The first experimental information on the strong interaction between $\Lambda$ and $\Xi^-$ strange baryons is presented in this Letter. The correlation function of $\Lambda-\Xi^-$ and $\overline{\Lambda}-\overline{\Xi}^{+}$ pairs produced in high-multiplicity proton-proton (pp) collisions at $\sqrt{s}$ = 13 TeV at the LHC is measured as a function of the relative momentum of the pair. The femtoscopy method is used to calculate the correlation function, which is then compared with theoretical expectations obtained using a meson exchange model, chiral effective field theory, and Lattice QCD calculations close to the physical point. Data support predictions of small scattering parameters while discarding versions with large ones, thus suggesting a weak $\Lambda-\Xi^{-}$ interaction. The limited statistical significance of the data does not yet allow one to constrain the effects of coupled channels like $\Sigma-\Xi$ and N$-\Omega$.
The $\Lambda$--$\Xi^{-}$ $\oplus$ $\overline{\Lambda}$--$\overline{\Xi}^{+}$ correlation function and the $\lambda$ parameters with the parametrization of the background contribution $C_\mathrm{mis.}(k^*)$
Results are presented from a search for physics beyond the standard model in proton-proton collisions at $\sqrt{s} =$ 13 TeV in channels with two Higgs bosons, each decaying via the process H $\to$$\mathrm{b\bar{b}}$, and large missing transverse momentum. The search uses a data sample corresponding to an integrated luminosity of 137 fb$^{-1}$ collected by the CMS experiment at the CERN LHC. The search is motivated by models of supersymmetry that predict the production of neutralinos, the neutral partners of the electroweak gauge and Higgs bosons. The observed event yields in the signal regions are found to be consistent with the standard model background expectations. The results are interpreted using simplified models of supersymmetry. For the electroweak production of nearly mass-degenerate higgsinos, each of whose decay chains yields a neutralino ($\tilde{\chi}^0_1$) that in turn decays to a massless goldstino and a Higgs boson, $\tilde{\chi}^0_1$ masses in the range 175 to 1025 GeV are excluded at 95% confidence level. For the strong production of gluino pairs decaying via a slightly lighter $\tilde{\chi}^0_2$ to H and a light $\tilde{\chi}^0_1$, gluino masses below 2330 GeV are excluded.
Predicted background and observed yields vs bin index
Cross section 95% CL upper limit vs m($\widetilde{\chi}^0_1$) for SMS model TChiHH-G.
Theory cross sections vs m($\widetilde{\chi}^0_1$) for SMS model TChiHH-G.
The associated production of a Higgs boson and a top-quark pair is measured in events characterised by the presence of one or two electrons or muons. The Higgs boson decay into a $b$-quark pair is used. The analysed data, corresponding to an integrated luminosity of 139 fb$^{-1}$, were collected in proton-proton collisions at the Large Hadron Collider between 2015 and 2018 at a centre-of-mass energy of $\sqrt{s}=13$ TeV. The measured signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model, is $0.35^{+0.36}_{-0.34}$. This result is compatible with the Standard Model prediction and corresponds to an observed (expected) significance of 1.0 (2.7) standard deviations. The signal strength is also measured differentially in bins of the Higgs boson transverse momentum in the simplified template cross-section framework, including a bin for specially selected boosted Higgs bosons with transverse momentum above 300 GeV.
Comparison between data and prediction for the DNN $P(H)$ output for the Higgs boson candidate prior to any fit to the data in the single-lepton boosted channel for $300\le p_T^H<450$ GeV. The dashed line shows the ${t\bar {t}H}$ signal distribution normalised to the total background prediction. The uncertainty band includes all uncertainties and their correlations.
Comparison between data and prediction for the DNN $P(H)$ output for the Higgs boson candidate prior to any fit to the data in the single-lepton boosted channel for $p_{{T}}^{H}\ge 450$ GeV. The dashed line shows the ${t\bar {t}H}$ signal distribution normalised to the total background prediction. The uncertainty band includes all uncertainties and their correlations.
Performance of the Higgs boson reconstruction algorithms. For each row of `truth' ${\hat{p}_{{T}}^{H}}$, the matrix shows (in percentages) the fraction of all Higgs boson candidates with reconstructed $p_T^H$ in the various bins of the dilepton (left), single-lepton resolved (middle) and boosted (right) channels.
The associated production of a W and a Z boson is studied in final states with multiple leptons produced in proton-proton (pp) collisions at a centre-of-mass energy of 13 TeV using 137 fb$^{-1}$ of data collected with the CMS detector at the LHC. A measurement of the total inclusive production cross section yields $\sigma_{\text{tot}}$(pp $\to$ WZ) = 50.6 $\pm$ 0.8 (stat) $\pm$ 1.5 (syst) $\pm$ 1.1 (lumi) $\pm$ 0.5 (theo) pb. Measurements of the fiducial and differential cross sections for several key observables are also performed in all the final-state lepton flavour and charge compositions with a total of three charged leptons, which can be electrons or muons. All results are compared with theoretical predictions computed up to next-to-next-to-leading order in quantum chromodynamics plus next-to-leading order in electroweak theory and for various sets of parton distribution functions. The results include direct measurements of the charge asymmetry and the W and Z vector boson polarization. The first observation of longitudinally polarized W bosons in WZ production is reported. Anomalous gauge couplings are searched for, leading to new constraints on beyond-the-standard-model contributions to the WZ triple gauge coupling.
Distribution of the three leading leptons flavour in the CR-ZZ with uncertainties evaluated after the inclusive cross section fit
Distribution of the jet multiplicity in the CR-ttZ with uncertainties evaluated after the inclusive cross section fit
Distribution of the three leading leptons flavour in the CR-conv with uncertainties evaluated after the inclusive cross section fit
Angular correlations of heavy-flavour and charged particles in high-energy proton-proton collisions are sensitive to the production mechanisms of heavy quarks and to their fragmentation as well as hadronisation processes. The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV with the ALICE detector is reported, considering D$^{0}$, D$^{+}$, and D$^{*+}$ mesons in the transverse-momentum interval $3 < p_{\rm T} < 36$ GeV/$c$ at midrapidity ($|y| < 0.5$), and charged particles with $p_{\rm T} > 0.3$ GeV/$c$ and pseudorapidity $|\eta| < 0.8$. This measurement has an improved precision and provides an extended transverse-momentum coverage compared to previous ALICE measurements at lower energies. The study is also performed as a function of the charged-particle multiplicity, showing no modifications of the correlation function with multiplicity within uncertainties. The properties and the transverse-momentum evolution of the near- and away-side correlation peaks are studied and compared with predictions from various Monte Carlo event generators. Among those considered, PYTHIA8 and POWHEG+PYTHIA8 provide the best description of the measured observables. The obtained results can provide guidance on tuning the generators.
Comparison of the azimuthal-correlation distributions of D mesons (average of D$^{0}$, D$^{+}$, and D$^{*+}$) with $3 < p_{\rm T} < 5$ GeV/$c$ and charged particles with $0.3 < p_{\rm T} < 1$ GeV/$c$, in pp collisions at $\sqrt{s} = $5, 7, and 13 TeV, after baseline subtraction. Rapidity range for the D mesons is $|y^{\rm D}_{\rm cms}| < 0.5$. Correlations are integrated for $|\Delta\eta|=|\eta_{\rm ch}-\eta_{\rm D}| < 1$. The azimuthal-correlation distributions are reported in the range $0 < \Delta\varphi < \pi$.
Comparison of the azimuthal-correlation distributions of D mesons (average of D$^{0}$, D$^{+}$, and D$^{*+}$) with $8 < p_{\rm T} < 16$ GeV/$c$ and charged particles with $0.3 < p_{\rm T} < 1$ GeV/$c$, in pp collisions at $\sqrt{s} = $5, 7, and 13 TeV, after baseline subtraction. Rapidity range for the D mesons is $|y^{\rm D}_{\rm cms}| < 0.5$. Correlations are integrated for $|\Delta\eta|=|\eta_{\rm ch}-\eta_{\rm D}| < 1$. The azimuthal-correlation distributions are reported in the range $0 < \Delta\varphi < \pi$.
Comparison of the azimuthal-correlation distributions of D mesons (average of D$^{0}$, D$^{+}$, and D$^{*+}$) with $16 < p_{\rm T} < 24$ GeV/$c$ and charged particles with $0.3 < p_{\rm T} < 1$ GeV/$c$, in pp collisions at $\sqrt{s} = $5, 7, and 13 TeV, after baseline subtraction. Rapidity range for the D mesons is $|y^{\rm D}_{\rm cms}| < 0.5$. Correlations are integrated for $|\Delta\eta|=|\eta_{\rm ch}-\eta_{\rm D}| < 1$. The azimuthal-correlation distributions are reported in the range $0 < \Delta\varphi < \pi$.
First measurements of balance functions (BFs) of all combinations of identified charged hadron $(\pi,\rm K,\rm p)$ pairs in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV recorded by the ALICE detector are presented. The BF measurements are carried out as two-dimensional differential correlators versus the relative rapidity ($\Delta y$) and azimuthal angle ($\Delta\varphi$) of hadron pairs, and studied as a function of collision centrality. The $\Delta\varphi$ dependence of BFs is expected to be sensitive to the light quark diffusivity in the quark$-$gluon plasma. While the BF azimuthal widths of all pairs substantially decrease from peripheral to central collisions, the longitudinal widths exhibit mixed behaviors: BFs of $\pi\pi$ and cross-species pairs narrow significantly in more central collisions, whereas those of $\rm KK$ and $\rm pp$ are found to be independent of collision centrality. This dichotomy is qualitatively consistent with the presence of strong radial flow effects and the existence of two stages of quark production in relativistic heavy-ion collisions. Finally, the first measurements of the collision centrality evolution of BF integrals are presented, with the observation that charge balancing fractions are nearly independent of collision centrality in Pb$-$Pb collisions. Overall, the results presented provide new and challenging constraints for theoretical models of hadron production and transport in relativistic heavy-ion collisions.
Balance function $B^{\pi\pi}$ measured in semicentral Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76\;\text{TeV}$ ($\pi,{\rm K}: 0.2 \leq p_{\rm T} \leq 2.0\;{\rm GeV}/c$; ${\rm p}: 0.5 \leq p_{\rm T} \leq 2.5\;{\rm GeV}/c$).
Balance function $B^{{\rm KK}}$ measured in semicentral Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76\;\text{TeV}$ ($\pi,{\rm K}: 0.2 \leq p_{\rm T} \leq 2.0\;{\rm GeV}/c$; ${\rm p}: 0.5 \leq p_{\rm T} \leq 2.5\;{\rm GeV}/c$).
Balance function $B^{{\rm p\bar{p}}}$ measured in semicentral Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76\;\text{TeV}$ ($\pi,{\rm K}: 0.2 \leq p_{\rm T} \leq 2.0\;{\rm GeV}/c$; ${\rm p}: 0.5 \leq p_{\rm T} \leq 2.5\;{\rm GeV}/c$).
A search for new top quark interactions is performed within the framework of an effective field theory using the associated production of either one or two top quarks with a Z boson in multilepton final states. The data sample corresponds to an integrated luminosity of 138 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} =$ 13 TeV collected by the CMS experiment at the LHC. Five dimension-six operators modifying the electroweak interactions of the top quark are considered. Novel machine-learning techniques are used to enhance the sensitivity to effects arising from these operators. Distributions used for the signal extraction are parameterized in terms of Wilson coefficients describing the interaction strengths of the operators. All five Wilson coefficients are simultaneously fit to data and 95% confidence level intervals are computed. All results are consistent with the SM expectations.
Expected and observed 95% CL confidence intervals for all Wilson coefficients. The intervals are obtained by scanning over a single Wilson coefficient, while fixing the other Wilson coefficients to their SM values of zero.
Expected and observed 95% CL confidence intervals for all Wilson coefficients. The intervals for all five Wilson coefficients are obtained from a single fit, in which all Wilson coefficients are treated as free parameters.
Covariance between the Wilson coefficients (in units of TeV$^{-4}$), after the 5D fit to data.
In quantum scattering processes between two particles, aspects characterizing the strong and Coulomb forces can be observed in kinematic distributions of the particle pairs. The sensitivity to the interaction potential reaches a maximum at low relative momentum and vanishing distance between the two particles. Ultrarelativistic heavy-ion collisions at the LHC provide an abundant source of many hadron species and can be employed as a measurement method of scattering parameters that is complementary to scattering experiments. This study confirms that momentum correlations of particles produced in Pb-Pb collisions at the LHC provide an accurate measurement of kaon-proton scattering parameters at low relative momentum, allowing precise access to the $ {K}^{-} p\rightarrow {K}^{-} p$ process. This work also validates the femtoscopic measurement in ultrarelativistic heavy-ion collisions as an alternative to scattering experiments and a complementary tool to the study of exotic atoms with comparable precision. In this work, the first femtoscopic measurement of momentum correlations of ${K}^{-} p\ ({K}^{+}\overline{p})$ and ${K}^{+}p ({K}^{-}\overline{p})$ pairs in Pb-Pb collisions at centre-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}} = 5.02$ TeV registered by the ALICE experiment is reported. The components of the ${K}^{-} p$ complex scattering length are extracted and found to be $\Re f_0=-0.91\pm~{0.03}$(stat)$^{+0.17}_{-0.03}$(syst) and $\Im f_0 = 0.92\pm~{0.05}$(stat)$^{+0.12}_{-0.33}$(syst). The results are compared with chiral effective field theory predictions as well as with existing data from dedicated scattering and exotic kaonic atom experiments.
K p (opposite charge) correlation function for centrality 0-5% from Pb-Pb collisions at 5020 GeV
K p (same charge) correlation function for centrality 0-5% from Pb-Pb collisions at 5020 GeV
K p (opposite charge) correlation function for centrality 5-10% from Pb-Pb collisions at 5020 GeV
This Letter presents the first experimental evidence of the attractive strong interaction between a proton and a $\phi$ meson. The result is obtained from two-particle correlations of combined p-$\phi \oplus \overline{\rm {p}}$-$\phi$ pairs measured in high-multiplicity pp collisions at $\sqrt{s}~=~13$ TeV by the ALICE collaboration. The spin-averaged scattering length and effective range of the p-$\phi$ interaction are extracted from the fully corrected correlation function employing the Lednický-Lyuboshits approach. In particular, the imaginary part of the scattering length vanishes within uncertainties, indicating that inelastic processes do not play a prominent role for the p-$\phi$ interaction. These data demonstrate that the interaction is dominated by elastic p-$\phi$ scattering. Furthermore, an analysis employing phenomenological Gaussian- and Yukawa-type potentials is conducted. Under the assumption of the latter, the N-$\phi$ coupling constant is found to be $g_{\rm{N}-\phi} = 0.14\pm 0.03\,(\mathrm{stat.})\pm 0.02\,(\mathrm{syst.})$. This work provides valuable experimental input to accomplish a self-consistent description of the N-$\phi$ interaction, which is particularly relevant for the more fundamental studies on partial restoration of chiral symmetry in nuclear medium.
Measured $\mathrm{p}-\phi$ $\oplus$ $\overline{\mathrm{p}}-\phi$ correlation function.
Genuine $\mathrm{p}-\phi$ $\oplus$ $\overline{\mathrm{p}}-\phi$ correlation function.
The interaction of $\Lambda$ and $\Sigma$ hyperons (Y) with nucleons (N) is strongly influenced by the coupled-channel dynamics. Due to the small mass difference of the $\rm N \Lambda$ and $\rm N \Sigma$ systems, the sizeable coupling strength of the $\rm N \Sigma\leftrightarrow N \Lambda$ processes constitutes a crucial element in the determination of the N$\Lambda$ interaction. In this letter we present the most precise measurements on the interaction of p$\Lambda$ pairs, from zero relative momentum up to the opening of the $\rm N \Sigma$ channel. The correlation function in the relative momentum space for $\mathrm{p}\Lambda\oplus\overline{\mathrm{p}}\overline{\Lambda}$ pairs measured in high-multiplicity triggered pp collisions at $\sqrt{s}~=~13$ TeV at the LHC is reported. The opening of the inelastic N$\Sigma$ channels is visible in the extracted correlation function as a cusp-like structure occurring at relative momentum $k^{*}$ = 289 MeV/$c$. This represents the first direct experimental observation of the $\rm N \Sigma\rightarrow N \Lambda$ coupled channel in the p$\Lambda$ system. The correlation function is compared with recent chiral effective field theory calculations, based on different strengths of the $\rm N \Sigma\leftrightarrow N \Lambda$ transition potential. A weaker coupling, as possibly supported by the present measurement, would require a more repulsive three-body NN$\Lambda$ interaction for a proper description of the $\Lambda$ in-medium properties, which has implications on the nuclear equation of state and for the presence of hyperons inside neutron stars.
p-$\Lambda$ correlation function in high-multiplicity pp collisions at $\sqrt{s}=13$ TeV.
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