I had been reading a book in particle physics very recently. The book has probably been written in the late 90's, (and obviously before 2000), and states that quarks, the underlying particles in all baryons and mesons, has not yet been detected in free state.

Is this still true, or have we been able to detect quarks in free states?


The quark-gluon plasma is a hot dense soup of (mostly) free quarks and gluons. It is created in heavy ion experiments like ALICE, and ATLAS Heavy Ion at the LHC or STAR at RHIC, among others, via two large (typically gold or lead) nuclei smashing together at close to the speed of light. However, this "free" quark state is very short lived, and it almost immediately cools down and re-hadronizes into confined states which are measured in the detectors for these experiments. So, we don't actually "see" free quarks but we can deduce that they must have been. In nature, the only place you might be able to find deconfined quarks is at the center of a neutron star, but that hasn't been observed.

  • $\begingroup$ I don't think it's correct to describe quarks in quark-gluon plasma as "free", as a better description might be "not bound" or "loosely bound". A quark-gluon plasma is really not free quarks and gluons as you can't actually separate the quarks and gluons - they have to exist in the same "mix" as it were. This compares to a "free" electron (for example) which can exist independently. $\endgroup$
    – StephenG
    Mar 25 '17 at 14:26
  • $\begingroup$ That's why I put it in quotes because it's not actually free. $\endgroup$
    – smelborp
    Mar 25 '17 at 14:38

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