Chemistry Faculty Making New Discoveries with STAR Detector

Two Stony Brook University chemistry professors are conducting research using the the Relativistic Heavy Ion Collider (RHIC) STAR detector that may lead to a deeper understanding of the properties and dynamics of the matter known as a quark-gluon plasma (QGP).

QGP is a soup of the quarks and gluons that make up the protons and neutrons of atomic nuclei at the heart of all visible matter in the universe. Scientists think the entire universe was filled with QGP just after the Big Bang some 14 billion years ago, before protons and neutrons formed. RHIC, a U.S. Department of Energy Office of Science user facility for nuclear physics research at Brookhaven National Laboratory (BNL), creates QGP by colliding the nuclei of atoms at nearly the speed of light.

The new analysis of data from RHIC’s STAR detector suggests that the shape of the QGP created in collisions of small nuclei with large ones may be influenced by the substructure of the smaller projectile — that is, the internal arrangement of quarks and gluons inside the protons and neutrons of the smaller nucleus. This is in contrast to publications on data from RHIC’s PHENIX detector, which reported that the QGP shape was determined by the larger-scale positions of the individual nucleons and thus the shapes of the colliding nuclei.

“The question of whether the shape of the QGP is determined by the positions of the nucleons or by their internal structure has been a longstanding inquiry in the field. The recent measurement conducted by the STAR collaboration provides significant clues to help resolve this question,” said Roy Lacey, professor in the College of Arts and Sciences Department of Chemistry and a principal author of the STAR paper recently published in Physical Review Letters.

As it turns out, the differences in the STAR and PHENIX results may be due to the way the two detectors made their respective measurements, each observing the QGP droplets from a different perspective.

“You use one particle to determine the direction and use another to measure the density around it,” said Jiangyong Jia, professor in the Department of Chemistry who has a joint appointment with Brookhaven National Laboratory. The closer the particles are in angles, the higher the density/more particles in that direction.

The STAR team analyzed the flow patterns from three different collision systems: single protons colliding with gold nuclei; two-nucleon deuterons (one proton and one neutron) colliding with gold; and three-nucleon helium-3 nuclei (two protons and one neutron) colliding with gold. The data were collected over three separate runs in 2014 (helium), 2015 (protons), and 2016 (deuterons).

This research was funded by the DOE Office of Science (NP), the U.S. National Science Foundation, and a range of international organizations and agencies listed in the scientific paper. The STAR team used computing resources at the Scientific Data and Computing Center at Brookhaven Lab, the National Energy Research Scientific Computing Center (NERSC) at DOE’s Lawrence Berkeley National Laboratory, and the Open Science Grid consortium.

Read the full story at the BNL Newsroom.