November 12, 2012
CERN Particle Collider To Become Planet’s Most Accurate Stopwatch
Alan McStravick for redOrbit.com - Your Universe Online
Just outside of Geneva, Switzerland is one of the world´s foremost ongoing experiments to explore not only the smallest components of our universe, but, in so doing, to understand the vastness of space, our universe as a whole, and just how it came into being.
The LHC, itself, is a particle accelerator. Physicists use the LHC to study the smallest known particles which are the fundamental building blocks of all things. While we were all taught in grade school that everything is made up of atoms, these physicists are seeking to understand what makes up atoms. And then to know what makes those individual particles.
The LHC works by firing off two beams of subatomic particles, called hadrons, in opposite directions inside the accelerator. As they complete each lap, they increase in speed. The LHC is used to try to recreate the conditions that existed just after the Big Bang. This is achieved by finally colliding those two beams head-on at a very high rate of energy. The international teams of physicists then use different detectors to analyze the particles that are created in the experiments.
Before the LHC, the Standard Model of particle physics stood as an acceptable means for understanding the fundamental laws of nature. The Standard Model, however, was unable to tell the whole story. The CERN physicists believe that the experimental data from the high energies achieved by the LHC will be instrumental in pushing human knowledge forward.
Physicists from the Vienna University of Technology (TU Vienna) have recently helped to push forward the bounds of human knowledge about the nature of light and time. They believe that heavy ion collisions at CERN will be able to produce the shortest light pulses ever created and they were able to demonstrate this assertion with computer simulations. One problem: These pulses are so short they cannot even be measured by today´s technological equipment. How do you address this issue? You build the world´s most precise stopwatch to measure the world´s shortest light pulses. This “stopwatch” detector will be installed at CERN in 2018.
Current experimentation that examines very short time scales are usually measured using short laser pulses. The best technology for these pulses today exists in the duration of attoseconds. An attosecond is literally billionths of a billionth of a second — or, more precisely, one quintillionth of a second. Even these mind blowing speeds are too slow for what the physicists at TU Vienna say could be achieved by using the LHC at CERN. “Atomic nuclei in particle colliders like the LHC at Cern or at the RHIC [Relativistic Heavy Ion Collider in Suffolk, NY] can create light pulses which are still a million times shorter than that,” says Andreas Ipp from TU Vienna.
This shorter light pulse will give more exact readings for many experiments. One in particular, the so-called ALICE experiment, involves the collisions of lead nuclei at nearly the speed of light. The collision creates debris from the scattered nuclei along with new particles that are created from the power of the impact, that form a quark-gluon plasma. Quark-gluon plasma — also known as ℠quark soup´ — is a state of matter that is so hot, even protons and neutrons melt. The base structures, quarks and gluons, move freely without being bound to one another. However, this plasma exists only for several yoctoseconds (a yoctosecond equals one septillionth of a second). This makes it very difficult to measure with current technological instrumentation.
The quark-gluon plasma that is created in the particle collider can emit light pulses. From these pulses, scientists could gain a deeper understanding of the plasma. However, as mentioned above, without better and faster measurement techniques, this information continues to be elusive and unknown. Current technology is unable to resolve flashes that occur on a yoctosecond timescale. “That´s why we make use of the Hanbury Brown-Twiss effect, an idea which was originally developed for astronomical measurements,” says Ipp.
Hanbury Brown-Twiss has been used to very accurately determine the diameter of stars. It does this by studying the correlations between two different light detectors. “Instead of studying spatial distances, the effect can just as well be used for measuring time intervals,” Ipp claims. He and his colleague, Peter Somkuti, have calculated that the yoctosecond dilemma of the pulses of the quark-gluon plasma could be resolved by a Hanbury Brown-Twiss experiment.
“It would be hard to do, but it would definitely be achievable,” continues Ipp. He contends that no new expensive sensor equipment would be necessary to run these experiments. All that would be needed would be a forward calorimeter. And, as luck would have it, CERN is supposed to have one that goes online in 2018. So, it is believed that the ALICE experiment will soon become the world´s most accurate stopwatch.
But what do we know about the physics of quark-gluon plasma and what do we hope to learn from it? What we already know is that it has an extremely low viscosity. In fact, it is far thinner than any liquid we know. If it starts out in an extreme disequilibrium, it can still reach a thermal equilibrium in very short order. If we are able to accurately study the light pulses from the quark-gluon plasma, we could derive extremely valuable new information that could only lead to a better and more concrete understanding of this state of matter.
Future application, once we have this improved understanding, could be used for nuclear research. “Experiments using two light pulses are often used in quantum physics,” explained Ipp. “The first pulse changes the state of the object under investigation, a second pulse is used shortly after that, to measure the change.” It is hoped that with improved measurement on the yoctosecond scale with light pulses that this well-established method could aid in advancement in areas that, up until now, have been completely inaccessible to this kind of research.