The discovery of new particles helps us to understand how the universe works. It is the dream of every high energy physicist, part of our raison d’Ãªtre. The Large Hadron Collider (LHC) under construction in Geneva Switzerland should be good at this. The Tevatron, currently in operation in Batavia Illinois, has a shot as well. We have reason to expect that the experiments at the LHC will discover a host of new particles. We’ve given the possibilities seemingly whimsical names: Higgs, squarks, gluinos, Z-primes, Kaluza-Klein gravitons, WIMPS, axi-gluons, etc., but each one serves a purpose in our candidate theories about nature.
However, merely producing new particles and cataloging them gives only part of the understanding. Rather, particles are messengers, telling a profound story about the nature of the universe, or what we like to refer to as the nature of matter, energy, space, and time. Learning about the new particles, studying their properties and how they interact, leads to discoveries of new theories or new symmetries of spacetime. That’s the role of the proposed International Linear Collider.
There’s plenty of historical precedent. When the positron, the brother of the electron, was first detected, the discovery was not just the identification of a particle. The positron revealed a hidden half of the universe: the world of antimatter. The positron showed us how to reconcile the laws of relativity with the laws of quantum mechanics, telling a brand new story about the structure of spacetime.
When physicists first observed the pion in cosmic ray experiments, they were puzzled. Within a few years, particle accelerators had produced a plethora of pion cousins: etas, deltas, omegas, etc. Physicists were running out of Greek letters to name them all, but finally the story became clear. These were not elementary particles after all, buy tiny bags of quarks, held together by a new force so strong that no quark could ever escape it.
We hope to break new ground with discoveries at the LHC and ILC; these accelerators will probe nature at energies where she has never before been tested. Here, we exect other aspects of nature to unveil themselves. One possibility is extra dimensions of space. An electron moving in tiny extra dimensions would generate much heavier partner particles, which are related to its motion in the additional dimensions. Producing these partner particles at an accelerator would be a great discovery; however, an equal challenge would be to pin down their identities as travelers in extra dimensions. How much we learn from these particles depends on how well we determine their properties. For example, by measuring their masses and interactions, physicists could discover the shape, size, and number of extra dimensions.
This is how our science works and is the message of a new report, Discovering the Quantum Universe: the Role of Particle Accelerators, which will roll off the presses this week. I was one of the authors and have liberally borrowed some of its text for this post. You can be sure I’ll be blog more about the contents in the future.