Between 17th and 19th June, the picturesque and historic Italian city of Trieste played host to a gathering of about 40 members of the CMS ECAL Group for the first "ECAL Days" outside of CERN since the LHC startup. LS1 is a pivotal period for ECAL, as well as the whole of CMS, with preparations for the next LHC run in full swing whilst, at the same time, decisions being made about the long-term future of the detector. The meeting was split about 50:50 on these two perspectives, with about half of the time devoted to discussion sessions on a variety of topics. These topics included the production of legacy papers and documentation to summarise the performance of ECAL during LHC Run I, training of newcomers to become "experts on call", and the ECAL-related content of the Phase II CMS Technical Proposal (TP). The discussion sessions were lively and open, with valuable contributions coming from not only the more experienced members of the group but also the newcomers.

Despite having no new data, the performance of ECAL has continued to improve during LS1. This is due to the final calibration, based on the full Run I data sample, being available, as well as the development of new calibration techniques such as containment corrections derived with MVA and the use of di-electron decays of the Z0 to calibrate the high pseudorapidity region of the endcaps that is not covered by the tracker. Data-driven analyses, for example using the ratio of energy (of electrons from Z decays) deposited in the Preshower to that in the ECAL endcaps has resulted in an improved understanding of the material upstream of the ECAL that has been fed back into the GEANT simulation - see figure 1 below. This work was the result of an excellent coordinated effort between the ECAL DPG and Tracker POG. The implementation of ageing and out-of-time pileup into the simulation, coupled with the better material description, has improved the matching between data and simulation significantly.

The turnover of ECAL personnel, as in other subsystems, results in a continuous need to train newcomers for "expert" duties. Documentation is being improved and a series of detailed tutorials is being planned. The first such tutorial - for the DAQ system - already took place just after the meeting. More will occur during the summer and autumn, such that by the time of CRUZET and CRAFT we will have a new group of experts to support and take over from the existing ones.

The ECAL part of the Phase II TP was scrutinized by the ECAL group, with a full read-through during the meeting, and the draft version signed-off for delivery to the first set of CMS readers. Some analyses are still ongoing but the overall key messages are rather strong - that the barrel part will continue to be performant throughout Phase II (with changes to the on- and off-detector electronics) but that the endcaps need to be replaced at the start of Phase II.

But the formal aspects of the meeting tell only half of the story. The discussions continued long into the evenings, often taking place in one of the many outdoor restaurants and sometimes accompanied by a World Cup match in the background. The highlight from the social perspective was a dinner in the exclusive Yacht Club Adriaco. It is not often that the staff in such a location overhear lively conversations on such things as the options for endcap calorimetry ten years from now, or the prospects of finding new fundamental particles next year!

I would like to thank Giuseppe della Ricca and his colleagues at the University of Trieste for the outstanding organization of this meeting.

by Dave Barney