Heavy Quarks Probe the Early Universe

New studies of behaviors of particles containing heavy quarks shed light into what the early universe looked like in its first microseconds.

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The Forward Silicon Vertex Detector (FVTX) in the PHENIX (Pioneering High Energy Nuclear Interaction eXperiment) at the Relativistic Heavy Ion Collider allows scientists to study how light (u, d) and heavy quarks (c, b) behave in one of the hottest media ever created in the laboratory: the quark-gluon plasma (QGP).

The Science

The early universe was made of extremely hot and dense matter. To learn more about the early universe, scientists study this matter, known as quark-gluon plasma, made at particle colliders. Scientists measure how certain particles behave transiting the plasma. The particles of interest contain quarks. Quarks are the building blocks of matter and have family members with different masses. Thanks to the Forward Silicon Vertex (FVTX) detector, scientists delved into hard-to-measure particles. They found that particles with charm quarks (not lightweight, not heavy) break when crossing the hot medium. Heavier bottom quarks don’t.

The Impact

It is a big challenge to identify which particles, known as hadrons, come from light and heavy quarks among the thousands of particles produced in a single high-energy collision. The FVTX at the Relativistic Heavy Ion Collider can recognize particles containing light, charm and bottom quarks. The detection technique opens the door to further explore how quarks with very different masses lose energy when crossing the plasma. This information elucidates the particles that existed in the moments after the big bang and how they changed to become the universe we know today.


Quarks are the fundamental building blocks of matter and have family members with different masses. The up and down quarks, which make up neutrons and protons, are the lightest quarks. The charm quark is about 600 times heavier than the up quark, and the bottom quark is around 2000 times heavier than the up quark. Particles containing these charm and bottom quarks have been used by nuclear physicists to probe a super hot (several trillion Kelvin) and dense matter state known as the quark-gluon plasma. In the plasma, D hadrons (formed by a charm quark and a light quark) and B hadrons (formed by a bottom quark and a light quark) travel a fraction of a millimeter before decaying into other particles. The FVTX detectors in the PHENIX (Pioneering High Energy Nuclear Interaction eXperiment) at the Relativistic Heavy Ion Collider (RHIC) can precisely measure the minimum distance between particle trajectories and the collision point, which is proportional to the particle’s flight path. Measuring the trajectories allows the identification of D and B hadrons among the thousands of particles produced in high-energy nucleus-nucleus collisions. D and B hadrons are produced before the quark-gluon plasma is formed and can serve as a hard probe to study the quark-gluon plasma microscopic structure. The first measurements with the FVTX indicate that no matter how dense the medium is in copper+gold collisions, the number of B hadrons is preserved. However, J/y and y’ particles are broken up in the nuclear medium. These measurements are a first step in precisely determining how much energy heavy quarks lose in the quark-gluon plasma medium along their path lengths. The research team expects particles that contain a heavier bottom quark (B hadrons) will be modified less by the nuclear medium compared to particles that contain the lighter charm quark (D hadrons). A more detailed study of the heavy quark, mass-dependent energy loss in the quark-gluon plasma medium, in heavy ion copper+gold and gold+gold collisions, is underway.


Ming Liu, Cesar Luiz da Silva, Xuan Li
Los Alamos National Laboratory
mliu@lanl.gov, cesar_luiz@lanl.gov, xuanli@lanl.gov


The U.S. Department of Energy (DOE), Office of Science, Nuclear Physics funded this research at Los Alamos National Laboratory. The detector used is located at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. Research at RHIC, a DOE Office of Science user facility, is supported by the Office of Science, Nuclear Physics, and these agencies and organizationsExternal link.


C. Aidala, et al., “The PHENIX forward silicon vertex detectorExternal link.” Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 755, 44 (2014). [DOI: 10.1016/j.nima.2014.04.017]

A. Adare, et al. (PHENIX Collaboration), “Measurements of the relative yields of ψ(2S) to ψ(1S) mesons produced at forward and backward rapidity in p+p, p+Al, p+Au, and 3He+Au collisions at √sNN = 200 GeVExternal link.” Physical Review C 95, 034904 (2017). [DOI: 10.1103/PhysRevC.95.034904]

C. Aidala, et al. (PHENIX Collaboration), “Measurements of B →J/ψ at forward rapidity in p+p collisions at √s = 510 GeVExternal link.” Physical Review D 95, 092002 (2017). [DOI: 10.1103/PhysRevD.95.092002]

C. Aidala, et al. (PHENIX Collaboration), “B-meson production at forward and backward rapidity in p+p and Cu+Au collisions at √sNN = 200 GeV.” Physical Review C, submitted (2017). [arXiv: 1702.01085]

Related Links

The PHENIX experiment at Brookhaven National LaboratoryExternal link

Highlight Categories

Program: NP

Performer/Facility: DOE Laboratory

Additional: Collaborations, Non-DOE Interagency Collaboration, International Collaboration

Last modified: 1/25/2018 4:57:45 PM