The Tevatron at Fermilab may not be active any longer, but the data it has collected over its lifetime is still capable of inspiring great thoughts. The data, now fully analysed, has revealed what the LHCb had already found earlier, thus giving more credence to hypothetical ideas. The data yields answers to questions as basic as “Why is there matter in the Universe?”.
In November 2011, we had reported about a reported CP violation in the charm quark sector. We inferred that by looking at the so-called D0-D0 bar mixing. The news can be found here. A more detailed discussion and explanation of the various things is given here.
So, let me just quote the basic figure. The LHCb quotes a figure of 0.82% deviation from the expected value of zero, from the Standard Model. A non-zero value of CP violation goes towards answering the question of why matter won over anti-matter, when equal amounts of the two were produced right after the Big Bang. Now, the CDF gives the same hints.
The CDF quotes a deviation of 0.67 % from zero. The result says -0.67% +/- 0.16%. Alongwith the LHCb results, the CP Violation stands at 3.8 sigma confidence level.
The Standard Model predicts that if CP violation is detected, it might signal the existence of new particles. So far, we have no data to indicate that so far!
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 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.
After the astonishing result from the OPERA collaboration of detecting neutrinos travelling faster than speed of light, Fermilab wants to double-check the claim. This is an inevitable step in the direction of validating the apparent finding. If Fermilab’s MINOS data doesn’t find anything that replicates the OPERA observations with high enough confidence, then the OPERA result, despite its hype, will become null and void.
Here’s the reason why, despite the care and beauty of the OPERA experiment, it needs independent corroboration: every scientific result must be reproducible. Fermilab has an advantage over other neutrino research labs in the world since it already has the data sets from the famous MINOS experiment.
MINOS was Fermilab’s version of the Super Kamiokande experiment,. Neutrinos come in three flavours or types electron, muon and tau. The curious thing is that neutrinos can oscillate’ or change between these types. An electron neutrino can become a muon neutrino. A theoretical mechanism, known as the see-saw mechanism, explains this, using certain unknown parameters, which need to be supplied experimentally. Super Kamiokande performed experiments in 1998 and confirmed the phenomenon of oscillation and measured the mixing angle’ too. Fermilab repeated this experiment and found consistent results. This was the MINOS experiment, MINOS standing for Main Injector Neutrino Oscillation Search.
Well known to scientists in the neutrino field, but virtually unthinkable to the outside world, is that fact that MINOS had actually detected neutrinos moving faster than light. However, these couldn’t survive analysis and presented only a 1.6 to 2 sigma confidence level, below the 3 sigma needed for validation and way below the 5 sigma needed for labeling it as a discovery. MINOS now plans to sift through their data and put it through rigorous analysis. MINOS should take less than 6 months, since the data is already available to them.
It won’t matter if the OPERA experiment isn’t proved wrong. If Fermilab and T2K don’t reproduce the data, OPERA will be up for grabs. Einstein, thou be stillâ€¦ at least for 6 months.
If a high energy collision means fast billiard balls colliding or a train wreck, this article is tailor made for you. As the world, or at least the 0.042% of it who are interested in particle physics, gets their opinions ready about the yet unsuccessful Higgs search at the Large Hadron Collider (LHC), CERN, we thought it might be a good idea to explain what physicists mean by what they say. However, we don’t want to explain why they speak that way.
Here we will list out a few things you’ve heard and are likely to hear in the coming days, along with what they might possibly mean.
Units and Particles:
In particle physics, people prefer to use units of energy, instead of that of mass to measure mass. The idea is a good one, since we can use Einstein’s relation E=mc2 directly. The unit of energy is an electron volt or eV. If you force an electron to go through one volt, then it has the energy of 1 eV. It’s too small to use, so people use 1Mega eV (MeV) 1 million eV, or 1Giga eV (GeV) 1 billion eV. If that is not large enough, the LHC demands that we use 1 Tera eV (TeV) or 1 million million eV. The LHC is currently operating at 7 TeV.
The more important point to note about energy is what is considered big! How much really is 1 TeV of energy in human scales? It’s much less than the kinetic energy of a house-fly! So why is it called high-energy physics? It’s because this energy is carried by particles that are really really small! If a proton having 3 TeV of energy is scaled up to our scales, then we would each have energy exceeding that of a Supersonic jet plane. There’s a large amount of energy packed into a small volume.
About particles, there are just two types Fermions and Bosons. Know that fermions don’t like hanging out together, while bosons have no such ego issues. You can stuff a lot of bosons at one place, while that is impossible in case of fermions. Leptons are one kind of fermions, which are electron-like. Photons are bosons. (As to why this happens, it’s related to the Pauli Exclusion Principle, a fundamental result from quantum mechanics, responsible for single-handedly creating all of chemistry! Fermions follow Pauli Principle, bosons do not).
This is probably the most important phenomenon in this story, so pay attention. This is the deal. Every modern physical theory has some symmetry associated with it. For example, if you made all the positive charges in the Universe negative and the negative charges positive, the Universe will still look exactly like it does. Here’s the crucial part with every (continuous) symmetry, is associated a quantity that is conserved, or doesn’t change value. Example: Take time translation. If time were to flow backwards, at the microscopic scale, we would notice nothing. This symmetry leads to conservation of energy. Symmetry breaking refers to the fact that under certain circumstances, a physical theory loses the symmetry it started out with. We can then distinguish between different states. We can choose.
A Useful Analogy
The best analogy I’ve heard asks you to picture a round table with 10 people sitting equally spaced from each other. There is one glass of water kept identically placed between each two adjacent persons, making it 10 glasses in total. Assuming that the glasses are all identical, one can go and reach out for either one there is no preferred choice as yet. (Situation 1 in the graphic below.) But, say someone does pick up a glass say the glass placed to his/her right.(Situation 2 in the graphic below.) Then, everybody will HAVE to pick the glass to his/her right (assuming that no one wants chaos!). Now, you can differentiate between this system and another such system in which someone went for the glass on the left. Symmetry breaking has allowed us to identify a parameter, which had earlier left the system invariant. The word spontaneous’ is clear from this context. The perturbation has to come from within the system and everyone will choose a glass. The symmetry has been spontaneously broken!
In physics too, there arises situations in which the ground state (or state of lowest energy) of a theory is invariant under certain symmetries. This symmetry can, however, be broken and spontaneously, too if the system interacts with a field. It can be shown that this leads to two distinguishable states one having mass. Physicist believe that this is how mass is generated. The interaction field is named Higgs field’ and the force carrying boson associated with the field (as with any force field) is the Higgs Boson.
We could like to conclude this brief glossary of explanations here. Know that these explanations are highly simplified and the whole picture is much richer in beauty and technical details than this. Unfortunately, I won’t be able to communicate that beauty to a person, not having enough background in physics (being a major in physics is a must) and maths. If you already have a background, you’ve probably already seen a bit of the beauty. Go in search of more.
The world is not only queerer than we suppose, remember; it is much queerer than we can possibly suppose. In the words of the immortal Richard Feynman, I think Nature’s imagination is so much greater than Man’s, She’s never going to let us relax.
Links to related articles:
The Higgs search being unsuccessful so far, ATLAS and CMS collaborations of CERN jointly announce. Initial report here.
The figures and numbers (statistics) from the CERN announcement here.
Lost jobs, growing fuel prices and rising public discontent is the scene in the US as far as the economy is concerned. Funds are short in all aspects of life, whether it concerns fuel prices (government subsidy), the education sector or business. The dollar falling against the Euro, or even the Indian Rupee, mirrors the sorry state of affairs. The worst hit, it seems, is the science sector, which has been left crippled by a spate of fund cuts across almost all disciplines. The reason for this: War.
The “War On Terror”
Yes, the American long drawn War on Terror’ is acting like a very effective pipe draining monetary resources from all other aspects of governance and life. An estimated $4 trillion has been spent on the war in Afghanistan and Iraq (sorry for not using the label War on Terror’). The achievements have been few and too far apart in time. The most significant achievement in the eyes of the public is the assassination of Osama Bin Laden, who, experts believe, wasn’t very active anyway in the terror network and the success was little more than symbolic. Al Qaeda has the same reach and structure as it had just before Bin Laden’s death. If anything, the martyrdom’ of Bin Laden (as it is viewed in many parts of the Islamic world) has helped Al Qaeda gain more recruits without resorting to covert recruitment procedures. Not to mention, the operation has undermined the relations between Pakistan and the US.
Victims No. 1
Science has had to suffer a lot, as this foolish carnage was unfolding. The most notable victim has been the James Webb Space Telescope. Recently, we reported the plans to scrap the successor of Hubble the James Webb Space Telescope (JWST) and once Hubble completes its lifetime in 2014, there will be no eye in space in the visible range of the spectrum with which we will be able to peer deep into the cosmos.
The giant telescope, which would make Hubble look like a pair of binoculars, was set to replace both Hubble and Spitzer in one stroke. Spitzer, which observes in the infra-red frequencies, is still operational and is expected to outlast Hubble. The fund cut by the Appropriations Sub-committee is bound to render astrophysics blind for, at least, the decade.
Victim No. 2
There has been other victims with lower profiles. We had also told you about the ATA (Allen Telescope Array) of SETI put out of operation due to the lack of funds. It is a widespread misconception that SETI’s only job is the search for extra-terrestrials. The ATA was being used for much more than intercepting intelligent radio signals from space, like looking at radio signals originating from very strong radio-sources like Active Galactic Nuclei (AGN’s) and looking at transient radio-sources. This would be extremely useful for studying how quasars truly operate. Further, looking at any active radiation source in many wavelengths is of the utmost essence in observational astronomy.
Victim No. 3
Arguably, the best telescope is The Chandra X-Ray Telescope (no, it’s not the Hubble). Orbiting the Earth, high above the atmosphere, it captures stunning images in the X-Ray band. The X-Ray band of radiation is notoriously difficult to capture on film. The primary reason for this is the extremely high penetrating power of X-Rays; lenses made of glass are useless. The mirrors used to focus a parallel beam of X-Ray radiation need to be at glancing angles (about a degree or so) to the direction of radiation. Further, the mirrors need to be coated with pure gold. Both these factors contribute to increased expenses, the former being responsible for the need of large mirror sheets and the latter being responsible for the obvious reasons. The question is what next? What after Chandra? With the recent spate, there is real worry about the maintenance and succession to the premier X-Ray Telescope.
Victim No. 4
The search for exotic gravitational waves is also expected to take a hit. The existing detector, Laser Interferometer Space Antenna or LISA, is capable of detecting a gravitational wave emanating from a powerful astronomical event in the cosmological vicinity the moment it passes Earth. The problem is the back-up observations. This needs to be followed up by observations in the electromagnetic spectrum, which will be impossible given that Hubble will not have a successor and radio telescopes on land are also in trouble. In other words, a goldmine of observations (say, LISA detects gravitational wave after gravitational wave) will be going to waste given that there is no back-up observation. LISA will be effectively out of operation.
This time it appears to be genuine. Fermilab has indeed detected a new particle the Xi-sub-b baryon.
A few days ago Fermilab got the entire physics community excited by announcing that it was almost sure of a discovery of a new particle the W/Z-bar boson. We covered the sensational news here. It turns out that it was not the case.
A baryon is a particle (technically, a bound state’) of three quarks. A proton is an example and is made up of two up and one down quark. Apart from these two types, there are four more types of quarks top(some people call it truth’), bottom (some prefer beauty’), strange and charm. The top quark is the most massive, followed by bottom, charm and strange in that order. The Xi-sub-b baryon has an up quark, a strange quark and a bottom quark. The discovery was made yesterday and reported today in Fermilab’s press release.
The Xi-sub-b baryon is extremely unstable, being able to travel just a fraction of a millimetre before disintegrating into lighter particles. The particle was detected in the CDF detector.
There have been 25 isolated detections, or events, that confirm the existence of the new particle. As we mentioned in earlier posts, the criteria for a discovery is confidence level’. We need a minimum of five-sigma confidence level, or a confidence of more than 99.997% that a certain detection is genuine. Here, Fermilab, after data analysis, puts the confidence level at seven sigma, much higher than the threshold!
The details of the discovery have been sent to Physical Review Letters (PRL) for publication.