RHIC

RHIC
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Name	Relativistic Heavy Ion Collider
Caption	Aerial view of the Brookhaven National Laboratory campus, showing the RHIC tunnel.
Location	Upton, New York, United States
Institution	Brookhaven National Laboratory
Type	Storage ring, Collider
Particle	Proton, Deuteron, Gold, Copper, Uranium ions
Energy	100 GeV per nucleon (for gold)
Circumference	3.834 km
Luminosity	~2×10²⁶ cm⁻²s⁻¹ (Au+Au)
Dates	2000 – present

RHIC. The Relativistic Heavy Ion Collider is a premier nuclear physics research facility located at the Brookhaven National Laboratory on Long Island. As the first and one of only two operating heavy-ion colliders in the world, alongside the Large Hadron Collider's heavy-ion program, it is designed to collide beams of heavy atomic nuclei at near-light speeds. Its primary mission is to recreate and study a state of matter known as the quark–gluon plasma, which is thought to have existed microseconds after the Big Bang. The facility also conducts a vibrant program of spin-polarized proton collisions to investigate the internal spin structure of the proton.

Overview

Operated by the United States Department of Energy, RHIC began operations in 2000 following the closure of the Alternating Gradient Synchrotron booster ring. It occupies a tunnel originally constructed for the ISABELLE project. The collider complex accelerates and stores counter-rotating beams of ions ranging from protons to fully stripped gold nuclei, enabling collisions at center-of-mass energies up to 200 GeV per nucleon pair for gold. This unique capability allows physicists to probe the fundamental force described by quantum chromodynamics under extreme conditions of temperature and density. Research at the facility is conducted by international collaborations such as the STAR collaboration and the PHENIX collaboration.

Design and operation

The accelerator complex consists of two independent, concentric storage rings, each 3.8 kilometers in circumference, housed in a tunnel utilizing superconducting niobium-titanium magnets. Ions are produced by an electron beam ion source, pre-accelerated by the Booster synchrotron, and then injected into the Alternating Gradient Synchrotron for further acceleration before transfer to the main rings. A key innovation is the use of Siberian snakes and spin rotators to maintain the polarization of proton beams. The rings intersect at six interaction points, four of which are instrumented with large detector systems. Operations are conducted in distinct runs, alternating between heavy-ion collisions and polarized proton-proton collisions, with the machine performance monitored and controlled from the Brookhaven National Laboratory control room.

Scientific discoveries and research

The landmark discovery at RHIC was the creation of a hot, dense, strongly interacting quark–gluon plasma, announced in 2005. Data from experiments like STAR and PHENIX showed the plasma behaves as a nearly perfect fluid with minimal viscosity, a finding quantified through measurements of elliptic flow. Subsequent research has precisely mapped the phase diagram of nuclear matter, searched for critical points, and observed the suppression of high-transverse-momentum particles, a phenomenon known as jet quenching. The polarized proton program has made definitive measurements of the proton's spin structure, revealing significant contributions from the orbital angular momentum of gluons and quarks, challenging earlier models like the Elliott model.

Experimental programs

Major detector experiments at RHIC include the large, general-purpose STAR detector, which tracks thousands of particles per event with its time projection chamber, and the PHENIX detector, optimized for detecting rare penetrating probes like muons and photons. The now-completed BRAHMS experiment and PHOBOS experiment provided crucial early measurements of particle yields and correlations. A dedicated experiment, the sPHENIX detector, is a major upgrade designed to study jet quenching and the thermal properties of the quark–gluon plasma with unprecedented precision. These collaborations involve thousands of scientists from hundreds of institutions worldwide, including MIT, the University of California, Berkeley, and international partners like the Weizmann Institute of Science.

Future and legacy

While RHIC concluded its traditional operations as a collider, its scientific legacy continues through the analysis of its vast data sets. The facility is transitioning to become the core accelerator for the Electron-Ion Collider, a next-generation project approved by the United States Department of Energy. The EIC will use one of RHIC's rings to collide electrons with protons and ions, aiming to precisely map the spatial and momentum distributions of quarks and gluons inside nuclei. The technological and operational expertise gained from RHIC, particularly in managing polarized beams and complex detector systems, provides a direct foundation for future discoveries in nuclear physics at facilities like the Facility for Rare Isotope Beams and the Large Hadron Collider.

Category:Particle accelerators Category:Brookhaven National Laboratory Category:Nuclear physics experiments