These long-awaited neutron-spin data indicate that, under some conditions, the previously overlooked orbital motions of valence quarks
make a major contribution to nucleon spin, comments theorist Gerald A.
For one thing, it could end what had been a puzzling absence of evidence for particles with groupings containing more than three quarks
or antiquarks, which theorists for decades have been expecting to show up in accelerators.
For instance, there could be yet-undiscovered heavy particles that interact differently with quarks
than with antiquarks, she says.
To fathom how five quark
components can coexist within one particle, theorists expect to reconsider their models of the interactions among quarks
and gluons, the particles that bind quarks
Jets are produced when two highly energetic quarks
bounce off each other.
Whatever the explanation, scientists are taking a second look at the theory of quantum chromodynamics, or QCD, which describes the possible interactions of quarks
If things go well, in the next several years, the up and down quarks
may finally weigh in, van Kolck says.
Called Xi-cc++, the newly detected particle contains two charm quarks
- one of the three known heavy flavors - and one up quark
- a light flavor.
The particles' masses, decay products and other data indicated a composition of a charm quark
, its antimatter counterpart, two up quarks
and a down quark
Electrically charged leptons are formed when the color charges of quarks
and antiquarks with different flavors are annihilated, while neutrinos are formed when both the electric and color charges of quarks
and antiquarks with the same flavor are annihilated.
As the nucleon is a composite system of strong interacting quarks
, the amplitude M of the process in Eq.
Murray Gell-Mann (see 1953), who had originated the quark
concept, labored to work out the rules governing the combination of quarks