Monday, January 09, 2006

Quark Gluon Plasma II: Strangelets

You have to follow the logic developement, which is confusing, because in one respect "Risk assessment" does not think of cosmic collisions as interesting comparisons to microstate production, yet as I travelled through the information held in context of Pierre Auger experiments, Jaffe's statement from 1999 makes for some interetsing discussion below.

Is it true or not?

In recent years the main focus of fear has been the giant machines used by particle physicists. Could the violent collisions inside such a machine create something nasty? "Every time a new machine has been built at CERN," says physicist Alvaro de Rujula, "the question has been posed and faced."

There does not appear to be suppression of particles with a high transverse momentum in Deuteron+Gold collisions: In order to confirm the observation of suppression, a control experiment was run by PHENIX in the Spring of 2003. Here, a collision was studied in which a medium such as the Quark-Gluon Plasma is not expected to be formed. The collisions studied were small deuteron nuclei colliding with Gold nuclei. In this case, more, rather than fewer, particles are seen with a high transverse momentum. This observation confirms that the suppression seen in Gold+Gold collisions is most likely due to the influence of a new state of matter being produced, such as a Quark-Gluon Plasma.

There are more protons than pions at high transverse momentum: PHENIX can identify different types of particles, including lighter pions and heavier protons and kaons. PHENIX finds that there are more protons than pions at high transverse momentum. This may indicate that the physical processes that produce these particles are occurring differently in heavy ion collisions. Also, there are almost as many anti-protons as protons, which is another indication that conditions are favorable for the production of a Quark-Gluon Plasma.

A large number of produced particles are observed: PHENIX finds that there are additional particles produced in collisions of Gold ions than what would be expected from measurements of simpler collisions of protons. This fact hints that conditions may be favorable for the production of a Quark-Gluon Plasma. Also, more particles are produced when the ions collide head on.

A large total amount of transverse energy production is observed: PHENIX can measure the amount of energy that comes out sideways, or transverse, to the direction the ions were originally travelling. Like the number of produced particles, the total transverse energy is largest when the ions collide head on. From this measurement, PHENIX estimates that the density of energy in the center of the collision is about 30 times that of a normal nucleus. This fact also hints that conditions may be favorable for Quark-Gluon Plasma production.

The source of produced particles is large and short-lived: Borrowing a technique from astronomy that has been applied to measure the radius of individuals stars, the size of the source volume where the particles are produced has been measured by PHENIX. The transverse size of the source appears to be much larger than the original size of the Gold nuclei, and lives for a very short time. The short life is contrary to what is expected from a Quark-Gluon Plasma and remains a mystery to be solved.

An electron signal above background is observed: PHENIX is unique at RHIC in that it can identify individual electrons coming from the collision, many of which are the result of decays of heavier particles within the collision. PHENIX measures a number of electrons that is above the expected background. The excess electrons are likely coming from decays of special particles with heavy charm quarks in them. Further study of these charmed particles will help us better understand if a Quark-Gluon Plasma has been formed.

Non-random fluctuations are observed, but they are likely due to the presence of jets: During a phase transition, it is typical to see fluctuations in some properties of the system. PHENIX has measured fluctuations in the charge and average transverse momentum of each collision. Thus far, PHENIX reports no large charge fluctuations that might be seen if there is a phase transition from a Quark-Gluon Plasma. PHENIX reports that there are excess fluctuations in transverse momentum, but they appear due to the presence of particles from jets. The behavior of the fluctuations is consistent with the jet suppression phenomenon mentioned previously.

The particles are flowing - a lot: PHENIX can measure how much the particles flow around in the collision. PHENIX observes a significant particle flow effect, which is expected when heavy ions collide. However, those high transverse momentum particles surprise again, and show a flow effect that is not yet understood and may be more evidence for the existence of a Quark-Gluon Plasma.

The collisions are strange: PHENIX can identify particles that contain strange quarks, which are interesting since strange quarks are not present in the original nuclei so they all must be produced. It is expected that a Quark-Gluon Plasma will produce a large amount of strange quarks. In particular, PHENIX has measured lambda particles. There are more lambda particles seen than expected.

I don't have to remind you of why I have taken this route to understand what is taking place as such proton proton collisions reveal some interesting perspectives.

Quark stars signal unstable universeBy William J. Cromie
Gazette Staff

In orbit around Earth, a satellite called the Chandra X-ray Observatory surveys the universe for sources of X-rays, which come from hot, active places. Such places include neutron stars, the still energetic corpses of burnt out stars once more massive than the Sun. When such stars use up their hydrogen fuel they explode into bright supernova, then their cores collapse into an extremely heavy ball of neutrons enveloped in a thin atmosphere containing iron and other debris from the explosion. In the core of the dying star, extreme pressure breaks atoms down into protons, neutrons, and electrons. The protons and electrons combine into neutrons, and the remaining material is so heavy that one tablespoon of it weighs about four trillion pounds.

But they noticed something very odd?

A Black Hole Ate My Planet

In 1995, Paul Dixon, a psychologist at the University of Hawaii, picketed Fermilab in Illinois because he feared that its Tevatron collider might trigger a quantum vacuum collapse. Then again in 1998, on a late night talk radio show, he warned that the collider could "blow the Universe to smithereens".

But particle physicists have this covered. In 1983, Martin Rees of Cambridge University and Piet Hut of the Institute of Advanced Study, Princeton, pointed out that cosmic rays (high-energy charged particles such as protons) have been smashing into things in our cosmos for aeons. Many of these collisions release energies hundreds of millions of times higher than anything RHIC can muster--and yet no disastrous vacuum collapse has occurred. The Universe is still here.

This argument also squashes any fears about black holes or strange matter. If it were possible for an accelerator to create such a doomsday object, a cosmic ray would have done so long ago. "We are very grateful for cosmic rays," says Jaffe.

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