The arrival of charm

Abstract

Some of the theoretical motivations and experimental developments leading to the discovery of charm are recalled. II ELECTROWEAK UNIFICATIONThe Fermi theory of beta decay [2] involved a pointlike interaction (for example, in the decay n → pe −ν e of the neutron). This feature was eventually recognized as a serious barrier to its use in higher orders of perturbation theory. By contrast, quantum electrodynamics (QED), involving photon exchange, was successfully used for a number of higher-order calculations, particularly following its renormalization by Feynman, Schwinger, Tomonaga, and Dyson [3].Attempts to describe the weak interactions in terms of particle exchange date back to Yukawa [4]. A theory of weak interactions involving exchange of charged spin-1 bosons was written down by Oskar Klein in 1938 [5], to some extent anticipating that of Yang and Mills [6] describing self-interacting gauge particles.Once the V − A theory of the weak interactions had been established in 1957 [7], descriptions involving exchange of charged vector bosons were proposed [8]. These tried to unify charged vector bosons (eventually called W ± ) with the photon (γ) within a single SU(2) gauge symmetry. However, the (massless) photon couples to a vector current, while the (massive) W 's couple to a V − A current. The SU(2) symmetry was inadequate to discuss this difference. Its extension by Glashow in 1961 [9] to an SU(2) × U(1) permitted the simultaneous description of electromagnetic and charge-changing weak interactions at the price of introducing a new neutral massive gauge boson (now called the Z 0 ) which coupled to a specific mixture of V and A currents for each quark and lepton.The Glashow theory left unanswered the mechanism by which the W ± and Z were to acquire their masses. This was provided by Weinberg [10] and Salam [11] through the Higgs mechanism [12], whereby the SU(2) × U(1) was broken spontaneously to the U(1) of electromagnetism. Proofs of the renormalizability of this theory, due in the early 1970's to G. 't Hooft, M. Veltman, B. W. Lee, and J. Zinn-Justin [13], led to intense interest in its predictions, including the existence of charge-preserving weak interactions due to exchange of the hypothetical Z 0 boson. By 1973, a review by E. Abers and B. W. Lee [14] already was available as a guide to searches for neutral weak currents and other phenomena predicted by the new theory.

The Standard Model and Beyond

“…In 1974, however, the J/ψ resonance was discovered simultaneously at Brookhaven and SLAC, and it was soon tentatively identified as a cc bound state. The existence of charm was subsequently confirmed by the identification of singly-charmed mesons and in neutrino scattering (see, e.g., Gaillard et al, 1975;Rosner, 1999).…”

Heavy Quarkonia Results from CLEO

“…However, it was discovered that large FSI phases are perhaps a general feature. Suzuki [22] and Rosner [23] have analyzed J/ψ decays into pseudoscalar-vector (PV) pairs, and pseudoscalar-pseudoscalar (PP) pairs, and find that the phase differences between strong and EM decay amplitudes in both PV and PP decays of J/ψ, measured as the interior angle δ of the triangle representing the amplitudes, is large…”

Charmonium decay physics

“…Rosner did significant damage control [48,49] for the future of B-Factory physics. He introduced (i) universal FSI as consequence that γ and 3g amplitudes for J/ψ are out of phase Table 5 Theoretical models up to 1990 and related experimental results.…”