Nav: Home

New evidence for small, short-lived drops of early universe quark-gluon plasma?

September 18, 2017

UPTON, NY -- Particles emerging from even the lowest energy collisions of small deuterons with large heavy nuclei at the Relativistic Heavy Ion Collider (RHIC https://www.bnl.gov/rhic/) -- a U.S. Department of Energy Office of Science User Facility for nuclear physics research at DOE's Brookhaven National Laboratory--exhibit behavior scientists associate with the formation of a soup of quarks and gluons, the fundamental building blocks of nearly all visible matter. These results from RHIC's PHENIX experiment suggest that these small-scale collisions might be producing tiny, short-lived specks of matter that mimics what the early universe was like nearly 14 billion years ago, just after the Big Bang.

Scientists built RHIC, in large part, to create this "quark-gluon plasma" (QGP) so they could study its properties and learn how Nature's strongest force brings quarks and gluons together to form the protons, neutrons, and atoms that make up the visible universe today. But they initially expected to see signs of QGP only in highly energetic collisions of two heavy ions such as gold. The new findings -- correlations in the way particles emerge from the collisions that are consistent with what physicists have observed in the more energetic large-ion collisions -- add to a growing body of evidence from RHIC and Europe's Large Hadron Collider (LHC) that QGP may be created in smaller systems as well.

The PHENIX collaboration has submitted the findings in two separate papers to the journals Physical Review Letters and Physical Review C, and will present these results at a meeting in Krakow, Poland this week.

"These are the first papers that come out of the 2016 deuteron-gold collisions, and this is one indication that we are probably creating QGP in small systems," said Julia Velkovska, a deputy spokesperson for PHENIX from Vanderbilt University. "But there are other things that we have seen in the larger systems that we have yet to investigate in this new data. We'll be looking for other evidence of QGP in the small systems using different ways to study the properties of the system we are creating," she said.

Collective flow

One of the earliest signs that RHIC's collisions of two gold ions were creating QGP came in the form of "collective flow" of particles. More particles emerged from the "equator" of two semi-overlapping colliding ions than perpendicular to the collision direction. This elliptical flow pattern, scientists believe, is caused by interactions of the particles with the nearly "perfect" -- meaning free-flowing -- liquid-like QGP created in the collisions. Since then, collisions of smaller particles with heavy ions have resulted in similar flow patterns at both RHIC and the LHC, albeit on a smaller scale. There has also been evidence that flow patterns have a strong relationship with the geometrical shape of the projectile particle that is colliding with the larger nucleus.

"With these results in hand, we wanted to try smaller and smaller systems at different energies," Velkovska said. "If you change the energy, you can change the time that the system stays in the liquid phase, and maybe make it disappear."

In other words, they wanted to see if they could turn the creation of QGP off.

"After so many years we have learned that when QGP is created in the collisions we know how to recognize it, but that doesn't mean we really understand how it works," Velkovska said. "We are trying to understand how the perfect-fluid behavior emerges and evolves. What we are doing now -- going down in energy, changing the size--is an effort to learn how this behavior arises in different conditions. RHIC is the only collider in the world that allows such a range of studies over different collision energies with different colliding particle species."

Turing down the energy

Over a period of about five weeks in 2016, the PHENIX team explored collisions of deuterons (made of one proton and one neutron) with gold ions at four different energies (200, 62.4, 39, and 19.6 billion electron volts, or GeV).

"Thanks to the versatility of RHIC and the ability of the staff in Brookhaven's Collider-Accelerator Department to quickly switch and tune the machine for different collision energies, PHENIX was able to record more than 1.5 billion collisions in this short period of time," Velkovska said.

For the paper submitted to PRC, Darren McGlinchey, a PHENIX collaborator from Los Alamos National Laboratory, led an analysis of how particles emerged along the elliptical plane of the collisions as a function of their momentum, how central (fully overlapping) the collisions were, and how many particles were produced.

"Using a deuteron projectile produces a highly elliptical shape, and we observed a persistence of that initial geometry in the particles we detect, even at low energy," McGlinchey said. Such shape persistence could be caused by interaction with a QGP created in these collisions. "This result is not sufficient evidence to declare that QGP exists, but it is a piece of mounting evidence for it," he said.

Ron Belmont, a PHENIX collaborator from the University of Colorado, led an analysis of how the flow patterns of multiple particles (two and four particles at each energy and six at the highest energy) were correlated. Those results were submitted to PRL.

"We found a very similar pattern in both two- and four-particle correlations for all the different energies, and in six-particle correlations at the highest energy as well," Belmont said.

"Both results are consistent that particle flow is observed down to lowest energy. So the two papers work together to paint a nice picture," he added.

There are other possible explanations for the findings, including the postulated existence of another form of matter known as color glass condensate that is thought to be dominated by the presence of gluons within the heart of all visible matter.

"To distinguish color glass condensate from QGP, we need more detailed theoretical descriptions of what these things look like," Belmont said.

Velkovska noted that many new students have been recruited to continue the analysis of existing data from the PHENIX experiment, which stopped taking data after the 2016 run to make way for a revamped detector known as sPHENIX .

"There is a lot more to come from PHENIX," she said.

Research at RHIC is funded by the DOE Office of Science (NP) and by the agencies and institutions associated with PHENIX listed here.

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov [science.energy.gov].

Follow @BrookhavenLab on Twitter or find us on Facebook.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit applied science and technology organization.
-end-
Related Links

Scientific paper: "Measurements of multiparticle correlations in d+Au collisions at 200, 62.4, 39, and 19.6 GeV and p+Au collisions at 200 GeV and implications for collective behavior"

Scientific paper: "Measurements of azimuthal anisotropy and charged-particle multiplicity in d+Au collisions at ?sNN=200, 62.4, 39, and 19.6 GeV"

Media contacts:

Karen McNulty Walsh, 631-344-8350, or Peter Genzer, 631-344-3174

DOE/Brookhaven National Laboratory

Related Energy Articles:

Quantum vacuum: Less than zero energy
According to quantum physics, energy can be 'borrowed' -- at least for some time.
New discipline proposed: Macro-energy systems -- the science of the energy transition
In a perspective published in Joule on Aug. 14, a group of researchers led by Stanford University propose a new academic discipline, 'macro-energy systems,' as the science of the energy transition.
How much energy storage costs must fall to reach renewable energy's full potential
The cost of energy storage will be critical in determining how much renewable energy can contribute to the decarbonization of electricity.
Energy from seawater
A new battery made from affordable and durable materials generates energy from places where salt and fresh waters mingle.
Shifts to renewable energy can drive up energy poverty, PSU study finds
Efforts to shift away from fossil fuels and replace oil and coal with renewable energy sources can help reduce carbon emissions but do so at the expense of increased inequality, according to a new Portland State University study
Putting that free energy around you to good use with minuscule energy harvesters
Scientists at Tokyo Tech developed a micro-electromechanical energy harvester that allows for more flexibility in design, which is crucial for future IoT applications.
A new way to transfer energy between cells
Researchers have described a new method for the transmission of electrons between proteins that refutes the evidence from experiments until now.
Renewable energy cooperatives, an opportunity for energy transition
Three researchers from the UPV/EHU's Faculty of Engineering -- Bilbao and the University of Valladolid have explored how renewable energy cooperatives have evolved.
MIT Energy Initiative study reports on the future of nuclear energy
In new MIT report, study authors analyze the reasons for the current global stall of nuclear energy capacity and discuss measures that could be taken to arrest and reverse that trend.
Wave energy converters are not geared towards the increase in energy over the last century
Wave energy converters are designed to generate the maximum energy possible in their location and take a typical year in the location as a reference.
More Energy News and Energy Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Risk
Why do we revere risk-takers, even when their actions terrify us? Why are some better at taking risks than others? This hour, TED speakers explore the alluring, dangerous, and calculated sides of risk. Guests include professional rock climber Alex Honnold, economist Mariana Mazzucato, psychology researcher Kashfia Rahman, structural engineer and bridge designer Ian Firth, and risk intelligence expert Dylan Evans.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at Radiolab.org/donate.