Lepton heavy

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... 

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... 

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])...

Stable Neutral Heavy Lepton Mass Limits... 

Mass m > 39.5 GeV, CL = 95% (Majorana) Neutral Heavy Lepton Mass Limits... 

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... 

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 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. 

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... 

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... 

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