Search for top squarks in final states with many light flavor jets and 0, 1, or 2 leptons in proton-proton collisions at sqrt(s) = 13 TeV

Several new physics models including versions of supersymmetry (SUSY) characterized by $R$-parity violation (RPV) or with additional hidden sectors predict the production of events with top quarks, low missing transverse momentum, and many additional quarks or gluons. The results of a search for top squarks decaying to two top quarks and six additional light-flavor quarks or gluons are reported. The search employs a novel machine learning method for data-driven background estimation using decorrelated discriminators referred to as the ABCDisCoTEC technique. The search is performed using events with 0, 1, or 2 electrons or muons in conjunction with at least six jets. No requirement is placed on the presence of missing transverse momentum. The result is based on a sample of proton-proton collisions at $\sqrt{s} = 13\,\mathrm{TeV}$ corresponding to $138\,\mathrm{fb}^{-1}$ of integrated luminosity collected with the CMS detector at the LHC in 2016-2018. The data are used to determine upper limits on the top squark pair production cross section in the frameworks of RPV and stealth SUSY. Models with top squark masses less than 700 $(920)\,\mathrm{GeV}$ are excluded at the $95\%$ confidence level for RPV (stealth) SUSY scenarios.

Search for excited tau leptons in the $\tau\tau\gamma$ final state in pp collisions at $\sqrt{s}=13\,\mathrm{TeV}$

We report the results of a test of the compositeness of the heaviest charged lepton, $\tau$, using data collected in proton-proton collisions at a center of mass energy of $13\,\mathrm{TeV}$ at the Large Hadron Collider at CERN in 2016--2018, corresponding to an integrated luminosity of $138\,\mathrm{fb}^{-1}$. We seek tau lepton pair production in which one tau lepton is produced in an excited state and decays to a ground state tau lepton and photon. The analysis selects events with two isolated tau lepton decay candidates plus a high energy photon. The mass of the excited tau lepton is reconstructed using the missing transverse momentum in the event, assuming the momentum of the neutrinos from each tau lepton decay lie along the visible tau lepton decay product direction. We observe no excess of events above the standard model background prediction and use this null result to set lower bounds on the excited tau lepton mass. For a compositeness scale $\Lambda$ equal to the excited tau lepton mass (10 TeV), we exclude excited tau leptons with masses below 4700 GeV (2800 GeV).

Search for a neutral gauge boson with non-universal fermion couplings in vector boson fusion processes in proton-proton collisions at $\sqrt{s}=$ 13$~\mathrm{TeV}$

The first search for a heavy neutral spin-1 gauge boson ($\mathrm{Z'}$) produced via vector boson fusion processes is presented. The analysis considers scenarios in which the $\mathrm{Z'}$ boson has non-universal fermion couplings, favoring higher-generation fermions. This offers a new physics phase space not yet fully explored at the LHC. The analysis is performed using LHC data at $\sqrt{s}=13~\mathrm{TeV}$, collected from 2016 to 2018, corresponding to an integrated luminosity of $138~\mathrm{fb}^{-1}$. The data are consistent with the standard model expectation. Upper limits are set on the product of the $\mathrm{Z'}$ cross section and the branching fraction for a $\mathrm{Z'}$ boson decaying to $\tau\tau$ or $\mathrm{WW}$. Masses below $2.45~\mathrm{TeV}$ are excluded, depending on the $\mathrm{Z'}$ coupling to weak bosons.

Angular analysis of the B0 to K*0(892) mu+ mu- decay at sqrt(s) = 13 TeV

The full set of optimised CP-averaged observables is measured in the angular analysis of the decay ${\mathrm{B}^0} \to \mathrm{K^{\ast 0}(892)} \mu^+\mu^-$ using a sample of proton-proton collisions at $\sqrt{s}=13$ TeV collected with the CMS detector at the LHC, corresponding to an integrated luminosity of ${140}~\mathrm{fb^{-1}}$. The analysis is performed in bins of the invariant mass squared of the dimuon system. These results are among the most precise experimental measurements of the angular observables of the $\mathrm{B}^0 \to \mathrm{K^{\ast 0}(892)} \mu^+\mu^-$ decay.

Dependence of two-particle azimuthal correlations on the forward rapidity gap width in pPb collisions at $\sqrt{s_{NN}}=8.16~\mathrm{TeV}$

Measurements of the Fourier coefficients ($V_{n\Delta}$) of the azimuthal distributions of charged hadron pairs produced in pPb collisions at 8.16 TeV are presented as functions of the forward rapidity gap width ($\Delta\eta^{\rm{F}} $) for events in which particle production is concentrated in the direction of the outgoing Pb beam. The sample includes contributions from pomeron and photon induced processes as well as nondiffractive events. The data correspond to a luminosity of 174.5 $\rm{nb}^{-1}$ recorded with the CMS detector in the LHC Run 2. The mean track multiplicity decreases by $53\%$ from the bin $0\leq\Delta\eta^{\rm{F}}<0.5$ to that with $\Delta\eta^{\rm{F}}>2.5$. The dependence of the results on the track multiplicity and the transverse momentum of the charged particles is also studied for the most forward events ($\Delta\eta^{\rm{F}}>2.5$). The measured values of $V_{1\Delta}$ are negative and decrease with $\Delta\eta^{\rm{F}} $, while those of $V_{2\Delta}$ are positive for the $\Delta\eta^{\rm{F}} $ bins $[0.5,1)$, $[1,1.5)$, $[2,2.5)$, and are consistent with zero elsewhere. The measured values of the elliptic flow coefficient ($v_2$) is provided for the $\Delta\eta^{\rm{F}} $ bins $[0.5,1)$, $[1,1.5)$, $[2,2.5)$. In the other bins, the $v_2$ results are consistent with zero. In these bins, upper limits at $95\%$ C.L. are determined, ranging up to 0.13 for the most inclusive category. The values of the upper limits are similar to the values of $v_2$ measured in $\gamma$p collisions with comparable multiplicity.

Azimuthal dependence of hyperon polarization along the beam direction in pPb collisions at $\sqrt{s_{_{NN}}}$ = 8.16 TeV

The polarization of the $\Lambda$ and $\overline{\Lambda}$ hyperons along the beam ($z$) direction, $P_z$, has been measured for the first time in pPb collisions at the LHC with $\sqrt{s_{_{NN}}}$ = 8.16 TeV data collected by the CMS experiment. Assuming the largest contributions to $P_z$ come from collective flow, this polarization can be characterized by the Fourier sine coefficients $P_{z,sn} = \langle P_{z}\sin(n\phi - n\Psi_{n}) \rangle$, where $\phi$ is the hyperon azimuthal emission angle and $\Psi_{n}$ is the $n$-th order flow plane angle. The second order Fourier sine coefficient $P_{z,s2}$ is reported for $\Lambda$ and $\overline{\Lambda}$ particles as a function of transverse momentum and event multiplicity. A significant positive $P_{z,s2}$ signal is observed for $0.8 < p_{\mathrm{T}} < 6.0$ GeV/c over the entire multiplicity range (from 3 to 250 charged particles). The measured $P_{z,s2}$ values increase as a function of $p_{\mathrm{T}}$ and decrease as a function of multiplicity. These results can provide new constraints on the potential creation of quark-gluon plasma droplets and the spin polarization mechanism in pp and pA systems.

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