Z' Phenomenology and the LHC

TL;DR

This work surveys Z' phenomenology arising from electroweak extensions of the Standard Model, detailing how Z' bosons would appear as dilepton resonances and how their spin, couplings, and underlying theory can be inferred. It contrasts indirect constraints from precision electroweak data with direct collider searches, outlines representative Z' models (including E6-based, LR, Little Higgs, and SSM-like benchmarks), and discusses the impact of Z–Z' mixing and potential extra fermions on decay patterns. The paper then assesses the LHC’s discovery potential and model-discrimination capabilities via dilepton observables such as differential cross sections, A_FB, and resonance shapes, as well as alternative channels, and discusses how the ILC can extend sensitivity indirectly and perform detailed coupling extractions post-discovery. The overarching message is that the LHC can discover and begin characterizing a Z', but a complete identification of its couplings and origin will rely on the complementary, high-precision capabilities of the ILC to achieve a full, model-dependent understanding of the new gauge sector.

Abstract

A brief pedagogical overview of the phenomenology of Z' gauge bosons is presented. Such particles can arise in various electroweak extensions of the Standard Model (SM). We provide a quick survey of a number of Z' models, review the current constraints on the possible properties of a Z' and explore in detail how the LHC may discover and help elucidate the nature of these new particles. We provide an overview of the Z' studies that have been performed by both ATLAS and CMS. The role of the ILC in determining Z' properties is also discussed.

Figures (23)

• Figure 1.1: Summer 2006 results from the LEPEWWG. (a) Fit for the Z leptonic partial width and $\sin^2 \theta_{lepton}$ in comparison to the SM prediction in the yellow band.(b) Comparison of a number of electroweak measurements with their SM fitted values.
• Figure 1.2: A comparison by E-158 of the predictions for the running value of $\sin^2 \theta_W$ with the results of several experiments as discussed in the text.
• Figure 1.3: Normalized leptonic angular distribution predicted from the decay of particles with different spin produced in $q\bar{q}$ annihilation. The dashed(solid,dotted) curves are for spin-0(2,1). The generated data corresponds to 1000 events in the spin-2 case.
• Figure 1.4: (a) The Drell-Yan distribution as seen by CDF. (b) CDF cross section lower bound in comparison to the predictions for the Z' in the SSM.
• Figure 1.5: Experimental lower bounds from CDF on a number of Z' models: (a) $E_6$ models (b) Little Higgs models.