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Unformatted text preview: 1 RARE KAON DECAYS Revised November 2009 by L. Littenberg (BNL) and G. Valencia (Iowa State University). A. Introduction : There are several useful reviews on rare kaon decays and related topics . Activity in rare kaon decays can be divided roughly into four categories: 1. Searches for explicit violations of the Standard Model 2. Measurements of Standard Model parameters 3. Searches for CP violation 4. Studies of strong interactions at low energy. The paradigm of Category 1 is the lepton avor violating decay K L e . Category 2 includes processes such as K + + , which is sensitive to | V td | . Much of the interest in Category 3 is focused on the decays K L , where e, , . Category 4 includes reactions like K + + + which constitute a testing ground for the ideas of chiral perturbation theory. Category 4 also includes K L and K L + . The former is important in understanding a CP-conserving contribution to K L 0 + , whereas the latter could shed light on long distance contributions to K L + . The interplay between Categories 2-4 can be illustrated in Fig. 1. The modes K are the cleanest ones theoretically. They can provide accurate determinations of certain CKM parameters (shown in the figure). In combination with alternate determinations of these parameters, they also constrain new interactions. The modes K L e + e and K L + are also sensitive to CKM parameters. However, they suffer from a series of hadronic uncertainties that can be addressed, at least in part, through a systematic study of the additional modes indicated in the figure. CITATION: K. Nakamura et al. (Particle Data Group), JPG 37 , 075021 (2010) (URL: http://pdg.lbl.gov) July 30, 2010 14:34 2 Figure 1: Role of rare kaon decays in deter- mining the unitarity triangle. The solid arrows point to auxiliary modes needed to interpret the main results, or potential backgrounds to them. B. Explicit violations of the Standard Model : Much ac- tivity has focussed on searches for lepton avor violation (LFV). This is motivated by the fact that many extensions of the min- imal Standard Model violate lepton avor and by the potential to access very high energy scales. For example, the tree-level exchange of a LFV vector boson of mass M X that couples to left- handed fermions with electroweak strength and without mixing angles yields B( K L e ) = 4 . 7 10 12 (148 TeV /M X ) 4 . This simple dimensional analysis may be used to read from Table 1 that the reaction K L e is already probing scales of over 100 TeV. Table 1 summarizes the present experimen- tal situation vis a vis LFV. The decays K L e and K + + e (or K L e ) provide complementary information on potential family number violating interactions, since the former is sensitive to parity-odd couplings and the latter is sensitive to parity-even couplings. Limits on certainlatter is sensitive to parity-even couplings....
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This note was uploaded on 06/07/2011 for the course PHYS 4132 taught by Professor Kutter during the Spring '11 term at University of Florida.
- Spring '11