With NSF Funding, UC Physicist Contributes to Newest Big Bang Theory

There’s a new particle in town. Physicists with the European Organization for Nuclear Research (CERN) can now confirm the pentaquark’s existence with certainty, after 51 years during which the elusive particle was surmised only on a theoretical basis.

A group of 750 scientists, including the University of Cincinnati’s Michael Sokoloff, professor of physics in the McMicken College of Arts and Sciences, are looking closely at subatomic particles by colliding protons at the highest energies produced by accelerators.

This is part of a series of ongoing particle physics experiments at the state-of-the-art underground Large Hadron Collider b-physics (LHCb) experiment in Geneva, Switzerland. The group has

submitted a paper

, released on July 14, that reports the findings to the journal "Physical Review Letters."

U.S. participation in the experiment is funded entirely by the National Science Foundation, which supports the research through nine awards to scientists from Syracuse University, the University of Maryland College Park, the Massachusetts Institute of Technology and to Sokoloff from the University of Cincinnati.

Smashing atoms is not easy, and how to detect the debris from the proton-proton collisions and analyze the data is a challenge. But the LHCb team successfully reconstructs particles produced inside the giant LHC accelerator, which lies deep underground in a 17-mile-long circular-ring tunnel that loops from Geneva, Switzerland to France and back.

 
ADDING CHARMS AND FLAVOR TO RESEARCH, NOT WHAT YOU THINK
The newly discovered pentaquark, as the name suggests, is explained as a particle consisting of five quarks bound together. And quarks are elementary particles that exist in six variations known as flavors. But these are not the flavors of ordinary English. Instead, flavor is one of the many whimsical terms that scientists have affectionately applied to particle categories.

The most common names for the quark flavors are up, down, charm, strange, top, and bottom, although the latter two are also known as truth and beauty.  Quarks bind together in different combinations to form a range of composite particles, of which the most common are baryons.  Consisting of three quarks each, these include the neutrons and protons that comprise the bulk of ordinary matter.

Sokoloff explains that a pentaquark is a new kind of composite state that groups four quarks and one anti-quark –– the related antimatter particle for a quark.

"The statistical evidence of these new pentatquark states is beyond question," says Sheldon Stone, Syracuse University professor of physics, who helped engineer the discovery. "Although some positive evidence was reported around 10 years ago, those results have been thoroughly debunked. Since then, the LHCb collaboration has been particularly deliberate in its study."

This discovery also solves a 51-year-old mystery. In 1964, American physicist Murray Gell-Mann predicted the existence of fundamental subatomic constituents called quarks, which form particles such as protons. Gell-Mann postulated that, in addition to a composite particle made from three quarks, there could be one with four quarks and an anti-quark, known as a pentaquark. Until now, the search for pentaquarks has been unfulfilled.

And as serendipitous as science is many times, this discovery happened by accident.
   
“Sometimes when you’re looking for something else, you happen across an even more exciting result,” says Adam Davis, UC graduate student working with Sokoloff in Geneva. “That’s what happened at LHCb, which is lucky because the analysts found these states while they were busy looking at another channel.”

Looking closely at composite states like ‘pentaquarks’ can help scientists better understand the mysterious properties of ordinary baryons and ordinary matter.

KICKING THE QUARKS UP A NOTCH
“In our UC NSF-funded Experimental Flavor Physics project, we are using the LHCb detector to study the interactions of composite particles containing heavy quarks created by protons colliding with other protons,” says Sokoloff.

A molecule’s nucleus is made of neutrons and protons, which are both made up of quarks. The most common quarks are what the scientists refer to as up and down. While a proton is made of two up quarks and one down quark, a neutron is made of two down quarks and one up quark, producing an almost perfect symmetry. These two flavors of quarks overwhelmingly form most of the ordinary matter in the universe.

“What we have discovered in the last 50 years, however, is that in addition to the ordinary quarks that exist in ordinary matter, you can produce massive quarks if there is a very high-energy collision,” says Sokoloff. “So when we go to very, very high energies we can produce even more massive quarks. Why these heavier cousins exist is a mystery.

“As Einstein said in his theory of relativity, higher and higher energies can produce higher and higher mass particles. Unfortunately, these particles don’t exist most of the time, and when they do, they live fleetingly short lifetimes of less than one millionth of a second and for many of them a millionth of a millionth of a second.”

OLD BANG, NEW BOOM
Conditions similar to those just after the Big Bang are produced in the LHCb detector. Sokoloff and his team study what is produced and how it decays, which is how they infer their properties. The goal is to better understand the underlying strong and weak nuclear interactions of these underlying constituents ––the quarks that are the building blocks of matter.

LHCb’s fundamental research and the newly discovered pentaquarks should help provide a more complete understanding of our world, much the same as Einstein’s theory of relativity provided for us today almost 100 years ago. At the time, his theory didn’t seem to relate to anything in the real world. Today, the basic understanding of space-time that he described is now necessary to make GPS satellites work correctly.

“We are trying to open doors for ourselves and others based on our research,” says Sokoloff. “We are trying to break the Standard Model of particle physics.”

“We can think of the LHCb research as a single experiment, but there are many analyses being done simultaneously, partly in parallel and partly in overlap, but the intellectual ownership in this collaboration is common,” says Sokoloff. “Where some of the collaborators are focusing on building the software, others are making the histograms used to extract the physics results; you can’t separate the contributions. I am working with over 700 of my best friends.

“In the end, all of this is necessary to obtain the final results. So this is a large enterprise, a community effort.”

Sokoloff has been in Switzerland for the past six months, along with UC graduate student Adam Davis and two UC post-doctoral fellows, Liang Sun and Antonio Augusto Alves, Jr. Here in Cincinnati, three undergraduate students, Emma Hand supported by the WISE program, Christopher Ontko supported by the MUSE program and Rebecca Swertfeger who was part of the QuarkNet program for high school students last summer, currently funded by the physics department, are also studying LHCb data. In addition, two high school students are doing internships with the group as part of the NSF-funded QuarkNet program. Aligning with UC Third Century and UC Forward, Sokoloff’s students are fostering progress through collaboration, innovation and real-world experiential learning.

SOKOLOFF’S RESEARCH FUNDING:

• $200,000/year for three years: NSF base grant from the experimental particle physics program.
• $220,000/year for three years: Physics at the Information Frontier PIF NSF grant supports a post-doctoral fellow and a grad student. This grant also funds collaborators at the Ohio Supercomputer Center.
• $250,000 per year for four years: an NSF grant in collaboration with researchers from Princeton, NYU, and the University of Nebraska to develop data intensive analysis tools for high-energy physics.
• $185,000 over five years as a construction grant for a large U.S. project to build hardware for the LHCb detector upgrade, scheduled to start taking data in 2020.
• Ohio Supercomputer Center has provided a 300,000 Research Unit annual allocation to do computing for the experiment.
  
• As a co-PI with Bruce Burton from UCIT, Sokoloff is one of the beneficiaries of hardware for the UCScienceNet project.
• For his summer Quarknet program, Sokoloff and Alex Sousa, an Assistant Professor of Physics, receive funding from the NSF via a University of Notre Dame sub-contract.
  

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