Particle Collisions Inside STAR Detector of RHIC
Credit: Brookhaven National Laboratory
A groundbreaking discovery involving rare particles formed from high-energy proton collisions may illuminate one of physics’ greatest enigmas: the emergence of mass from empty space. This finding could reshape our understanding of particle mass acquisition.
According to quantum chromodynamics (QCD), the prevailing theory describing the strong forces binding quarks in protons and neutrons, a vacuum is not empty; it teems with transient disturbances in the underlying energy of space, known as virtual particles. These disturbances include fleeting quark-antiquark pairs.
While these pairs typically vanish as soon as they appear, QCD posits that injecting sufficient energy into the vacuum can transform them into real, detectable particles with mass.
The STAR Collaboration, an international group of physicists at the Relativistic Heavy Ion Collider in New York, has successfully observed this intriguing phenomenon for the first time.
By bombarding protons in a vacuum, they created a spray of particles, anticipating that some would be quark-antiquark pairs originating from the vacuum. However, as quarks cannot exist independently, they rapidly amalgamate into composite particles.
Luckily for the researchers, these specific particles reveal clues about their formation. Quarks and antiquarks exhibit correlated spins, reflecting their shared quantum state inherited from the vacuum.
The researchers discovered that this spin correlation remains intact even as the quarks and antiquarks evolve into larger particles known as hyperons, which decay in less than a billionth of a second. Identifying these spin-aligned hyperons following proton collisions confirmed that their constituent quarks originated from the vacuum.
“This is the first time I’ve witnessed the entire process,” remarked Tu Chowdungmin, a member of the STAR collaboration.
“I’m thrilled to see this measurement,” added Daniel Bohr, who was not part of the research team and is affiliated with the University of Groningen, Netherlands. He noted that many mysteries still loom around quarks, such as their inability to exist isolated. “This experiment is particularly intriguing for that reason.”
Tu believes this research opens new avenues to directly examine vacuum properties, potentially enabling scientists to investigate how particles acquire mass. QCD theory suggests that quarks gain additional mass by interacting with the vacuum, though the exact mechanisms remain unclear.
Alessandro Bachetta, a researcher at the University of Pavia in Italy, emphasized that the results are not yet definitive, as reconstructing particle collision events can be convoluted. Researchers must first effectively eliminate alternative explanations that could produce similar signals, he stated.
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Source: www.newscientist.com
