Super strong magnetic fields leave imprint on nuclear matter

A new analysis of the STAR contribution to the Relativistic Heavy Ion Collider (RHIC), a particle collider at the US Department of Energy’s (DOE) Brookhaven National Laboratory, provides the first direct evidence of an imprint left by the universe’s most powerful object. does. Magnetic fields on “deconfined” nuclear matter. The evidence comes from measurements at this DOE Office of Science user facility of how differently charged particles separate when emerging from collisions of nuclear nuclei.

As stated in the journal. Physical examination XThe data show that the powerful magnetic fields produced in off-center collisions Electric current Quarks and gluons break free, or deconfined, from protons and neutrons through particle smash-ups.

The findings give scientists a new way to study the electrical conductivity of this “quark gluon plasma” (QGP) to learn more about the basic building blocks of atomic nuclei.

“This is the first measurement of how the magnetic field interacts with Quark gluon plasma (QGP),” said Deo Shen, a star physicist at China’s Fudan University and leader of the new analysis. Indeed, measuring the effects of this interaction provides direct evidence that these powerful magnetic fields exist.

More powerful than a neutron star

Scientists have long believed that off-center collisions of heavy atomic nuclei such as gold, also known as heavy ions, would create powerful magnetic fields. That’s because some of the non-colliding positively charged protons—and neutral neutrons—that make up the nuclei spin as the ions side-swipe past each other at near the speed of light.

“Those fast-moving positive charges should create a very strong magnetic field, which is predicted to be 10¹⁸ Gauss,” said Geng Wang, a star physicist at the University of California, Los Angeles. For comparison, he noted that neutron stars, the densest objects in the universe, have about 10 fields.¹⁴ gauss, while refrigerator magnets produce a field of about 100 gauss and our home planet’s shielding magnetic field measures just 0.5 gauss.

“It’s probably the strongest magnetic field in our universe.”

But because things happen so fast in heavy-ion collisions, the field doesn’t last long. It wears off in less than 10 minutes.^-23 Seconds—ten millionths of a billionth of a second—make it difficult to observe.

So, instead of trying to measure the field directly, STAR scientists looked for evidence of its effects on particles ejected from the collision.

“Specifically, we were looking at the collective motion of charged particles,” Wang said.

Deviation detection

It is well known that magnetic fields can affect the movement of charged particles and even induce electromagnetic fields in conductive forms of matter such as metals. This is the same thing that is happening here but on a much smaller scale.

“We wanted to see if the charged particles produced in off-center heavy-ion collisions are being removed in a way that can only be explained by the presence of an electromagnetic field in the small spots of the QGP,” said Aihong Tang. can be done,” said Aihong Tang. , a Brookhaven Lab physicist, and member of the STAR collaboration.

The team used STAR’s sophisticated detector systems to track the collective motion of various pairs of charged particles while ruling out the influence of competing non-electromagnetic effects. They were most interested in ruling out deflections caused by charged quarks moving as part of colliding nuclei. Fortunately, those “transported quarks” produce a pattern of deflection that is triggered by an electric current induced by a magnetic field, known as Faraday induction.

A clear indication

“Finally, we see a charge-dependent deflection pattern that can only be triggered by an electromagnetic field in the QGP—a clear sign of Faraday induction,” Tang said.

The scientists observed this strong signal not only in the external collision between two gold nuclei. High energygold-gold at 200 billion electron volts, or GeV—but also in off-center collisions of smaller nuclei—ruthenium-ruthenium and zirconium-zirconium, both at 200 GeV.

“This effect is universal. It happens not only in a large system, but also in a small system,” Shen said.

The scientists saw an even stronger signal when they analyzed data from gold-gold collisions at a relatively low energy: 27 GeV. This finding provides further supporting evidence that Strong magnetic field The particle ejectors produced by off-center collisions induce an electromagnetic field.

This is because Faraday induction occurs when the magnetic field dissipates. In low-energy collisions, this happens more slowly.

“This effect is stronger at lower energy because the lifetime of the magnetic field is longer at lower energy; the speed of the atomic fragments is slower, so the magnetic field and its effects last longer,” Wang said.

Implications

Now that scientists have evidence that magnetic fields induce electromagnetic fields in the QGP, they can use induction to probe the QGP’s conductivity.

“This is a fundamental and important property,” Shane said. “We can estimate the value of the conductivity from our measurements of collective motion. The extent to which the particles deviate is directly related to the strength of the electromagnetic field and the conductivity in the QGP—and no one has measured the conductivity of the QGP. of. First.”

Understanding the fundamental electromagnetic properties of QGP can offer insights into important questions in physics. For one thing, magnetic fields that produce electromagnetic effects can contribute to an interesting separation of particles according to their “handedness” or chirality.

“This study provides strong evidence of a magnetic field, which is one of the prerequisites for this ‘chiral magnetization effect,'” said Shen.

The magnetic field and electromagnetic properties of the QGP also play a role in determining the conditions under which free, unbound quarks and gluons combine to form composite particles called hadrons—such as protons. and neutrons that make up normal nuclei.

“We want to map the nuclear ‘phase diagram,’ which shows at what temperature quarks and gluons can be considered free and at what temperature they ‘freeze out’ to become hadrons. Those properties and “The fundamental interactions of quarks and gluons, which are mediated by the strong force, will be altered under a strong electromagnetic field,” Wang said.

With this new investigation of QGP’s electromagnetic properties, he added, “we can probe these fundamental properties in another dimension to provide more information about the strong interaction.”

For now, the scientists point out, theorists will look to these results to help refine interpretations.