Subatomic Physics

216 Additive Conservation Laws
Table 7.2: Quantum Number Assignments
for the Six Quarks.
Quantum Number
Quark A S C B T Ygen
d 1/3 0 0 0 0 1/3
u 1/3 0 0 0 0 1/3
s 1/3 −1 0 0 0 −2/3
c 1/3 0 1 0 0 4/3
b 1/3 0 0 −1 0 −2/3
t 1/3 0 0 0 1 4/3
and his collaborators at SLAC (31) simultaneously discovered a new particle, J/ψ.
The long lifetime, the decay characteristics, and the excited states of this particle
proved that it was the bound state (cc). We will return to the J/ψ in Section10.9.
Here we use only one result of these experiments, namely the existence of the
new additive quantum number C. With four leptons and four quarks, lepton–
quark symmetry is satisfied, and nature might have stopped here. However, more
particles with new additive quantum numbers were discovered. In Section 5.6, we
briefly described the heaviest known lepton, the tau. If lepton–quark symmetry
holds, and there are sound theoretical reasons for this symmetry, the tau and its
neutrino call for two more quarks called bottom and top with associated quantum
numbers B and T . Indeed, in 1977, Lederman and his collaborators found a new
particle which they called upsilon (Υ). (32) The experimental evidence implies that
the upsilon is a (bb) bound state; we will return to it in Section 10.9. The particle
(tt) has also been found, and we list some of the quantum numbers of all six quarks
in Table 7.2.
With the new additive quantum numbers C, B, andT , a generalized hypercharge
can be introduced and Eqs. (7.48) and (7.49) become
7.7 References
Ygen = A + S + C + B + T =2〈q/e〉. (7.50)
A guide to the literature on new particles and reprints of many papers quoted in the
present chapter can be found in J.L. Rosner, New Particles, A.A.P.T., Stony Brook,
New York, 1981. It is based on “Resource Letter NP-1”, Am. J. Phys. 48, 290
(1980). A further guide is Quarks, (O.W. Greenberg, ed.) A.A.P.T., Stony Brook,
New York, 1986 based on “Resource Letter Q-1” Am. J. Phys. 50, 1074 (1982).
31J. E. Augustin et al., Phys. Rev. Lett. 33, 1406 (1974).
32S.W. Herb et al., Phys. Rev. Lett. 39, 252 (1977); L.M. Lederman, Sci. Amer. 239, 72
(October 1978).