Charm mesons

It turns out, however, that the lightest charm meson has a mass of 1863 MeV/c so that J/4 (3097) [as well as (3684)] is below the threshold for decay into in contradistinction to which was just... 

As an example Fig. 13.7 shows the mass distribution in channels occurring in charged B decays. The clear B-peak at 5275.8 1.3 3.0 MeV/c is evident. It is found that Bs decay predominantly into charm mesons, in agreement with the decay mechanism illustrated in Fig. 13.2. 

We draw attention in Tables 13.1 and 13.2 to the large difference between the lifetimes of non-strange charged and neutral charm mesons. We shall return to this point in Section 13.2.1. 

Despite this, the masses of charm mesons were predicted (by, for example, de Rujula, Georgi and Glashow, 1975) before their actual discovery. That these predictions (Table 13.3) are quite reasonable can be seen by comparing with the experimental data reported in Table 13.1. 

As we shall soon see, the total decay rate of D and (into hadrons) can be estimated to be of the order of 10 — 10 s so that the purely leptonic decay rate of charm mesons leads to branching ratios which are, at most, of order 10 — 10 and can, therefore, be neglected. Indeed up to the present, none of the leptonic decays has been observed (on this question, the Particle Data Group (1992) reports BR( > — ... 

Semi-leptonic and hadronic decays of charm mesons... 

Semi-leptonic decays of charm mesons with an electron in the final state were first observed at DESY by the DASP collaboration shortly after the first evidence for charm had been reported in hadronic decays. 

As for the strange charm meson Ds cs) it transforms into as with a cos 9c amplitude and into sd with a sin 6c one. Thus, we expect r(D+ to be suppressed by tan 9c compared with T Df... 

From the previous discussion, we would expect the heavy lepton mass to be around 1.8-2.0 GeV, i.e. extremely close to the mass of the charm meson. That there are no heavy leptons with mass <1.5 GeV has been established (Bernardini et al., 1973 Zichichi, 1977) by earlier experimental searches. The cross-section for lepton pair production, within QED, 7 T+T , assuming point-like spin particles, is given by... 

One suggestion is to have colliding high luminosity e" e beams with energy in the range 3.0-4.2 GeV with the aim of producing up to 10 r lej)-tons per year. This would involve production of about 10 J/ and 10 charm mesons per year. The design luminosity is 10 cm /s. 

---