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Unformatted text preview: 1 SUPERSYMMETRY, PART II (EXPERIMENT) Updated August, 2009 by J.-F. Grivaz (LAL - Orsay). II.1. Introduction: Low-energy supersymmetry (SUSY) is probably the most extensively studied among the theories be- yond the Standard Model (SM). Reasons are its success in solving some of the deficiencies of the SM, such as the stabi- lization of the Higgs boson mass or gauge coupling unification, while not being in contradiction with the precision electroweak measurements. If unbroken, SUSY would predict the existence of partners of the SM particles, differing by half a unit of spin, but otherwise sharing the same properties. Since no such particles have been observed with the same mass as their SM counterpart, SUSY is a broken symmetry. With an appropriate choice of SUSY-breaking terms, denoted soft, and with super- partner masses at the TeV scale, the good properties of SUSY, such as those mentioned above, however, remain preserved. SUSY and SM particles are distinguished by a multiplicative quantum number, R-parity, with R = ( 1) 3( B L )+2 S where B and L are the baryon and lepton numbers, and S is the spin. Therefore, SM particles have R = 1 while SUSY particles have R = 1. If R-parity is violated, the exchange of SUSY particles may lead to an unacceptably fast proton decay. It is therefore commonly assumed that R-parity is conserved. As a consequence, SUSY particles are produced in pairs, and a SUSY particle decays (possibly via a cascade) into SM particles accompanied by the lightest SUSY particle (LSP) which is stable. Cosmological constraints require that the LSP be neutral and colorless. The first part of this review, by H.E. Haber, provides details of the theoretical aspects of supersymmetry, of the various SUSY-breaking schemes, and of the structure of the minimal supersymmetric extension of the Standard Model (MSSM), as well as an extensive set of references. The same notations and terminology are used in the following. As will unfortunately appear in this review, no evidence for SUSY particle production has been found up to now. The search CITATION: K. Nakamura et al. (Particle Data Group), JPG 37 , 075021 (2010) (URL: http://pdg.lbl.gov) July 30, 2010 14:34 2 results are therefore presented in terms of production cross- section upper limits or of mass lower limits. In the following, all such limits are given at the 95% confidence level. II.2. SUSY models: In the MSSM, every degree of freedom of the SM is balanced by a new one differing by half-a-unit of spin. There are, for instance, two scalar-quark weak eigenstates q L and q R , associated with the left and right chirality states of a given quark avor. Two Higgs doublets are, however, needed, in contrast to the minimal Standard Model, in order to give masses to both up-type and down-type quarks, with vacuum expectation values v 2 and v 1 , the ratio of which is denoted tan ....
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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