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A bit of history of particle physics that takes an unexpected turn today. In 2003 the BaBar experiment at SLAC reported a particle decaying to a Ds meson and a neutral pion, with a mass of 2317 MeV. arxiv.org/abs/hep-ex/0...

Patrick Koppenburg 🐧

@koppenburg.ch

They also saw a peak in the combination of a Bs meson, a pion and a photon, but were unsure what it was.

Patrick Koppenburg 🐧

@koppenburg.ch

I was at Belle in Japan at the time and we had the data to confirm this observation. So I wrote a quick analysis in the morning and after lunch I had a peak with 340 events (I no longer have the plot, sadly).

24/9/26, 9:00 am0 reposts2 likes

Patrick Koppenburg 🐧

@koppenburg.ch

Things went very fast. A week later the CLEO experiment confirmed the particle at 2317 MeV and also that at 2460. arxiv.org/abs/hep-ex/0...

Patrick Koppenburg 🐧

@koppenburg.ch

And in Summer Belle reported the quantum properties of the two particles arxiv.org/abs/hep-ex/0... and arxiv.org/abs/hep-ex/0... .

Patrick Koppenburg 🐧

@koppenburg.ch

So what is this particle at 2317 MeV? The decay to Ds and pion says it's a strong interaction process. But that should be forbidden as it does not respect isospin, a symmetry between light quarks that the strong interaction conserves.

Patrick Koppenburg 🐧

@koppenburg.ch

The quark content says it's an excited strange-charmed meson, which usually decay to a D meson and a strange kaon. But that's not allowed as its mass is too low. So the only chance it has is to violate isospin conservation.