Physicists discover a new class of pentaquarks



Dipole magnets with large hadron collider. Credit: CERN

Tomasz Skwarnicki, professor of physics at the Faculty of Arts and Sciences at Syracuse University, has discovered new information about a class of particles called pentaquarks. His discoveries could lead to a new understanding of the structure of matter in the universe.

Assisted by Liming Zhang, associate professor at Tsinghua University in Beijing, Skwarnicki analyzed data from the Large Hadron Collider Beauty (LHCb) experiment at CERN's Large Hadron Collider (LHC) in Switzerland. The experimental physicist discovered traces of three unpublished pentaquarks, each divided into two parts.

"Until now, we had thought that a pentaquark was composed of five elementary particles [called quarks], glued together. Our findings prove otherwise, "says Skwarnicki, a member of the American Physical Society.

Skwarnicki is part of a team of researchers, including members of the High Energy Physics Group (HEP) of Syracuse, who study the particles and fundamental forces of the universe. Most of their work is done at the CERN laboratory, where the LHC is the largest and most powerful particle detector in the world.

It is within the LHC that protons are thrown together at high energies, and then collide with each other. What lies inside the particles, when it is open, helps scientists explore the mysteries of the fundamental universe.

By studying the proton collisions of 2015-18-18, Skwarnicki confirmed the existence of a substructure in a pentaquark. The gift, he says, was a trio of narrow peaks in the LHC's cinematic data.

Each peak refers to a particular pentaquark, namely a divided into two parts: a baryon containing three quarks and a meson with two quarks.

A peak also suggests resonance, a phenomenon of short duration during particle disintegration, in which an unstable particle is transformed into several others. The resonance occurs when the protons (a type of baryon) meet or, more precisely, slip into each other, during an LHC collision.

What is unique about each of these three pentaquarks is that its mass is slightly less than the sum of its parts – in this case the masses of the baryon and the meson. "Pentaquark has not decreased by its usual process of easy decomposition," says Skwarnicki. "Instead, it's broken down by rearranging his quarks slowly and laboriously, forming a close resonance."

Skwarnicki's specialty is understanding how particles interact and bond. In 2015, he then obtained his PhD. Students Nathan Jurik G & # 39; 16, distinguished professor Sheldon Stone and Zhang made the headlines with their role in the detection of pentaquark by LHCb. Theorized half a century earlier, their discovery is based on 2011-12 LHC data.

The latest data from LHCb used an energy beam almost twice as powerful. This method, combined with more accurate data selection criteria, resulted in a larger range of proton collisions.

"It also provided us with 10 times more data and allowed us to observe pentaquark structures more clearly than before," Skwarnicki says. "What we thought was a single pentaquark turned out to be two narrow, with little space between them."

The data also revealed a third pentaquark "companion". "The three pentaquarks had the same motive – a baryon with a meson substructure, their masses were below the appropriate baryon-meson threshold," he adds.

The Skwarnicki discovery occurred relatively quickly, considering that LHCb stopped collecting data less than three months ago.

Eric Sedore, DSI Associate for Infrastructure Services in Information Technology Services (ITS), played a supporting role. His computer research team provided Skwarnicki with the firepower needed to achieve his goals.

HEP includes, besides Skwarnicki and Stone, Professors Marina Artuso and Steven Blusk and Assistant Professor Matthew Rudolph. The group is currently building on campus a device called Upstream Tracker (UT), which will be shipped and installed at CERN next year as part of a major upgrade to LHCb.

"The UT will dramatically improve LHCb, which is composed of about 10 sub-detectors." I hope the UT will lead to more discoveries, "said Skwarnicki, adding that" I'm not sure what's going on. " Artuso and Stone were respectively the chief and the sous-chef of the project.

Skwarnicki is excited about the LHCb because it helps explain the behavior of the smaller constituents of the material. His latest discovery, for example, proves that pentaquarks are constructed in the same way as protons and neutrons, which are bonded together in the nucleus of an atom.

"Pentaquarks may not play a significant role in the material of which we are composed, but their existence could significantly affect our patterns of matter found in other parts of the universe, such as the neutron stars ".


Explore further:
The CERN LHCb experiment reports the observation of exotic pentaquark particles

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Syracuse University


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