The leading theory of the beginning of the universe is the Big Bang, which states that the universe existed as a singularity 14 billion years ago, a one-dimensional point containing a multitude of fundamental particles. Extremely high heat and energy caused it to bloat and then expand into the cosmos as we know it – and the expansion continues today.
The first result of the Big Bang was an intense hot and energetic liquid that lasted only microseconds and was about 10 billion degrees Fahrenheit (5.5 billion Celsius). This liquid contained nothing less than the building blocks of all matter. As the universe cooled, the particles crumbled or mingled, which … well, everything.
Quark Gluon Plasma (QGP) is the name for this mysterious substance, which is so named because it consists of quarks – the basic particles – and gluons, which the physicist Rosi J. Reed uses as "what quarks to talk to each other ".
Scientists like Reed, an assistant professor in the Department of Physics at Lehigh University, whose research includes experimental high-energy physics, can not go back in time to study how the universe began. Thus, they re-create the circumstances by colliding heavy ions like gold at near-light speed, creating an environment 100,000 times hotter than the sun's interior. The collision mimics how the quark-gluon plasma became matter after the Big Bang, but the other way round: The heat melts the protons and neutrons of the ions, releasing the quarks and gluons hidden inside.
Currently, there are only two accelerator worlds capable of colliding heavy ions – and only one in the USA: the Relativistic Heavy Ion Collider (RHIC) of Brookhaven National Lab. It is about three hours drive from Lehigh in Long Island, New York.
Reed is part of the STAR Collaboration, an international group of scientists and engineers that conduct experiments with the Solenoidal Tracker at RHIC (STAR). The STAR detector is massive and actually consists of many detectors. It's the size of a house and weighs 1,200 tons. STAR's specialty is the tracking of the thousands of particles generated by each ion collision at RHIC in search of the signature of quark gluon plasma.
"When you do experiments, there are two" buttons "that we can change: the species – for example, gold or proton on protons – and the collision energy," says Reed. "We can accelerate the ions differently to achieve a different energy-to-mass ratio."
With the various STAR detectors, the team collides ions at different collision energies. The goal is to map the quark-gluon plasma tracing diagram or the various transition points as the material changes under different pressure and temperature conditions. The mapping of the quark-gluon plasma phase diagram also maps the strong nuclear force, also known as Quantum Chromodynamics (QCD). This force holds positively charged protons together.
"At the center of an ion, there are a number of protons and neutrons," explains Reed. "These are positively charged and should repel one another, but there is a 'strong force' that holds them together – strong enough to overcome their tendency to disperse."
The phase diagram of quark-gluon plasmas and the location and existence of the phase transition between plasma and normal matter is of fundamental importance, says Reed.
"It's a unique opportunity to learn how one of the four fundamental forces of nature works at a temperature and energy density similar to those that existed only microseconds after the plasma, Big Bang," says Reed.
Updating RHIC detectors to better correlate "strong force"
The STAR team uses a Beam Energy Scan (BES) for phase transformation imaging. During the first part of the project, known as BES-I, the team collected observable evidence with "intriguing results." Reed presented these results at the 5th Joint Meeting of the APS Department of Nuclear Physics and the Physical Society of Japan in October 2018 in Hawaii in a paper titled: "Testing Quark Gluon Plasma Thresholds with Energy and Arsenal Scans." RHIC. "  However, limited statistics, acceptance, and insufficient resolution of the event level did not allow for unambiguous conclusions for a discovery. The second phase of the project, known as BES-II, is under way and includes an enhancement to Reed working with STAR team members: an upgrade to the Event Plan Detector. Collaborators include scientists from Brookhaven and Ohio State University.
The STAR team plans to conduct further experiments and collect data using the new 2019 and 2020 Event Plan detectors. According to Reed, the new detector will determine exactly where the collision will take place, and it will help to characterize the collision, especially how "head-on" it is.
"It also improves the measurement capabilities of all other detectors," says Reed.
The STAR collaboration expects to conduct its next experiments in March 2019 at RHIC.
Small, short-lived drops of early universe matter