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To Infinity and Beyond

Feb 12, 2011

As theoretical particle physicists, Professors Jim Hetrick, Kieran Holland and K. Jimmy Juge have massive goals. They are working to understand the fundamental laws of nature in the universe.

"There is remarkable intricacy, delicacy and symmetry in the physical laws of Nature that mankind has discovered," said Dr. Holland. "The community that explores these ideas has existed for centuries, and the truths we are looking for are universal. If one day we make contact with an alien civilization, they won't share our language but they will share our knowledge of what every atom in the universe is made of."

For those of us whose understanding of physics ended with protons and neutrons making up the nuclei of an atom—there's a whole new world out there. Particles such as quarks, gluons, and leptons, and the forces that cause them to interact in specific ways, are now studied with unprecedented sophistication.

Quantum Chromodynamics: May the Strong Force Be With You

Lattice TableSince the late 1970s, the primary system for understanding matter is known as the Standard Model. Quantum Chromodynamics (QCD) is one aspect of the Standard Model that describes the "strong force" that affects quarks and holds subatomic nuclei together.

Theoretical physicists use mathematical analysis to create simulations and make predictions about these strong interactions to better understand them. Because of the complexity of the math involved, scientists cannot easily solve the equations.

"We have two challenges," said Dr. Hetrick, Chair of the Physics Department. "One is having the brain power to create the equations, and the other is having the computing power to solve them."

Lattice Gauge Theory to the Rescue

Lattice gauge theory is a way to perform the complex numerical calculations using supercomputers. With lattice gauge methods, quarks are represented on a four-dimensional space-time grid, and highly sophisticated mathematical algorithms are used to evaluate their characteristics.

The Physics Department acquired its own supercomputer (affectionately called "Mother") a couple of years ago, thanks to a National Science Foundation (NSF) grant. The group, which has been remarkably successful at obtaining external grant support, is on its second 3-year NSF grant.

The department's supercomputer is not adequate for all the research in progress, so the team also relies on access to large national computer centers.

Mother
"Mother"—the Physics Department Supercomputer

It Takes a Community

Lattice gauge researchers tend to work in small groups and collaborate with one another. Believe it or not, Pacific's trio is one of the largest groups of lattice gauge theory faculty at any university in the U.S.

Combined, the three professors have had over 10 refereed papers on lattice gauge theory published since 2006. In addition, they have delivered dozens of presentations at conferences around the world. In summer 2011 they and a colleague from Lawrence Livermore National Lab will host the annual Lattice Field Theory conference, which brings together researchers from all over the world. Since the meeting is too large to be held at Pacific, the physicists will take over the whole of Squaw Village at Lake Tahoe for the week-long symposium.

Students Get Involved

The Physics Department has employed a number of students in the past few years to work on lattice gauge research. Dr. Juge had a student study the interaction between a quark and an anti-quark to determine if a simple model matched what has been observed in experiment.

Other students have focused on the computing side by managing very large data structures for a lattice data archive run by Dr. Hetrick at the National Energy Research Supercomputing Center in Berkeley.

From Theory to Experiment: Searching for Answers

Mother
Photograph
by Despina Chatzifotiadou, March 30, 2010) Particle tracks fly out from one of the first collisions at 7 TeV (seven trillion electronvolts) at the Large Hadron Collider.

The counterpart to theoretical physics is experimental physics—actual demonstrations to determine if the theory's predictions hold true. While on sabbatical last spring, Dr. Hetrick attended a major event at the CERN particle physics lab in Geneva, Switzerland, where the highest energy collisions to date were initiated with the new Large Hadron Collider.

This experiment set in motion an avalanche of new data that physicists will use to prove or disprove their theories. "Our hope is actually that what we discover will be different than our theories," said Dr. Hetrick. "We all want to have some surprise."

Because many things are not explained by the Standard Model, physicists believe there are underlying concepts missing from our understanding of how the universe works. This idea is referred to as "physics beyond the Standard Model" or a "theory of everything."

As the field of particle physics advances, we will have a better picture of the behavior of matter during the "Big Bang" as well as a clearer idea of how the world works at the fundamental level. According to Dr. Juge, "This discovery becomes part of the base knowledge people can use to develop new ideas in fields such as chemistry, biology and engineering."

Pacific's Lattice Gauge Theorists

Each professor has a different area of focus and participates in different collaborations within the QCD/Lattice Gauge community.

Dr. James E. HetrickDr. Jim Hetrick: Works with the MILC group (mostly based at U.S. universities)

The gluon fields, responsible for the strong force between quarks, are extremely complex. A kind of topological "knot" that can appear in these fields is thought to have a significant impact on the quantum behavior of nearby quarks. One of Dr. Hetrick's current research projects is modeling these knots (called instantons) and studying their effect on quarks. Dr. Hetrick is also part of the International Lattice Data Grid project, which is a global collaboration tasked with making the sharing of data between researchers around the world easier and more efficient.

Dr. Kieran HollandDr. Kieran Holland: Works in the Lattice Higgs Collaboration (U.S. and Europe)

A goal of the Large Hadron Collider is to discover how the symmetry connecting the electromagnetic and weak nuclear forces is broken. The catalyst is thought to be the Higgs particle, which has long been sought but not yet found. Dr. Holland works on alternative possibilities, where the Higgs particle is replaced by new particles called techniquarks. If techniquarks are discovered at the Large Hadron Collider, scientists will have uncovered a completely new fundamental force in nature.

 

Dr. K. Jimmy JugeDr. K. Jimmy Juge: Works with the Hadron Spectrum Group (U.S. and Europe)

Protons and neutrons (nucleons) are composite particles made from quarks and gluons. Dr. Juge is working on a new algorithm that will allow calculations about these particles that were unthinkable in the past but are now possible with the computing power available today. The algorithm will enable scientists to compute the masses and other properties of known particles and ones that have not been seen before. He believes they are close to publishing a good algorithm that will provide new insight to QCD—the theory of the strong interactions.

Particle Physics—A Language of its Own


The lexicon of a particle physicist is fascinating and colorful. Common words are often used in uncommon ways. For example, consider this statement from an article in Physics Today1:

“a recent lattice-gauge calculation … shows how the fluctuation of net strangeness density increases with temperature in a hot, flavor-neutral ensemble of quarks and antiquarks.”

Here are a few of the many quirky-sounding terms (no pun intended!) in particle physics2:

Learn More

Quarks

A quark is one of the fundamental constituents of matter. Quarks come in six "flavors": up, down, strange, charm, bottom, and top. Protons and neutrons are composed of up and down quarks.

Color-flavor locking

No, we're not talking about a food storage bag. In the world of particle physics flavor denotes a symmetry of the weak force that allows electrons to change into neutrinos and charmed quarks to turn into strange quarks when they interact. Imagine if each lick of your ice cream cone changed it from chocolate to cherry, or from vanilla to pistachio!

Color is a property assigned to quarks and gluons that has nothing to do with colors perceived by the human eye. Gluons can exchange color between quarks and other gluons. This process is the origin of the strong force.

Gluons

Gluons are considered to be the fundamental exchange particle mediating the strong interaction between quarks. They are also responsible, ultimately, for the forces between protons and neutrons that power nuclear reactors and the core of the Sun.

Hadrons

A hadron is any particle made out of quarks and/or anti-quarks. Protons (two up quarks and a down quark), neutrons (two downs and an up), and anti-protons (two anti-ups and an anti-down) are just a few of the many types of hadrons.

Leptons

Along with quarks, leptons make up all known matter. Leptons come in three "flavors": electron, muon, and tau.

Lagrangian density

Sounding like something from a "Star Trek: The Next Generation" episode, this concept is named after Joseph Louis LaGrange (1736-1813) and refers to the energies of particles caused by a combination of their motion and mutual attraction and repulsion.

Staggered fermion

Are you thinking intergalactic plant species? Wrong. A fermion is a particle that has "half-integer spin," such as the common electron. Translating the laws of physics into a digital computer program usually introduces unwanted effects, called discretization errors. Staggering the different components of the fermions in a lattice gauge theory calculation mitigates one of the main discretization errors associated with fermions.

1. DeTar C, Gottlieb S. Lattice Quantum Chromodynamics Comes of Age. Physics Today. February 2004.

2. Most of the glossary definitions are based on: http://www.interactions.org/cms/?pid=1002289, accessed November 16, 2010.

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