Study of the $\psi_2(3823)$ and $\chi_{c1}(3872)$ states in $B^+\to (J/\psi \pi^+\pi^-)K^+$ decays

Information

LHCb-PAPER-2020-009
CERN-EP-2020-071
arXiv:2005.13422 [PDF]

(Submitted on 27 May 2020)
JHEP 08 (2020) 123
Inspire 1798040

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Abstract

The decays $B^+\rightarrow J/\psi \pi^+ \pi^- K^+$ are studied using a data set corresponding to an integrated luminosity of 9fb$^{-1}$ collected with the LHCb detector in proton-proton collisions between 2011 and 2018. Precise measurements of the ratios of branching fractions with the intermediate $\psi_2(3823)$, $\chi_{c1}(3872)$ and $\psi(2S)$ states are reported. The decay of $B^+\rightarrow \psi_2(3823)K^+$ with $\psi_2(3823)\rightarrow J\psi\pi^+\pi^-$ is observed for the first time with a significance of 5.1 standard deviations. The mass differences between the $\psi_2(3823)$, $\chi_{c1}(3872)$ and $\psi(2S)$ states are measured to be $$ \begin{array}{rcl} m_{\chi_{c1(3872)}} - m_{\psi_2(3823)} &= & 47.50 \pm 0.53 \pm 0.13 \mathrm{MeV/}c^2 , \\ m_{\psi_2(3823)} - m_{\psi(2S)} &= & 137.98 \pm 0.53 \pm 0.14 \mathrm{MeV/}c^2 , \\ m_{\chi_{c1}(3872)} - m_{\psi(2S)} &= & 185.49 \pm 0.06 \pm 0.03 \mathrm{MeV/}c^2 , \end{array} $$ resulting in the most precise determination of the $\chi_{c1}(3782)$ mass. The width of the $\psi_2(3823)$ state is found to be below 5.2MeV at 90% confidence level. The Breit-Wigner width of the $\chi_{c1}(3872)$ state is measured to be $$ \Gamma^{\mathrm{BW}}_{\chi_{c1}(3872)} = 0.96^{+0.19}_{-0.18}\pm0.21 \mathrm{MeV},$$ which is inconsistent with zero by 5.5 standard deviations.

Figures and captions

Distribution for the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ \pi ^- K ^- $ mass for selected $ B ^+$ candidates (points with error bars). A fit, described in the text, is overlaid.	Fig_1.pdf [100 KiB] HiDef png [249 KiB] Thumbnail [190 KiB] *.C file tex code
Distributions of the (left) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ $\pi ^+$ $\pi ^-$ $ K ^+$ and (right) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ $\pi ^+$ $\pi ^-$ mass for selected (top) $ B ^+ \rightarrow \psi {\rm{(2S)}} K ^+ $ , (middle) $ B ^+ \rightarrow \psi _2(3823) K ^+ $ and (bottom) $ B ^+ \rightarrow \chi _{ c 1} (3872) K ^+ $ candidates shown as points with error bars. A fit, described in the text, is overlaid.	Fig_2.pdf [245 KiB] HiDef png [927 KiB] Thumbnail [664 KiB] *.C file tex code
Likelihood profiles for the Breit--Wigner width of (left) $\psi _2(3823)$ and (right) $\chi _{ c 1} (3872)$ states.	Fig_3.pdf [96 KiB] HiDef png [104 KiB] Thumbnail [86 KiB] *.C file tex code
Animated gif made out of all figures.	PAPER-2020-009.gif Thumbnail

Tables and captions

Parameters of interest and derived quantities from the simultaneous unbinned extended maximum-likelihood two-dimensional fit. Results and statistical uncertainties are shown for the three fit regions.	Table_1.pdf [93 KiB] HiDef png [48 KiB] Thumbnail [22 KiB] tex code
Relative systematic uncertainties (in %) for the ratios of branching fractions $\mathcal{R}^{\mathrm{X}}_{\mathrm{Y}}$.	Table_2.pdf [79 KiB] HiDef png [85 KiB] Thumbnail [37 KiB] tex code
Systematic uncertainties (in $\text{ Me V /}c^2$ ) for the mass splitting between the $\psi _2(3823)$ , $\chi _{ c 1} (3872)$ and $\psi {\rm{(2S)}}$ states.	Table_3.pdf [78 KiB] HiDef png [62 KiB] Thumbnail [26 KiB] tex code

Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [434 KiB]
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