Physicists have confirmed a 'glued-together' form of matter that doesn't fit our standard model of how the universe is built.
April 17, 2026
Original Paper
Observation of the Exotic State $\pi_{1}(1600)$ in $\psi(2S)\rightarrow\gamma\chi_{c1},\chi_{c1}\rightarrow\pi^{+}\pi^{-}\eta'$
arXiv · 2604.12524
The Takeaway
In the standard view of physics, matter (mesons) is made of a quark and an anti-quark. But this discovery of the pi_1(1600) particle—with a massive 21-sigma statistical certainty—reveals 'exotic' matter where the 'glue' that holds quarks together actually plays an active role in the particle's structure. It’s like finding a house where the mortar is just as important as the bricks themselves. This proves there are entire families of particles we haven't mapped yet, showing that the 'strong force' holding atoms together is much weirder than we thought. Understanding this helps us solve the mystery of why we exist at all by revealing the hidden layers of the subatomic world.
From the abstract
A partial wave analysis of the process $\psi(2S)\rightarrow\gamma\chi_{c1}, \chi_{c1}\rightarrow\pi^+\pi^-\eta^{\prime}$ is performed using $(2712.4\pm14.3)\times10^{6}$ $\psi(2S)$ events collected with the BESIII detector. An isovector state with exotic quantum numbers $J^{PC}=1^{-+}$, denoted as $\pi_{1}(1600)$, is observed for the first time in the charmonium decay of $\chi_{c1}\rightarrow\pi_{1}^{\pm}(1600)\pi^{\mp}$, $\pi_{1}^{\pm}(1600)\rightarrow\pi^{\pm}\eta^{\prime}$ with a statistical