The neuroscientist should address "what is beauty" like any other question: first, is beauty an intrinsic property of things, like magnetism, or is it a sensation, like pain?

If the former, we need to ask the physicists or others about the properties of beauty, but this seems pretty counterfactual at this point, so we won't consider it.

If the latter, we ask questions about what triggers the sensation (we can ask people about that), and, yes, we try to find neurological or chemical correlates of that. We then could ask if there are similar correlates in other organisms, and if yes, if we can manipulate the correlates directly and if so whether that causes behavior that mimics beauty-associated behavior. If yes, we then could go back to humans, change the correlates, and see if we affected the sensation of beauty. Then we would have a decent description of "what is beauty" at the sensory level.

We also have the question of what evokes the sensation of beauty. This is, in a possibly biology-and-culture-dependent sense, what "is" beautiful. Because there is no intrinsic beauty beyond what is perceived as such, we may find that there isn't as much regularity in the description of beauty as we would like, but if beauty is indeed in the "eye of the beholder", the best we can do here is to get a model of what the eye tends to like to behold (probably a statistical or, these days, generative AI model).

And then we know what there is to know about beauty. We know about the implementation of beauty-sense in humans (and maybe other animals); and we know to the extent it's summarizable what external stimuli trigger that beauty-sense.