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Comment by akomtu | Hacker News Reader

The article (light on details, as usual) mentions that a slightly different configuration of a tetraquark would be very stable (again, not sure if that means nanoseconds or hours). If such stable multiquarks exist, without an electric charge they would be effectively untraceable, right? The only way to see such a particle would be to hit it precisely with an even smaller particle and get it to bounce back.

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>The only way to see such a particle would be to hit it precisely with an even smaller particle and get it to bounce back.

Bounce back from what force? Whatever forces would make it interact with a single particle would make it interact with a detector, which is itself made out of particles.

They say the extra-stable tetraquark would only be susceptible to decay via the weak force, which means you'd have to wait around until it decayed, and then you'd often be able to see some charged remnants.

Can such tetraquarks form semi stable macroscopic structures like atoms? For example, if they aren't completely neutral, a group of them would be able to maybe attract an electron and become a quasiatom of some sort.

The stable-to-strong-decay species they're talking about, bb anti-u anti-d, would have a charge of (-1 -1 -2 -1)/3 = -5/3 times the electron charge. I guess its antiparticle would be positive, so maybe an electron could hang around for a while. I don't know how long that tetraquark is expected to live, though.

The charge would actually be (-2 + 1 - 1 - 1)/3 = -1 of a proton's charge. There isn't any physically viable combination of quarks that would produce a non-integer charge. The article mentions the bb tetraquark can only decay through the weak force, but I'm not sure how long it'd live either.

I don't think that's a unique property to tetraquarks. Neutrons or neutrinos also are not electrically charged. I'm not sure what you mean by untraceable, but neutrinos rarely interact with other particles and many, many of them pass through you every second without you even noticing.

The more likely (I'm not a physicist) is to watch the decay of the particle and trace it back from there.

A stable heavy-quark tetraquark shouldn't live longer than, say, the B_c meson, which has a lifetime of about 5×10^-13 s

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