Evidence is presented for the decay $B_c+\rightarrow J/\psi 3\pi^+2\pi^$ using protonproton collision data, corresponding to an integrated luminosity of 3fb$^{1}$, collected with the LHCb detector. A signal yield of $32\pm8$ decays is found with a significance of 4.5 standard deviations. The ratio of the branching fraction of the $B_c^+\rightarrow J/\psi 3\pi^+ 2\pi^$ decay to that of the $B_c^+ \rightarrow J/\psi \pi^+$ decay is measured to be $$ \frac{Br (B_c^+ \rightarrow J/\psi 3\pi^+2\pi^)}{Br (B_c^+ \rightarrow J/\psi \pi^+)} = 1.74\pm0.44\pm0.24, $$ where the first uncertainty is statistical and the second is systematic.
Mass distribution for selected $ B _ c ^+ \rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} 3\pi ^+ 2\pi ^ $ candidates. The result of a fit using the model described in the text (red solid line) is shown together with the background component (blue dashed line). 
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Backgroundsubtracted distribution of fivepion mass from $ B _ c ^+ \rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} 3\pi ^+ 2\pi ^ $ events (points with error bars). The model prediction from Ref. [14] is shown by a red solid line, and the expectation from the phase space model is shown by a blue dashed line. 
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Mass distribution for selected $ B _ c ^+ \rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \pi ^+ $ candidates. The result of a fit using the model described in the text (red solid line) is shown together with the background component (blue dashed line). 
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Signal parameters of the unbinned extended maximum likelihood fit to the $ { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} 3\pi ^+ 2\pi ^ $ mass distribution. Uncertainties are statistical only. 
Table_1.pdf [78 KiB] HiDef png [28 KiB] Thumbnail [13 KiB] tex code 

Relative systematic uncertainties for the ratio $R_{5\pi }$. The total uncertainty is the quadratic sum of the individual components. 
Table_2.pdf [63 KiB] HiDef png [93 KiB] Thumbnail [43 KiB] tex code 
Created on 05 March 2021.