Probing universal extra dimension at the International Linear Collider

Abstract

In the context of an universal extra-dimensional scenario, we consider production of the first KaluzaKlein electron positron pair in an e + e − collider as a case-study for the future International Linear Collider. The Kaluza-Klein electron decays into a nearly degenerate Kaluza-Klein photon and a standard electron, the former carrying away missing energy. The Kaluza-Klein electron and photon states are heavy with their masses around the inverse radius of compactification, and their splitting is controlled by radiative corrections originating from bulk and brane-localised interactions. We look for the signal event e + e − + large missing energy for √ s = 1 TeV and observe that with a few hundred fb −1 luminosity the signal will be readily detectable over the standard model background. We comment on how this signal may be distinguished from similar events from other new physics. Introduction: If extra-dimensional models in a few hundred GeV scale [1] are realised in Nature, one can not only undertake their precision studies at the proposed International Linear Collider (ILC) [2] but also can distinguish them from other new physics. In this paper, we consider such models with one extra dimension having inverse radius of compactification in the range R −1 = 250 − 450 GeV. We examine production of the first Kaluza-Klein (KK) electron positron pair (E + 1 E − 1 ) in a linear e + e − collider operating at √ s = 1 TeV. The heavy modes E ± 1 would decay into the standard (zero modes) e ± and the first KK photon (γ 1 ), the latter carrying away missing energy. The splitting between E ± 1 and γ 1 comes from the bulk and brane-localised radiative corrections. The cross section of the final state e + e − plus missing energy is quite large and the standard model (SM) background is tractable, so that even with a one year run of ILC at √ s = 1 TeV with approximately 300 fb −1 enough statistics would accumulate. Forward-backward asymmetry of the final state electron mildly depends on the initial polarisations. Even though the mass spectrum of KK excitations of different SM particles may resemble the supersymmetric pattern, angular distribution of the final electrons can be used to discriminate the intermediate KK electrons from selectrons or other new physics scalars.

Search for Higgs bosons of the universal extra dimensions at the large Hadron collider

“…The presence of KK-towers for charged and neutral CP-odd Higgs bosons provides a concrete example of this. The phenomenology of KK-excitations has been studied in great detail in recent times which covers its implications at colliders [3,4,5,6,7,8,9,10,11,12,13,14,15,16], in electroweak/flavour sector via various low-energy observables [17,18,19,20,21,22,23,24,25,26,27,28] and for dark matter/cosmology [5,13,29,30,31,32,33,34,35,36,37,38,39,40] In MUED there are only two extra free parameters when compared to the SM. These are the radius of compactification R (or, alternately R −1 , the scale of compactification) and the cutoff scale Λ of the theory.…”

Physics beyond the standard model and cosmological connections: A summary from LCWS06

“…In another presentation [28], a model of universal extra dimension, where all the particles are free to propagate in a fifth dimension which is compactified on a S 1 /Z 2 orbifold, was considered. Kaluza-Klein (KK) number conservation in the model yields the lightest KK particle (LKP) which is γ 1 .…”

Boundary localized terms in universal extra-dimensional models through a dark matter perspective

“…The possibility of a not too high R À1 motivates the continuing search for signatures of the model at the Tevatron and the LHC [28,29] and also at the ILC or CLIC [30] in the future.…”