Comparison of the $m_{miss}$ shapes for the simulated signal events within the fiducial region and those outside it, after including the effect of PU protons as describe in the text, for a generated $m_{X}$ mass of 1000 GeV. The distributions are shown for multi(+z)-multi(−z) proton reconstruction categories.
Comparison of the $m_{miss}$ shapes for the simulated signal events within the fiducial region and those outside it, after including the effect of PU protons as describe in the text, for a generated $m_{X}$ mass of 1000 GeV. The distributions are shown for multi(+z)-single(−z) proton reconstruction categories.
Comparison of the $m_{miss}$ shapes for the simulated signal events within the fiducial region and those outside it, after including the effect of PU protons as describe in the text, for a generated $m_{X}$ mass of 1000 GeV. The distributions are shown for single(+z)-multi(−z) proton reconstruction categories.
The production of four top quarks ($\mathrm{t\bar{t}t\bar{t}}$) is studied with LHC proton-proton collision data samples collected by the CMS experiment at a center-of-mass energy of 13 TeV, and corresponding to integrated luminosities of up to 138 fb$^{-1}$. Events that have no leptons (all-hadronic), one lepton, or two opposite-sign leptons (where lepton refers only to prompt electrons or prompt muons) are considered. This is the first $\mathrm{t\bar{t}t\bar{t}}$ measurement that includes the all-hadronic final state. The observed significance of the $\mathrm{t\bar{t}t\bar{t}}$ signal in these final states of 3.9 standard deviations (1.5 expected) provides evidence for $\mathrm{t\bar{t}t\bar{t}}$ production, with a measured cross section of 36 $^{+12}_{-11}$ fb. Combined with earlier CMS results in other final states, the signal significance is 4.0 standard deviations (3.2 expected). The combination returns an observed cross section of 17 $\pm$ 4 (stat) $\pm$ 3 (syst) fb, which is consistent with the standard model prediction.
The jet multiplicity for $N_\textrm{b} \geq 4$ in the opposite-sign dilepton channel for the combined 2017--2018 dataset with dilepton decay categories combined. Here, $\textrm{t}\bar{\textrm{t}} + \geq 1 \textrm{b}$ refers to $\textrm{t}\bar{\textrm{t}}$ events with at least one additional b jet, $\textrm{t}\bar{\textrm{t}} + 0 \textrm{b}$ includes all other $\textrm{t}\bar{\textrm{t}}$ events not produced in association with a boson, and EW refers to events that contain W and Z bosons but no top quarks. The backgrounds and $\textrm{t}\bar{\textrm{t}}\textrm{t}\bar{\textrm{t}}$ signal (derived from the fit) are shown as a stacked histogram. The hatched bands correspond to the estimated total uncertainty after the fit.
The distribution of the BDT discriminants for the 2016--2018 data set for three different categories in the combined single-electron and single-muon channels. The three categories are defined by the number of resolved t tags ($N_\textrm{RT}$), b tags ($N_\textrm{b}$), and jets ($N_\textrm{j}$), selected as representative based on their sensitivity to signal. Here, $\textrm{t}\bar{\textrm{t}} + \geq 1 \textrm{b}$ refers to $\textrm{t}\bar{\textrm{t}}$ events with at least one additional b jet, while $\textrm{t}\bar{\textrm{t}} + 0 \textrm{b}$ includes all other $\textrm{t}\bar{\textrm{t}}$ events not produced in association with a boson. The TOP grouping contains single top quark production along with the other $\textrm{t}\bar{\textrm{t}}$ processes not explicitly shown, and EW refers to events that contain W and Z bosons but no top quarks. The backgrounds and $\textrm{t}\bar{\textrm{t}}\textrm{t}\bar{\textrm{t}}$ signal (derived from the fit) are shown as a stacked histogram. The hatched bands correspond to the estimated total uncertainty after the fit. While the bins are shown to be equal width, they do not correspond to equal width in BDT value.
The distribution of the BDT discriminants for the full 2016--2018 data set in the all-hadronic channel. The sample VR category shown is defined by $N_\textrm{RT}=1$, $N_\textrm{BT} \geq 1$, $H_T > 1400$ GeV. The background from QCD multijet and $\textrm{t}\bar{\textrm{t}}$ production is derived from control regions in the data. Estimates for the $\textrm{t}\bar{\textrm{t}}\textrm{t}\bar{\textrm{t}}$ signal and other backgrounds are shown using simulated samples. The hatched bands correspond to the estimated total uncertainty.
A search for decays to invisible particles of Higgs bosons produced in association with a top-antitop quark pair or a vector boson, which both decay to a fully hadronic final state, has been performed using proton-proton collision data collected at $\sqrt{s}$ = 13 TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. The 95% confidence level upper limit set on the branching fraction of the 125 GeV Higgs boson to invisible particles, $\mathcal{B}$(H $\to$ inv), is 0.54 (0.39 expected), assuming standard model production cross sections. The results of this analysis are combined with previous $\mathcal{B}$(H $\to$ inv) searches carried out at $\sqrt{s}$ = 7, 8, and 13 TeV in complementary production modes. The combined upper limit at 95% confidence level on $\mathcal{B}$(H $\to$ inv) is 0.15 (0.08 expected).
Observed and expected 95% CL upper limits on ${{(\sigma_{\text{H}}/\sigma_{\text{H}}^{\mathrm{SM}}) \times {{\mathcal{B}(\text{H} \to \text{inv})}}}}$ for hadronic final states of ttH and resolved VH channels, and their combination, using data from 2016--2018 and assuming a SM Higgs boson with a mass of 125 GeV.
Observed and expected 95% CL upper limits on ${{(\sigma_{\text{H}}/\sigma_{\text{H}}^{\mathrm{SM}}) \times {{\mathcal{B}(\text{H} \to \text{inv})}}}}$ for the VBF, ttH, VH and ggH channels using all available CMS data, and their combination, assuming a SM Higgs boson with a mass of 125 GeV.
Observed and expected 95% CL upper limits on ${{(\sigma_{\text{H}}/\sigma_{\text{H}}^{\mathrm{SM}}) \times {{\mathcal{B}(\text{H} \to \text{inv})}}}}$ for the VBF, ttH, VH and ggH channels using Run2 CMS data, and their combination, assuming a SM Higgs boson with a mass of 125 GeV.
A search for the electroweak production of a vector-like quark T$'$, decaying to a top quark and a Higgs boson is presented. The search is based on a sample of proton-proton collision events recorded at the LHC at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. This is the first T$'$ search that exploits the Higgs boson decay to a pair of photons. For narrow isospin singlet T$'$ states with masses up to 1.1 TeV, the excellent diphoton invariant mass resolution of 1-2% results in an increased sensitivity compared to previous searches based on the same production mechanism. The electroweak production of a T$'$ quark with mass up to 960 GeV is excluded at 95% confidence level, assuming a coupling strength $\kappa_\mathrm{T}$ = 0.25 and a relative decay width $\Gamma/M_{\mathrm{T}'}$ $\lt$ 5%.
The combined, leptonic plus hadronic, expected (dotted black) and observed (solid black) upper limits at 95% CL on $\sigma_{T^\prime bq} \times \mathcal{B}_{T^\prime \rightarrow tH}$ displayed as a function of $\rm{M}_{T^\prime}$. The green (yellow) band represents the 68% (95%) of the limit values expected under the background-only hypothesis. The theoretical cross sections for the singlet $T^\prime$ production with representative $\kappa_T$-values fixed at 0.1, 0.15, 0.2 and 0.25 (for $\Gamma/\rm{M}_{T^\prime} < 5\%$) are shown as solid red lines. The theoretical cross sections for the singlet $T^\prime$ production with $\Gamma/\rm{M}_{T^\prime}$ = 1 and 5% are also shown in table.
The combined, leptonic plus hadronic, expected (dotted black) and observed (solid black) upper limits at 95% CL on the $T^\prime$ coupling to third-generation quarks, $\kappa_{T}$, under the narrow width approximation (NWA) displayed as a function of $\rm{M}_{T^\prime}$. The green (yellow) band represents the 68% (95%) of the limit values expected under the background-only hypothesis. The theoretical $\kappa_{T}$ values corresponding to the $\Gamma/\rm{M}_{T^\prime}$-values fixed at 1, 2, 3, 4, and 5% are shown as red dashed lines.
The expected (dotted black) and observed (solid black) upper limits at 95% CL on $\sigma_{T^\prime bq(T^\prime \rightarrow tH)}$ in the leptonic channel displayed as a function of $\rm{M}_{T^\prime}$. The green (yellow) band represents the 68% (95%) of the limit values expected under the background-only hypothesis. The theoretical cross sections for the singlet $T^\prime$ production with representative $\kappa_T$-values fixed at 0.1, 0.15, 0.2 and 0.25 (for $\Gamma/\rm{M}_{T^\prime} < 5\%$) are shown as solid red lines.