University of Florida physicists are using photon-proton collisions to trap particles in an unexplored energy region, giving new insight into matter that binds parts of the nucleus together.
"We want to understand not just the core, but everything that makes up the core," said FSU professor of physics with FSU Paul Eugenio. "We are working to understand the particles and forces that make up our world."
FSU's Hadron Physics Group is a leading member of the GlueX Collaboration at the American National Acceleration Institute, Thomas Jefferson. The group has been running highly sophisticated experiments for months over a number of years, over a period of several years, starting in 2016. Their main goal is to gather new information about a material – called the gluon field – that bonds into quarks. Quarks are the fundamental particles that produce protons and neutrons.
In a new paper published in Physical examination letters , a group of hadron physics at the University of Florida, and their associates set up the first measurements of a subatomic particle – called J / psi particle – created from energy in photon-proton collisions.
"It's really cool to see," said Assistant Professor of Physics Sean Dobbs. "This opens a new frontier of physics."
When researchers run these experiments, they explode a photon beam into a GlueX spectrometer where it passes through a canister of liquid hydrogen and reacts with protons in the nucleus of these hydrogen atoms. From there, detectors measure the particles created in these collisions, which allows physicists to reconstruct the details of the collision and learn more about the created particles.
Dobbs likened it to a car wreck. You may not see the wreck happening, but you see the result and it can work backwards. In this case, the researchers collected about one to two million gigabytes of data a year through this process to try to put together a puzzle.
The J / psi particle is made up of a pair of quarks – charm charm and anti-charm quark. In measuring J / psi particles in these collisions, scientists may also be looking to manufacture other subatomic particles containing charms.
Measurements were made at the energy threshold below where previous research looked at production levels, meaning that it was more sensitive to the distribution of gluons in the proton and their contribution to the proton mass.
Scientists have discovered much higher production of J / psi particles than expected, which means that this gluon structure contributes greatly to the mass of the proton structure, and thus to the nucleus as a whole. These initial measurements suggest that gluons directly contribute more than 80 percent of the proton mass. Further measurements of these currently ongoing reactions will give more insight into how gluons are distributed around nucleons.
These measurements also called into question observations from a large hadron collision test, a particle detector at CERN, the European Organization for Nuclear Research. Scientists there briefly glimpsed what they call pentakwarks – short-lived particles made of five quarks.
FSU physicists did not specifically see pentacquarks in their data, which excluded several models attempting to describe the structure of these pentacquarks. Further measurements are expected to give a more definitive answer to how the five quarks are distributed in these particles.
A. Ali et al. First Threshold Measurement J / ψ Exclusive proton photographic production, Physical examination letters (2019). Doi: 10.1103 / PhysRevLett.123.072001
Physics researchers break new ground, explore unknown energy regions (2019, October 10)
retrieved October 10, 2019
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