cern.ch

Search for excited $B_c^+$ states

[to restricted-access page]

Information

Tools

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 [421 KiB]
Thumbnail [271 KiB]
 Fig1.pdf

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 [105 KiB]
Thumbnail [63 KiB]
 Fig2a.pdf
Fig2b.pdf [16 KiB]
HiDef png [113 KiB]
Thumbnail [67 KiB]
 Fig2b.pdf
Fig2c.pdf [15 KiB]
HiDef png [104 KiB]
Thumbnail [61 KiB]
 Fig2c.pdf
Fig2d.pdf [15 KiB]
HiDef png [102 KiB]
Thumbnail [58 KiB]
 Fig2d.pdf

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 [201 KiB]
Thumbnail [174 KiB]
 Fig3a.pdf
Fig3b.pdf [17 KiB]
HiDef png [199 KiB]
Thumbnail [171 KiB]
 Fig3b.pdf
Fig3c.pdf [17 KiB]
HiDef png [204 KiB]
Thumbnail [178 KiB]
 Fig3c.pdf
Fig3d.pdf [17 KiB]
HiDef png [207 KiB]
Thumbnail [183 KiB]
 Fig3d.pdf

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 [248 KiB]
Thumbnail [231 KiB]
 Fig4a.pdf
Fig4b.pdf [16 KiB]
HiDef png [328 KiB]
Thumbnail [285 KiB]
 Fig4b.pdf
Fig4c.pdf [16 KiB]
HiDef png [329 KiB]
Thumbnail [285 KiB]
 Fig4c.pdf
Fig4d.pdf [16 KiB]
HiDef png [332 KiB]
Thumbnail [287 KiB]
 Fig4d.pdf

Animated gif made out of all figures.

 PAPER-2017-042.gif
Thumbnail
thumbnail_PAPER-2017-042.gif

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 [66 KiB]
HiDef png [42 KiB]
Thumbnail [19 KiB]
tex code 		Table_1.pdf

Summary of the systematic uncertainties entering the upper limit calculation for the four MLP categories.

 Table_2.pdf [90 KiB]
HiDef png [67 KiB]
Thumbnail [30 KiB]
tex code 		Table_2.pdf

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 [51 KiB]
HiDef png [33 KiB]
Thumbnail [16 KiB]
tex code 		Table_3.pdf

Supplementary Material [file]

Supplementary material full pdf

 Supple[..].pdf [160 KiB]
 Supplementary.pdf

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 [195 KiB]
Thumbnail [170 KiB]
*C file
Fig1.pdf

Created on 26 April 2024.