Probing the Nature of Compactification with Kaluza-Klein Excitations at the Large Hadron Collider

Abstract

It is shown that the nature of compactification of extra dimensions in theories of large radius compactification can be explored in several processes at the Large Hadron Collider (LHC). Specifically it is shown that the characteristics of the Kaluza-Klein (KK) excitations encode information on the nature of compactification, i.e., on the number of compactified dimensions as well as on the type of compactification, e.g., of the specific orbifold compactification. The most dramatic signals arise from the interference pattern involving the exchange of the Standard Model spin 1 bosons ($γ$ and Z) and their Kaluza-Klein modes in the dilepton final state $pp\to l^+l^-X$. It is shown that LHC with 100$fb^{-1}$ of luminosity can discover Kaluza-Klein modes up to compactification scales of $\approx 6$ TeV as well as identify the nature of compactification. Effects of the Kaluza-Klein excitations of the W boson and of the gluon are also studied. Exhibition of these phenomena is given for the case of one extra dimension and for the case of two extra dimensions with $Z_2\times Z_2, Z_3$, and $Z_6$ orbifold compactifications.

Figures (6)

• Figure 1: Plot of the production cross section of a charged lepton pair in the process $pp\rightarrow l^+l^-+X$ (solid line) as a function of the mass scale $M_R$ via exchange of photonic and Z Kaluza-Klein modes of the compactified dimension. The same analysis for the sequential Standard Model Z' boson is shown by the dashed line.
• Figure 2: Differential cross section $d\sigma/dm_{ll}$ as a function of the invariant mass $m_{ll}$ of the charged lepton pair for three different values of the compactified dimension $M_R$. For comparison the analysis for the SM case is also shown.
• Figure 3: Plot of the production cross section $pp\rightarrow l^{\pm}\nu_l +X$ via exchange of the Kaluza-Klein excitations of $W$ as a function of $M_R$ (solid). For comparison the cross section for the sequential Standard Model $W'$ boson is also given (dashed).
• Figure 4: The differential cross section $d\sigma/dm_{jj}$ ($j\neq t$) for dijet production in the process $pp\rightarrow jj+X$ including Kaluza-Klein gluon exchange as a function of the dijet invariant mass $m_{jj}$ for the cases when the mass scale $M_R$ of the compactified dimension is 2 TeV, 5 TeV, 8 TeV, and for the SM. The cross section is evaluated at the leading order. A rapidity cut $\eta<0.5$ is imposed for both jets.
• Figure 5: Plot of the production cross section $pp\rightarrow jj+X$ ($j \neq t$) as a function of the compactified dimension with jj invariant mass cut of $m_{jj}>1$ TeV, $m_{jj}>3$ TeV, and $m_{jj}>5$ TeV. A rapidity cut $\eta<0.5$ is imposed for both jets.