New results on searches for new physics beyond the standard model in the D0 experiment
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EMENTARY PARTICLES AND FIELDS Theory
New Results on Searches for New Physics beyond the Standard Model in the D0 Experiment А. V. Popov* (On behalf of the D0 Collaboration) Institute for High Energy Physics, Protvino, Moscow oblast, 142284 Russia Received May 19, 2009
Abstract—The latest results obtained from searches for particles and phenomena beyond the Standard Model (new physics) in the D0 experiment at the Tevatron [Fermi National Accelerator Laboratory (FNAL), USA] on the basis of a statistical sample corresponding to an accumulated luminosity of 1 to 3 fb−1 in 2008 are considered. DOI: 10.1134/S1063778810060153
1. INTRODUCTION Many years of investigations have proven that the Standard Model [1] is viable, satisfactorily describing observed processes and phenomena in particle physics. Yet, it is not free from significant flaws, which furnish motivations to seek Standard Model extensions such that they provide answers to questions existing within the Standard Model. Problems that call for an explanation include the hierarchy problem, the dark-matter phenomenon, and the unification of gauge constants. Before the Large Hadron Collider (LHC, CERN, Switzerland) will have been completely commissioned, the Tevatron accelerator at the Fermi National Accelerator Laboratory (FNAL, USA), rated at the c.m. colliding-beam energy of 1.96 TeV, remains the most appropriate testing ground for new-physics searches. Along these lines, a vast range of studies, including searches for supersymmetric partners of quarks, gluons, and gauge and Higgs bosons and searches for leptoquarks, additional spatial dimensions and effects associated with them, new heavy gauge bosons, and excited lepton states, is being performed in the D0 experiment at the Tevatron. In the present study, we give a survey of the latest results obtained on the basis of a statistical sample that corresponds to the accumulated luminosity of about 1 to 3 fb−1 [2]. 2. SUPERSYMMETRY Supersymmetry (SUSY) theory postulates the presence of symmetry between boson and fermion *
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states and predicts the existence of supersymmetric partners for Standard Model particles. The supersymmetric partners differ only in spin values (bosons correspond to fermions, and vice versa). In the theory, one introduces, the concept of R parity, which is a multiplicative quantum number equal to +1 for Standard Model particles and to −1 for their supersymmetric partners. In minimal supersymmetric extensions of the Standard Model (Minimal Supersymmetric Standard Model or MSSM), one postulates R-parity conservation (but there are supersymmetry models in which there is no R-parity conservation), and this leads two important consequences: only pair production of supersymmetric particles is possible, and the lightest supersymmetric particle must be stable (naturally providing a solution to the darkmatter problem). To date, no experimental corroboration of the existence of supersymmetric particles has been found. This suggests their high masses and, hence, a large mass differ
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