Properties of the underlying-event in $pp$ interactions are investigated primarily via the strange hadrons $K_{S}^{0}$, $\Lambda$ and $\bar\Lambda$, as reconstructed using the ATLAS detector at the LHC in minimum-bias $pp$ collision data at $\sqrt{s} = 13$ TeV. The hadrons are reconstructed via the identification of the displaced two-particle vertices corresponding to the decay modes $K_{S}^{0}\rightarrow\pi^+\pi^-$, $\Lambda\rightarrow\pi^-p$ and $\bar\Lambda\rightarrow\pi^+\bar{p}$. These are used in the construction of underlying-event observables in azimuthal regions computed relative to the leading charged-particle jet in the event. None of the hadronisation and underlying-event physics models considered can describe the data over the full kinematic range considered. Events with a leading charged-particle jet in the range of $10 < p_T \leq 40$ GeV are studied using the number of prompt charged particles in the transverse region. The ratio $N(\Lambda + \bar\Lambda)/N(K_{S}^{0})$ as a function of the number of such charged particles varies only slightly over this range. This disagrees with the expectations of some of the considered Monte Carlo models.
Mean multiplicity of $K^{0}_{S}$ per unit $(\eta, \phi)$ in the away region vs. leading-jet $p_{T}$
Statistical covariance between bins of Table 1
Mean multiplicity of $K^{0}_{S}$ per unit $(\eta, \phi)$ in the towards region vs. leading-jet $p_{T}$
A measurement of the invisible width of the $Z$ boson using events with jets and missing transverse momentum is presented using 37 $\mbox{fb\(^{-1}\)}$ of 13 TeV proton-proton data collected by the ATLAS detector in 2015 and 2016. The ratio of $Z\rightarrow \textrm{inv}$ to $Z\rightarrow\ell\ell$ events, where inv refers to non-detected particles and $\ell$ is either an electron or a muon, is measured and corrected for detector effects. Events with at least one energetic central jet with $p_{\textrm{T}} \geq 110$ GeV are selected for both the $Z\rightarrow \textrm{inv}$ and $Z\rightarrow\ell\ell$ final states to obtain a similar phase space in the ratio. The invisible width is measured to be $506\pm2 \textrm{ (stat.)} \pm12 \textrm{ (syst.)}$ MeV and is the single most precise recoil-based measurement. The result is in agreement with the most precise determination from LEP and the Standard Model prediction based on three neutrino generations.
Measured invisible width of the $Z$ boson, $\Gamma(Z\rightarrow \textrm{inv})$.
Measured $\mathrm{R}^{\mathrm{miss}}_{ee}$.
Measured $\mathrm{R}^{\mathrm{miss}}_{\mu\mu}$.
Measurements of the differential production cross-sections of prompt and non-prompt $J/\psi$ and $\psi(2$S$)$ mesons with transverse momenta between 8 and 360 GeV and rapidity in the range $|y|<2$ are reported. Furthermore, measurements of the non-prompt fractions of $J/\psi$ and $\psi(2$S$)$, and the prompt and non-prompt $\psi(2$S$)$-to-$J/\psi$ production ratios, are presented. The analysis is performed using 140 fb$^{-1}$ of $\sqrt{s}=13$ TeV $pp$ collision data recorded by the ATLAS detector at the LHC during the years 2015-2018.
Summary of results for cross-section of prompt $J/\psi$ decaying to a muon pair for 13 TeV data in fb/GeV. Uncertainties are statistical and systematic, respectively.
Summary of results for cross-section of non-prompt $J/\psi$ decaying to a muon pair for 13 TeV data in fb/GeV. Uncertainties are statistical and systematic, respectively.
Summary of results for cross-section of prompt $\psi(2S)$ decaying to a muon pair for 13 TeV data in fb/GeV. Uncertainties are statistical and systematic, respectively.
The inclusive top-quark-pair production cross section $\sigma_{t\bar{t}}$ and its ratio to the $Z$-boson production cross section have been measured in proton--proton collisions at $\sqrt{s} = 13.6$ TeV, using 29 fb${}^{-1}$ of data collected in 2022 with the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge electron-muon pair and $b$-tagged jets, and assuming Standard Model decays, the top-quark-pair production cross section is measured to be $\sigma_{t\bar{t}} = 850 \pm 3\mathrm{(stat.)}\pm 18\mathrm{(syst.)}\pm 20\mathrm{(lumi.)}$ pb. The ratio of the $t\bar{t}$ and the $Z$-boson production cross sections is also measured, where the $Z$-boson contribution is determined for inclusive $e^+e^-$ and $\mu^+\mu^-$ events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the $t\bar{t}$ cross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, $R_{t\bar{t}/Z} = 1.145 \pm 0.003\mathrm{(stat.)}\pm 0.021\mathrm{(syst.)}\pm 0.002\mathrm{(lumi.)}$ is consistent with the Standard Model prediction using the PDF4LHC21 PDF set.
The fiducial phase-space definition for the $Z$-boson measurement. Born-level leptons are used.
The measured $t\bar{t}$ cross section and the ratio of the cross sections of $t\bar{t}$ and the $Z$-boson. Full phase-space is considered for $t\bar{t}$, while fiducial phase-space is considered for the $Z$-boson.
Table with pre-fit yields in the four regions used in the measurement
Using a data sample of $\sqrt{s} =$ 13 TeV proton-proton collisions collected by the CMS experiment at the LHC in 2017 and 2018 with an integrated luminosity of 103 fb$^{-1}$, the B$^0$$\to$$\psi$(2S)K$^0_\mathrm{S}$ and B$^0_\mathrm{S}$$\to$$\psi$(2S)K$^0_\mathrm{S}\pi^+\pi^-$ decays are observed with significances exceeding 5 standard deviations. The resulting branching fraction ratios, measured for the first time, correspond to $\mathcal{B}$(B$^0_\mathrm{S}$$\to$$\psi$(2S)K$^0_\mathrm{S}$) / $\mathcal{B}$(B$^0$$\to$$\psi$(2S)K$^0_\mathrm{S}$) = (3.33 $\pm$ 0.69 (stat) $\pm$ 0.11 (syst) $\pm$ 0.34 ($f_\mathrm{s} / f_\mathrm{d}$)) $\times$ 10$^{-2}$ and $\mathcal{B}$(B$^0$$\to$$\psi$(2S)K$^0_\mathrm{S}\pi^+\pi^-$) / $\mathcal{B}$(B$^0$$\to$$\psi$(2S)K$^0_\mathrm{S}$) = 0.480 $\pm$ 0.013 (stat) $\pm$ 0.032 (syst), where the last uncertainty in the first ratio is related to the uncertainty in the ratio of production cross sections of B$^0_\mathrm{s}$ and B$^0$ mesons, $f_\mathrm{s} / f_\mathrm{d}$.
The measured branching fraction ratios
Transverse momentum distribution for B-candidate
The measured branching fractions
A measurement of inclusive four-jet production in proton-proton collisions at a center-of-mass energy of 13\TeV is presented. The transverse momenta of jets within $\lvert\eta\rvert \lt$ 4.7 reach down to 35, 30, 25, and 20 GeV for the first-, second-, third-, and fourth-leading jet, respectively. Differential cross sections are measured as functions of the jet transverse momentum, jet pseudorapidity, and several other observables that describe the angular correlations between the jets. The measured distributions show sensitivity to different aspects of the underlying event, parton shower, and matrix element calculations. In particular, the interplay between angular correlations caused by parton shower and double-parton scattering contributions is shown to be important. The double-parton scattering contribution is extracted by means of a template fit to the data, using distributions for single-parton scattering obtained from Monte Carlo event generators and a double-parton scattering distribution constructed from inclusive single-jet events in data. The effective double-parton scattering cross section is calculated and discussed in view of previous measurements and of its dependence on the models used to describe the single-parton scattering background.
Comparison of the pT spectrum for the leading jet from data to different PYTHIA8 (P8),HERWIG++ (H++),and HERWIG7 (H7) tunes.
Comparison of the pT spectrum for the sub-leading from data to different PYTHIA8 (P8),HERWIG++ (H++),and HERWIG7 (H7) tunes.
Comparison of the pT spectrum for the third-leading from data to different PYTHIA8 (P8),HERWIG++ (H++),and HERWIG7 (H7) tunes.
A search is performed for the rare decay W$^\pm\to\pi^\pm\gamma$ in proton-proton collisions at $\sqrt{s} =$ 13 TeV. Data corresponding to an on W integrated luminosity of 137 fb$^{-1}$ were collected during 2016 to 2018 with the CMS detector. This analysis exploits a novel search strategy based on W boson production in top quark pair events. An inclusive search for the W$^\pm\to\pi^\pm\gamma$ decay is not optimal at the LHC because of the high trigger thresholds. Instead, a trigger selection is exploited in which the W boson originating from one of the top quarks is used to tag the event in a leptonic decay. The W boson emerging from the other top quark is used to search for the W$^\pm\to\pi^\pm\gamma$ signature. Such decays are characterized by an isolated track pointing to a large energy deposit, and by an isolated photon of large transverse momentum. The presence of b quark jets reduces the background from the hadronization of light-flavor quarks and gluons. The W$^\pm\to\pi^\pm\gamma$ decay is not observed. An upper exclusion limit is set to this branching fraction, corresponding to 1.50 $\times$ 10$^{-5}$ at 95% confidence level, whereas the expected upper limit exclusion limit is 0.85 $^{+0.52}_{-0.29}$ $\times$ 10$^{-5}$.
The product of signal efficiency and acceptance per year and per lepton channel (muon or electron).
Expected and observed upper exclusion limits on the branching fraction of the decay of a W boson into a pion and a photon, using 2016 to 2018 data.
The ratios of the production cross sections between the excited $\Upsilon$(2S) and $\Upsilon$(3S) mesons and the $\Upsilon$(1S) ground state, detected via their decay into two muons, are studied as a function of the number of charged particles in the event. The data are from proton-proton collisions at $\sqrt{s} =$ 7 TeV, corresponding to an integrated luminosity of 4.8 fb$^{-1}$, collected with the CMS detector at the LHC. Evidence of a decrease in these ratios as a function of the particle multiplicity is observed, more pronounced at low transverse momentum $p_\mathrm{T}^{\mu\mu}$. For $\Upsilon$(nS) mesons with $p_\mathrm{T}^{\mu\mu}$ $\gt$ 7 GeV, where most of the data were collected, the correlation with multiplicity is studied as a function of the underlying event transverse sphericity and the number of particles in a cone around the $\Upsilon$(nS) direction. The ratios are found to be multiplicity independent for jet-like events. The mean $p_\mathrm{T}^{\mu\mu}$ values for the $\Upsilon$(nS) states as a function of particle multiplicity are also measured and found to grow more steeply as their mass increases.
The measured ratios $\Upsilon(2$S$)\,/\,\Upsilon(1$S$)$ and $\Upsilon(3$S$)\,/\,\Upsilon(1$S$)$ with $p_T(\Upsilon(n$S$))>7\,GeV$ and $|y(\Upsilon(n$S$))| < 1.2$, as a function of track multiplicity $N_{track}$
The measured ratios $\Upsilon(2$S$)\,/\,\Upsilon(1$S$)$ and $\Upsilon(3$S$)\,/\,\Upsilon(1$S$)$ with $p_T(\Upsilon(n$S$))>0\,GeV$ and $|y(\Upsilon(n$S$))| < 1.93$, as a function of track multiplicity $N_{track}$.
Mean $p_T$ values of the $\Upsilon(1$S$)$, $\Upsilon(2$S$)$, and $\Upsilon(3S)$ states with $p_T\,>\,7\,GeV$ and $|y|\,<\,1.2$ as a function of track multiplicity $N_{track}$
Using a data sample of proton-proton collisions at $\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 140 fb$^{-1}$ collected by the CMS experiment in 2016-2018, the B$^0_\mathrm{s}$ $\to$ X(3872)$\phi$ decay is observed. Decays into J/$\psi\,\pi^+\pi^-$ and K$^+$K$^-$ are used to reconstruct, respectively, the X(3872) and $\phi$. The ratio of the product of branching fractions $\mathcal{B}($B$^0_\mathrm{s}$ $\to$ X(3872)$\phi)\,\mathcal{B}($X(3872) $\to$ J$/\psi\,\pi^+\pi^-)$ to the product $\mathcal{B}($B$^0_\mathrm{s}$ $\to$ $\psi$(2S)$\phi)\,\mathcal{B}(\psi$(2S) $\to$ J/$\psi\,\pi^+\pi^-)$ is measured to be (2.21 $\pm$ 0.29 (stat) $\pm$ 0.17 (syst))%. The ratio $\mathcal{B}($B$^0_\mathrm{s}$ $\to$ X(3872)$\phi) / \mathcal{B}($B$^{0}$ $\to$ X(3872)K$^0)$ is found to be consistent with one, while the ratio $\mathcal{B}($B$^0_\mathrm{s}$ $\to$ X(3872)$\phi) / \mathcal{B}($B$^+$ $\to$ X(3872)K$^+)$ is two times smaller. This suggests a difference in the production dynamics of the X(3872) in B$^0$ and B$^0_\mathrm{s}$ meson decays compared to B$^+$. The reported observation may shed new light on the nature of the X(3872) particle.
The measured ratio of branching fraction products
Measurements are presented of the single-diffractive dijet cross section and the diffractive cross section as a function of the proton fractional momentum loss $\xi$ and the four-momentum transfer squared $t$. Both processes pp$\to$pX and pp$\to$Xp, ie with the proton scattering to either side of the interaction point, are measured, where X includes at least two jets; the results of the two processes are averaged. The analyses are based on data collected simultaneously with the CMS and TOTEM detectors at the LHC in proton-proton collisions at $\sqrt{s}$= 8 TeV during a dedicated run with $\beta^{\ast} =$ 90 m at low instantaneous luminosity and correspond to an integrated luminosity of 37.5 nb$^{-1}$. The single-diffractive dijet cross section $\sigma^\mathrm{pX}_{\mathrm{jj}}$, in the kinematic region $\xi \lt$ 0.1, 0.03 $\lt |$t$| \lt 1$ GeV$^2$, with at least two jets with transverse momentum $p_\mathrm{T} >$ 40 GeV, and pseudorapidity $|\eta| \lt$ 4.4, is 21.7$\pm$0.9 (stat)$^{+3.0}_{-3.3}$ (syst) $\pm$ 0.9 (lum) nb. The ratio of the single-diffractive to inclusive dijet yields, normalised per unit of $\xi$, is presented as a function of $x$, the longitudinal momentum fraction of the proton carried by the struck parton. The ratio in the kinematic region defined above, for $x$ values in the range $-$2.9 $\leq \log_{10} x \leq$$-$1.6, is $R = (\sigma^\mathrm{pX}_{\mathrm{jj}}/\Delta\xi)/\sigma_{\mathrm{jj}} =$ 0.025$\pm$0.001 (stat) $\pm$ 0.003 (syst), where $\sigma^\mathrm{pX}_{\mathrm{jj}}$ and $\sigma_{\mathrm{jj}}$ are the single-diffractive and inclusive dijet cross sections, respectively. The results are compared with predictions from models of diffractive and nondiffractive interactions. Monte Carlo predictions based on the HERA diffractive parton distribution functions agree well with the data when corrected for the effect of soft rescattering between the spectator partons.
Differential cross section as a function of $t$ for single-diffractive dijet production, in the kinematic region $\xi < 0.1$, $0.03 < \lvert t \rvert < 1\,\mathrm{GeV}^2$, with at least two jets with transverse momentum $p_{\mathrm{T}} > 40\,\mathrm{GeV}$, and pseudorapidity $\lvert \eta \rvert < 4.4$.
Differential cross section as a function of $\xi$ for single-diffractive dijet production, in the kinematic region $\xi < 0.1$, $0.03 < \lvert t \rvert < 1\,\mathrm{GeV}^2$, with at least two jets with transverse momentum $p_{\mathrm{T}} > 40\,\mathrm{GeV}$, and pseudorapidity $\lvert \eta \rvert < 4.4$.
Ratio per unit of $\xi$ of the single-diffractive and inclusive dijet cross sections in the region given by $\xi < 0.1$ and $0.03 < \lvert t \rvert < 1\,\mathrm{GeV}^2$, with at least two jets with transverse momentum $p_{\mathrm{T}} > 40\,\mathrm{GeV}$, and pseudorapidity $\lvert \eta \rvert < 4.4$.
Forum