Polarization and spin effects in neutralino production and decay

Abstract

We study polarization and spin correlation effects in the MSSM and in extended supersymmetric models at an e + e − linear collider with polarized beams. The production of light neutralinos e + e − →χ 0 1χ 0 2 and the subsequent decayχ 0 2 →χ 0 1 e + e − including full spin correlations is compared in three supersymmetric models: MSSM, NMSSM and an E 6 -inspired model with an additional U (1) ′ gauge group. It is shown that polarization and spin effects can lead to a complete different behavior of these models. Finally, the dependence of the cross section and the decay angular distribution on the gaugino mass parameter M 1 for polarized beams is briefly outlined.

Momentum reconstruction at the LHC for probingCPviolation in the stop sector

“…Using the formalism of Refs. [38,39], the squared amplitude |T | 2 of the full process can be factorised into the processes of production gg →t 1t * 1 and the subsequent decays t 1 → tχ 0 2 ,χ 0 2 →lℓ N ,l →χ 0 1 ℓ F and t → W b. We apply the narrow-width approximation but include the full spin correlations for the production and the decay of the intermediate particles,t 1 ,χ 0 2 ,l and t. The use of the narrow-width approximation is appropriate since the widths of the respective particles are much smaller than the masses in all cases.…”

Probing CP violation with and without momentum reconstruction at the LHC

“…2. It is sensitive to CP-violating supersymmetric couplings and its structure has been studied in detail in [31,32,43], cf. Appendix A.…”

Measurement of CP violation in stop cascade decays at the LHC

“…2. It is very sensitive to CP-violating supersymmetric couplings, and its structure has been studied in detail in [38,39]. The phase φ M 1 (and also φ µ , which has been set to zero here) affects the mass of theχ 0 2 , as well as its couplings and decay rates.…”

“…Using the formalism of [39,40], the squared amplitude |T | 2 of the full process can be factorized into the processes of production gg →t 1t1 and the subsequent decayst 1 → tχ + ℓ − and t → W b, with the secondt 1 being unobserved. We apply the narrowwidth approximation for the masses of the intermediate particles,t 1 ,χ 0 2 and t, which is appropriate since the widths of the respective particles are in all cases much smaller than their masses, cf.…”

“…where the T-odd kinematical factor is given by Here we give the analytical expressions for the different contributions to the decay density matrix for the three-body decay, where we sum over the spins of the final-state particles [39]. The contributions independent of the polarisation of the neutralinoχ …”