Collisions between protons and lead ions at the Large Hadron Collider (LHC) may have produced a new type of matter known as colour-glass condensate.
When particle beams interact at high speeds, the collisions yield hundreds of new particles, most of which fly away from the collision point at close to the speed of light. However, the Compact Muon Solenoid (CMS) team at the LHC found that in a sample of 2 million lead-proton collisions, some pairs of particles flew away from each other in the same direction.
“Somehow they fly at the same direction even though it’s not clear how they can communicate their direction with one another. That has surprised many people, including us,” said MIT physics Professor Gunther Roland, who led the group.
Two years ago, MIT researchers observed the same distinctive pattern in proton-proton collisions when ions of lead or other heavy metals, such as gold or copper, collided with one another.
Heavy-ion collisions produce a wave of quark gluon plasma, the hot soup of particles that existed for the first few millionths of a second after the Big Bang. In the LHC, this wave forces some of the resulting particles away in the same direction.
However, quark-gluon plasma isn’t possible with lead-proton collisions. So it has been speculated that the proton-proton collisions in the study may produce a liquid-like wave of gluon known as colour-glass condensate. Gluons are elementary particles related to the strong force that sticks quarks together inside protons and neutrons.
The mechanism may depend on the phenomenon of quantum entanglement. Entangled gluon in the colour-glass condensate could explain how two particles can retain a connection even after they fly away from each other.
“You don’t expect quark gluon plasma effects with lead-proton collisions,” explained Roland. “It was supposed to be sort of a reference run – a run in which you can study background effects and then subtract them from the effects that you see in lead-lead collisions.”
Details of the discovery will be published in the journal Physical Review B