The LHC startup is getting closer and closer. A few previous blog entries already informed you that there was a successful insertion of beam into the LHC. This is of course great news, but means that the testing and final preparations of the detectors has now become serious business. As the CMS pixel detector was planned to be installed as one of the final components before the first beam was delivered, we are very much under pressure to be ready in time. 
You can read that as ‘continuously on shift until things are stable enough to be run by non-experts’. This also explains the lack of blog entries by me and some of the other people working closely on the detector, at the moment the pressure is really on and the detector comes first!
Fortunately the pixel insertion and first testing all went very smoothly (I think this was at least marginally related to the color of the protective foil. But mostly the excellent installation team definitely deserves kudos) and the detector is performing great. Of course there are still hiccups and things to be fixed, but all in all I think everyone is confident we will have a great detector to hunt for new physics. As we have to look at many separate detector elements (the CMS pixel detector has 67 million pixels) we make use of summary plots to see how the detector is doing. If you want to know more about pixel detectors I suggest you read Seth’s excellent introduction to pixel detectors. Although obviously I prefer the CMS version, haha.
Here I show such a summary plot, in this case only for the forward pixel detector. The plot shows separate pixel detector modules (each typically containing 4 to 50 thousand pixels) in some arbitrary numbering on the horizontal axis and the efficiency of the front-end electronics on the vertical axis (note that the efficiency never goes below 0.99, the vertical axis is cut off there!). We now spend most of our time improving the detector modules that are not performing at 100%. Most of the inefficiency can be recovered by changing settings on the readout electronics. However, on average we are already performing as we planned we would when the detector was designed, which is all good news.
At the moment we are collecting data from cosmic ray tracks for a few days a week while spending the rest of the week improving our detector. There are many exciting and quite interesting new results. But I’ll show those in due time, so stay tuned!
Tags: CMS, commissioning, electronics, installation, pixel, pixels, shift
