# First observation of the $B_{s2}^\ast(5840)^0 \to B^{\ast+} K^-$ and studies of excited $B^0_s$ mesons

[to restricted-access page]

## Abstract

Properties of the orbitally excited (L=1) $B_s$ states are studied using 1.0 fb$^{-1}$ of pp collisions at $\sqrt{s} =7$ TeV collected with the LHCb detector. The first observation of the $B_{s2}^*(5840)^0$ meson decaying to $B^{*+} K^-$ is reported, and the corresponding branching fraction measured relative to the $B^+ K^-$ decay mode. The $B_{s1}(5830)^0 \to B^{*+} K^-$ decay is observed as well. The width of the $B_{s2}^*(5840)^0$ state is measured for the first time and the masses of the two states are determined with the highest precision to date. The observation of the $B_{s2}^*(5840)^0 \to B^{*+} K^-$ decay favours the spin-parity assignment $J^P = 2^+$ for the $B_{s2}^*(5840)^0$ meson. In addition, the most precise measurement of the mass difference $m(B^{*+})-m(B^+) = 45.01 \pm 0.30 (stat) \pm 0.23 (syst)$ MeV/$c^2$ is obtained.

## Figures and captions

 Invariant mass spectra of the final $B ^+$ candidates. The signal lineshape is fitted with a double Gaussian distribution, while the background is modelled with a second order polynomial . (a) $B ^+ \rightarrow J/\psi K ^+$, (b) $B ^+ \rightarrow \overline{ D }{} ^0 ( K ^+ \pi ^- ) \pi ^+$, (c) $B ^+ \rightarrow \overline{ D }{} ^0 ( K ^+ \pi ^- \pi ^+ \pi ^- ) \pi ^+$, and (d) $B ^+ \rightarrow \overline{ D }{} ^0 ( K ^+ \pi ^- ) \pi ^+ \pi ^- \pi ^+$ decays. The ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ and $D ^0$ masses are constrained to their world average values. Figure1a.eps [42 KiB] HiDef png [241 KiB] Thumbnail [230 KiB] *.C file Figure1b.eps [45 KiB] HiDef png [266 KiB] Thumbnail [259 KiB] *.C file Figure1c.eps [45 KiB] HiDef png [279 KiB] Thumbnail [271 KiB] *.C file Figure1d.eps [46 KiB] HiDef png [287 KiB] Thumbnail [281 KiB] *.C file Mass difference distribution $m( B ^+ K ^- )-m( B ^+ )-m( K ^- )$. The three peaks are identified as (left) $B _{ s 1} \rightarrow B ^{*+} K ^-$, (middle) $B ^{*}_{ s 2} \rightarrow B ^{*+} K ^-$, and (right) $B ^{*}_{ s 2} \rightarrow B ^+ K ^-$. The total fit function is shown as a solid blue line, while the shaded red region is the spectrum of like-charge $B ^+ K ^+$ combinations. The inset shows an expanded view of the $B _{ s 1} / B ^{*}_{ s 2} \rightarrow B ^{*+} K ^-$ signals. The bottom plot shows the fit pulls. Figure2.eps [124 KiB] HiDef png [393 KiB] Thumbnail [333 KiB] *.C file Animated gif made out of all figures. PAPER-2012-030.gif Thumbnail

## Tables and captions

 Summary of the orbitally excited ($L=1$) $B ^0_ s$ states. Table_1.pdf [54 KiB] HiDef png [60 KiB] Thumbnail [30 KiB] tex code Results of the fit to the mass difference distributions $m( B ^+ K ^- )-m( B ^+ )-m( K ^- )$. The first uncertainties are statistical and the second are systematic. Table_2.pdf [120 KiB] HiDef png [98 KiB] Thumbnail [49 KiB] tex code Absolute systematic uncertainties for each measurement, which are assumed to be independent and are added in quadrature. Table_3.pdf [76 KiB] HiDef png [75 KiB] Thumbnail [33 KiB] tex code

Created on 21 October 2019.