The decay Bc+ > J/psi pi+pipi+ is observed for the first time, using 0.8 fb1 of pp collisions at sqrt{s}=7 TeV collected by the LHCb experiment. The ratio of branching fractions BR(Bc+ > J/psi pi+pipi+)/BR(B_c+ > J/psi pi+) is measured to be 2.41+0.30+0.33, where the first uncertainty is statistical and the second systematic. The result is in agreement with theoretical predictions.
Invariant mass distribution of $B_c^+\rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \pi^+\pi^\pi^+$ (top) and $B_c^+\rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \pi^+$ (bottom) candidates. The maximum likelihood fits of $B_c^+$ signals are superimposed. 
fig3p_[..].pdf [18 KiB] HiDef png [261 KiB] Thumbnail [245 KiB] *.C file 

Invariant mass distribution of the $\pi^+\pi^\pi^+$ combinations for the sidebandsubtracted $B_c^+\rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \pi^+\pi^\pi^+$ data (points) and signal simulation (lines). The solid blue line corresponds to the BLL simulations, the PH model is shown as a green dashed line and the PHPOL model is shown as a red dotted line. All error bars are statistical. 
fig3p_ppp.pdf [15 KiB] HiDef png [239 KiB] Thumbnail [224 KiB] *.C file 

Invariant mass distribution of the $\pi^+\pi^$ combinations (two entries per $B_c^+$ candidate) for the sidebandsubtracted $B_c^+\rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \pi^+\pi^\pi^+$ data (points) and signal simulation (lines). The solid blue line corresponds to the BLL simulations, the PH model is shown as a green dashed line and the PHPOL model is shown as a red dotted line. All error bars are statistical. 
fig3p_pp.pdf [16 KiB] HiDef png [243 KiB] Thumbnail [234 KiB] *.C file 

Distributions of the cosine of the angle between the $\mu^+$ and $B_c^+$ boosted to the rest frame of the $ { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} $ meson for the sidebandsubtracted $B_c^+\rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \pi^+$ (top) and $B_c^+\rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \pi^+\pi^\pi^+$ (bottom) data (points) and signal simulation (lines). In the bottom plot, the solid blue line corresponds to the BLL simulations, the PH model is shown as a green dashed line and the PHPOL model is shown as a red dotted line. All error bars are statistical. 
fig3p_[..].pdf [16 KiB] HiDef png [195 KiB] Thumbnail [189 KiB] *.C file 

Animated gif made out of all figures. 
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Created on 19 February 2021.