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Abstract:

Charged-hadron distributions in heavy-flavor jets are measured in proton-proton collisions at a center-of-mass energy of s=13 TeV collected by the LHCb experiment. Distributions of the longitudinal momentum fraction, transverse momentum, and radial profile of charged hadrons are measured separately in beauty and charm jets. The distributions are compared to those previously measured by the LHCb collaboration in jets produced back-to-back with a Z boson, which in the forward region are primarily light-quark-initiated, to compare the hadronization mechanisms of heavy and light quarks. The observed differences between the heavy- and light-jet distributions are consistent with the heavy-quark dynamics expected to arise from the dead-cone effect, as well as with a hard fragmentation of the heavy-flavor hadron as previously measured in single-hadron fragmentation functions. This measurement provides additional constraints for the extraction of collinear and transverse-momentum-dependent heavy-flavor fragmentation functions and offers another approach to probing the mechanisms that govern heavy-flavor hadronization.

Abstract:

The first four-dimensional amplitude analysis of the $B^{+}→\mathrm{ψ}(2S)K_{\mathrm{S}}^0{\mathrm{π}}^{+}$ decay is performed with proton-proton collision data collected by the LHCb experiment at $\sqrt{s}=13\mathrm{TeV}$ , corresponding to an integrated luminosity of $5.4\mathrm{f}{\mathrm{b}}^{−1}$ . The data cannot be fully explained by $B^{+}→\mathrm{ψ}(2S)K^{*+}$ contributions alone. A significantly better description of the data is obtained by adding a $T_{c\stackrel{¯}{c}}^{+}$ contribution decaying to $\mathrm{ψ}(2S){\mathrm{π}}^{+}$ . The properties of the $T_{c\stackrel{¯}{c}}^{+}$ structure are consistent with the exotic state $T_{c\stackrel{¯}{c}1}(4430{)}^{+}$ reported in the isospin-related ${\stackrel{¯}{B}}^0→\mathrm{ψ}(2S)K^{−}{\mathrm{π}}^{+}$ decay. Effects of a possible $T_{c\stackrel{¯}{c}1}(4430{)}^{+}→{\stackrel{¯}{D}}_1^{*}(2600{)}^0{D}^{+}$ decay mode on the $T_{c\stackrel{¯}{c}1}(4430{)}^{+}→\mathrm{ψ}(2S){\mathrm{π}}^{+}$ mass distribution are investigated through a Flatté parametrization, providing constraints on the relative decay strength. A description of the $T_{c\stackrel{¯}{c}1}(4430{)}^{+}$ structure using the triangle singularity mechanism is studied and also found to be consistent with the data.

Abstract:

The first observation of the ${\mathrm{χ}}_{c1}(3872)→J/\mathrm{ψ}{\mathrm{μ}}^{+}{\mathrm{μ}}^{−}$ decay is reported using proton-proton collision data recorded with the LHCb detector corresponding to an integrated luminosity of $9{\mathrm{fb}}^{−1}$ . The decay mode is observed for the first time, with a significance of $6.5\mathrm{σ}$ . Its branching fraction is measured relative to the ${\mathrm{χ}}_{c1}(3872)→J/\mathrm{ψ}{\mathrm{Ï€}}^{+}{\mathrm{Ï€}}^{−}$ decay mode $\frac{\mathcal{B}({\mathrm{χ}}_{c1}(3872)→J/\mathrm{ψ}{\mathrm{μ}}^{+}{\mathrm{μ}}^{−})}{\mathcal{B}({\mathrm{χ}}_{c1}(3872)→J/\mathrm{ψ}{\mathrm{Ï€}}^{+}{\mathrm{Ï€}}^{−})}=(1.68Â\pm 0.32Â\pm 0.05)×{10}^{−3}$ , where the first uncertainty includes both statistical contributions and systematic contributions which are uncorrelated between data-taking periods, and the second represents the systematic contributions that are correlated between data-taking periods.

Abstract:

A search for $K_{\mathrm{S}(\mathrm{L})}^0→{\mathrm{π}}^{+}{\mathrm{π}}^{−}{\mathrm{μ}}^{+}{\mathrm{μ}}^{−}$ decays is performed using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{−1}$ . No $K_{\mathrm{S}(\mathrm{L})}^0→{\mathrm{π}}^{+}{\mathrm{π}}^{−}{\mathrm{μ}}^{+}{\mathrm{μ}}^{−}$ signals are found and upper limits are set for the first time on the branching fractions $\mathcal{B}(K_{\mathrm{S}}^0→{\mathrm{π}}^{+}{\mathrm{π}}^{−}{\mathrm{μ}}^{+}{\mathrm{μ}}^{−})<1.4×{10}^{−9}$ and $\mathcal{B}(K_{\mathrm{L}}^0→{\mathrm{π}}^{+}{\mathrm{π}}^{−}{\mathrm{μ}}^{+}{\mathrm{μ}}^{−})<6.6×{10}^{−7}$ , at the 90% confidence level.

Abstract:

A search for long-lived heavy neutral leptons produced in B-meson decays and decaying to a μ±π∓ final state is performed with data collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5 fb−1. The results are interpreted in both lepton-number-conserving and lepton-number-violating scenarios. No significant excess is observed. Constraints are placed on the squared mixing element |UμN|2 to the active muon neutrino, under the assumption that couplings to other lepton flavours are negligible, in the mass range of 1.6–5.5 GeV.