Searches for extra dimensions in the CMS experiment at the Large Hadron Collider (LHC)
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EMENTARY PARTICLES AND FIELDS Theory
Searches for Extra Dimensions in the CMS Experiment at the Large Hadron Collider (LHC) S. V. Shmatov* (On behalf of the CMS Collaboration) Joint Institute for Nuclear Research, Dubna, Moscow oblast, Russia Received May 28, 2010; in final form, October 4, 2010
Abstract—Predictions of multidimensonal theories are analyzed, and the possibility of detecting signals from extra spatial dimensions in the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) is studied. DOI: 10.1134/S1063778811030161
INTRODUCTION Although the Standard Model of particle interactions (SM) possesses a high predictive power and has passed thorough experimental tests, it features a number of flaws and unresolvable problems. In view of this, it cannot be thought to be an ultimate version of the theory. In particular, very large (infinite in the absence of an upper cutoff in energy or the scale of applicability of the theory) corrections to the Higgs boson mass are present in the Standard Model. In order to cancel these corrections, it is necessary to implement an ad hoc procedure for tuning the theory. The Higgs boson mass is specified by the scale of electroweak-symmetry breaking, Mew ∼ 200 GeV. Quantum corrections to this value are controlled by the maximum energy to which a quantum-field description is still valid—that is, to the scale above which effects of quantum gravity become significant: MPl ∼ 1019 TeV. Therefore, the problem of tuning the theory is also called the hierarchy problem (that is, the problem of the existence of two energy scales differing greatly in magnitude—Mew and MPl ). The tuning in question is referred to as a fine tuning since an extremely small value is obtained for the ratio of these two scales: MPl /Mew ∼ 102 /1019 ∼ 10−17 . The existence of the hierarchy itself and of its tuning to this astounding precision presents a serious problem for the Standard Model as a theoretical construction. Models involving extra spatial dimensions (multidimensional models) propose a nice solution to this problem. This solution consists in reducing the upper limit from Planck energies to a much smaller energy scale in order to push it closer to Mew . *
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Present-day multidimensional scenarios are dealing with rather large extra spatial dimensions (not of the Planck size) and predict new physics effects, which can manifest themselves at energy scales in the TeV range. Therefore, such effects can be studied at modern accelerators—for example, at the Large Hadron Collider (LHC), which was constructed in order to perform experiments in colliding proton beams √ of energy up to S = 14 TeV in the c.m. frame. From the experimental point of view, objects of observation may include infinite spectra of special three-dimensional states known as Kaluza–Klein excitations (KK modes) of ordinary particles—these are their perfect copies in quantum numbers (charge, spin, and lepton or baryon number) but differ by increasing masses. In various scenarios, a complete multidimensional des
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