Quarkonium

In particle physics is called with quarkonium (plural: quarkonia ) the bound states of a quark and its antiquark. In other words, it involves mesons with no electric charge or flavor.

Bound states of heavy quarks () have their own names: bound states (ie charm quark and anti-quark ) are called charmonium, bottomonium bound states. A proof of the hypothetical system Toponium is extremely difficult, if not impossible, since its formation time is probably longer than the lifetime of the top quark, which is extremely short-lived due to its high mass.

Bound quark- antiquark states of light quarks () mix due to the small mass difference of quantum mechanics - especially with. Therefore, the mesons formed from them not a single quark species can be assigned.

Nomenclature

Quantum numbers and spectroscopic states

The name is similar to Quarkonium positronium in which an electron and a positron are attached to. As in the case of positronium in identifying quarkonia by the following quantum numbers:

  • Principal quantum number
  • Coupling of the quark spins ( number or value ) or multiplicity ( number or value )
  • Angular momentum and
  • Total angular momentum (possible values ​​due to the spin -orbit coupling )

In the nomenclature ( term symbol ) or ( spectroscopic designation), with the following marking is valid for the orbital angular momentum:

Note the following difference in the naming: While positronium the nomenclature of atomic physics applies to the principal quantum number ( for the number of nodes of the radial wave function, small for the orbital angular momentum ), one uses the quarkonium the nomenclature of nuclear physics. A 23P1 - 13P1 - positronium here, a charmonium.

Observable in addition to the total angular momentum only:

  • Parity and
  • The charge conjugation.

Orbital angular momentum and quark spin coupling can be derived.

Mesons

: (, PDF, 66 kB Particle Data Group) for the mesons formed from these states following nomenclature applies

  • For from heavy quarks () mesons formed the spectroscopic designation () is, if known, specified with - eg - As well as another index - eg. The latter is not required if that is at, because then. Is not possible, a spectroscopic assignment for lack of data, the mass will provide more detailed descriptions given in MeV/c2, eg.
  • For the light quarks from () mesons formed one does not use the spectroscopic designation; Instead, the mass is given in MeV/c2 for a more detailed description.
  • At the lowest states you can leave out this information - so and.

Charmonia and Bottomia

The quantum numbers of the X ( 3872 ) particle are the subject of current investigations, its identity is not fully understood. It can be:

  • A candidate for the 11D2 - state;
  • A hybrid charmonium state;
  • A molecule.

In 2005, the BaBar experiment published the discovery of the new state Y ( 4260 ). The observations were confirmed by the experiments, CLEO and Belle. First, the new particle was considered to be a charmonium, but now the observations suggest more exotic explanations, such as a D- " molecule", a tetra quark or a hybrid meson.

Notes:

Antiparticle Hypothesis Exponential decay#Mean lifetime Termsymbol Ground state Isospin Rho meson Omega meson Phi meson Upsilon meson Belle-Experiment Tetraquark arXiv Digital Object Identifier
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