rpp2010-rev-searches-quark-lep-compositeness

rpp2010-rev-searches-quark-lep-compositeness - 1 SEARCHES...

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–1– SEARCHES FOR QUARK AND LEPTON COMPOSITENESS Revised 2001 by K. Hagiwara (KEK), and K. Hikasa and M. Tanabashi (Tohoku University). If quarks and leptons are made of constituents, then at the scale of constituent binding energies, there should appear new interactions among quarks and leptons. At energies much below the compositeness scale (Λ), these interactions are suppressed by inverse powers of Λ. The dominant eFect should come from the lowest dimensional interactions with four fermions (contact terms), whose most general chirally invariant form reads [1] L = g 2 2 h η LL ψ L γ μ ψ L ψ L γ μ ψ L + η RR ψ R γ μ ψ R ψ R γ μ ψ R +2 η LR ψ L γ μ ψ L ψ R γ μ ψ R i . (1) Chiral invariance provides a natural explanation why quark and lepton masses are much smaller than their inverse size Λ. We may determine the scale Λ unambiguously by using the above form of the eFective interactions; the conventional method [1] is to ±x its scale by setting g 2 / 4 π = g 2 (Λ) / 4 π = 1 for the new strong interaction coupling and by setting the largest magnitude of the coefficients η αβ to be unity. In the following, we denote Λ=Λ ± LL for ( η LL RR LR )=( ± 1 , 0 , 0) , ± RR for ( η LL RR LR )=(0 , ± 1 , 0) , ± VV for ( η LL RR LR ± 1 , ± 1 , ± 1) , ± AA for ( η LL RR LR ± 1 , ± 1 , 1) , (2) as typical examples. Such interactions can arise by constituent interchange (when the fermions have common constituents, e.g. , for ee ee ) and/or by exchange of the binding quanta (when- ever binding quanta couple to constituents of both particles). Another typical consequence of compositeness is the appear- ance of excited leptons and quarks ( ± and q ). Phenomeno- logically, an excited lepton is de±ned to be a heavy lepton which shares leptonic quantum number with one of the existing leptons (an excited quark is de±ned similarly). ²or example,
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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.

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rpp2010-rev-searches-quark-lep-compositeness - 1 SEARCHES...

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