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Avast ye tetraquarks!

New Scientist has a story today that claims the discovery of tetraquark particles—particles that are made of four quarks instead of the usual three.

The story appears to be off the back of this paper published last month in Physical Review Letters. Ahmed Ali at the Deutsches Elektronen-Synchrotron DESY in Hamburg, Germany, analysed data from a Japanese experiment known as Belle and found that a particularly rapid decay from a particle collision might be explained if the accelerator were creating particles made of a bottom quark, an up quark, and their two corresponding antiparticles.

Quarks normally come in twos or threes. Three-quark particles, known collectively as baryons, are quite common and include the protons and neutrons that make up much of the author of this post. Particles made of quarks and their anti-quark pairs (known as mesons) are a little more exotic, but still pretty common in particle collisions.

But higher-number quark particles are another kettle of fish. In 2002, Japanese physicists thought they had seen a pentaquark particle made of five quarks. But subsequent measurements showed that the anomalies spotted by the Japanese were probably statistical rather than real, and the pentaquark faded from view.

Hints of tetraquarks have also been seen elsewhere. At the April 2008 meeting of the American Physical Society, Eric Swanson of the University of Pittsburgh gave a press conference presented a talk on a particle known as X(3782), which might be a tetraquark.

The new paper certainly doesn’t appear to be a smoking gun. It says that the analysis provides “excellent fits” for the unusually quick decays, but concedes more data from Belle will be needed before the researchers can conclusively claim evidence of a tetraquark state.


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    Ahmed Ali said:

    Following Paul Dirac’s maxim,

    a good theory is easily falsifiable, the tetraquark interpretation of the Belle

    measurements has to be verified in independent experiments and by verifying various predicted features by

    the Belle collaboration in their new data which they are collecting. For me, this list of checks include: confirmation of the

    isotopic doublet nature of

    the tetraquarks, which can be done by doing an energy scan in e+ e- annihilation

    experiments, confirmation of the resonant structure in the dipion invariant masses, and observations of the Yb and related tetraquarks at the Tevatron and the LHC. However, it must be emphasized that, unlike the pentaquarks, Belle’s measurements for Yb are robust. It is the theoretical interpretation, which has to be checked in detail.

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    David Harris said:

    One small point, the talk by Eric Swanson wasn’t a press conference. It was just a conference session, although I’ve seen it mistakenly written as a press conference in a few cases.

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