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View Full Version : OT: For all you belivers in Supersymmetry, time to find something else...



cuemaker
11-13-2012, 12:09 AM
http://www.bbc.co.uk/news/science-environment-20300100

Large Hadron Collider making news again.

I only understood the very basics of it, but I couldnt pass up the chance to post a title about something I have no clue about to make myself look kinda smart.

dp
11-13-2012, 01:04 AM
My go to guy for this stuff is Luboš Motl at http://motls.blogspot.com/. If string theory every hits the crapper floor I'm going to be uber unhappy as I've spent a lot of time understanding it and I don't want to have to start over! :) (this link is not about this supersymmetry story, but the linked page will follow it, certainly).

Evan
11-13-2012, 01:20 AM
They have constrained it fairly severely but there are several variants that survive. It isn't quite dead but there is a trace of a rattle. They need MORE POWER.

Paul Alciatore
11-13-2012, 03:07 PM
They have constrained it fairly severely but there are several variants that survive. It isn't quite dead but there is a trace of a rattle. They need MORE POWER.

More power? I guess the next step is a collider that circles the earth. We need to find a great circle with as much land under it as possible. And we will need fusion power to power it. Or perhaps as much ocean for political reasons. But do you want it in your neighborhood?

Fasttrack
11-13-2012, 11:12 PM
More power? I guess the next step is a collider that circles the earth. We need to find a great circle with as much land under it as possible. And we will need fusion power to power it. Or perhaps as much ocean for political reasons. But do you want it in your neighborhood?

Why wouldn't I want an accelerator in my neighborhood? :rolleyes: Actually, the LHC will be undergoing an enhancement soon to increase it's CoM energy. Personally, I say we build an accelerator that circles the moon. It's not as crazy as it sounds ... if you had oodles of money and resources, that is. ;)

Evan is correct; the recent results out of LHCb exclude what we call high-tan(beta) variants of the theory. The parameter space for SUSY is quickly disappearing. Early experiments put constraints on the lightest mass of the super-symmetric partners and those constraints are driving the mass higher and higher - so if they exist, we need to be looking at higher energy scales. At some point, though, we have to ask about the validity of a model whose internal symmetry is broken so "badly".

Evan
11-14-2012, 02:33 PM
The Moon is much too lumpy. Build it in orbit around the Moon. The cost of getting there and back would be far less too.

rohart
11-14-2012, 02:40 PM
Am I right in thinking that we wouldn't need tubes and a vacuum, or would the vacuum of space not be enough ? If we built in orbit around something, we wouldn't need much structure linking adjacent magnet blocks either.

Evan
11-14-2012, 02:54 PM
Not much structure but it would need ion thrusters at intervals around the structure. A ring in orbit is an inherently unstable structure.

Fasttrack
11-14-2012, 03:46 PM
Am I right in thinking that we wouldn't need tubes and a vacuum, or would the vacuum of space not be enough ? If we built in orbit around something, we wouldn't need much structure linking adjacent magnet blocks either.

I think we would still need a beam pipe. We operate in the UHV regime, ~ 10^-9 torr. I suspect that the vacuum of space at any reasonable distance from Earth would be on the order of 10^-6 torr. Far enough away from Earth and the Sun, the vacuum of space becomes much better than what we can achieve on Earth - something like 10^-15 torr. Plus the beam pipe provides shielding from electromagnetic fields.



On a more realistic note, a far more interesting breed of accelerator is the muon accelerator. This technology is currently under development. It has a couple of unique characteristics. First is the fact that no beam pipe is needed. A relativistic muon travels through large amounts of matter without interacting so we can effectively shoot them through solid earth and have the beam come out the other end more or less "intact". The second feature (and the most important one!) is that muons are fundamental particles. This means that we can use them to do precision physics. The only difference between an electron and a muon is mass; the muon is about 200 times heavier than the electron. This is important because the energy radiated by a charged particle traveling in a circle is inversely proportional to the 4th power of its mass (roughly speaking). That's why high energy accelerators like the LHC accelerate protons (or other heavy nuclei). Trying to accelerate an electron to TeV energies in a ring the size of the LHC is technologically impossible because of the amount of energy required. The efficiency (defined as the energy of the particle divided by the energy "put in" by the accelerating cavities) drops to a ridiculously small number. The only problem is that muons have finite lifetimes so we have to generate the muon and then accelerate it up to relativistic speeds in about 2 microseconds. Once it is at relativistic speeds, it will last much longer due to time dilation.

(In reality, the power radiated goes like gamma^4 and gamma is calculated from the relativistic energy of the particle, which is a function of the particle's rest mass. The classic examples is LEP - the accelerator that used to occupy the tunnels where the LHC is now located. For a 50 GeV electron, gamma is roughly 100,000. For a proton at 50 GeV, gamma is roughly 50. You can see how the energy loss due to radiation quickly becomes a problem for light particles!)

Fasttrack
11-14-2012, 03:50 PM
I'm going to be uber unhappy as I've spent a lot of time understanding it and I don't want to have to start over! :)

As a clarification point to those who may not know, string theory and SUSY are not mutually exclusive. There are a number of string theories that "require" supersymmetry. Killing SUSY kills a number of string theories, as well.

Evan
11-14-2012, 06:48 PM
Trying to accelerate an electron to TeV energies in a ring the size of the LHC is technologically impossible because of the amount of energy required.

Which is also why synchrotrons make such excellent "light" sources. Which is all directly related to Bremsstrahlung which is German for "Braking Radiation". When an electron (or positron) is forced to spiral in a magnetic field it gives up energy as photons. With high energy electrons the Bremsstrahlung generates hard x-rays.

Note: This does not include thermal bremsstrahlung, that is a different matter.

Evan
11-14-2012, 06:53 PM
Killing SUSY kills a number of string theories, as well.

So where does that leave us in respect of unification?

Fasttrack
11-14-2012, 07:06 PM
So where does that leave us in respect of unification?

To be honest, I'm not qualified to answer that question. However, I have noticed a growing number of physicists who have serious doubts as to whether or not a GUT is theoretically possible. Regardless, there are problems with the SM that need to be addressed. Whether or not a GUT is the way to address these problems is another matter.

Don't forget that there are a huge multitude of other theories out there, though. SUSY and string theory are the most well known and SUSY is the most studied because it is so elegant and solves a number of challenging problems.

Evan
11-14-2012, 07:49 PM
It has occurred to me that the macroscale and the microscale may simply not be describable by the same mathematics. The question is, is that inherent in the universe or is simply a lack of our mathematical skills? At the macroscale the universe is very elegant, at the quantum scale it tends to be far less so. It's a bit like a digital image. Don't look too close because there is no perceptible image there. I have thought for many years that the universe is at some scale granular rather than analogue. If so that scale is very very fine but still granular. Quantum Mechanics uses Planck's Constant at 6.626 069 57(29) x 10-34 J s. But, what exactly does that represent in terms of the granularity of matter, energy and space/time?

In case anyone thinks these questions are purely hypothetical, that couldn't be farther from the truth. Current semiconductors are pushing toward the physical limits of size at which point they can no longer be made smaller. Recent research points at 7 nanometres as the absolute physical limit of feature size for semiconductors. Below that quantum effects start to dominate. Then the designs and the theories upon which they are based no longer describe the physics. We are within spitting distance of that limit with the newest designs leaving only one more generation smaller. At that point it becomes impossible to fit more logic on a chip using anything resembling current technology.