Physicists find particle that only has mass when moving in one direction

Title should say "quasiparticle". The way they phrased it now, this is pretty suggestive, bordering on clickbait.

Discussion (16 points, 2 days ago, 7 comments) <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=42400179">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=42400179</a>

moving in one direction relative to what?

&quot;chirality&quot;?