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Restart of Large Hadron Collider At CERN
Taco Cowboy contributes this news from the BBC: After a two-year hiatus the LHC (Large Hadron Collider ) at CERN has been restarted. For the past two years an upgrade program was carried out for the LHC. Due to the upgrade, the LHC is enjoying a double dose of energy, as compared to its previous self before the upgrade. Particle beams have now travelled in both directions, inside parallel pipes, at a whisker below the speed of light.
Actual collisions will not begin for at least another month. Currently the protons are being injected at a relatively low energy to begin with. But over the coming months, engineers hope to gradually increase the beams' energy to 13 trillion electronvolts: double what it was during the LHC's first operating run. The experiment teams have already detected 'splashes' of particles, which occur when stray protons hit one of the shutters used to keep the beam on-track. If this happens in part of the pipe near one of the experiments, the detectors can pick up some of the debris. ... Debris from the tiny but history-making smash-ups might contain new particles, or tell-tale gaps betraying the presence of dark matter or even hidden dimensions. But first we need collisions — due in May at the earliest — and then a steady torrent of data will make its way to physicists around the world, so that the massive analysis effort can begin."
What should we expect from this doubling of energy? The already found the Higgs. What are they looking for now? Are they just slamming hadrons together to see what happens, or is there a specific goal?
Searching for the Higgs boson has been only a small percentage of the work the LHC is being used for. There are a lot of measurements being done checking various calculations of the standard model, looking for any place there might be hints on exactly what is needed to replace it. This can vary from just simple checking for existence of new particles, to very detailed measurements looking for very small errors in reactions that have been know about for some time. In other cases it involves improving measurements of fundamental constants.
It isn't just about the raw max energy and looking for heavier particles. The production rate of lower energy reactions can increase with additional energy (after all, the mass of the Higgs boson is much smaller than what the Tevatron could reach, but not produced in practical numbers). Also, the overall luminosity, the number of particles colliding, will increase production rate. The LHC does quite well at this (with potential upgrades to increase it even more, without more energy per particle). More production, means better signal to noise, means seeing stuff you might have missed before, or making measurements with more precision.
The mass of the Higgs Boson is what's called "finely tuned" - a mathematical expression of Occam's Razor. Physics as a field is highly skeptical of models which involve "fine tuning" of constants - a constant which could, by the model, take a very wide range of values, but just happens to take this one extremely convenient value. That's another way of saying: the model fails to explain this important fact about the universe from first principles, and was instead just written to incorporate it after the fact. There's a lot of that in the Standard Model, which is why there's a lot of dissatisfaction with it, despite it being great at predicting new data.
It's a clear sign that we're missing something fundamental, something that explains all these constants, and likely a whole lot more. In a sense, Dark Matter wasn't that big of a shock because that sense of missing something fundamental has been growing for so long.
To me, it's not just the Higgs, it's all the particle masses. Particle masses aren't quantized, and the mass of quarks still has a lot of guesswork. The mass of the up quark is "1.7 to 3.1", for goodness sake. Everything else is quantized, and there is theory that sets bounds on particle masses, but there's nothing that says "here's the mass quantum, and here's the multiple of that for each particle, and here's why". Missing something fundamental, something big.
If you shrink from "doesn't feel right", understand that science starts from guesswork. And it's exactly this sort of intuition by those who work professionally in the field and (unlike me) have useful intuitions about this stuff that makes science happen. To quote Feynman:
Now I'm going to discuss how we would look for a new law. In general, ... First, we guess it (audience laughter), no, don't laugh, that's the truth. Then we compute the consequences of the guess, to see what, if this is right, if this law we guess is right, to see what it would imply and then we compare the computation results to nature or we say compare to experiment or experience, compare it directly with observations to see if it works.
If it disagrees with experiment, it's wrong. In that simple statement is the key to science. It doesn't make any difference how beautiful your guess is, it doesn't matter how smart you are who made the guess, or what his name is... If it disagrees with experiment, it's wrong. That's all there is to it.
Maybe you didn't know where it all starts, when you got snarky about the scientific method?
Socialism: a lie told by totalitarians and believed by fools.
I'm very familiar with the scientific model, which is why they are running experiments at the LHC rather than just announcing supersymmetry as fact.
However, the scientific model doesn't tell you what experiments to run, or what theories to form or test. Scientists have to decide what they think "needs" an explanation, then they can look around for an explanation which fits the existing data and devise experiments to acquire new data to test it. If the new data fits the theory well enough the theory becomes part of our model of the universe, which is now a little more complete and precise. If it doesn't they try again. The last part is what is usually called "scientific method" but it doesn't help you decide what to try and explain, or which explanations to test first.
In this case, physicists, backed by decades of experience have identified the low mass of the Higgs boson (relative to the Planck mass, as it happens) as the kind of thing that might be expected to have an explanation (beyond just "that's how the universe is") so they have looked around for such an explanation. There are a few competing ones, of which supersymmetry is the best worked out. Actually supersymmetry is not just one theory, it has many variations, The new LHC run may support or exclude some or all of these.
I was hooked to this real-time monitoring when the LHC was operating two years ago : http://op-webtools.web.cern.ch...
Posting this in case anyone is interested.
Jicehix