First observation of $\overline{B}^{0}_{s} \to D^{*+}_{s2}X\mu^{-}\overline{\nu}$ decays

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Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the semileptonic decays Bs -> Ds+ X mu nu and Bs -> D0 K+ X mu nu are detected. Two structures are observed in the D0 K+ mass spectrum at masses consistent with the known D^+_{s1}(2536) and $D^{*+}_{s2}(2573) mesons. The measured branching fractions relative to the total Bs semileptonic rate are B(Bs -> D_{s2}^{*+} X mu nu)/B(Bs -> X mu nu)= (3.3\pm 1.0\pm 0.4)%, and B(Bs -> D_{s1}^+ X munu)/B(Bs -> X mu nu)= (5.4\pm 1.2\pm 0.5)%, where the first uncertainty is statistical and the second is systematic. This is the first observation of the D_{s2}^{*+} state in Bs decays; we also measure its mass and width.

Figures and captions

The invariant $K^+K^-\pi^+$ mass spectra for events associated with a muon for the 3 pb$^{-1}$ sample in the pseudorapidity interval $2<\eta<6$ for RS combinations (a) and WS combinations (c). Also shown is the natural logarithm of the IP distributions of the $D_s^+$ candidates for (b) RS and (d) WS $D^+_s$ muon candidate combinations. The labelling of the curves is the same on all four sub-figures. In descending order in (a): green-solid curve shows the total, the blue-dashed curve the Dfb signal, the black-dotted curve the sideband background, the purple-dot-dashed the misinterpreted $\Lambda_c^+\to pK^-\pi^+$ contribution, the black dash-dash-dot curve the $D^{*+}\to \pi^+D^0\to K^+K^-\pi^+$ contribution, and the barely visible red-solid curves the Prompt yield. The Dfb signal, the $\Lambda_c^+$ reflection and $D^{*+}$ signal are too small to be seen in the WS distributions. The insert in (b) shows an expanded view of the region populated by Prompt charm production.

Ds-ove[..].eps [195 KiB]
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The mass difference $m(K^-\pi^+K^+)-m(K^-\pi^+)$ added to the known $D^0$ mass for events with $K^-\pi^+$ invariant masses within $\pm$20 MeV of the $D^0$ mass (black points) in semileptonic decays. The histogram shows wrong-sign events with an additional $K^-$ instead of a $K^+$. The curves are described in the text. (a) For the 3 pb$^{-1}$ data sample and (b) for the 20 pb$^{-1}$ sample.

ds2_3p[..].eps [117 KiB]
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Animated gif made out of all figures.


Created on 11 July 2020.