How to catch a perfect wave: Scientists take a closer look inside the
perfect fluid

Date:
September 16, 2021
Source:
DOE/Lawrence Berkeley National Laboratory
Summary:
Scientists have reported new clues to solving a cosmic conundrum:
How the quark-gluon plasma -- nature's perfect fluid -- evolved
into the building blocks of matter during the birth of the early
universe.



FULL STORY ========================================================================== Scientists have reported new clues to solving a cosmic conundrum: How
the quark-gluon plasma -- nature's perfect fluid -- evolved into matter.


==========================================================================
A few millionths of a second after the Big Bang, the early universe took
on a strange new state: a subatomic soup called the quark-gluon plasma.

And just 15 years ago, an international team including researchers from
the Relativistic Nuclear Collisions (RNC) group at Lawrence Berkeley
National Laboratory (Berkeley Lab) discovered that this quark-gluon
plasma is a perfect fluid -- in which quarks and gluons, the building
blocks of protons and neutrons, are so strongly coupled that they flow
almost friction-free.

Scientists postulated that highly energetic jets of particles fly
through the quark-gluon plasma -- a droplet the size of an atom's
nucleus -- at speeds faster than the velocity of sound, and that like
a fast-flying jet, emit a supersonic boom called a Mach wave. To study
the properties of these jet particles, in 2014 a team led by Berkeley
Lab scientists pioneered an atomic X- ray imaging technique called jet tomography. Results from those seminal studies revealed that these jets
scatter and lose energy as they propagate through the quark-gluon plasma.

But where did the jet particles' journey begin within the quark-gluon
plasma? A smaller Mach wave signal called the diffusion wake, scientists predicted, would tell you where to look. But while the energy loss was
easy to observe, the Mach wave and accompanying diffusion wake remained elusive.

Now, in a study published recently in the journal Physical Review Letters,
the Berkeley Lab scientists report new results from model simulations
showing that another technique they invented called 2D jet tomography
can help researchers locate the diffusion wake's ghostly signal.

"Its signal is so tiny, it's like looking for a needle in a haystack
of 10,000 particles. For the first time, our simulations show one can
use 2D jet tomography to pick up the tiny signals of the diffusion wake
in the quark-gluon plasma," said study leader Xin-Nian Wang, a senior
scientist in Berkeley Lab's Nuclear Science Division who was part of
the international team that invented the 2D jet tomography technique.

To find that supersonic needle in the quark-gluon haystack, the
Berkeley Lab team culled through hundreds of thousands of lead-nuclei
collision events simulated at the Large Hadron Collider (LHC) at CERN,
and gold-nuclei collision events at the Relativistic Heavy Ion Collider
(RHIC) at Brookhaven National Laboratory. Some of the computer simulations
for the current study were performed at Berkeley Lab's NERSC supercomputer
user facility.

Wang says that their unique approach "will help you get rid of all this
hay in your stack -- help you focus on this needle." The jet particles' supersonic signal has a unique shape that looks like a cone -- with a
diffusion wake trailing behind, like ripples of water in the wake of a fast-moving boat.

Scientists have searched for evidence of this supersonic "wakelet"
because it tells you that there is a depletion of particles. Once the
diffusion wake is located in the quark-gluon plasma, you can distinguish
its signal from the other particles in the background.

Their work will also help experimentalists at the LHC and RHIC understand
what signals to look for in their quest to understand how the quark-gluon plasma - - nature's perfect fluid -- evolved into matter. "What are we
made of? What did the infant universe look like in the few microseconds
after the Big Bang? This is still a work in progress, but our simulations
of the long-sought diffusion wake get us closer to answering these
questions," he said.

========================================================================== Story Source: Materials provided by
DOE/Lawrence_Berkeley_National_Laboratory. Original written by Theresa
Duque. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Wei Chen, Zhong Yang, Yayun He, Weiyao Ke, Long-Gang Pang,
Xin-Nian Wang.

Search for the Elusive Jet-Induced Diffusion Wake in Z/g-Jets with
2D Jet Tomography in High-Energy Heavy-Ion Collisions. Physical
Review Letters, 2021; 127 (8) DOI: 10.1103/PhysRevLett.127.082301 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210916142808.htm

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