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.
Miracles of the Past, Regular for Tevatron
It should be quite clear that these are merely the most spectacular results that tumbled out of the high energy behemoth. Lesser achievements included the regular production of the W and Z bosons, which are also products of the Standard Model framework. It studied the decay processes and taught us how W’s interact. This would later become invaluable in the search for the Higgs boson.
Rolf Heuer, Director General of CERN, showed his own appreciation for the old workhorse. He said:
The Tevatron has made phenomenal contributions to particle physics. Top of the list has to be the discovery of the top quark in 1995, but there are many more.
One More Success Story
Many more contributions! How true! For one, it discovered Gell-Mann’s missing Omega. In 2009, CDF detected the Omega particle, which was a prediction of the Standard Model and remained just that for 40 years. The Omega discovery was a test for the Standard Model, just like the missing elements were a test for the Periodic Table in Chemistry. CDF’s accurate detection of the particle and its excellent agreement with what the Standard Model predicted was a further confirmation of the wonders of symmetry of the Universe. Need I repeat that it could only have been the Tevatron?
It Has Saved Lives!!
Great, but how does this affect you? Well, even if you might not know it, Tevatron may have saved the life of someone close to you. How? By establishing superconducting magnets as a mainstay of the magnet industry. Tevatron’s enormous need for superconducting magnets (for focusing the colliding beams) and suitable wires established an industry that has never had to look back. It has made MRI magnets commonplace and, consequently, the MRI scan that you can get done at your local medical diagnosis center is a mundane exercise.
LHC v/s Tevatron: No competition… Almost
The Tevatron has been beaten thoroughly by the LHC at CERN. LHC’s energy at 7 TeV (and soon-to-be 14 TeV) far outstrip that of Tevatron’s, which clocks in at 1.96 TeV, maximum. The LHC detectors are state-of-the-art, far better than CDF’s or D-Zero’s. The greatest superiority of LHC lies in the luminosity of the beam. Simply put, LHC regularly packs more punch in one beam than the Tevatron can hope to achieve. It is natural for people to discount the Tevatron as an aging monster, well past its prime. A quick look at the data for the Higgs search tells a very different story. Tevatron has been instrumental in the low-mass range search for the Higgs boson, ruling out the low-mass Higgs as a possible particle. LHC could never have competed with the Tevatron in the low-mass regime.
The days of American dominance of the high energy physics world had ended five years back. Europe has taken the lead and by a huge margin. None of that counts when one looks back and admires a machine, which revolutionized our understanding of the Universe, gave tremendous confidence in the model that we have and helped chart the road forward. It had to be the Tevatron.
Here’s bidding the irreplaceable Tevatron a sad farewell!