1/2 spin antigravity is experimentally proven via neutrons: The Nonlocal Gravitational Stern-Gerlach Spin Rotation Effect: Mashhoon

 The apparent coupling of nuclear spin of atomic mercury with the rotation of the
earth has been observed by Venema et al. [Phys. Rev. Lett. 68 ( 1992) 1351. The significance and implications of this result for the physics of accelerated systems are briefly discussed.

 Mashhoon, B. (1995). On the coupling of intrinsic spin with the rotation of the earth. Physics Letters A, 198(1), 9–13. doi:10.1016/0375-9601(95)00010-z

 

 

 

 

 

 https://arxiv.org/pdf/2310.13118.pdf

 

 Review of the Gravitomagnetic Clock Effect, 2023

A consequence of this spin-gravitomagnetic field coupling is the violation of the universality of free fall; for instance, a free neutron with spin up will in general fall differently in the gravitational field of the Earth than a free neutron with spin down [90, 91]. For a recent treatment of spin-gravity coupling, see [92].

https://arxiv.org/pdf/2210.07103.pdf

 arXiv:2210.07103v2 [gr-qc] 1 Jul 2023
On free fall of fermions and antifermions

 In particular, the free-fall observation of neutrons [1–3] shows that the Standard Model has to be extended to comprise general relativity. This circumstance leads to a problem of field quantisation in curved spacetime.

https://arxiv.org/pdf/2210.07103.pdf

The local curvature length nearby such black holes can be much smaller than the hydrogen-atom size. Thus, the question arises as to whether the wave-packet description of elementary and composite particles is adequate once their quantum size
is comparable to a local curvature length