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    Observation of enhanced long-range elliptic anisotropies inside high-multiplicity jets in pp collisions at s\sqrt{s} = 13 TeV

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    International audienceA search for partonic collective effects inside jets produced in proton-proton collisions is performed via correlation measurements of charged constituents using the CMS detector at the CERN LHC. The analysis uses data collected at a center-of-mass energy of s\sqrt{s} = 13 TeV, corresponding to an integrated luminosity of 138 fb−1^{-1}. Jets are reconstructed with the anti-kTk_\mathrm{T} algorithm with a distance parameter of 0.8 and are required to have transverse momentum greater than 550 GeV and pseudorapidity ∣η∣\lvert\eta\rvert<\lt 1.6. Two-particle correlations among the charged constituents within the jets are studied as functions of the particles' azimuthal angle and pseudorapidity separations (Δϕ∗\Delta\phi^* and Δη∗\Delta\eta^*) in a jet coordinate basis, where constituents' η∗\eta^*, ϕ∗\phi^* are defined relative to the direction of the jet. The correlation functions are studied in classes of in-jet charged-particle multiplicity up to NchjN_\text{ch}^\mathrm{j}≈\approx 100. Fourier harmonics are extracted from long-range azimuthal correlation functions to characterize azimuthal anisotropy for ∣Δη∗∣\lvert\Delta\eta^*\rvert>\gt 2. For low-multiplicity jets, the long-range elliptic anisotropic harmonic, v2∗v^*_2, is observed to decrease with NchjN_\text{ch}^\mathrm{j}. This trend is well described by Monte Carlo event generators. However, a rising trend for v2∗v^*_2 emerges at NchjN_\text{ch}^\mathrm{j}≳\gtrsim 80, hinting at a possible onset of collective behavior, which is not reproduced by the models tested. This observation yields new insights into the dynamics of parton fragmentation processes in the vacuum

    Test of lepton flavor universality in B±^{\pm}→\to K±μ+μ−^{\pm}\mu^+\mu^- and B±^{\pm}→\to K±^{\pm}e+^+e−^- decays in proton-proton collisions at s\sqrt{s} = 13 TeV