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## Study of the ψ2(3823) and χc1(3872) states in B+→(J/ψπ+π−)K+ decays

Journal of High Energy Physics. 2020. Vol. 2020. No. 8. P. 1-27.

The decays B+  J/ψπ+πK+ are studied using a data set corresponding to an integrated luminosity of 9 fb1 collected with the LHCb detector in proton-proton collisions between 2011 and 2018. Precise measurements of the ratios of branching fractions with the intermediate ψ2(3823), χc1(3872) and ψ(2S) states are reported. The values are

B+→ψ2(3823)K+×ψ2(3823)→J/ψπ+π−B+→χc1(3872)K+×χc1(3872)→J/ψπ+π−=(3.56±0.67±0.11)×10−2,B+→ψ2(3823)K+×ψ2(3823)→J/ψπ+π−B+→ψ(2S)K+×ψ(2S)→J/ψπ+π−=(1.31±0.25±0.04)×10−3,B+→χc1(3872)K+×χc1(3872)→J/ψπ+π−B+→ψ(2S)K+×ψ(2S)→J/ψπ+π−=(3.69±0.07±0.06)×10−2,BB+→ψ2(3823)K+×Bψ2(3823)→J/ψπ+π−BB+→χc1(3872)K+×Bχc1(3872)→J/ψπ+π−=(3.56±0.67±0.11)×10−2,BB+→ψ2(3823)K+×Bψ2(3823)→J/ψπ+π−BB+→ψ(2S)K+×Bψ(2S)→J/ψπ+π−=(1.31±0.25±0.04)×10−3,BB+→χc1(3872)K+×Bχc1(3872)→J/ψπ+π−BB+→ψ(2S)K+×Bψ(2S)→J/ψπ+π−=(3.69±0.07±0.06)×10−2,

where the first uncertainty is statistical and the second is systematic. The decay of B+  ψ2(3823)K+ with ψ2(3823)  J/ψπ+π is observed for the first time with a significance of 5.1 standard deviations. The mass differences between the ψ2(3823), χc1(3872) and ψ(2S) states are measured to be

𝑚χc1(3872)−𝑚ψ2(3823)=47.50±0.53±0.13MeV/𝑐2,𝑚ψ2(3823)−𝑚ψ2(2S)=137.98±0.53±0.14MeV/𝑐2,𝑚χc1(3872)−𝑚ψ2(2S)=185.49±0.06±0.03MeV/𝑐2,mχc1(3872)−mψ2(3823)=47.50±0.53±0.13MeV/c2,mψ2(3823)−mψ2(2S)=137.98±0.53±0.14MeV/c2,mχc1(3872)−mψ2(2S)=185.49±0.06±0.03MeV/c2,

resulting in the most precise determination of the χc1(3872) mass. The width of the ψ2(3823) state is found to be below 5.2 MeV at 90% confidence level. The Breit-Wigner width of the χc1(3872) state is measured to be

ΓBWχc1(3872)=0.96+0.19−0.18±0.21MeVΓχc1(3872)BW=0.96−0.18+0.19±0.21MeV

which is inconsistent with zero by 5.5 standard deviations.