2019 is approaching its end with it the first year of the LHC Long Shutdown 2 (LS2),a break that focuses on the upgrade and maintenance of the LHC. It’s been twelve intense months for the growing CMS collaboration that counts 53 member countries. Let’s have a glimpse on the CMS 2019 year.

In 2019, CMS reported outstanding results in a wide range of physics topics: searches for new particles, precision measurements of known particles (in particular the top quark and the Higgs boson), B- and heavy-ion physics.  New algorithms, that mostly rely on machine learning techniques, are being used for the reconstruction of objects used in analysis and event classification to increase the sensitivity of analyses. One of the impressive achievements for the collaboration this year is that new results coming out on the large Run 2 dataset that are often not just repetitions of previous analyses and substantially improve both our experimental techniques and knowledge of Nature at the smallest scale.

Early this year, CMS published the first measurement using the full dataset from LHC Run 2: for the first time two excited B mesons were observed, Bc+(2S) and Bc∗+(2S), which are separated in mass by only 30 MeV. (Link) Over 90 results were to follow, including many measurements such as a new combined Higgs boson mass measurement that yields the most precise result to date of this fundamental parameter of the Standard Model of particle physics. (Link)

The CMS detector upgrades also started in early January with the extraction of the pixel detector and the beam pipe, from the heart of CMS. Currently, new components for the innermost layer of the detector, are being produced, assembled, and tested, including a chip called the Token Bit Manager (TBM). (Link-Link) The beam pipe will be upgraded to make it compatible with the geometry of the future CMS pixel detector, its cylindrical section will be extended opening more space for the Phase-2 pixel detector. (Link)

Another major upgrade of the CMS detector that started this year is the installation of the Gas Electron Multiplier (GEM) detectors. This new sub-system will greatly improve muon measurement in the difficult forward region in CMS, right next to the beam pipe. Between July and October a total number of 72 GEM chambers were installed (Link-Link) and the same amount will be installed next year. On the occasion of the last GEM installation this year, for the first time at CERN, a 360 live broadcast from the CMS experimental cavern was shared on social media and turned out to be a great success.

Also the Hadron Calorimeter (HCAL) completed its Phase-1 upgrade. A key aspect of the HCAL barrel (HB) upgrade was the replacement of old hybrid photodetectors (HPDs) with new silicon photomultipliers (SiPMs) that have three times the photon detection efficiency and 200 times the gain. (Link)

A big CERN-wide event that happened in 2019 was the CERN Open Days. CMS was of course one of the big attractions, and thanks to very good organization was a big success. For a weekend in the middle of September, the CMS site was able to accommodate several thousands of visitors, of whom more than 6000 had the chance to visit the detector 100m underground. Around 300 volunteers managed to keep many activities going successfully, for both young and adults. Volunteers’ smiles, their energy, kindness and knowledge have been one of the primary reasons of CMS visitors satisfaction. Another unique event was a very special solo performance from the CMS experimental cavern, by the artist and musician Vladimir Tarasov. Extremely rare to listen drums and percussion in front of the CMS detector.

The Open Days were not the only way for CMS to be open to people. In fact, this year the CMS collaboration announced the release of its fourth batch of open data to the public. This brings the volume of its open data to more than 2 PB (or two million GB), and provides open access to 100% of CMS research data recorded in proton–proton collisions in 2010. In the new release, CMS the open data address the ever-growing application of machine learning (ML) to challenges in high-energy physics. (Link)

Speaking about CMS data, on 2019 the CMS Data Analysis School (CMSDAS) celebrated ten years of life. The CMSDAS, that involves several hundreds of CMS members for the benefit of some 1500 students in 10 years. The students are CMS physicists from across the collaboration, who want to learn (or to learn more) about data analysis in CMS. Judging from their opinions, the CMSDAS confirmed its quality also this year (Link)

Many other remarkable events and achievements happened at CMS during 2019, like multiple awards and recognitions for CMS collaboration members, such as the PhD Thesis Awards and Young Researchers Prize winners. (Link - Link) Fueled by the achievements and milestones reached in 2019, the CMS collaboration is ready for the new challenges coming in 2020.

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