Science & Technology

Physicists scrutinize light smash-ups to guide future research beyond the Standard Model

A US physicist worked with a collider on the Large Hadron Collider in Europe to study the collision of light that produces matter. Researchers have shown that the starting angle of debris from smash-up is subtly distorted by the pre-collision quantum interference pattern of light.Credit: Illustration by

Understanding photon collisions can be useful in exploring physics beyond the Standard Model.

Immediately after demonstrating an 87-year-old prediction that matter could be produced directly from light, Rice University physicists and their colleagues show how the process affects primitive future research. I explained in detail plasma Physics beyond the Standard Model.

“We are essentially focusing on light collisions,” said Rice, an associate professor of physics and astronomy. Physical review letter..

“We know from Einstein that energy can be converted to mass,” says what in experiments with high-energy particle accelerators such as the Large Hadron Collider (LHC) at the European Organization for Nuclear Research and the Brookhaven National Laboratory. Li, a particle physicist working with hundreds of colleagues, said. Laboratory Relativistic Heavy Ion Collider (RHIC).

Accelerators like the RHIC and LHC routinely convert energy into matter by accelerating atomic fragments near the speed of light and crushing them together. NS Discovery of the Higgs boson in 2012 A notable example at the LHC. At that time, the Higgs boson was the last unobserved particle. Standard model, A theory that explains the basic forces and components of an atom.

Wei Lee and Shuai Yang

Wei Li (left), a professor of rice physics, and Shuai Yang, a doctoral researcher, collaborated with colleagues in a compact muon solenoid experiment of the Large Hadron Collider (LHC) to detect the material-producing light generated in the heavy ion experiment at LHC. I studied collisions. Yang led a newly published study detailing how the starting angle of debris from a smash-up is subtly distorted by pre-collision quantum interference patterns.Credit: Photo by Jeff Fitlow

Impressively, physicists know that the Standard Model describes only about 4% of the matter and energy of the universe. Lee said this week’s study, led by Postdoctoral Researcher Shuai Yang, will affect the search for physics beyond the Standard Model.

“A paper that predicts that new particles can be created from these ion collisions, and that these photon-photon interactions can create new physics beyond the Standard Model because of the very high density of photons in these collisions. There is, “says Li.

Mr. Yang said: “To look for new physics, we need to understand the standard model process very accurately. The effect we saw here suggests that people use photon-photon interactions to look for new physics. It wasn’t taken into account before, and it’s very important to take it into account. “

The effect detailed by Yang and his colleagues occurs when a physicist accelerates the opposite beam of heavy ions in opposite directions and directs the beams toward each other. Ions are the nuclei of giant elements such as gold and lead, and ion accelerators are especially useful for studying the strong forces that bind the neutrons of the nucleus to the basic building blocks called proton quarks. Physicists have used heavy ion collisions to overcome these interactions and observe both quarks and gluons. Particle quarks interact and exchange through strong forces.

However, it is not only the nuclei that collide with heavy ion accelerators. Ion beams also generate electric and magnetic fields that cover each nucleus in the beam with a unique cloud of light. These clouds move with the nucleus, and when the clouds from the opposite beam meet, individual light particles called photons can meet head-on.

so PRL study published in July, Yang et al. Using data from RHIC Photon-Show photon collisions Produces matter from pure energy. In the experiment, a light smash-up occurred with a nuclear collision, producing a primitive soup called quark-gluon plasma (QGP).

“At RHIC, quark-gluon plasma can be formed and at the same time its mass is generated by photon-photon collisions,” says Yang. “So you are creating this new mass in the quark-gluon plasma.”

Yang’s PhD RHIC Data Treatise Study Published on PRL in 2018 The proposed photon collisions may affect the plasma in a small but measurable way. This is interesting and surprising, as photon collisions are an electromagnetic phenomenon and the quark-gluon plasma is dominated by a much stronger force than the electromagnetic force, Lee said.

“It’s not enough to have an electric charge to interact strongly with the quark-gluon plasma,” says Li. “You wouldn’t expect it to interact very strongly with the quark-gluon plasma.”

He said various theories were provided to explain Yang’s unexpected findings.

“One of the suggested explanations is that the photon-photon interactions look different because the two ions are closer to each other, not because of the quark-gluon plasma,” Li said. “This is related to the quantum effect and how photons interact with each other.”

If the quantum effect caused anomalies, Yang speculated that the ions missed each other slightly, but could create a detectable interference pattern when photons from each cloud collided.

“Therefore, the two ions do not collide directly with each other,” says Yang. “They actually pass by. Photons collide, but the ions do not collide with each other, so this is called a super-peripheral collision.”

Compact muon solenoid experiment at LHC

Compact muon solenoid experiment at the Large Hadron Collider of the European Organization for Nuclear Research. Credit: CERN

Theory suggests that the quantum interference pattern from super-peripheral photon-photon collisions should change in direct proportion to the distance between passing ions. Using data from the LHC Compact Muon Solenoid (CMS) experiment, Yang, Li and colleagues found that this distance or collision parameter could be determined by measuring something completely different.

“As the two ions get closer, they are more likely to be excited and start emitting neutrons. The neutrons go straight down the beamline,” says Li. “The CMS has a detector for this.”

Each super-peripheral photon-photon collision produces a pair of particles called muons. Muons usually fly in the opposite direction from a collision. As predicted by theory, Yang, Li et al. Found that quantum interference distorts the starting angle of muons. Also, the shorter the distance between near miss ions, the greater the distortion.

Lee said the effect results from the movement of colliding photons. Each is moving in the direction of the beam with its host ion, but photons can also move away from their host.

“Photons also move vertically,” he said. “And, to be precise, we found that as the collision parameters became smaller and smaller, their vertical movement became stronger.

“This makes it look like something is changing the muon,” says Li. “It looks like one is moving at a different angle than the other, but it’s not. This is because the movement of the photons is changing perpendicular to the direction of the beam before the collision that creates the muon. It’s an artifact of the way. “

Yang said the study explained most of the anomalies he had previously identified. Meanwhile, this study established a new experimental tool for controlling collision parameters of photon interactions that affect a wide range.

“I can comfortably say that the majority came from this QED effect,” he said. “But that doesn’t rule out that there are still effects associated with quark-gluon plasma. This work gives a very accurate baseline, but requires more accurate data. QGP data in CMS. It has been at least 15 years to collect the data, but the accuracy of the data is getting higher and higher. “

Reference: A. M. Sirunyan et al. “Observation of dim-on coplanarity forward neutron multiplicity dependence in super-peripheral Pb-Pb collisions at √sNN = 5.02TeV”. (CMS Collaboration), September 17, 2021 Physical review letter..
DOI: 10.1103 / PhysRevLett.127.122001

LHC and CMS are supported by the European Atomic Energy Agency, the Ministry of Energy, the National Science Foundation, and scientific funding agencies in Austria, Belgium, Brazil, Bulgaria, China, Colombia, Croatia, Cyprus, Ecuador, Estonia, Finland and France. increase. , Germany, Greece, Hungary, India, Iran, Ireland, Italy, South Korea, Latvia, Lithuania, Malaysia, Mexico, Montenegro, New Zealand, Pakistan, Poland, Portugal, Russia, Serbia, Spain, Sri Lanka, Switzerland, Taiwan, Thailand, Turkey , Ukraine, United Kingdom.

Physicists scrutinize light smash-ups to guide future research beyond the Standard Model Physicists scrutinize light smash-ups to guide future research beyond the Standard Model

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