A General Method for Model-Independent Measurements of Particle Spins, Couplings and Mixing Angles in Cascade Decays with Missing Energy at Hadron Colliders

Understand

We outline a general strategy for measuring spins, couplings and mixing angles in the case of a heavy partner decay chain terminating in an invisible particle.

• We consider the common example of a new scalar or fermion D decaying sequentially to other new particles C, B and A by emitting a quark jet j and two leptons ln and lf.
• We derive analytic formulas for the dilepton {ln,lf} and the two jet-lepton ({j,ln} and {j,lf}) invariant mass distributions for most general couplings and mixing angles of the new partners.
• We then consider various spin assignments for the particles A, B, C and D, and derive the relevant functional basis for the invariant mass distributions which contains the intrinsic spin information and does not depend on the couplings and mixing angles.