It’s the end of an era, as the Tevatron at Fermilab retires. It has done everything that was expected of it and much much more. It has probably even saved your life, or the life of someone you know. It was the big thing, eclipsed by the next big thing. The Tevatron is really that Wise Old Man, who has done some wonderful things during his lifetime, hung around and supported everyone around him when there was no one else and is now being neglected in his old age, because someone else has stolen the limelight. The Tevatron was the mainstay of the physics community for nearly 25 years until the super-powerful Large Hadron Collider (LHC) at CERN came along. Even then, Tevatron’s edge had only slightly withered and it could still give the LHC a run for its money, while breathing its last.
The Final Hurrah – Webcast Link : http://www-visualmedia.fnal.gov/live/110930Tev.htm
The Old Warhorse
The Tevatron was the old world’s greatest accelerator till the LHC came along. Stationed at Fermilab, it could easily produce energies in excess of 512 GeV (512 Billion Electron Volts). Constructed in 1983, it was fondly called the Energy Doubler’ owing to the successive increases of energy as upgrades came in. Its aim was simple verify the Standard Model.
The Standard Model is a mainstay of particle physics. It is the theoretical framework, which describes all the interactions in the Universe, with the sole exception of gravity, which is well-described by the classical General Theory of Relativity. It is the fruit of over six decades of intense work by the most brilliant minds of the 20th century, starting from the 1920’s and ending in the late 1980’s. What the theoretical framework needed was the experimental verification of the heavy particles that it predicted. Could the beautiful theory, constructed by considering the most wonderful aspects of symmetries in Nature, stand up to the test of reality? Tevatron was the only way to know.
The First Big Break – A Top Achievement
The first big break came in 1995 with the discovery of the top quark. The top quark is one of the six types of quarks predicted and belonged to the third generation of the quarks (Graphic above).This means that it is one of the heaviest particles known and is extremely difficult to produce and even harder to detect. According to Einstein’s famous relation E=mc2, we need a minimum energy mc2 to create a particle of mass m’. The problem is that a particle cannot be created in isolation; it comes in with an antiparticle, which has the same mass ‘m’. Thus, you can’t produce just a top, but a top-antitop pair, which means that you need at least 2mc2 to produce the top quark. As a rule of thumb, the energy of the beams colliding within the accelerator has to be about twice the needed energy. For the top quark (rest mass energy of nearly 175 GeV), this amounts to 700 GeV minimum. It had to be the Tevatron.
However, energy scale is not the only thing that the Tevatron redefined. It redefined the sensitivity of the detectors. Its detectors – the CDF and the D0 (D-Zero) – were the most sensitive in the world before the ones at LHC came along. The massive top quark immediately decays into lighter quarks, mainly the bottom quark. The decay happens so very fast that without great detectors, the top quark would’ve remained elusive. It could only have been the Tevatron.
Now, running at nearly 2 TeV, the Tevatron regularly produces the top quark. The exact mass of the top was also provided by Tevatron in 2007 to an accuracy of 1%.
What about the Bottom-Strange particles, you ask? Well, it had to be the Tevatron with the answer. Regular matter particles, called baryons, are made up of quarks. Certain particles, called mesons, are made up of just two quarks, in contrast to protons or neutrons, which are made up of 3 quarks. Each meson contains one quark and one anti-quark. The Standard Model predicts that such particles will undergo baryonic oscillation’ before decaying. Simply put, in a bound state of Bottom and Anti-strange quarks (remember, a quark-anti-quark combination), the bottom will go to anti-bottom and anti-strange will go to strange. They will zip in between these two states, before ultimately decaying into lighter particles. This is a firm prediction of the Standard Model. In 2006, Tevatron’s CDF made measurements of this process. As I said before, it could only have been the Tevatron.