The first search for soft unclustered energy patterns (SUEPs) is performed using an integrated luminosity of 138 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}$ = 13 TeV collected in 2016-2018 by the CMS detector at the LHC. Such SUEPs are predicted by Hidden Valley models with a new, confining force with a large 't Hooft coupling. In events with boosted topologies, selected by high-threshold hadronic triggers, the multiplicity and sphericity of clustered tracks are used to reject the background from standard model quantum chromodynamics. With no observed excess of events over the standard model expectation, limits are set on the cross section for production via gluon fusion of a scalar mediator with SUEP-like decays.
A search is presented for the resonant production of a pair of standard model-like Higgs bosons using data from proton-proton collisions at a centre-of-mass energy of 13 TeV, collected by the CMS experiment at the CERN LHC in 2016-2018, corresponding to an integrated luminosity of 138 fb$^{-1}$. The final state consists of two b quark-antiquark pairs. The search is conducted in the region of phase space where at least one of the pairs is highly Lorentz-boosted and is reconstructed as a single large-area jet. The other pair may be either similarly merged or resolved, the latter reconstructed using two b-tagged jets. The data are found to be consistent with standard model processes and are interpreted as 95% confidence level upper limits on the product of the cross sections and the branching fractions of the spin-0 radion and the spin-2 bulk graviton that arise in warped extradimensional models. The limits set are in the range 9.74-0.29 fb and 4.94-0.19 fb for a narrow radion and a graviton, respectively, with masses between 1 and 3 TeV. For a radion and for a bulk graviton with widths 10% of their masses, the limits are in the range 12.5-0.35 fb and 8.23-0.23 fb, respectively, for the same masses. These limits result in the exclusion of a narrow-width graviton with a mass below 1.2 TeV, and of narrow and 10%-width radions with masses below 2.6, and 2.9 TeV, respectively.
The effective lifetime of the B$^0_\mathrm{s}$ meson in the decay B$^0_\mathrm{s}$$\to$ J/$\psi$K$^0_\mathrm{S}$ is measured using data collected during 2016-2018 with the CMS detector in $\sqrt{s}$ = 13 TeV proton-proton collisions at the LHC, corresponding to an integrated luminosity of 140 fb$^{-1}$. The effective lifetime is determined by performing a two-dimensional unbinned maximum likelihood fit to the B$^0_\mathrm{s}$ meson invariant mass and proper decay time distributions. The resulting value of 1.59 $\pm$ 0.07 (stat) $\pm$ 0.03 (syst) ps is the most precise measurement to date and is in good agreement with the expected value.
The ratio of branching ratios of the $W$ boson to muons and electrons, $R^{\mu/e}_W=B(W\rightarrow \mu\nu)/B(W\rightarrow e\nu)$, has been measured using 140 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV collected with the ATLAS detector at the LHC, probing the universality of lepton couplings. The ratio is obtained from measurements of the $t\bar{t}$ production cross-section in the $ee$, $e\mu$ and $\mu\mu$ dilepton final states. To reduce systematic uncertainties, it is normalised by the square root of the corresponding ratio $R^{\mu\mu/ee}_Z$ for the $Z$ boson measured in inclusive $Z\rightarrow ee$ and $Z\rightarrow\mu\mu$ events. By using the precise value of $R^{\mu\mu/ee}_Z$ determined from $e^+e^-$ colliders, the ratio $R^{\mu/e}_W$ is determined to be $R^{\mu/e}_W = 0.9995 \pm 0.0022 \pm 0.0036 \pm 0.0014$. The three uncertainties correspond to data statistics, experimental systematics and the external measurement of $R^{\mu\mu/ee}_Z$, giving a total uncertainty of 0.0045, and confirming the Standard Model assumption of lepton flavour universality in $W$-boson decays at the 0.5% level.
The polarizations of prompt and non-prompt J$/\psi$ and $\psi$(2S) mesons are measured in proton-proton collisions at $\sqrt{s}$ = 13 TeV, using data samples collected by the CMS experiment in 2017 and 2018, corresponding to a total integrated luminosity of 103.3 fb$^{-1}$. Based on the analysis of the dimuon decay angular distributions in the helicity frame, the polar anisotropy, $\lambda_\theta$, is measured as a function of the transverse momentum, $p_\mathrm{T}$, of the charmonium states, in the 25-120 and 20-100 GeV ranges for the J$/\psi$ and $\psi$(2S), respectively. The non-prompt polarizations agree with predictions based on the hypothesis that, for $p_\mathrm{T}$$\gtrsim$ 25 GeV, the non-prompt J$/\psi$ and $\psi$(2S) are predominantly produced in two-body B meson decays. The prompt results clearly exclude strong transverse polarizations, even for $p_\mathrm{T}$ exceeding 30 times the J$/\psi$ mass, where $\lambda_\theta$ tends to an asymptotic value around 0.3. Taken together with previous measurements, by CMS and LHCb at $\sqrt{s}$ = 7 TeV, the prompt polarizations show a significant variation with $p_\mathrm{T}$, at low $p_\mathrm{T}$.
Charge-dependent two- and three-particle correlations measured in Xe-Xe collisions at $\sqrt{s_{\mathrm{NN}}} = 5.44$ TeV are presented. Results are obtained for charged particles in the pseudorapidity range $|\eta|<0.8$ and transverse momentum interval $0.2 \le p_{\rm T}<5.0$ GeV/$c$ for different collision centralities. The three-particle correlator ${\gamma_{\alpha\beta}} \equiv {\langle \cos(\varphi_\alpha + \varphi_\beta - 2{\Psi_{\rm 2}}) \rangle}$, calculated for different combinations of charge sign $\alpha$ and $\beta$, is expected to be sensitive to the presence of the Chiral Magnetic Effect (CME). Its magnitude is similar to the one observed in Pb-Pb collisions in contrast to a smaller CME signal in Xe-Xe collisions than in Pb-Pb collisions predicted by Monte Carlo (MC) calculations including a magnetic field induced by the spectator protons. These observations point to a large non-CME contribution to the correlator. Furthermore, the charge dependence of ${\gamma_{\alpha\beta}}$ can be described by a blast wave model calculation that incorporates background effects and by the Anomalous Viscous Fluid Dynamics model with values of the CME signal consistent with zero. The Xe-Xe and Pb-Pb results are combined with the expected CME signal dependence on the system size from the MC calculations including a magnetic field to obtain the fraction of CME contribution in ${\gamma_{\alpha\beta}}$, $f_{\rm CME}$. The CME fraction is compatible with zero for the 30% most central events in both systems and then becomes positive; averaging over the 0-70% centrality interval yields an upper limit of 2% (3%) and 25% (32%) at 95% (99.7%) confidence level for the CME signal contribution to ${\gamma_{\alpha\beta}}$ in Xe-Xe and Pb-Pb collisions, respectively.
The chiral magnetic effect (CME) is a phenomenon that arises from the QCD anomaly in the presence of an external magnetic field. The experimental search for its evidence has been one of the key goals of the physics program of the Relativistic Heavy-Ion Collider. The STAR collaboration has previously presented the results of a blind analysis of isobar collisions (${^{96}_{44}\text{Ru}}+{^{96}_{44}\text{Ru}}$, ${^{96}_{40}\text{Zr}}+{^{96}_{40}\text{Zr}}$) in the search for the CME. The isobar ratio ($Y$) of CME-sensitive observable, charge separation scaled by elliptic anisotropy, is close to but systematically larger than the inverse multiplicity ratio, the naive background baseline. This indicates the potential existence of a CME signal and the presence of remaining nonflow background due to two- and three-particle correlations, which are different between the isobars. In this post-blind analysis, we estimate the contributions from those nonflow correlations as a background baseline to $Y$, utilizing the isobar data as well as Heavy Ion Jet Interaction Generator simulations. This baseline is found consistent with the isobar ratio measurement, and an upper limit of 10% at 95% confidence level is extracted for the CME fraction in the charge separation measurement in isobar collisions at $\sqrt{s_{\rm NN}}=200$ GeV.
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.
The production yields of the $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$ resonances are measured in pp collisions at $\sqrt{s}=13$ TeV with ALICE. The measurements are performed as a function of the charged-particle multiplicity $\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta \rangle$, which is related to the energy density produced in the collision. The results include transverse momentum ($p_{\rm T}$) distributions, $p_{\rm T}$-integrated yields, mean transverse momenta of $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$, as well as ratios of the $p_{\rm T}$-integrated resonance yields relative to yields of other hadron species. The $\Sigma(1385)^{\pm}/\pi^{\pm}$ and $\Xi(1530)^{0}/\pi^{\pm}$ yield ratios are consistent with the trend of the enhancement of strangeness production from low to high multiplicity pp collisions, which was previously observed for strange and multi-strange baryons. The yield ratio between the measured resonances and the long-lived baryons with the same strangeness content exhibits a hint of a mild increasing trend at low multiplicity, despite too large uncertainties to exclude the flat behaviour. The results are compared with predictions from models such as EPOS-LHC and PYTHIA 8 with Rope shoving. The latter provides the best description of the multiplicity dependence of the $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$ production in pp collisions at $\sqrt{s}=13$ TeV.
The inclusive production of the charm-strange baryon $\Omega^{0}_{\rm c}$ is measured for the first time via its semileptonic decay into $\Omega^{-}\rm e^{+}\nu_{e}$ at midrapidity ($|y|<0.8$) in proton$-$proton (pp) collisions at the centre-of-mass energy $\sqrt{s}=13$ TeV with the ALICE detector at the LHC. The transverse momentum ($p_{\rm T}$) differential cross section multiplied by the branching ratio is presented in the interval $2<p_{\rm T}<12~{\rm GeV}/c$. The branching-fraction ratio ${\rm BR}(\Omega^0_{\rm c} \rightarrow \Omega^{-}{\rm e}^{+}\nu_{\rm e})/ {\rm BR}(\Omega^0_{\rm c} \rightarrow \Omega^{-}{\pi}^{+})$ is measured to be 1.12 $\pm$ 0.22 (stat.) $\pm$ 0.27 (syst.). Comparisons with other experimental measurements, as well as with theoretical calculations, are presented.
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