Chuck Bednar for redOrbit.com – @BednarChuck
During an experimental run at the US Department of Energy’s Brookhaven National Laboratory in Upton, New York, the Relativistic Heavy Ion Collider (RHIC) set a new record for producing polarized proton collisions at 200-giga-electron-volt collision energy.
The two-ringed, 2.4-mile-circumference particle accelerator, which is used for research in the field of nuclear physics, shattered its old record by delivering 1200 billion subatomic collisions per week – more than double the amount regularly achieved during its last run in 2012.
Using electron lensing to ramp-up collision rates
One of the reasons for the accomplishment is a technique known as “electron lensing,” which officials at the laboratory explain uses negatively charged electrons as a way to compensate for the tendency of the positively charged protons in one beam to repel the like-charged protons in the a second beam circulating in the opposite direction when the pass through each other.
Three years ago, the interactions between those beams limited their ability to generate collisions at high rates, said Wolfram Fischer, head of the Brookhaven Collider-Accelerator Department’s accelerator division. So he and his colleagues commissioned electron lenses and a new lattice to help mitigate the effect of these beam-beam interactions, making the RHIC the first-ever particle collider to use electron lenses in this manner.
They also upgraded the source that produced the polarized protons to generate and feed more of them indo the circulating beams, and made other improvements in the accelerator chain in order to achieve the highest possible collision rates (also known to physicists as luminosity).
Meeting more science goals through increased luminosity
Doing so will allow them to generate high volumes of data quickly, Brookhaven Lab associate director for nuclear and particle physics Berndt Mueller explained. The increased luminosity will give the RHIC team time to achieve multiple “high-priority science goals” in a single run.
Among the goals RHIC physicists hope to accomplish during the initial stage of the accelerator’s current run will be colliding high-energy 200 GeV polarized protons whose individual spins are aligned in a particular direction with another proton bean to figure out how the building blocks of those protons (quarks and gluons) contribute to their overall spin.
The RHIC was the first collider to discover that gluons play a key role in this particle property, and the new results will look to improve on the precision of those measurements while solving a long-standing physics mystery in the process, the laboratory said. It will also allow scientists to study the coupling between the spin and momentum of the quarks, they added.
So what is the overall significance of this accomplishment?
Fischer told redOrbit via email the achievement was significant for two reasons.
“First, the 2x higher collision rates allow for more scientific output,” he said. “The higher rate can be used to either reduce the experimental errors, or complete a measurement in half the time, thereby allowing for additional measurements. In our case, we are considering collisions of polarized protons with aluminum ions later this year as an additional measurement. Such a combination was never done before and would give us new information in the understanding of what happens inside nuclear matter.”
“Second, the beam-beam compensation scheme implemented to allow for higher collision rates advances the state of the art in accelerator science and technology,” Fischer added. “The electron lenses (you can think of them as very unusual magnets) are devices that can be used in other applications too. Beam-beam compensation itself is a long-standing topic in particle colliders, and has been operationally tried only once in the 1970s, unsuccessfully at the time.
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