Things evidently went extremely well over the weekend at the LHC, with simultaneous circulating beams achieved this morning. Speculation is that first collisions (at the injection energy of 450 GeV/beam) are imminent. Places for up to the minute information include here, here and here.
Update: It looks like first collisions have been seen at the LHC. Announcement comes from a muzzled blogger….
Update: Modified posting title.
Update: For a series of talks about events during the first few days since beam injection at the LHC, see here. Progress was dramatic during the first few days, although it has slowed up recently. As data starts to come in, the first scientific task for the experiments is to re-discover the Standard Model. So far, CMS has managed to rediscover the pi-zero.
The CMS e-commentary site just splashed a collision image, then pulled it, then put it back. Probably good to mirror that one… http://sifter.org/~aglisi/albums/LHCfirstcollisions.png
Here is the official site’s picture.
http://cmsdoc.cern.ch/cms/performance/FirstBeam/pictures221109/CollisionEvent.png
Good you have it mirrored.
Why are they so secretive? We know they are just playing around; this not some sort of political kabuki where everybody has to protect cherished anatomical parts before the poll results are in … or is it?
Yatima, I laughed out loud reading your post
*Why are they so secretive? We know they are just playing around; this not some sort of political kabuki where everybody has to protect cherished anatomical parts before the poll results are in … or is it?*
I like the turns of phrase. But I have to say that from my perspective I think CERN is now being admirably open. They are being a lot better than they could be. There is an impressive amount of web access. And they also (so far as I know) have been allowing Chris Stevens’ unofficial “LHC Portal” website which assembles a huge amount of stuff.
I think there’s been some improvement and they’ve gotten more enlightened—this openness will, I think, benefit CERN and science generally (assuming it continues.) The public relations benefit of allowing a kind of fly-on-wall participation via web will greatly outweigh any possible temporary embarrassments.
But obviously my sense of proportion about this is very different from yours.
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They ramped a beam up to 560 GeV also. I guess it will take a few attempts to get it ramping smoothly to over a TeV.
The USLHC blog has some more pictures, which appear to be official releases (?), of what they call “candidate” collision events.
What does “candidate” mean in this context?
Trying to make sure I understand: Normally the LHC would use two opposing particle beams, and “collisions” would be between the particles of the two beams. In this case they were only testing 1 beam, however because the vacuum in the detector chamber is necessarily imperfect the beam would have collided with like a marauding atom or something to produce the “candidate” collision. Is this right?
Coin,
These “candidate” collisions are real collisions, the experiments are just being overly cautious about what they call something that has not yet been carefully analyzed.
They have two beams in the machine, and got them to cross at the correct interaction points inside the detectors. These are now real colliding beams of the sort the machine is designed to produce, only problem is that the energy/beam is 450 GeV, not 3.5 TeV, and the luminosity is something absurdly low. They have made a huge amount of progress very quickly, this was supposed to take much longer.
Now all they need to do is to ramp the beam energy up to 3.5 TeV, and work on getting a usable luminosity (a lot more collisions). The machine’s quench protection system is only commissioned up to 1.2 TeV/beam, so that should be as high as they can go before Christmas. After Christmas, they’ll first have to work on commissioning to 3.5 TeV, then ramping up the beam energy.
Thanks for clarifying.
Another general question, when they get the energy and luminosity up, do they just sweep the whole energy range and collect data? From what I have read, it seems like it takes an incredible amount of data at to show an unobserved particle exists, so maybe they guess energies and focus on the ones where the not yet signifigant data looks most interesting?
Mitch,
In these experiments the collision energy is fixed. They will basically always run at the highest beam energy the machine can achieve. There’s no structure in the proton-proton cross-section at these energies like a resonance that would make it desirable to run at a specific energy.
The products of a collision are very complicated, and the search for new particles is all about trying to find evidence for it amongst these collision products. You want as a high a collision energy as you can get, because that will allow you to produce the highest possible mass particles, in the highest numbers.
Thanks for the answer Peter.
Mitch,
In electron-positron collisions where (to current knowledge) the particles have no sub-structure the energies ARE tuned e.g. at LEP to Z0 resonance.
In proton-proton collisions the energy is already smeared out over the quarks and gluons so there is no need to tune.