The sPHENIX Detector
sPHENIX is a radical makeover of the PHENIX experiment, one of the original detectors designed to collect data at Brookhaven Lab’s Relativistic Heavy Ion Collider. It includes many new components that significantly enhance scientists’ ability to learn about quark-gluon plasma (QGP), an exotic form of nuclear matter created in RHIC’s energetic particle smashups.
The sPHENIX detector is about the size of a two-story house and weighs 1,000 tons. Like a giant, 3D digital camera, the detector will capture snapshots of 15,000 particle collisions per second, more than three times faster than PHENIX. With these capabilities, sPHENIX will take advantage of the many accelerator improvements that have been made to increase collision rates at RHIC.
Magnet at the core
The cylindrical superconducting magnet at the core of sPHENIX began its life as part of the BaBar experiment at SLAC National Accelerator Laboratory in California. After a cross-country journey and extensive testing at Brookhaven, the 20-ton solenoid was installed as part of the sPHENIX assembly project in 2021. When sPHENIX begins collecting data in 2023, the powerful magnet will bend the trajectories of charged particles produced in proton and ion collisions at RHIC so scientists can tease out subtle details about how the building blocks of matter interact. For example, the bending power of the sPHENIX magnet will allow physicists to differentiate among particles that come in three different mass states to learn about the force that binds quarks and gluons into larger particles such as protons and neutrons.
Unlike simple refrigerator magnets, a superconducting solenoid is a complex electromagnetic machine in which a powerful magnetic field is generated by running electricity through coils of superconducting wire. These wires can carry electrical current with no energy loss, but to operate they must be chilled to 4 degrees Kelvin, or -452 degrees Fahrenheit. The sPHENIX assembly will include pipes with valves and joints that make up a cryogenic system for circulating super-cold liquid helium to cool the superconducting coils, and external power supplies to deliver the field-generating current.
Inner and outer calorimeters
Detector components called calorimeters arrayed within and around the central core of the sPHENIX magnet will measure the energy and other properties of particles emitted from each collision. By adding up the energy of the sprays of particles emitted when high-energy quarks and gluons traverse the quark-gluon plasma (QGP)—and how much energy these particles lose along the way—physicists hope to understand how the QGP’s remarkable properties emerge from the individual quark and gluon interactions.