# Search for excited $B_c^+$ states

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## Abstract

A search is performed in the invariant mass spectrum of the $B_c^{+}\pi^{+}\pi^{-}$ system for the excited $B_c^{+}$ states $B_c(2^{1}S_{0})^+$ and $B_c(2^{3}S_{1})^+$ using a data sample of $pp$ collisions collected by the LHCb experiment at the centre-of-mass energy of $\sqrt{s} = 8 {\mathrm{TeV}}$, corresponding to an integrated luminosity of $2 {\mathrm{fb^{-1}}}$. No evidence is seen for either state. Upper limits on the ratios of the production cross-sections of the $B_c(2^{1}S_{0})^+$ and $B_c(2^{3}S_{1})^+$ states times the branching fractions of ${B_c(2^{1}S_{0})^+} \to {B_c^{+}\pi^{+}\pi^{-}}$ and ${B_c(2^{3}S_{1})^+} \to {B_c^{*+}\pi^{+}\pi^{-}}$ over the production cross-section of the $B_c^{+}$ state are given as a function of their masses. They are found to be between 0.02 and 0.14 at $95\%$ confidence level for $B_c(2^{1}S_{0})^+$ and $B_c(2^{3}S_{1})^+$ in the mass ranges $[6830, 6890] {\mathrm{MeV}}/c^{2}$ and $[6795,6890] {\mathrm{MeV}}/c^{2}$, respectively.

## Figures and captions

 Invariant mass distribution of the selected $B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+$ candidates. The points with error bars represent the data. The blue solid line is the fit to data. The red cross-hatched area shows the signal. The green shaded area represents the $B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^{+}$ background. The violet dash-dotted line is the combinatorial background. Fig1.pdf [30 KiB] HiDef png [424 KiB] Thumbnail [273 KiB] Mass distributions of the selected $B _ c ^+ \pi ^+ \pi ^-$ candidates in the range $[6795,6890] {\mathrm{ Me V /}c^2}$ for the four MLP categories. Fig2a.pdf [15 KiB] HiDef png [134 KiB] Thumbnail [145 KiB] Fig2b.pdf [16 KiB] HiDef png [144 KiB] Thumbnail [156 KiB] Fig2c.pdf [15 KiB] HiDef png [134 KiB] Thumbnail [141 KiB] Fig2d.pdf [15 KiB] HiDef png [131 KiB] Thumbnail [134 KiB] The $M( B _ c ^+ \pi ^+ \pi ^- )$ distributions in the same-sign (darkgreen shaded areas) and data (points with error bars) samples in the range $[6600,7300] {\mathrm{ Me V /}c^2}$ with the background model (blue solid line) overlaid, for the four MLP categories. The areas between the two vertical red lines are the signal regions. Fig3a.pdf [17 KiB] HiDef png [214 KiB] Thumbnail [175 KiB] Fig3b.pdf [17 KiB] HiDef png [219 KiB] Thumbnail [177 KiB] Fig3c.pdf [17 KiB] HiDef png [232 KiB] Thumbnail [192 KiB] Fig3d.pdf [17 KiB] HiDef png [241 KiB] Thumbnail [199 KiB] The upper limits on the ratio $\mathcal{R}( B _ c ^{(*)}(2S)^+ )$ at $95\%$ and $90\%$ confidence levels under different mass splitting $\Delta M$ hypotheses. Fig4a.pdf [15 KiB] HiDef png [249 KiB] Thumbnail [233 KiB] Fig4b.pdf [16 KiB] HiDef png [337 KiB] Thumbnail [288 KiB] Fig4c.pdf [16 KiB] HiDef png [337 KiB] Thumbnail [288 KiB] Fig4d.pdf [16 KiB] HiDef png [341 KiB] Thumbnail [290 KiB] Animated gif made out of all figures. PAPER-2017-042.gif Thumbnail

## Tables and captions

 Efficiencies for the $B _ c ^{(*)}(2S)^+$ states in the regions $p_{\mathrm{ T}} \in [0,20] {\mathrm{ Ge V /}c}$ and $y \in [2.0,4.5]$ for each MLP category. The efficiencies obtained before applying the MLP classifier are $0.0091 \pm 0.0002$ and $0.0086 \pm 0.0001$ for $B _ c (2S)^+$ and $B _ c ^{*}(2S)^+$, respectively. The uncertainties are statistical only, and are due to the limited size of the simulated sample. Table_1.pdf [51 KiB] HiDef png [48 KiB] Thumbnail [23 KiB] tex code Summary of the systematic uncertainties entering the upper limit calculation for the four MLP categories. Table_2.pdf [75 KiB] HiDef png [80 KiB] Thumbnail [38 KiB] tex code Comparison of the $\mathcal{R}$ value between the LHCb upper limits at 95% CL and the ATLAS measurement [18], where $0 < \varepsilon_{7,8} \leq 1$ are the relative efficiencies of reconstructing the $B _ c ^{(*)}(2S)^+$ candidates with respect to the $B _ c ^+$ signals for the 7 and $8 {\mathrm{ Te V} }$ data, respectively. Table_3.pdf [37 KiB] HiDef png [39 KiB] Thumbnail [19 KiB] tex code

## Supplementary Material [file]

 Supplementary material full pdf Supple[..].pdf [160 KiB] This ZIP file contains supplemetary material for the publication LHCb-PAPER-2017-042. The files are: Supplementary.pdf : An overview of the extra figure and contents *.pdf, *.png, *.eps, *.C : The figure in variuous formats Fig1.pdf [16 KiB] HiDef png [237 KiB] Thumbnail [172 KiB] *C file

Created on 20 August 2019.Citation count from INSPIRE on 23 August 2019.