Quantum Diaries

It’s been a little while since I’ve posted anything, but I wanted to write a bit about some of the testbeam efforts at CERN right now. In the middle of July this year, the Proton Synchrotron, or PS, the second ring of boosters/colliders which are used to get protons up to speed to collide in the LHC, saw its first beam since the shutdown at the end Run I of the LHC. In addition to providing beam to experiments like CLOUD, the beam can also be used to create secondary particles of up to 15 GeV/c momentum, which are then used for studies of future detector technology. Such a beam is called a testbeam, and all I can say is WOOT, BEAM! I must say that being able to take accelerator data is amazing!

The next biggest milestone is the testbeams from the SPS, which started on the 6th of October. This is the last ring before the LHC. If you’re unfamiliar with the process used to get protons up to the energies of the LHC, a great video can be found at the bottom of the page.

Just to be clear, test beams aren’t limited to CERN. Keep your eyes out for a post by my friend Rebecca Carney in the near future.

I was lucky enough to be part of the test beam effort of LHCb, which was testing both new technology for the VELO and for the upgrade of the TT station, called the Upstream Tracker, or UT. I worked mainly with the UT group, testing a sensor technology which will be used in the 2019 upgraded detector. I won’t go too much into the technology of the upgrade right now, but if you are interested in the nitty-gritty of it all, I will instead point you to the Technical Design Report itself.

I just wanted to take a bit to talk about my experience with the test beam in July, starting with walking into the experimental area itself. The first sight you see upon entering the building is a picture reminding you that you are entering a radiation zone.

The Entrance!!

Then, as you enter, you see a large wall of radioactive concrete.

Don’t lick those!

This is where the beam is dumped. Following along here, you get to the control room, which is where all the data taking stuff is set up outside the experimental area itself. Lots of people are always working in the control room, focused and making sure to take as much data as possible. I didn’t take their picture since they were working so hard.

Then there’s the experimental area itself.

The Setup! To find the hardhat, look for the orange and green racks, then follow them towards the top right of the picture.

Ah, beautiful. 🙂

There are actually 4 setups here, but I think only three were being used at this time (click on the picture for a larger view). We occupied the area where the guy with the hardhat is.

Now the idea behind a tracker testbeam is pretty straight forward. A charged particle flies by, and many very sensitive detector planes record where the charged particle passed. These planes together form what’s called a “telescope.” The setup is completed when you add a detector to be tested either in the middle of the telescope or at one end.

Cartoon of a test beam setup. The blue indicates the “telescope”, the orange is the detector under test, and the red is the trajectory of a charged particle.

From timing information and from signals from these detectors, a trajectory of the particle can be determined. Now, you compare the position which your telescope gives you to the position you record in the detector you want to test, and voila, you have a way to understand the resolution and abilities of your tested detector. After that, the game is statistics. Ideally, you want to be in the middle of the telescope, so you have the information on where the charged particle passed on either side of your detector as this information gives the best resolution, but it can work if you’re on one side or the other, too.

This is the setup which we have been using for the testbeam at the PS.  We’ll be using a similar setup for the testbeam at the SPS next week! I’ll try to write a follow up post on that when we finish!

And finally, here is the promised video.