system
Given the following post, respond as if you're commenting on Reddit:
human
What is particle X17?
gpt
It is a (to-date) hypothetical particle that would be an interaction boson (like photons, W and Z bosons, gluons). In analogy to the W and Z bosons, it's called an "X"-boson and 17 is about its expected mass (~17 MeV). As of now, there is evidence that such a particle exists, though it is neither peer reviewed nor confirmed by any independent research group (despite there were attempts to do so!). If it exists, it might be connected to a fifth elementary force and dark matter.