Observation of sizeable $\omega$ contribution to $\chi_{c1}(3872) \to \pi^+\pi^- J/\psi$ decays

Information

LHCb-PAPER-2021-045
CERN-EP-2022-049
arXiv:2204.12597 [PDF]

(Submitted on 26 Apr 2022)
Phys. Rev. D 131 (2023) L011103
Inspire 2682599

Tools

Abstract

Resonant structures in the dipion mass spectrum from $\chi_{c1}(3872)\to\pi^+\pi^- J/\psi$ decays, produced via $B^+\to K^+\chi_{c1}(3872)$ decays, are analyzed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 $fb^{-1}$. A sizeable contribution from the isospin conserving $\chi_{c1}(3872)\to\omega J/\psi$ decay is established for the first time, $(21.4\pm2.3\pm2.0)\%$, with a significance of more than $7.1\sigma$. The amplitude of isospin violating decay, $\chi_{c1}(3872)\to\rho^0 J/\psi$, relative to isospin conserving decay, $\chi_{c1}(3872)\to\omega J/\psi$, is properly determined, and it is a factor of six larger than expected for a pure charmonium state.

Figures and captions

Distribution of $m_{\pi ^+ \pi ^- { J \mskip -3mu/\mskip -2mu\psi } }$ ($m_{ K ^+ \pi ^+ \pi ^- { J \mskip -3mu/\mskip -2mu\psi } }$ in the inset) from $ B ^+ \rightarrow K ^+ \pi ^+ \pi ^- { J \mskip -3mu/\mskip -2mu\psi } $ candidates within $\pm2 \sigma$ around the $ B ^+ $ ($\chi _{c1}(3872) $) mass, overlaid with the fit including the total (solid blue), signal (dashed red) and background (dashed green) components.	xmass_[..].pdf [48 KiB] HiDef png [314 KiB] Thumbnail [255 KiB] *.C file
Distribution of $m_{\pi ^+ \pi ^- }$ in $\chi _{c1}(3872) \rightarrow \pi ^+ \pi ^- { J \mskip -3mu/\mskip -2mu\psi } $ decays, fit with the $\rho ^0 $-only model.	mpipi_[..].pdf [24 KiB] HiDef png [182 KiB] Thumbnail [166 KiB] *.C file
Distribution of $m_{\pi ^+ \pi ^- }$ in $\chi _{c1}(3872) \rightarrow \pi ^+ \pi ^- { J \mskip -3mu/\mskip -2mu\psi } $ decays, fit with the default $K$-matrix model.	mpipi_[..].pdf [43 KiB] HiDef png [235 KiB] Thumbnail [203 KiB] *.C file
Distribution of $m_{\pi ^+ \pi ^- }$ in $\chi _{c1}(3872) \rightarrow \pi ^+ \pi ^- { J \mskip -3mu/\mskip -2mu\psi } $ decays, fit with the Gounaris--Sakurai model. The dashed line represents the $\rho'$ contribution multiplied by a factor of 10.	mpipi_[..].pdf [47 KiB] HiDef png [242 KiB] Thumbnail [205 KiB] *.C file
Amplitude model for $\chi _{c1}(3872) \rightarrow \pi ^+ \pi ^- { J \mskip -3mu/\mskip -2mu\psi } $ decays, obtained by the default fit to the LHCb data (Fig. 3), with the phase-space integration limit extended by setting the $\chi _{c1}(3872) $ mass to $4000 \text{ Me V} $. The actual phase-space limit, imposed by the measured $\chi _{c1}(3872) $ mass, is indicated by the vertical dashed line. Neither mass resolution nor detector efficiency are applied here.	mpipi_[..].pdf [31 KiB] HiDef png [206 KiB] Thumbnail [169 KiB] *.C file
Animated gif made out of all figures.	PAPER-2021-045.gif Thumbnail