Date of Award

Winter 12-22-2021

Degree Type


Degree Name

Doctor of Philosophy (PhD)




Skwarnicki, Tomasz

Subject Categories

Physical Sciences and Mathematics | Physics


Resonant structure in the dipion mass spectrum produced via \decay{\Bu}{\X\Kp}, \decay{\X}{\jpsi \pip \pim}, with \decay{\jpsi}{\mu^+\mu^-} is analyzed using Run 1 and Run 2 data samples from the LHCb experiment. The spectrum is dominated by $\rhoz\to\pi^+\pi^-$, but cannot be described by this contribution alone. A significant $\omega\to\pi^+\pi^-$ contribution, interfering with $\rhoz$, is observed for the first time. This is a more significant observation ($>7.1\sigma$) of $\X\to\omega\jpsi$ decays, than previously achieved with $\omega\to\pi^+\pi^-\pi^0$ decays. The relative contribution of $\omega$ to the total $\X\to\pi^+\pi^-\jpsi$ rate is at the level expected from the measured $\X\to(\omega\to\pi^+\pi^-\pi^0)\jpsi$ rate, if the interference between the $\rho^0$ and $\omega$ amplitudes is neglected, $(1.9\pm0.4\pm0.3)\%$. The interference enhances the importance of $\omega$ contribution by an order of magnitude to $(21.4\pm2.3\pm2.0)\%$. The results support interpretations of the $\X$ state as an exotic hadron, since its isospin violating $\rhoz\jpsi$ decay rate, relative to isospin conserving $\omega\jpsi$ decay, is an order of magnitude larger than expected for an ordinary charmonium state.


Open Access

Included in

Physics Commons