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Pam Klabbers | USLHC | USA

View Blog | Read Bio

Little Things

This week was our last “Global Run” for the year. We called it GREN (Global Run End of November) since it was only supposed to be a week, but was extended until the end of this first week of December.

During the GREN we include parts of the CMS detector that are located underground in the data taking stream. This includes the trigger electronics, the system that decides if an interesting event has taken place, and the system that I am most involved with. For the first time since we started these Global Runs (GREJ,GREA, GRES, etc.) my beloved (perhaps that is a bit too personal) Regional Calorimeter Trigger has joined in. And not only one or two crates, as is often the case when we test “slices” from the calorimeters (see previous posts), but the whole thing. Eighteen crates of our electronics receiving bits of data representing energy from the Hadron Calorimeter (HCAL) electronics (which gets its data from the central part of the HCAL) then processing it, and sending out the results to the Global Calorimeter Trigger, which sorts it and forwards the highest energies (including location in the HCAL) to the Global Trigger (GT), who finally combines it to find coincident signals in the top and bottom of the HCAL. (Phew!) If it then it passes the requirements set at the GT, i.e. energy greater than some value and the coincidence, the GT sends out a Level-1 Accept (L1A) to the systems that just sent it. This L1A tells the electronics that that was a good event (it is saved in a memory until told otherwise) and the data is retrieved and sent on to the High-Level Trigger, a computer farm, for processing. There we can refine the tracks in the muon chambers and tracker, the energy deposit in the calorimeters…for later analysis.

Our source of events is cosmic-ray muons (basically heavy electrons) caused by protons and nuclei from space interacting in the atmosphere. The higher energy muons can get through a lot of material relatively unscathed (to our detector underground), and we can use the light they leave in the calorimeter as the pass through as a way of detecting them. It’s exciting to see my system in its final form, working!

Of course, we are not ready yet. Though all the electronics are there, it is still somewhat rough. I still have to get another system into the mix, the electromagnetic calorimeter, who are busy commissioning right now. They have to be timed in with the HCAL. And we are using only one of the two spigots out of the RCT – one still lacks the connections out, and will need intense testing, very soon.

I am pretty happy about it. I will post a picture of one of our triggered events here soon!

One of my colleagues remarked that we were not “On the Critical Path”, which was an opinion I was glad to hear. This was the “little thing” that made my day. However, there is no time to sit back and relax yet!

A la prochain…

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