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Abstract:

A sample of $pp$ collision data, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{−1}$ and collected by the LHCb experiment during LHC Run 2, is used to measure the ratio of the lifetime of the ${\mathrm{Ó\copyright }}_b^0$ baryon to that of the ${\mathrm{Âì}}_b^0$ baryon, $r_{\mathrm{Ï„}}≡{\mathrm{Ï„}}_{{\mathrm{Ó\copyright }}_b^0}/{\mathrm{Ï„}}_{{\mathrm{Âì}}_b^0}$ . The value $r_{\mathrm{Ï„}}^{\mathrm{Run}2}=1.004Â\pm 0.009Â\pm 0.006$ is obtained, where the first uncertainty is statistical and the second systematic. This value is averaged with the corresponding value from Run 1 to obtain $r_{\mathrm{Ï„}}=1.004Â\pm 0.008Â\pm 0.005$ . Multiplying by the known value of the ${\mathrm{Âì}}_b^0$ lifetime yields ${\mathrm{Ï„}}_{{\mathrm{Ó\copyright }}_b^0}=1.475Â\pm 0.012Â\pm 0.008Â\pm 0.009\mathrm{ps}$ , where the last uncertainty is due to the limited knowledge of the ${\mathrm{Âì}}_b^0$ lifetime. This measurement improves the precision of the current world average of the ${\mathrm{Ó\copyright }}_b^0$ lifetime by about a factor of two, and is in good agreement with the most recent theoretical predictions.

Abstract:

The LHCb collaboration presents a novel suite of heavy-flavour jet substructure measurements at forward rapidity in proton-proton collisions at a centre-of-mass energy of s = 13 TeV. The jet mass is a perturbatively calculable probe of the virtuality of hard-scattered quarks and gluons, connecting small-distance quantum chromodynamics (QCD) with long-distance experimental measurement. The jet mass is dominated by nonperturbative corrections at small values, presenting an excellent test of QCD across a broad range of jet energies. Measuring heavy-flavour jet mass with a theoretically unambiguous flavour definition for the first time probes the gluon splitting mechanism for heavy-flavour production and offers tests of perturbative QCD at new levels of theoretical precision. Utilising the soft drop jet-grooming technique to access the perturbative jet core further enhances constraints on first-principles theory. Measurements of the jet mass for jets containing fully reconstructed B ± hadrons are reported with and without grooming. The unique phase space instrumented by LHCb offers a different quark-gluon fraction than at midrapidity. These results offer unparalleled tests of quark flavour and mass dependence in QCD and provide a baseline for future studies of heavy-flavour jet quenching in heavy-ion collisions.

Abstract:

Using $e^{+}{e}^{−}$ data taken at the center-of-mass energy of 3.773 GeV with the BESIII detector, corresponding to an integrated luminosity of $20.3{\mathrm{fb}}^{−1}$ , we report the first measurement of the decay dynamics of the semileptonic decays $D^{+(0)}→K^{−}{\mathrm{Ï€}}^{+}{\mathrm{Ï€}}^{0(−)}{e}^{+}{\mathrm{ν}}_e$ . The amplitude analysis gives the hadronic form factors of the semileptonic $D$ transitions into the axial-vector meson ${\stackrel{¯}{K}}_1(1270)$ to be $r_A=(−11.2Â\pm {1.0}_{\mathrm{stat}}Â\pm {0.9}_{\mathrm{syst}})×{10}^{−2}$ and $r_V=(−4.3Â\pm {1.0}_{\mathrm{stat}}Â\pm {2.5}_{\mathrm{syst}})×{10}^{−2}$ . This is the first in the semileptonic decays of heavy mesons into axial-vector mesons. The angular analysis yields an up-down asymmetry ${\mathcal{A}}_{\mathrm{ud}}^{′}=0.01Â\pm 0.11$ , which is consistent with the standard model prediction. In addition, the branching fractions of $D^{+}→{\stackrel{¯}{K}}_1(1270{)}^0{e}^{+}{\mathrm{ν}}_e$ and $D^0→K_1(1270{)}^{−}{e}^{+}{\mathrm{ν}}_e$ are determined with improved precision to be $(2.27Â\pm 0.11_{\mathrm{stat}}Â\pm 0.07_{\mathrm{syst}}Â\pm 0.07_{\text{input}})×{10}^{−3}$ and $(1.02Â\pm 0.06_{\mathrm{stat}}Â\pm 0.06_{\mathrm{syst}}Â\pm 0.03_{\text{input}})×{10}^{−3}$ , respectively. No significant signals of $D^{+}→{\stackrel{¯}{K}}_1(1400{)}^0{e}^{+}{\mathrm{ν}}_e$ and $D^0→K_1(1400{)}^{−}{e}^{+}{\mathrm{ν}}_e$ are observed and their branching fraction upper limits are set as $1.4×{10}^{−4}$ and $0.7×{10}^{−4}$ at 90% confidence level, respectively.