RHIC's STAR Experiment Sees Unexpected Dip in Gold Collisions, Hinting at Nuclear Critical Point
Physicists at Brookhaven's RHIC found an unexpected dip in particle-flow variations while smashing gold nuclei at nearly light speed, a possible hint of a long-sought critical point, though researchers say it is not proof.
The signal was detected by the STAR experiment at RHIC, according to the report. In every collision, particles are flung out sideways, and how hard they are flung, on average, varies slightly from one collision to the next. Physicists expected the size of these variations to change smoothly as they adjusted the collision energy. Instead, the variations dipped, shrinking and then growing again.
That dip could be a sign of a long-sought critical point, a special set of conditions at which nuclear matter changes the way it transforms from one form to another. The report said the signal is strong enough that it is very unlikely to be a statistical accident. Researchers cautioned, however, that the dip is a tantalizing hint, not proof of the long-sought transition.
The team analyzed roughly 1 billion collisions, measuring how hard charged particles were flung sideways out of the fireball, according to Live Science. The findings were published Sept. 22 in the journal Physical Review Letters.
'It does point to a set of conditions where the behavior of nuclear matter changes, and it gives theorists a new, precise measurement to test their calculations against,' study co-author Rutik Manikandhan told Live Science.