Spin and chirality effects in antler-topology processes at high energy $$\varvec{e^+e^-}$$ colliders

Abstract

We perform a model-independent investigation of spin and chirality correlation effects in the antler-topology processes e + e − → P + P − → ( + D 0 )( −D0 ) at highenergy e + e − colliders with polarized beams. Generally the production process e + e − → P + P − can occur not only through the s-channel exchange of vector bosons, V 0 , including the neutral Standard Model (SM) gauge bosons, γ and Z , but also through the s-and t-channel exchanges of new neutral states, S 0 and T 0 , and the u-channel exchange of new doubly charged states, U −− . The general set of (nonchiral) three-point couplings of the new particles and leptons allowed in a renormalizable quantum field theory is considered. The general spin and chirality analysis is based on the threshold behavior of the excitation curves for P + P − pair production in e + e − collisions with longitudinal-and transverse-polarized beams, the angular distributions in the production process and also the production-decay angular correlations. In the first step, we present the observables in the helicity formalism. Subsequently, we show how a set of observables can be designed for determining the spins and chiral structures of the new particles without any model assumptions. Finally, taking into account a typical set of approximately chiral invariant scenarios, we demonstrate how the spin and chirality effects can be probed experimentally at a high-energy e + e − collider.

Singularity variables for missing energy event kinematics

“…1(d) and 1(e). The latter is known as the "antler" topology [81] and has been previously discussed in the context of both hadron colliders [12,[81][82][83][84][85][86][87][88][89][90] and lepton colliders [91,92]. At the same time, the diagram of Fig.…”

Generation of arbitrarily polarized GeV lepton beams via nonlinear Breit-Wheeler process

“…Commonly, longitudinal and transverse polarizations are studied separately since those corresponding effects are independent to each other [4,12]. However, it deserves to point out that the arbitrarily spin-polarized (ASP) lepton beams (having both longitudinal and transverse polarization components) also attract broad interests, because they can introduce three mutually orthogonal axes (required by fully reconstructing the density matrix of a spin-1/2 particle), modify effective BSM vertices [14,20,21], and thus play an unique role in future BSM experiments in e + e − colliders, e.g., rendering special spin structure functions as being observable in vector and axial-vector type BSM interactions [16], producing polarized top quark pairs as a probe of new physics [22,23] and diagnosing spin and chirality structures of new particles in antler-topology processes [24].…”