PHOBOS detectorThe PHOBOS experiment is based on the premise that interesting collisions will be rare, but that when they do occur, new physics will be readily identified. Thus the PHOBOS detector is designed to examine and analyze a very large number of unselected gold ion collisions. For each collision, the detector gives a global picture of the consequences of the collision and detailed information about a small subset of the nuclear fragments ejected from the high energy-density region.

PHOBOS consists of many silicon detectors surrounding the interaction region. With these detectors, physicists will be able to count the total number of produced particles and study their angular distribution. With this array they will be looking for unusual events, such as fluctuations in the number of particles or angular distribution. Physicists know from other branches of science that a characteristic of phase transitions is a fluctuation in observable events. In order to obtain more detailed information about these events, the PHOBOS detector will also have two high-quality magnetic spectrometers which will study one percent of the produced particles in detail.

PHOBOS diagram

The PHOBOS detector is able to measure quantities such as the temperature, size, and density of the fireball produced in the collision. It also studies the ratios of the various particles produced. With this information it should be possible to both detect and study a phase transition that might occur between quark-gluon plasma and ordinary matter. The PHOBOS group hopes to discover the quark-gluon plasma and learn more about the early universe.

Seventy scientists from 12 institutions in three nations are working on PHOBOS, which is located at the 10 o'clock position on the RHIC ring.

PHOBOS experimental group home page

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PHOBOS beamline
This horizontal beamline transports heavy ions into the PHOBOS experiment.

PHOBOS silicon detectors
Adjusting the PHOBOS silicon detectors.