Type of hanger on hanging beam?

I’ve never seen a hanger with those design requirements. I like the idea of using a hanger that allows the joists to “sit” in a hanger’s pocket rather than using straps to tie the joists up to the beam. However.....

However, installing such a hanger under joists without damaging the drywall, would be difficult.

I’d try a strap such as Simpson’s HTSQ twist strap.

https://www.strongtie.com/twiststraps_specialtystraps/htsq_strap/p/htsq.

If the joists span half the width of the building (16’) and only supports a ceiling load, then the load on each joists is:

Joists = 2 psf (per square foot)

Plaster = 8-10 psf (depending on type)

Total load = 12 psf x 16’ x 1.33 (to get to 16” oc)

For a total load on each joist = 255 lbs. / 2 (to get load at each end = 128 lbs.

As you can see, these straps are rated up to 720 lbs. depending on the species and grade for uplift. (Your resistance is the reverse of uplift, but is the same principle, but upside down. )

Now, the shortest strap is 16” long, which means 8” should be on each member. However, your joists are 6” tall so they won’t have the intended “cover”. But, your load is so much smaller than the maximum the straps could support, that I’m sure they’ll be fine.

You also have one more issue: If your new beam deflects (sags) at all, then the joists will sag and the ceiling will crack. Plaster is notorious for cracking with minimal deflection.

I have not allowed weight for anything in the attic, (like insulation, light fixtures, etc.)