Particle Physics Research | What are quarks?

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  • Quarks are elementary particles with no substructure. Understanding them is crucial to learning how physics works at the smallest levels.
  • By studying the collisions of incredibly small particles made up of quarks known as J/psi particles, scientists have been able to better understand matter in a fundamental way.
  • By measuring J/psi particles, Florida State scientists found results that contradicted earlier studies at CERN.

    Quarks are one of the fundamental parts of all matter. These are particles that combine to form what are called hadrons, some of which are protons and neutrons, the building blocks of atomic nuclei. Studying photons to better understand quarks, scientists at Florida State University have made the first-ever measurements of a subatomic particle known as the J/psi particle, which is created from the energy of collisions photon-proton.

    Some quick facts: quarks and photons are elementary particles, which means they are subatomic particles. They therefore themselves have no substructure; they simply…exist. Protons, on the other hand, are composite particles, meaning they are made up of two or more elementary particles. Scientists therefore wanted to collide photons with a composite particle like a proton to understand how the particles work.

    “It’s really cool to see,” assistant professor of physics Sean Dobbs said in a press release. “This opens up a new frontier of physics.”

    Dobbs compares his team’s experiences to an extremely small car accident. To create their crash, they used the GlueX spectrometer at the Thomas Jefferson National Accelerator Facility in Virginia. The team blasted a beam of photons into a spectrometer, and the beam then passed through a canister of liquid hydrogen and reacted with protons in the nucleus of the canister’s hydrogen atoms.

    Although scientists weren’t able to capture these tiny reactions and collisions as they happened, they did work backwards. They established what happened when the beam passed through the cartridge, with around one to two million gigabytes of data per year to help them.

    The J/psi particle, first discovered independently by two separate groups in 1974, is composed of a pair of quarks: a charm quark and an anti-charm quark. There are six types of quarks. The most common are the “up” and “down” quarks, which make up protons and neutrons. Charmed quarks are (comparatively) heavier than these and only have a short lifespan before they decay into more conventional particles. The J/psi particle was the first chance to prove that the so-called “quark model” accurately described nature.

    By studying the J/psi particle in these collisions, the team was able to study the production of other subatomic particles containing charmed quarks. They found more J/psi particles than expected.

    This means that the gluonic structure (the gluons that can make protons) contributes greatly to the mass of the protonic structure. In fact, according to the scientists, gluons directly contribute more than 80% of the mass of the protons studied. Understanding how gluons contribute to protons gives scientists a clearer picture of the fundamental nature of matter.

    The results challenge other studies from the CERN collider in Switzerland earlier this year, which detected short-lived particles called pentaquarks that the FSU team did not find. Particle physics is a complex subject, but amid the car crash of photons, gluons and quarks, scientists are getting closer to understanding the complexity of existence.

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