LHCb

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 $D^{+(0)}\to K^{-}{\pi }^{+}{\pi }^{0(-)}{e}^{+}{\nu }_e$ . The amplitude analysis gives the hadronic form factors of the semileptonic $D$ transitions into the axial-vector meson ${\overline{K}}_1(1270)$ to be $r_A=(-11.2\pm {1.0}_{\mathrm{stat}}\pm {0.9}_{\mathrm{syst}})\times {10}^{-2}$ and $r_V=(-4.3\pm {1.0}_{\mathrm{stat}}\pm {2.5}_{\mathrm{syst}})\times {10}^{-2}$ . This is the first in the semileptonic decays of heavy mesons into axial-vector mesons. The angular analysis yields an up-down asymmetry ${\mathcal{A}}_{\mathrm{ud}}^{\prime }=0.01\pm 0.11$ , which is consistent with the standard model prediction. In addition, the branching fractions of $D^{+}\to {\overline{K}}_1(1270{)}^0{e}^{+}{\nu }_e$ and $D^0\to K_1(1270{)}^{-}{e}^{+}{\nu }_e$ are determined with improved precision to be $(2.27\pm 0.11_{\mathrm{stat}}\pm 0.07_{\mathrm{syst}}\pm 0.07_{\text{input}})\times {10}^{-3}$ and $(1.02\pm 0.06_{\mathrm{stat}}\pm 0.06_{\mathrm{syst}}\pm 0.03_{\text{input}})\times {10}^{-3}$ , respectively. No significant signals of $D^{+}\to {\overline{K}}_1(1400{)}^0{e}^{+}{\nu }_e$ and $D^0\to K_1(1400{)}^{-}{e}^{+}{\nu }_e$ are observed and their branching fraction upper limits are set as $1.4\times {10}^{-4}$ and $0.7\times {10}^{-4}$ at 90% confidence level, respectively.

Abstract:

A study on the Bose-Einstein correlations for triplets of same-sign pions is presented. The analysis is performed using proton-proton collisions at a centre-of-mass energy of s = 7 TeV, recorded by the LHCb experiment, corresponding to an integrated luminosity of 1.0 fb−1. For the first time, the results are interpreted in the core-halo model. The parameters of the model are determined in regions of charged-particle multiplicity. This measurement provides insight into the nature of hadronisation in terms of coherence, being consistent with the presence of coherent emission of pions.

Abstract:

Using $e^{+}{e}^{-}$ collision data collected with the BESIII detector operating at the Beijing electron positron collider, the cross section of $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{h}_c$ is measured at 59 points with center-of-mass energy $\sqrt{s}$ ranging from 4.009 to 4.950 GeV with a total integrated luminosity of $22.2{\mathrm{fb}}^{-1}$ . The cross section between 4.3 and 4.45 GeV exhibits a plateaulike shape and drops sharply around 4.5 GeV, which cannot be described by two resonances only. Three coherent Breit-Wigner functions are used to parametrize the $\sqrt{s}$ -dependent cross section line shape. The masses and widths are determined to be $M_1=({4223.6}_{-3.7-2.9}^{+3.6+2.6})\mathrm{MeV}/c^2$ , ${\mathrm{\Gamma }}_1=({58.5}_{-11.4-6.5}^{+10.8+6.7})\mathrm{MeV}$ , $M_2=({4327.4}_{-18.8-9.3}^{+20.1+10.7})\mathrm{MeV}/c^2$ , ${\mathrm{\Gamma }}_2=({244.1}_{-27.1-18.3}^{+34.0+24.2})\mathrm{MeV}$ , and $M_3=({4467.4}_{-5.4-2.7}^{+7.2+3.2})\mathrm{MeV}/c^2$ , and ${\mathrm{\Gamma }}_3=({62.8}_{-14.4-7.0}^{+19.2+9.9})\mathrm{MeV}$ . The first uncertainties are statistical and the second are systematic. The inclusion of the relatively narrower third component proves crucial for reproducing the drop at around 4.5 GeV. The statistical significance of the three-resonance assumption over the two-resonance assumption is greater than $5\sigma$ .