Meson decay

After discovery of the combined charge and space parity violation, or CP-violation, in iT°-meson decay [7], the search for the electric dipole moments (EDMs) of elementary particles has become one of the most fundamental problems in physics [6, 8, 9, 10, 1]. A permanent EDM is induced by the weak interaction that breaks both the space symmetry inversion and time-reversal invariance [11]. Considerable experimental effort has been invested in probing for atomic EDMs induced by EDMs of the proton, neutron and electron, and by P,T-odd interactions between them. The best available restriction for the electron EDM, de, was obtained in the atomic T1 experiment [12], which established an upper limit of de < 1.6 X 10 e-cm, where e is the charge of the electron. The benchmark upper limit on a nuclear EDM is obtained in atomic experiment on i99Hg [13], ]dHgl < 2.1 X 10 e-cm, from which the best restriction on the proton EDM, dp < 5.4 x 10 " e-cm, was also recently obtained by Dmitriev Sen kov [14] (the previous upper limit on the proton EDM was obtained in the TIE experiment, see below). 

Observation of ultrarelativistic positronium and measurement of the branching ratio for the 7T°-mesons decay into a photon and A2e. 

Richard L. Garwin, Leon M. Lederman, and Marcel Weinrich, Observation of the Failure of Conservation of Parity and Charge Conjugation in Meson Decays The Magnetic Moment of the Free Muon, Physical Review 103, 1415-1417 (1957). 

A-z-k) in the lab system, respectively, wave function of TT+TT bound state with the Coulomb potential only squared at the origin with the principal quantum number n and the orbital momentum Z = 0, Pb is the Bohr momentum in 2, dan/dpidp2 is the double inclusive production cross section for tt+tt -pairs from short lived sources without taking into account 7r+7T Coulomb interaction in the hnal state, p and P2 are the 7t+ and 7t momenta in the lab system. The momenta of 7t+ and 7t mesons obey the relation Pi P2 The A2W are produced in states with different principal quantum numbers n and are distributed according to n Wi = 83%, W2 = 10.4%, W3 = 3.1%, W >4 = 3.5%. The probability of A2tt production in K, K, p, p, xp and T mesons decay were calculated in [34]. 

Muons suffered a similar fate to that of neutrons. A mu meson decays into an electron and two neutrinos with a half-life of only 2.2 x 10-6 second ... 

Meson me- Zan, ma-, me-, - San [ISV mes-+ -on] (1939) n. Two types of particles of mass intermediate between that of the electron and proton have been discovered in cosmic radiation and in the laboratory. The one particle with mass about 215me is called p-meson, the other with about 280 me Ti-meson. Mesons of both positive and negative charge have been found and there is now reasonably good evidence for neutral mesons. Both types of mesons decay spontaneously. Some evidence exists for a meson of mass about 100 mg. 

CP violation has been experimentally established also in B meson decays. However, the observed matter-antimatter asymmetry of the Universe requires additional sources of CP violation. 

Recently (Allen et a/., 1990) the same reaction was studied more precisely at the Meson Physics Facility (LAMPF) of the Los Alamos National Laboratory, using a beam-stop source of i/e. (Stopped tt " mesons decay into and u. The /i" " leptons are stopped and decay into and with end-point energies of 53 MeV the mean i/ energy is 31.7 MeV.) The result is... 

Fig. 13.6 shows how the value of R, in crossing the T(4s) peak at y s 10.55 GeV, rises by about 0.33 signalling the production of a new flavour with charge The detailed reconstruction of B meson decays is extremely difficult and was first achieved by the Argus and the CESR groups in 1987 (ARGUS, 1987b CLEO, 1987). 

Indirect evidence of limits on the H mass comes from double-A hypemuclei. There have been two reports of the observance of the formation and subsequent weak mesonic decay of a nucleus with two bound A s. Fh sumably, if the H existed and was bound by more than 10 MeV, the two A s would have formed an H before the weak decay occurred. This was not observed. Unfortunately, the events have not been confirmed in later experiments. If correctly interpreted, the data may place a lower limit on the H mass around 2220 MeV. It should be noted that there have been arguments that the production rate of the H from a double-A hypernucleus may be severely depressed if the H is very light, i.e. slightly above the deuteron mass. 

The hypemuclear decay branching ratios and the lifetime, x = l/(r7r + F7jo + Fn + Fp) = 1 / F are measurable quantities which can be used to extract the partial rates. The recoiling nucleon from the mesonic decays is of relatively low energy (about 5 MeV), and therefore these decays are inhibited by Pauli blocking in nuclei. As a consequence, the nonmesonic decay channels dominate in all but the lightest hypemuclei. 

J. Cohen, Weak Non-Mesonic Decays of Lambda Hypernuclei, (Review article to be published, 1990)... 

Figure 1.3 are LEGO plots showing the correlation between laboratory momentum and polar angle for a variety of particles produced in B meson decays at the T(4S) at p y = 0.56. 

The boost has a substantial effect on solid angle coverage. Figure 1.4 shows the single track efficiency as a function of maximum polar angle 9 in the forward and backward directions for B meson decays at the T(4S) with a boost of 7 = 0.56. Since it is necessary to reconstruct a minimum of three tracks for a measurement of sin 2a using + 7r "7r, and at least five tracks for a measurement of sin 2/ using B there... 

A Fast RICH is the reference particle identification system. The R D on this technology has been pursued primarily, but not exclusively, by the European Fast RICH Collaboration. A Fast RICH with a liquid radiator and pixel readout can provide 4cr separation for particles from two-body B meson decays over most of the solid angle. An important concern here is whether a sufficient number of Cerenkov photons can be detected in a ring with adequate angular resolution, with a device having a 20 cm radial extent and 15% of a radiation length at 90°. 

Figure 4.1. Distributions in momentum and angle for all pious and kaons produced in B meson decays for beam energies of 9 on 3.1 GeV a) momentum distribution for pions b) momentum distribution for kaons c) angular distribution for pions d) distribution of the average momentum versus the cosine of the polar angle 6 for pions e) distribution of the average momentum versus the cosine of the polar angle 9 for kaons.

We expect PEP-II to produce high statistics samples of meson decays, thus presenting a wealth of new physics opportunities, beyond the principal objective of probing ti e origin of CP violation. These opj>ortunities in other aspects of 6-quark weak and electromagnetic decay, in charm decay, in r decay, and in two-photon physics have been discussed in detail in [1]. This section l)iiefly summarize and updates tliat discussion. 

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