STAR (Solenoidal Tracker at RHIC)

overview: Nuclear physics is a study of the atomic nucleus. The nucleus occupies a very, very small space inside an atom (radius of atom ~ angstrom, radius of nucleus ~ fermi), but the nucleus holds more than 99% of the mass of the entire atom! The protons and neutrons (collectively called "nucleons") which make up the nucleus, however, are not the smallest. We can study their components by smasing them together at high speed.

In a low energy run at RHIC (10 GeV energy per nucleon), each nucleon travels at 99.5% the speed of light, or over 4 million times as fast as the fastest tennis ball ever served (155 mph). When these nucleons hit each other, many new particles get produced.

Very big machines (particle accelerators) are used to accelerate and study these very small particles to explore the Universe's "building blocks." At RHIC, we collide heavy nuclei which contain lots of protons and neutrons so that we can study a nuclear "matter" of these fundamental constituents.

what it is: STAR is a large international experiment at RHIC that study the collisions of relativistic heavy ions and the properties of the dense and hot collision region and the produced particles. The goal is to detect the existence and the nature of a state called the quark-gluon plasma (QGP). This can give us an insight into what the Universe was like at the beginning and what this QGP matter is like. Hundreds of people work on various aspects (detectors, magnets, safety, electronics, data analysis, operation, etc.) of STAR. Many graduate students (names, in pdf) received their degrees working on STAR research.

Spectra is a study of distributions of things such as energy, momentum, and multiplicity of the particles produced from the collisions. Their characteristics tell us about the nature of the collisions. Their fluctuations or transitions can suggest interesting phenomena such as phase transitions.

how it's done: A large cylindrical detector system collects the information that particle tracks leave behind and store the large amount of data. Software performs computations to take those raw data and turn them into reconstructed particle tracks and collision vertices in 3 dimensions. Other information such as rate of energy loss and momentum of the produced particles are recorded as well.

why it is exciting: The temperatures of the collisions are hotter than the Sun. Exotic particles that come out to play. The extremely fast ions of gold collide and create extremely dense and hot fireball, unleashing thousands of new particles. The higher the energy, the higher the multiplicity (number of produced particles), and the more exotic the particles.

STAR website
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