Optimal polarized observables for model-independent new-physics search at e+e− colliders

Abstract

For the processes e + e − → µ + µ − , τ + τ − , bb and cc at a future e + e − collider with √ s = 0.5TeV, we examine the sensitivity of the helicity cross sections to four-fermion contact interactions. If longitudinal polarization of the electron beam were available, two polarized integrated cross sections would offer the opportunity to separate the helicity cross sections and, in this way, to derive model-independent bounds on the relevant parameters. The measurement of these polarized cross sections with optimal kinematical cuts could significantly increase the sensitivity of helicity cross sections to contact interaction parameters and could give crucial information on the chiral structure of such new interactions.

New physics signatures at a linear collider: model-independent analysis from ‘conventional’ polarized observables

“…Actually, in this regard, one could compare the sensitivities shown in Table 1 (and Figs. 1-3) with the model-independent constraints on the parameters αβ previously obtained using a set of polarized cross sections integrated in 'optimal' angular ranges as basic experimental observables [9][10][11]. One finds that, with few exceptions relevant to specific cases in the bb and cc sectors, although defining a somewhat more involved procedure the latter observables produce more stringent constraints compared to the simpler (and more practical) observables used here (mostly asymmetries).…”

“…To this aim, in the case of the process (1) at the LC considered here, a possibility is offered by initial beam polarization, that enables us to extract from the data the individual helicity cross sections through the definition of particular, and optimal, polarized integrated cross sections and, consequently, to disentangle the constraints on the corresponding CI constants [8][9][10][11]. In this article, we wish to to present a model-independent analysis of the CI that complements that of Refs.…”

Contact interaction probes at the Linear Collider with polarized electron and positron beams

“…In what follows, we extend the analysis of Ref. [4] and discuss the case where also positron beam longitudinal polarization is available at the LC with the same c.m. energy.…”

“…with σ LR and σ RL obtained from σ LL and σ RR , respectively, replacing σ + by σ − . Actually, for the purpose of optimizing the resulting bounds on Λ αβ , one can more generally define the polarized cross sections integrated over the a priori arbitrary kinematical ranges (−1, z * ) and (z * , 1) [4]:…”

“…energy. Specifically, after giving the main definitions and briefly reviewing the procedure and findings for the sensitivity on Λ αβ obtained in [4], we start by considering the effect of the uncertainty on the electron beam polarization that was disregarded there. We then consider the case of both electron and positron longitudinal polarizations, including in the analysis also the uncertainty on these polarizations.…”