A new study published in Physical Review Letters presents evidence for the creation of matter and antimatter from energy, specifically light particles (photons). In doing so, it offers a splendidly concrete example of the world’s most famous equation: E=mc2. The equation, derived by Einstein, dictates how energy (E) is equivalent to mass (m) times the speed of light (c) squared. In the study, physicists at the Relativistic Heavy Ion Collider (RHIC), part of the Department of Energy’s Brookhaven National Laboratory, were able to turn light particles, which are energy, into pairs of electrons and positrons, which are matter (matter being that which has mass). To be precise, positrons are antimatter, but antimatter follows the same energy-mass equivalence.
The researchers were able to generate the matter-antimatter pairs by utilizing beams of gold ions. They took atoms of gold, stripped away all their electrons to make them positively charged ions, and then shot the ions past each other at ultrarelativistic speeds (99.995% the speed of light, or roughly 186,000 miles per second). The ions create a strong magnetic field which rotates around them. This magnetic field interacts with the perpendicular electric field, and packets of the resulting electromagnetic field are what we call photons, or light. As the ions travel through the particle accelerator, they are accompanied by clouds of these photons.
Zhangbu Xu, Brookhaven Lab physicist and a member of the RHIC’s STAR (Solenoid Tracker at RHIC) Collaboration, described the experiment setup: “We have two clouds of photons moving in opposite directions with enough energy and intensity that when the two ions graze past each other without colliding, those photon fields can interact…” This interaction is what creates the pairs of electrons and positrons.
While a similar result was achieved in 1997 at the SLAC National Accelerator Laboratory, the process at that time was more complicated and involved more steps. This finding stands out as “clear evidence of direct, one-step creation of matter-antimatter pairs from collisions of light as originally predicted by [20th century physicists Gregory] Breit and [John A.] Wheeler,” according to Daniel Brandenburg, a Goldhaber Fellow at the Brookhaven Lab.
The study also provides evidence of another previously theoretical prediction about the interaction between polarized photons and empty space vacuums. Physicists in the 20th century (specifically Werner Heisenberg, Hans Heinrich Euler, and John Toll) predicted that a vacuum of empty space would deflect certain polarized photons if the vacuum itself was also polarized. This phenomenon is called vacuum birefringence and had not been observed in any Earth-based experiment until now.
Like how a polarized pair of sunglasses blocks and absorbs certain light from passing through its lenses, the vacuum plus magnetic field blocks and absorbs certain light as well. This light is what then turns into the electron-positron pairs. The researchers were able to determine this relationship because “…the angular distribution of the [electron-positron pairs] depends on the angle of the polarization of the light. This indicates that the absorption (or passing) of light depends on its polarization…” as Chi Yang, a STAR collaborator from Shandong University, puts it.
This research provides deeper insight into vacuums, their interaction with light, and the relationship between energy and matter. With new, powerful technology, we can confirm (or deny) predictions of the past and present, slowly continuing our journey to understand and appreciate the universe that makes up us and everything we know.
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