Hexbyte Glen Cove
The speed of sound in this environment can be obtained from the rate at which pressure changes in response to variations in energy density or, alternatively, from the rate at which temperature changes in response to variations in entropy, which is a measure of disorder in a system.
In heavy-ion collisions, the entropy can be inferred from the number of electrically charged particles emitted from the collisions. The temperature, on the other hand, can be deduced from the average transverse momentum (i.e., the momentum transverse to the collision axis) of those particles.
Using data from lead–lead collisions at an energy of 5.02 trillion electronvolts per pair of nucleons (protons or neutrons), the CMS collaboration has measured for the first time how the temperature varies with the entropy in central heavy-ion collisions, in which the ions collide head-on and overlap almost completely.
From this measurement, they obtained a value for the speed of sound in this medium that is nearly half the speed of light and has a record precision: in units of the speed of light, the squared speed of sound is 0.241, with a statistical uncertainty of 0.002 and a systematic uncertainty of 0.016. Using the mean transverse momentum, they also determined the effective temperature of the quark–gluon plasma to be 219 million electronvolts (MeV), with a systematic uncertainty of 8 MeV.
The results match the theoretical expectation and confirm that the quark–gluon plasma acts as a fluid made of particles that carry enormous amounts of energy.
The paper is published on the arXiv preprint server.
More information:
Extracting the speed of sound in the strongly interacting matter created in ultrarelativistic lead-lead collisions at the LHC, arXiv (2024). DOI: 10.48550/arxiv.2401.06896
Journal information:
arXiv
Citation:
CERN researchers measure speed of sound in the quark–gluon plasma more precisely than ever before (2024, February 16)
retrieved 17 February 2024
from https://phys.org/news/2024-02-cern-quarkgluon-plasma-precisely.html
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