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LHCb Confirms Existence of Exotic Hadrons
An anonymous reader sends this news from CERN:
"The Large Hadron Collider beauty (LHCb) collaboration today announced results that confirm the existence of exotic hadrons – a type of matter that cannot be classified within the traditional quark model. Hadrons are subatomic particles that can take part in the strong interaction – the force that binds protons inside the nuclei of atoms. Physicists have theorized since the 1960s, and ample experimental evidence since has confirmed, that hadrons are made up of quarks and antiquarks that determine their properties. A subset of hadrons, called mesons, is formed from quark-antiquark pairs, while the rest – baryons – are made up of three quarks. ... The Belle Collaboration reported the first evidence for the Z(4430) in 2008. They found a tantalizing peak in the mass distribution of particles that result from the decays of B mesons. Belle later confirmed the existence of the Z(4430) with a significance of 5.2 sigma on the scale that particle physicists use to describe the certainty of a result. LHCb reports a more detailed measurement of the Z(4430) that confirms that it is unambiguously a particle, and a long-sought exotic hadron at that. They analyzed more than 25,000 decays of B mesons selected from data from 180 trillion (180x10^12) proton-proton collisions in the Large Hadron Collider."
It *is* made up of quarks - a charm quark, an anti-charm quark, down quark, and anti-up quark. The interesting thing is that this is a pairing never before seen - all previous hadrons were either two quarks (quark + antiquark of same color) or three quarks (three quarks or antiquarks, all of different colors). Two quarks and two antiquarks has been postulated but never observed, until now.
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Fuck it, we're doing five quarks.
Would someone tell me how this happened? We were the fucking vanguard of particles in this universe. The meson was the hadron to own. Then the other guy came out with a three-quark nucleon. Were we scared? Hell, no. Because we hit back with a little thing called the proton. That's three quarks and a positive charge. For positivity. But you know what happened next? Shut up, I'm telling you what happened—the bastards went to four quarks. Now we're standing around with our cocks in our hands, selling three quarks and a charge. Charge or no, suddenly we're the chumps. Well, fuck it. We're going to five quarks.
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Is this the MPAA? Is this the RIAA? Is this the DMCA? I thought it was the USA!
To get Psi' you need c-cbar; to get a pi you need an up and a down. The final state they observe is a mu-,mu+ K pi. The production of the muons in pairs means that they came out of the same reaction -- that is you can put them together to get a Psi' with good reliability. So you that leaves you with Psi' k and pi, you could have an initial state that decays to a psi' and a (k+pi) in a baggy (aka the K* resonances), or a psi' and a k and a pi that don't interact with each other (but three prong decays are well down from pair wise decay chains), or a k + (psi' pi) in a baggy. Since momentum and energy are conserved having K*'s in the produced stuff can reflect into the other pairings (this is the crux of the venerable Dalitz plot analysis). The reflections are insufficient to explain away a k +(psi' pi) decay chain --it's not an echo from other known physics. The psi' is a pure ccbar state and the quark content of the pion is well known -- either all four quarks are present in the (psi' pi) baggy or something really weird is going on. Whip out the Occam's razor and you claim a tetraquark. (It's not clear however that the ancient a0(980) and f0(980) are not tetraquarks or molecules ... it's just a very very hard place to work -- here the muon decays help a lot at cleaning up the states -- there's not a great analog of the psi' below 1GeV that is a clean resonance to beat against.