On hadron colliders, dark matter and black holes

[torstan]

Sorry Gidde, I let that slip. Things have been a little busy.

The LHC is not at the point where it will detect gravitons - and indeed no planned collider would be able to. Gravity is very weak, very very weak. Now the chance you produce a particle in a collision is related to the strength of its coupling. The strongly coupled matter - gluons, quarks and any new strongly coupled particle like a gluino or a squark (the supersymmetric partners) - will be produced most often. Then weakly coupled matter - like W and Z bosons - will be produced less often. As the couplings decrease, the percentage of events that will produce the relevant particle decreases. There are other factors too, but the overall production rate depends on the coupling strength in all cases. The graviton coupling is so small that you will never produce enough gravitons for them to be observed.

I'm afraid I'm a terrible person to ask about popular science books. I tend to relax with good sci-fi or other fiction. I tend not to read science books outside work. I can say that Lise Randall is a lovely person - she visits NYU a lot and uses the office 2 doors down - but I've no idea what her book is like! Sorry not to be more help.

[torstan]

In other news - beam is now half way around the ring and they're starting to do their final tests before getting a fully circulating beam. It should only be a matter of days (hopefully) before beam makes it all the way round once again.

At that point they'll work on getting the beam running for long periods of time, then work on increasing the energy, focusing the beam in the experiments and getting everything working towards the high energy, high density collisions that we'll need to start investigating new physics. Currently it's all going well. There will be hiccups and delays, but for now things seem to be going smoothly.

One other thing - there was a story last week about a bird and a baguette shutting down the LHC. The claim was that a baguette fell on a wire and broke the LHC. That's not quite what happened. Basically one of the substations had a power cut. This substation helped power the cryogenics that cools the sectors of the ring and keeps the magnets superconducting. The magnets warmed up a little (a degree or so) before power was restored and they were cooled again. This happens, and the machine is built to handle it. It didn't cause a delay - though if it had happened during running they'd have lost a day or so.

The reason the story became big news was that feathers and bread crumbs were found at the substation. This sparked a rumour that a bird and baguette had caused the outage. There is (sadly) no evidence that this is the case, but it made for an excellent headline.

In the meantime my collaborators at CERN are working hard. Hopefully we'll hear more from CERN soon.

[Redrobes]

Hey this is cool. Its a link from one of the Atlas guys which pulls together some of the status pages from the LHC which are supposed to all be public but are hard to find.

http://www.lhcportal.com/Portal/index.htm

[torstan]

Very nice!

Small update (garnered from the CMS facebook age ) - apparently they're looking to get beam going all the way round in both directions this weekend! So all signs look good.

[torstan]

Protons have now gone all the way round. They're looking to stabilise the beam over the weekend.

[Redrobes]

Hi Torstan, I read this week of some novel quantum images being produced by a camera which was not pointing at the scene imaged but collecting photons which had somehow quantum entangled with other photons which had come from the site of the image. I don't get exactly whats going on but it is claiming that you can view stuff through thick fog like a model soldier in the lab I saw. I may be wrong but perhaps each photon contains information about the entire scene in it and that as long as you can get some photons back it does not matter which or how many, the scene can be reconstructed.

http://futurismic.com/2008/07/01/gho...antum-physics/
http://www.sciencedaily.com/releases...0612141344.htm
etc

Anyway, you said that at the energies involved with the LHC there is some non trivial probability that you may create and make detectable some extra dimensional spaces and some particles might travel through this space and some may not.

So heres my thought. What particles do photons quantum entangle with in such a way that what subset of the particle zoo might be able to come through one of these spaces and may in the future allow us to get images of what it looks like through these extra dimensional spaces - all assuming that photons themselves don't go through the spaces so that we can just look and see - because I guess we would have already seen them before.

Just say if I am a million miles from being sensible here... I just want to see through a stargate

[torstan]

Before answering that - ATLAS has seen it's first collisions! I had a very happy experimental colleague come running past my office this morning with a print out of the first event. This is amazingly good news. They weren't expecting to get collisions for another two weeks. They're still low energy - 450GeV - but the plan will be to ramp up the energy over the coming weeks. There's a meeting for the experimental collaborations here this morning so we should know more soon.

@Redrobes: Those stories are very cool. I missed those initially - thanks for the link.

The quantum entangled photons work a little differently than that. I'm not entirely sure precisely what they're doing. However the theory is that when you produce two photons in a particular manner, that they are entangled. So even though they may go to entirely different places, they're states are fundamentally linked. If one photon interacts in one way, then it will force it's partner to interact in another. So if you generate such a twin beam and point one at the thing you want to look at then you can find out information about your target by measuring the second beam - the one that's gone nowhere near the target. The photons from the first beam still need to hit the object - just as normal photons would need to. Now it has to be more complicated than that to extract any sort of image - but the fact they can do it at all is amazing.

So, for the second part of your question. Whatever you quantum entangled with would have to go through the extra dimension, so yes, standard photons wouldn't do the trick. I guess you could do the same trick with whatever particle we find that could go through the extra dimension - so say it was a heavy copy of the electron then you'd create a sample of these heavy electrons, keep one of each pair and send the other through the extra dimension. Then by measuring the state of the ones you keep you'd stand a chance of being able to extract information.

Now I'm sure that's actually a similar proposal to the black hole information paradox. I might have to go looking for that. It's possible that it wouldn't work, but I'll see what I can dig up when I have a moment.

[waldronate]

Hooray! Looks like somebody finally got around to doing compressed sensing with entangled photons! Or maybe I totally misunderstood.
Edit: Yep, looks like I misunderstood. When I'm wrong I like to be really wrong.

I wonder if light slowing media adversely affect the entanglement. You could emit a split stream of entangled photons that allows one branch to propagate through free space and the other to take the slow path. Measure the slow path photons at various times and you'll be able to tell something about the free-space photons. Exactly what you can tell is an interesting question.

(If you're unfamiliar with compressed sensing then http://www.compressedsensing.com/ may be of interest).

[Turgenev]

All I can say is, man I love this thread! Fascinating stuff. Many thanks for the continuing update torstan.

[torstan]

@Waldonrate: That's pretty interesting - and way outside my field. Thanks for the link.

@Turgenev: Thanks! It's really exciting to see the LHC finally starting to come together. We're still a long way from new physics data, but given the fact that this was first conceived in '83 - this is a huge milestone. It's just great to have news that things are working. Certainly exciting times ahead.