ACU professors involved in groundbreaking physics research findings
For immediate release
Three Abilene Christian University physics professors have helped in research that points to the discovery of a new form of matter called the quark-gluon plasma, which is believed to have existed in the first microseconds after the birth of the universe.
Dr. Donald Isenhower, professor of physics and chair of the Department of Physics; Dr. Mike Sadler, professor of physics; and Dr. Rusty Towell, assistant professor of physics, are all members of the PHENIX collaboration (Pioneering High Energy Nuclear Interaction eXperiment) at the U.S. Department of Energy's Brookhaven National Laboratory. These recent results were announced June 18 at a special colloquium at Brookhaven.
The PHENIX project works with the Relativistic Heavy Ion Collider, known as RHIC, which is the world's most powerful facility for heavy ion nuclear physics research.
While the results of the research do not yet officially confirm discovery of the quark-gluon plasma, the results indicate that the researchers are on the right track, according to Isenhower.
“If this bears out, it will be the confirmation of one of the major reasons RHIC was built,” Isenhower said.
In addition to the three ACU faculty members, each summer several ACU undergraduate students and recent graduates travel to Brookhaven to work on the project. This summer Ross Baldwin, junior physics major from Kenai, Alaska; James Drachenberg , senior physics major from Humble; Sako Hagiwara, senior physics major from Aurora, Colo.; Larry Isenhower, junior physics major from Abilene; Soji Omiwade, senior computer science major from Lagos, Nigeria; and Christopher Smith, computer science major from College Station, are all working on the project.
Papers submitted in conjunction with the deuteron-gold collisions will bear the names of not only the three ACU faculty members, but also Larry Isenhower; Jeb Qualls, ACU graduate in ’02; Chris Kuberg, ACU graduate in ’02; Cody McCain, senior physics major from Dumas; and Drachenberg for their help with the research.
ACU has received nearly $2 million in nuclear physics research funding from the U.S. Department of Energy over the past 11 years. ACU faculty and students have worked with the PHENIX project for the past three years.
The latest RHIC findings come from experiments conducted from January through March of 2003, in which a beam of heavy gold nuclei collides head-on with a beam of deuterons (much smaller and lighter nuclei, each consisting of one proton plus one neutron). These deuteron-gold experiments, along with other experiments using two colliding beams of protons, serve as a basis for comparison with collisions of two gold beams at RHIC.
The gold-gold collisions, which bring nearly 400 protons and neutrons into collision at once, are designed to recreate, for a fleeting instant in the laboratory, the extremely hot, dense conditions of the early universe. When two gold nuclei collide head-on, the temperatures reached are so extreme (more than 300 million times the surface temperature of the sun) that the individual protons and neutrons inside the merged gold nuclei are expected to melt, releasing the quarks and gluons normally confined within them to form a tiny sample of particle "soup" called quark-gluon plasma. In contrast, the small deuteron passes through the large gold nucleus like a bullet, without heating or compressing it very much. The gold nucleus remains in its usual state, composed of distinct protons and neutrons.
In either type of collision, a pair of energetic quarks can be knocked loose from within a proton or neutron. Each of these loose quarks will produce a "jet" of ordinary particles, and the two jets will emerge back-to-back from the collision region. Scientists can use these jets to probe nuclear environments.
In the deuteron-gold experiments conducted this spring, back-to-back jets were seen to emerge, but in head-on collisions from the earlier gold-gold experiments, one of the two jets was missing. In addition, fewer highly energetic individual particles are observed coming from gold-gold than from deuteron-gold collisions. Scientists are intrigued by these distinctions, which clearly show that head-on gold-gold collisions are producing a nuclear environment quite different from that of deuteron-gold collisions.
One possible explanation of the missing jets is that a quark traveling through this new environment would interact strongly and lose a substantial amount of its energy. Thus, if a quark pair is produced near the surface of the nuclear fireball resulting from a head-on collision of gold nuclei, the outward-bound quark is able to escape, while the inward-bound quark is absorbed. Only one jet is detected by the physicists. This phenomenon is called "jet quenching" and was predicted to occur in quark-gluon plasma. The same calculations also predicted the observed suppression of high-energy individual particles.
If further scientific research proves that a quark-gluon plasma has been made, the physics story has just begun. By studying the behavior of free quarks and gluons in the plasma, RHIC scientists hope to learn more about the strong nuclear force - the force that holds quarks together in protons and neutrons.
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