Decays of Bs and B0 mesons into J/\psi \pi +\pi \pi +\pi  final states, produced in pp collisions at the LHC, are investigated using data corresponding to an integrated luminosity of 3/fb collected with the LHCb detector. B^0_(s) > J\psi f_1(1285) decays are seen for the first time, and the branching fractions are measured. Using these rates, the f_1(1285) mixing angle between strange and nonstrange components of its wave function in the qqbar structure model is determined to be \pm (24.0^{+3.1+0.6}_{2.60.8}) degrees. Implications on the possible tetraquark nature of the f_1(1285) are discussed.
Invariant mass distribution for $ { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \pi^+\pi^\pi^+\pi^$ combinations. The data are fit with Crystal Ball functions for $\overline{ B }{} ^0$ [(red) dashed curve] and $\overline{ B }{} ^0_ s $ [(purple) dotdashed curve] signals, an exponential function for combinatoric background (black) dotted, and a Gaussian shape for lower mass background (blue) longdashed. The total is shown with a (blue) solid curve. 
fitdata.pdf [43 KiB] HiDef png [456 KiB] Thumbnail [257 KiB] *.C file 

Background subtracted invariant mass distributions of the four pions in (a) $\overline{ B }{} ^0_ s $ and (b) $\overline{ B }{} ^0$ decays are shown in the histogram overlaid with the (black) filled points with the error bars indicating the uncertainties. The open (red) circles show the helicity $\pm$1 components of the signals. 
m4pi_h[..].pdf [38 KiB] HiDef png [287 KiB] Thumbnail [191 KiB] *.C file 

Fits to the fourpion invariant mass in (a) $\overline{ B }{} ^0_ s $ and (b) $\overline{ B }{} ^0$ decays. The data are shown as points, the signals components as (black) dashed curves, the combinatorial background by (black) dotted curves, and the higher mass resonance tail by (red) dotdashed curves. 
fitBf[..].pdf [39 KiB] HiDef png [337 KiB] Thumbnail [182 KiB] *.C file 

Animated gif made out of all figures. 
PAPER2013055.gif Thumbnail 
Fit results for $\overline{ B }{} ^0_ s \rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} f_1(1285)$ and $\overline{ B }{} ^0 \rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} f_1(1285)$ decays. 
Table_1.pdf [43 KiB] HiDef png [30 KiB] Thumbnail [15 KiB] tex code 

Systematic uncertainties of the branching fractions ${\cal{B}}(\overline{ B }{} \rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} f_1(1285) , f_1(1285)\rightarrow \pi^+\pi^\pi^+\pi^)$ and the $\overline{ B }{} ^0 /\overline{ B }{} ^0_ s $ rate ratio. The "+" and "" signs indicate the positive and negative uncertainties, respectively. All numbers are in (%). 
Table_2.pdf [40 KiB] HiDef png [74 KiB] Thumbnail [35 KiB] tex code 

Branching fractions used for normalization. 
Table_3.pdf [75 KiB] HiDef png [50 KiB] Thumbnail [24 KiB] tex code 
Created on 06 March 2021.