The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has shattered its own record for producing polarized-proton collisions at 200 GeV collision energy. In the experimental run currently underway, accelerator physicists are delivering 1.2 × 1012 collisions per week – more than double the number routinely achieved in 2012, the last run dedicated to polarized-proton experiments at this collision energy.
The achievement is, in part, the result of a method called “electron lensing”, which uses negatively charged electrons to compensate for the tendency of the positively charged protons in one circulating beam to repel the like-charged protons in the other beam when the two oppositely directed beams pass through one another in the collider. In 2012, these beam–beam interactions limited the ability to produce high collision rates, so the RHIC team commissioned electron lenses and a new lattice to mitigate the beam–beam effect. RHIC is now the first collider to use electron lenses for head-on beam–beam compensation. The team also upgraded the source that produces the polarized protons to generate and feed more particles into the circulating beams, and made other improvements in the accelerator chain to achieve higher luminosity.
With new luminosity records for collisions of gold beams, plus the first-ever head-on collisions of gold with helium-3, 2014 proved to be an exceptional year for RHIC. Now, the collider is on track towards another year of record performance, and research teams are looking forward to a wealth of new insights from the data to come.