The heavy lepton

The ratio R = T(e e — anything)/ 7 (e e M M ) qed around the charm threshold is shown in Fig. 14.1 which indicates how complicated this energy region is. 

In the low energy region (i.e. below charm threshold 3.5 GeV) the quark model result R gives the correct value within 20% 

In the 3.5-4 GeV region, a very complex structure emerges which was partly explained within the charmonium picture. However, the experimental jump Ail 2.5 in going from 3.5 to 4.5 GeV fails to be explained by the jump expected theoretically on crossing the charm threshold 

The possibility of new quarks in this mass range is made unlikely by the overall qualitative success of the charmonium model (Chapter 11), which assumes that only the charm quarks have come into play in the strong interaction sector, and the next known quark (the b) lies too high up in mass to be of any relevance here. 

The only possibility left to explain the jump in AR within this framework is that new leptons (heavy ones ) are produced and are mixed with the hadrons as a result of their large mass. Any such charged lepton 

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The contribution of the muon polarization operator was already considered above. One might expect that contributions of the diagrams in Fig. 10.8 with the heavy particle polarization loops are of the same order of magnitude as the contribution of the muon loop, so it is natural to consider this contribution here. Respective corrections could easily be calculated by substituting the expressions for the heavy particle polarizations in the unsubtracted skeleton integral in (10.3). The contribution of the heavy lepton t polarization operator was obtained in [37, 38] both numerically and analytically... 

The present evidence for semi-leptonic decays comes from a study of inclusive electron production. Some care is necessary in separating the products of D decay from those of the heavy lepton t, since D and t are very close in mass. 

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... 

In this picture the simplest option is that the heavy lepton is a sequential lepton (i.e. endowed with lepton quantum number of its own, distinct from those of both the electron and the muon). This case can... 

While the heavy lepton neutrino Ur has not yet been identified with absolute certainty, there are good reasons to believe that it exists. If not, it would be meaningless to assign a new lepton number to the t, and the T would be able to decay into // or e. In that case, a non-negligible contribution to r decay would for instance come from the reaction... 

The experimental signatures of a phase transition include (a) suppression of production of the heavy vector mesons J/XV and E and the upsilon states, (b) the creation of a large number of ss quark-antiquark pairs, and (c) the momentum spectra, abundance, and direction of emission of di-lepton pairs. The first phase experiments in this held have been carried out. Energy densities of 2 GeV/fm3 were created. Strong J/XV suppression has been observed relative to p-A collisions along with an increase in strangeness production. 

This new result, which exceeds bounds from previous experiments [58,64] by a factor of 2500 and the one from an early stage of the experiment [59] by 35, has some impact on speculative models. A certain model is ruled out with more than 4 generations of particles where masses could be generated radiatively with heavy lepton seeding [66]. A new lower limit of... 

The Science Teacher Electron, Muon, and Tau Heavy Lepton— Are These the Truly Elementary Particles (pp. 18-19) Volume 47, Number 9, December 1980... 

As we have mentioned above it is possible to evaluate the electromagnetic lepton pair production in the limiting case of infinite Lorentz factors y. One interesting aspect among others is that peripheral heavy-ion collisions at ultrarelativistic energies offer... 

Fig. 10. Simulation of an electron-capture supernova following the collapse of an O-Ne core. The time evolution of the radius of various mass shells is displayed with the inner boundaries of the O+Ne, C+O and He shells marked by thick lines. The inner core of about 0.8 M is mainly made of Ne at the onset of collapse ([21], and references therein). The explosion is driven by the baryonic wind caused by neutrino heating around the PNS. The thick solid, dashed, and dash-dotted lines mark the neutrino spheres of ve, ve, and heavy-lepton neutrinos, respectively. The thin dashed line indicates the gain radius which separates the layers cooled from those heated by the neutrino flow. The thick line starting at t = 0 is the outward moving supernova shock (from [22])...

Precise test of QED for the two lepton bound state and of the behavior of the muon as a heavy electron. 

T", the triton (fiomtritos, literal Greek, meaning third in English), or tauonic lepton, is a lepton with a high mass (of baryonic order - see below) considered as heavy lepton, discovered in 1977 by the Peierls with tan neutrino (tauon) experimentally identified in 1990. 

The cancellation of the badly behaved part of diagram (a) forces the introduction of either neutral vector bosons or heavy leptons, or both. Note that most of the troubles that occur in other reactions, such as W W or i>ee —> can also be cured by the same sort... 

We consider now that part of the Lagrangian containing the leptons and their interactions with the gauge fields. We consider just the electron e and its neutrino i/g. Analogous statements hold for the muon p and its neutrino and for the heavy electron r and its neutrino Ut. 

Above the charm and heavy lepton thresholds we expect... 

Given the uncertainties in the experimental calibration one sees that the measured values of R are in reasonable agreement with a scheme based on coloured quarks with the usual fractional charges, and with the existence of a heavy lepton. Note too that the data is compatible with the charge assignment Qc = for the charm quark. 

As already mentioned in Chapter 9 (and Section 9.5.3 in particular), some theoretical arguments support the need for more than foiu quarks (i.e. to go beyond charm) as a consequence of the discovery in 1977 of the new heavy lepton r (Perl et o/., 1977). Its properties will be discussed in Chapter 14. 

As can be seen from (13.2.6), decays into will totally dominate over decays into e+i/g because of the very large mass ratio (m /me). The decay rate Df T Ur (heavy lepton) is expected to be about 16 times larger than Df iX Vix but is unfortunately very difficult to observe. 

The term heavy lepton is of course self-contradictory (an oxymoron) since lepton is borrowed from the Greek for weak or light as compared with hadron for strong or heavy . The t is heavier than most known hadrons, which means that mass alone does not allow one to characterize the elementarity of a particle. In the following, the elementarity of leptons will be taken to imply their nearly point-like behaviour at least down to distances... 

It should be noted that the heavy mass of the r (and, therefore, its ability to decay weakly into ordinary hadrons) makes it a unique probe of the coupling to the standard quarks and leptons of any new weak boson. Also, the T may represent one of the dominant and more tractable decay modes of charged Higgs bosons. 

Second Quantized Description of a System of Noninteracting Spin Particles.—All the spin particles discovered thus far in nature have the property that particles and antiparticles are distinct from one another. In fact there operates in nature conservation laws (besides charge conservation) which prevent such a particle from turning into its antiparticle. These laws operate independently for light particles (leptons) and heavy particles (baryons). For the light fermions, i.e., the leptons neutrinos, muons, and electrons, the conservation law is that of leptons, requiring that the number of leptons minus the number of antileptons is conserved in any process. For the baryons (nucleons, A, E, and S hyperons) the conservation law is the... 

Heavy neutrino The WIMP par excellence is a heavy neutrino. The example we consider is a thermal Dirac neutrino v of the fourth generation with Standard Model interactions and no lepton asymmetry. Figure 3 summarizes... 

Abstract. Muonium is a hydrogen-like system which in many respects may be viewed as an ideal atom. Due to the close confinement of the bound state of the two pointlike leptons it can serve as a test object for Quantum Electrodynamics. The nature of the muon as a heavy copy of the electron can be verified. Furthermore, searches for additional, yet unknown interactions between leptons can be carried out. Recently completed experimental projects cover the ground state hyperfine structure, the ls-2s energy interval, a search for spontaneous conversion of muonium into antimuonium and a test of CPT and Lorentz invariance. Precision experiments allow the extraction of accurate values for the electromagnetic fine structure constant, the muon magnetic moment and the muon mass. Most stringent limits on speculative models beyond the standard theory have been set. 

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