Paul Scherrer Institute (PSI)

The High-Energy Physics Group at the Paul Scherrer Institute (PSI) near Zurich, now consists of six physicists, an electronics engineer, a technician and students. It joined CMS in 1994 and made major contributions to the Pixel Tracker and the Electromagnetic Calorimeter (ECAL), both requiring advanced technological developments.

The group led the development of the original Pixel Tracker, and together with the ETHZ and the University of Zurich constructed the barrel part of the detector. In addition it developed key parts such as the read-out chip required for the full detector as well as advanced construction techniques such as the bump bonding. Its performance has exceeded expectations and it was a key device for track and vertex reconstruction.

The group followed this success by leading a project to replace the Pixel Tracker with an upgraded one, with twice the number of channels and first layer much closer to the beam. This detector was installed in early 2017 and is now taking data.

The group also proposed using Avalanche Photo-Diodes (APDs) to read out the signals from the ECAL. This enabled a compact high-performance ECAL, the performance of which was key to the discovery of the Higgs boson. The APDs were developed by HPK in collaboration with CMS, with PSI being the partner responsible for guiding the development.

The group has also analysed physics channels which rely on the Pixel Tracker. It led the search for the previously unseen decay Bs0→μ+μ, which has a branching fraction of 3x10−9 and is sensitive to physics beyond the Standard Model. Currently, the group is analysing the recent data to improve the accuracy on this, and to measure its decay rate.

About Paul Scherrer Institute (PSI)

From: Switzerland

CMS member since: 1994



In October 1992, a ‘Letter of Intent’ was submitted to the LHC Experiments Committee (LHCC), offically marking the formation of the CMS Collaboration. This website commemorates the 25th anniversary of CMS, celebrated in 2017.