RHIC Sets Temperature Record
At the “April” meeting, physicists from Brookhaven National Lab announced that they measured the hottest temperature ever recorded, thus recreating an exotic form of matter that hasn’t existed since microseconds after the Big Bang. This is the first time that physicists were able to positively confirm the creation of the much sought after quark-gluon plasma.
“The RHIC at Brookhaven created matter that seems to be at a temperature of 4 trillion degrees Celsius. This is the hottest matter ever created in a laboratory,” said Steven Vigdor, Associate Laboratory Director for Nuclear Particle Physics at the Lab, “We’re talking about the highest temperature in the known universe,”
The Relativistic Heavy Ion Collider smashed gold ions together resulting in collisions close to 370 MeV per nucleon, energetic enough to melt protons into their constituent parts. At these temperatures, roughly 250,000 times hotter than the core of the Sun, the bonds that hold quarks together in protons and neutrons break apart, producing a free flowing liquid-like state of matter. For less than a billionth of a trillionth of a second, quarks and gluons flowed freely in a “perfect” frictionless fluid that hasn’t existed for 13.7 billion years.
Members of the PHENIX collaboration used a technique that measured the energy distribution of the gamma rays emitted by the hot plasma to definitively record the temperature of the matter for the first time.
In 2005, physicists at RHIC announced that the first results from their experiments indicated that the quark-gluon plasma would behave more akin to a liquid rather than a gas as previously predicted. At the time, however, they were unable to pin down the precise temperature of the collisions, and it was unclear if the quark-gluon plasma had been produced.
Analyzing this exotic state of matter, sometimes referred to as “quark soup,” offers insight into the nature of the universe at a very young age. By recreating conditions shortly after the Big Bang on a small scale, physicists can analyze how matter cooled from its initial energetic state to the universe of protons and neutrons that exists today.
“We can model some of the phenomena that occur at even higher temperatures in the even earlier universe, such as the generation of matter-antimatter asymmetry,” said Dmitri Kharzeev, a theoretical physicist at the Lab.
Brookhaven physicists analyzing the behavior of the quark-gluon plasma created at the lab, reported hints of unusual “bubbles” of broken symmetry in the movements of charged quarks. Observations by the STAR collaboration found that magnetic fields induced by the high-speed ions caused positively charged quarks to move preferentially in one direction along magnetic field lines while negatively charged quarks tended to move in the opposite direction. These preferences were slight, only a few parts per 10,000, but significant enough to pique interest.
“These bubbles really are twists in the gluon fields,” said Kharzeev, “We are not yet claiming observation of this, but it is very suggestive.”
Physicists hope that this could lead to greater insights about the fundamental asymmetry of matter and antimatter in the early universe. The full results of the experiments were published in a recent edition of Physical Review Letters.
The temperature record is likely to stand until after the LHC starts its heavy ion collisions near the end of 2010. Once they begin, Vigdor estimates that it could take four to five years before they are able to make a definitive measurement of a higher temperature.