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Zoe Louise Matthews | ASY-EOS | UK

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Beam circulation and beyond: pre-Christmas LHC activities

Hi!

You will have seen various blogs tonight (20th Nov 2009) celebrating the first circulation of the proton beams this year. It is a great achievement for the LHC, and a very exciting time for all of us. I am one of the lucky people here at CERN to witness history unfolding and it has to be the best Christmas present of my life 🙂 As of tomorrow midnight (21st – 22nd Nov) I am on shift for 6 days 0:00-8:00 and will be posting once a night to update you on what’s going on – keep glued to our blogs! I will once again be shift leader, so it will have to be brief and with a few updates through the night, because I will be rather busy! Photos will be uploaded after my 9am meeting, because I can’t upload pictures on shift unfortunately.

From the developments of today, with a bit of luck, all the LHC experiments will be able to make use of what they see while beam passes through their detectors – of course this is not centre of mass collisions yet, but simply protons from the beam colliding with the very low levels of gas in the beam pipe. It is still very exciting! By now, the ALICE detector is used to catching cosmic rays in its detector, often one at a time, so when the SPS beam was being injected into the LHC earlier this year and “dumped” downstream of our detector, and similarly ATLAS had their own beam splash events today (see previous post) it was really something to celebrate – hundreds of thousands of tracks in our detector, much more than we expect from a typical LHC collision, even at high energy, and even with heavy ions!

The reason for this is because the whole beam, with something like 100,000,000,000 protons coming all at once in a “bunch”, is fired into a concrete block, these particles then interacting and showering in the material to lose energy and be absorbed. The term “bunch” always makes me laugh when you consider how many it’s talking about! In a typical colliding of two “bunches” of particles, though, even though the LHC works hard to squeeze them close together (to a few microns across, less than the width of a human hair), it is most likely there will only be a handful of these protons colliding at a time. Now, with beam travelling through the beam-pipe, we get to look at something not too dissimilar from the collisions we have been waiting for – but as you can imagine, there is still a lot of work to do before then. Colliding these beams will take alot of precision! (Think of trying to use magnets to collide two pins point-first…and at nearly the speed of light too!)

And the question on everyone’s lips is “When do we get collisions?” Not least me, as I am eagerly awaiting some data to play with! Unfortunately, we have to be very open to change at a time like this, and I am not about to tell anyone a date because apart from anything else, I don’t have one. 😉 However, I can tell you that I am on shift for the next 6 days, and again for a week at the start of December, and I can mention that it is my guess, and hope, that one of these days sees collisions! If it does, you will be informed 😀

Questions are welcome, and I will answer as soon as I can.

I want to finish on this: a friend of mine is working on the coldest physics in the universe. Often LHC steals that line, on account of its 1.9K superconducting magnets. Now, whilst the ALICE detector, when we collide heavy ions in the next year or so, will be quite possibly the hottest place in the universe since the big bang, (for about 10^-30 of a second)…we can’t claim low temperature. Various supercold labs around the world are beating us (including the Kosice Physical Sciences Lab, see my previous blogs) down to temperatures of the order nK and less. And yet, tonight this friend was nice enough to tell me that, in many ways, I am “one of the coolest people in the world at the moment”. Thanks for that Matt, and I wouldn’t say coolest (I do play dungeons and dragons on occasion, let’s not get carried away!) but I am certainly one of the lucky ones and there’s no denying that.

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