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Richard Ruiz | Univ. of Pittsburgh | U.S.A.

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Ever Wonder Why The Tevatron is Such a Big Deal?

Really though, have you? To date, it has not discovered the higgs boson, or Supersymmetry, or any kind of new physics. In fact, all the Tevatron has done since 1987 was find Standard Model physics. Though, that is my point.

Fig. 1: Aerial view Fermilab‘s Tevatron Accelerator Complex. These images were  taken around that big pool of water, in the center of the Tevatron Ring. (Photo: Symmetry Mag.)

The Tevatron, for the past 24 years, has done everything to prove that the idiotic, nonsensical, and just plain weird idea that all of matter is composed of quarks & leptons (plus some bosons) is actually correct. Of course CERN’s Large Electron Positron is due its respect for confirming the Standard Model first through precision measurements, however, the Tevatron set the thing in stone. Over the past decades, many, many clever physicists have tried to modify the Standard Model by introducing new particles, new interactions, new particles & new interactions, but one-by-one they have been shot down. In my opinion, the Tevatron will always be known as The Standard Model Factory.

The Tevatron: Past & Present

My history with the Tevatron dates back to the summer of 2007, when I was a physics undergraduate who was hired by my then advisor to do some summer research. Since then, I have spent quite a bit of time at Fermilab and have been present for quite a few events. So like many other physicists, I am saddened by the fact that the collider will be shutting down September 30th (next Friday!). Consequentially, I decided to put together a little grocery list of Tevatron discoveries. In full disclosure: below is really just summary of all of Fermilab’s press releases since 1995, which in its own right borderlines on being an encyclopedia of particle physics.

  • February 1995 – Discovery of the top quark. Not exactly sure where to begin with this one. I mean, the top quarks existence is evidence of several things: (1) the quark structure of matter; (2) the universality of the Weak force, meaning all quarks & leptons have partners under Weak nuclear charge, e.g., up & down, charm & strange, top & bottom; (3) and also provides a tidy way of explaining some of the differences between matter & antimatter in something called the CKM matrix. The then head of the Dept. of Energy had this to say about the top quark, “This discovery serves as a powerful validation of federal support for science.” Below is the top quark, as imagined by the Particle Zoo.
  • March 1999 – Direct measurement that matter and antimatter behave differently (CP violation). The Kaons at the Tevatron (KTeV) experiment diverted protons from the Tevatron accelerator to produce a well-known particle called a Kaon, in order to measure its lifetime. The significantly larger-than-expected measurement of CP violation implied (1) CP violation was not negligibly small and (2) all particle theories have to accommodate this fact. An attractive and popular theory at the time, called the Superweak Theory, nicely explained a number of different phenomena but implied zero CP violation. You can guess why no one talks about that theory today.
  • March 2001 – Tevatron Run II begins. From this day on, the Tevatron began colliding protons & antiprotons at an impressive 1.96 TeV. It took the remainder of the decade for that record to be topped.
  • November 2001 – The Neutrinos at the Tevatron (NuTeV) Experiment discover a worrisome discrepancy between theoretical predictions and experiment measurements of the quantity sin2θW, which can be thought of as the ratio between the mass of the W boson and the mass of the Z boson. The NuTeV Experiment, like KTeV, diverted Tevatron protons to produce a different particle. In this case, neutrinos were produced and then were sequentially fired into 700 tons of steel. This anomaly had less than a 0.25% chance of being a random, statistical fluctuation (~3σ), and is now believed to related to the superstructure of protons & neutrons in a nucleus.
  • June 2004 – Tevatron results set the first “modern” constraints on the higgs boson. Thanks to the top quark, the DZero Experiment was able to set a best estimate of the higgs boson’s mass (117 GeV/c2) and a definite upper bound (251 GeV/c2). Of course these numbers exclude new physics, but so began Today’s hunt for the higgs boson.
  • April 2005 – Tevatron analyses go global. In order to cope with the huge amount of data being generated, the Tevatron detector experiments decide to connect their networks to The Grid, a global network of computers with the sole purpose of acting like one, giant computer, not unlike Deep Thought or planet Earth. This computing model is the heart and soul of the way CERN processes the LHC’s 15 petabytes a year.
  • September 2006 – Oscillations in the recently famed Bs meson are discovered! A Bs (pronounced: B-sub-s) is a bound state that occurs when a b-quark and a s-quark begin to orbit around each other, like an electron and a proton in a hydrogen atom. The “oscillations” refer to how often the two quarks exchange a W boson. This high precision measurement is considered a benchmark tests of the Standard Model due to its sensitivity to new physics. They Bs mixing Feynman diagram is below (pulled from the QD image library).
  • October 2006 – The “Period Table of Particles” is fleshed out. Just like how the theory of electrons, neutrons, & protons implies the existence of the period table of elements, the theory of quarks implies the existence of a gigantic number of combinations. This is the point of no return: The Standard Model works. It may be incomplete, it may be missing attachments, but from here on out no one can say that it is wrong.
  • December 2006 – The production of individual top quarks is identified. Okay, this needs a bit of explanation. Top quarks are heavy, like really heavy. We are talking over 40 times heavier than the second heaviest quark and well over 300,000 times heavier than the electron; it weighs as much as 180 hydrogen atoms. According to the Standard Model, it is actually easier to produce a top quark and anti-top quark at the same time than individually. This is because individual top quark production involves the Weak nuclear force and just shrinks the chances of producing one. Like Bs, single top quark production is a Standard Model benchmark because it is very sensitive to new physics. Interestingly enough, single top quark production also provides a mean for testing Supersymmetry, Technicolor, and different higgs boson models.
  • July 2008 – Diboson production is at long last discovered. The Standard Model predicts that it is possible to produce two Z bosons, simultaneously, from collisions. It is a very rare thing to see and most every addition to the Standard Model affects the rate two Z bosons are produced. There are plenty of ways to modify the oscillation rate of Bs or the rate of single top quark production and still maintain consistency with the Standard Model; modifying diboson production rates is a whole different behemoth… good luck with that. I was actually at the talk when this was announced; I remember that week very well because it was rumored that the higgs boson had been found. 🙂
  • August 2008 – “Tevatron Experiments Double-Team Higgs Boson.” The CDF & DZero Experiments combine their powers to call Captain Pla… I mean, for the first time, combine their independent higgs boson searches and begin directly excluding possible mass values for the boson. This juggernaut of an analysis (plot below) was quickly recognized for its level of sophistication and set expectations for the LHC experiments.
  • May 2010 – The infamous dimuon asymmetry is discovered. Remember how in “September 2006” I mentioned that B mesons, like Bs, are sensitive to new physics? Well, B mesons can decay into two muons or two anti-muons, plus some other things. When the number of muon pairs & anti-muon pairs were measured, it was discovered that more muon pairs were produced than anti-muon pairs. The LHC experiments still need more data to be as sensitive to confirm this high precision measurement but this might actually be the first detection of physics beyond the Standard Model at a collider. If a reader knows of an earlier collider experiment signal that hints at Beyond the Standard Model physics, I am happy to pass the title on to that.
  • August 2011 – The Tevatron’s updates its higgs boson mass exclusion with over 8 fb-1. (Below)

The Standard Model Factory

You know, when I started writing this post I had an idea how impressive the Tevatron is/was. Having systematically gone through each of Fermilab’s press releases in search for major milestones, and trust me I omitted a fair number, I do not really know what else to say. I am a bit star-struck. Yes, the Tevatron has been running since 1987 and I happily acknowledge that it just simply cannot compete with the LHC beyond 2012 projections. Just recently, the LHC reached the 3 fb-1 threshold, which translates to generating 1/3rd of the entire Tevatron data set in about 9 months; but really Really, the LHC has some pretty big shoes to fill.

Congratulations to the Tevatron Experiments, past & present, for undeniably establishing the Standard Model of Particle Physics.

More importantly, congratulations to the Tevatron Accelerator Division, for having repeatedly done the impossible because you could.


Happy Colliding.
– richard (@bravelittlemuon)


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