[Paleopsych] Space.com: Mini Big Bang Created, Puzzling Results Too Explosive

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Mini Big Bang Created, Puzzling Results Too Explosive
     By [23]Michael Schirber
     Staff Writer
     posted: 21 March 2005
     06:27 am ET

     What do you get when you turn the temperature up to a trillion

     Quite a heating bill.

     Actually physicists claim that at this temperature nuclear material
     melts into an exotic form of matter called a quark-gluon plasma
     thought to have been the state of the universe a microsecond after the
     Big Bang.

     Recreating this primordial soup is the primary purpose of the
     Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National
     Laboratory. After five years of data, it appears as if RHIC may have

     But a big mystery looms over the detection: the putative plasma
     explodes more violently than predicted.

     "We expected to bring the nuclear liquid to a boil and produce a steam
     of quark-gluon plasma," said John Cramer from the University of
     Washington. "Instead, the boiler seems to be blowing up in our faces."

     The explosive result, which goes by the name of the HBT puzzle, may
     call into question what RHIC is making in its high-speed collisions,
     or it might mean the theory needs retuning.

     Cramer and his colleagues have another alternative explanation, too:
     perhaps the explosion is not as explosive as the data suggests. The
     scientists use 50-year old physics to reinterpret the measurements at

     "We have taken a quantum mechanics technique, called the nuclear
     optical model, from an old and dusty shelf and applied it to puzzling
     new physics results," said Gerald Miller, a coauthor also at the
     University of Washington. "It's really a scientific detective story."

     Collecting clues

     The main suspect in this detective story is the quark-gluon plasma.
     But how do you know when youve seen it? The plasma cannot be observed
     directly it disappears in less than a hundredth of a billionth of a
     trillionth of a second. All that researchers can hope to do is detect
     the particles that fly out when the plasma freezes back into normal

     "You cant go in there and directly measure the quarks and gluons,"
     Miller told SPACE.com. "You have to work back from what you measure to
     what you believe was there."

     Scott Platt from Michigan State University, who didn't participate in
     the new research, compares detecting the quark-gluon plasma to what
     astronomers have to do when studying an exploding star.

     "They only see the light coming from the stars surface and then try to
     infer what happened inside. We [physicists] have the same problem," he

     Instead of light, RHIC researchers see thousands of particles mostly
     pions, which are tiny things weighing about one-seventh as much as a
     proton, itself subatomic. The pions show up in detectors set up around
     collision points, where gold nuclei traveling at 99.995 percent of the
     speed of light hit each other head-on.

     To see a movie of a gold-on-gold collision click [24]here (note that
     the gold nuclei look like pancakes because they are traveling so

     "We cant stick a barometer or thermometer into the collision center,"
     Platt explained, but by a careful reconstruction of the flight paths
     of all the debris coming out, scientists can extract information about
     the brief, but intense, furnace created when gold nuclei smash into
     each other.

     From the RHIC data, research teams have identified three smoking guns
     for the quark-gluon plasma:
       * the collision center is under high pressure
       * the collision center behaves a lot like a fluid
       * very high energy particles do not escape

     Although this evidence appears solid, [25]physicists are hesitant to
     say they have created the melted nuclear goop. "That debate is going
     on as we speak," Platt said.

     One of the reasons for this conservative approach has to do with how
     fast the supposed plasma appears to freeze back into ordinary matter.
     Theory assumed this phase transition would take almost twice as long
     as was measured.

     "In science, if you have a bunch of things that are right, it wont
     matter if one thing goes wrong," Miller said.

     The apparent explosion of pions and other particles coming from the
     phase transition is the so-called HBT puzzle.

     "It is the one RHIC observation that deserves the word puzzle or
     surprise," Platt said.

     HBT puzzle

     To measure the duration of the plasmas phase transition, physicists
     use an astronomy tool, called Hanbury Brown-Twiss (HBT)
     interferometry, which can find the diameter of stars using the radio
     signals from two separate telescopes.

Insert:                      Tiny Terms

     Quark: subatomic particle that is the building block of protons,
     neutrons and short-lived particles like pions.

     Gluon: a particle that transmits the strong nuclear force literally
     gluing quarks together into protons and neutrons and such.

     Plasma: a separate form of matter often referring to a gas of freed
     electrons and ions. In the case of the quark-gluon plasma, the quarks
     and gluons are liberated from their usual bonds, and can interact with
     one another freely.

     Pion: Unlike protons and neutrons, which are made of three quarks, the
     pion is made of just two quarks. Pions eventually decay into photons,
     electrons and neutrinos.

     Phase transition: A change between two forms of matter, like when
     water freezes or boils. There is a phase transition between the
     quark-gluon plasma and ordinary matter.

     Michael Schirber, SPACE.com

End of insert

     Instead of comparing radio waves, physicists compare two pions flying
     out from the collision center. But these measurements require a lot of
     modeling and approximations, Platt explained.

     Cramer and Miller and their collaborators have redone the
     calculations, incorporating something called the nuclear optical
     model. This dates back to 1950s, when scientists were beginning to
     understand the strong interactions inside the nucleus.

     Effectively, this old-school physics accounts for the fact that, as
     pions form out of the cooling plasma, they will have to climb their
     way out of an attractive field similar to the gravitational field that
     a rocket has to overcome to escape a planets clutches.

     "This is not surprising, since it has already been shown that the
     medium is very dense," Miller said. "It is as if the pions are trying
     to leave a crowded room."

     According to Cramer, this crowded room "distorts" the data, making the
     transition look more explosive than it really is. In a sense, the HBT
     puzzle could be a simple misinterpretation of what the data shows.

     Platt is unsure that Cramer and Millers work, published this month in
     Physical Review Letters, indeed clears up the HBT puzzle entirely.

     "They pointed out one of the ways that the calculations can be
     improved," he said. "But the analysis is ongoing."

     If the puzzle does end up being solved, will physicists be ready to
     claim victory?

     "It is not for me to say that we have found the quark-gluon plasma,"
     Cramer said. "But we have made an important step."

     This article is part of SPACE.com's weekly Mystery Monday series.


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