By CMS Collaboration


The time has come to wrap up the year! Ready? Let’s do it!

Not only did CMS celebrate the restart of LHC Run 3 in April at the record energy of 13.6 TeV, but this year also saw the long-awaited Heavy-Ion run. It marked the first Heavy-Ion run of Run 3 and the longest one so far. The best part? Everyone got to experience the excitement through a live broadcast!

Heavy-Ion Collision Event Display
Event Display of heavy-ion collision from 26 September 2023. CMS, CERN

While the detector was collecting data throughout the year, our scientists diligently worked on analysing previous data to publish new results! Specifically, CMS published a big set of publications and explained some of these results through 31 physics briefings in just one year!

Among the highlights of the year were a series of searches for long-lived particles, covering event signatures ranging from muon tracks starting at a distance from the primary interaction point to showers in the muon system [EXO-20-010 Briefing, EXO-21-008 Briefing, EXO-22-017 Briefing] and establishing the most stringent limits today for many models. These results included the first search using data from LHC Run 3 [EXO-23-014 Briefing]. CMS continued to explore rare processes with the observation of the production of four top quarks [TOP-22-013 Briefing]. The observation of the decay of the eta meson into four muons that occurs only a few times in a billion decays demonstrated the potential of special data streams with reduced event content [BPH-22-003 Briefing]. The production of Higgs bosons at high momentum became accessible to measurement using dedicated algorithms to identify strongly collimated tau-lepton and b-quark pairs [HIG-21-017 Briefing, HIG-21-020 Briefing].

Many of these new results were unveiled at major physics conferences like Moriond, LHCP, EPS-HEP, BOOST, and Lepton Photon. Members of our collaboration volunteered to provide live updates from these conferences on our social media platforms to take everybody along the exciting journey with them! Likewise, our PhD students faced a fun, yet challenging task of presenting their research posters in just 1 minute.

Sharing our results and maintaining transparency are core values at CMS, and a clear testament to this commitment is the release of an extensive collection of heavy-ion data from LHC Run-1 this year. You can access all Run 1 CMS data collected during 2010-2013 through the CERN Open Data portal.

2023 made everybody in the physics community reflect on the fact that a discovery is just the beginning of a new era of exploration. CERN celebrated the 40th anniversary of the discovery of the two elementary particles, the W- and Z- bosons, with a symposium looking back at the incredible physics that has taken place since the discovery, and the extensive use of these particles in CMS operations (e.g. calibration of the calorimeters) and physics analyses. Thanks to the knowledge gathered in these last few decades, CMS continues to push the boundaries of fundamental physics research. We look forward to what next year may bring - stay tuned!

Detector exhibit at the CERN Science Gateway
Photograph of the detector exhibit in CERN’s Science Gateway. (Image: S.Hurst, CERN)

In case you were wondering where the symposium took place, the answer is in CERN’s brand new educational and outreach centre, Science Gateway. The exhibitions are excellent for anyone who appreciates science, regardless of their scientific background and age. Of particular interest to CMSers is the room dedicated to LHC detectors. In the middle of this room, visitors can admire a structure containing pieces from the four largest LHC experiments. Featured items include a petal of the silicon strip endcap tracker, a crystal from the ECAL, and a GEM muon chamber prototype - all from CMS!

Nothing compares to seeing the real thing though - and for that you need to venture just across the border into France. Once again our Visits team organized hundreds of in-person visits, including going down 100m to the experimental cavern to see the detector. Although the detector is only viewable while the LHC is not running, there are other underground areas that can be visited year round - a definite highlight! However, not everybody who saw the detector this year was there in person: CMS’ Virtual Visits allowed people from across the globe to tune in online. 2023 saw almost 50 virtual visits organised for schools, universities, and organisations worldwide, reaching over 7400 people. Two of these virtual visits were open for everyone to participate in, and one was even live-broadcasted on CMS’ social media. Both guided and virtual visits will continue throughout 2024, so be sure to book so you too can join, interact, and ask questions to our scientist-guides.

Visitors inside the CMS experimental cavern

Visitors inside the experimental cavern to see the CMS detector. (Image: S.Hurst, CERN)

The CMS Young Scientists Committee once again supported early-career members of the collaboration. Some of their achievements include hosting 2 Job Matching Events, 1 Soft Skills Workshop, guiding nearly 50 people on their newcomers’ tours, and co-organizing the LHC Early Career Mentoring Programme, for which they were invited to present at the LHCP conference earlier this year. They look forward to continuing their efforts to improve the professional lives of untenured CMS members in 2024.

Embracing inclusivity in a collaboration as large and diverse as CMS is an integral part of how it works. For the International Day of Girls and Women in Science, 27 CMS scientists shared their stories in their own languages, inspiring young students to pursue STEM. On LGBTQIA+ in STEM Day, the CMS Diversity and Inclusion Office joined CERN’s initiative to raise the Inclusive Progress Pride flag in the Esplanade des Particules, alongside the flags of member states.

CMS, in collaboration with IPPOG - the International Particle Physics Outreach Group -, organized more than 50 masterclasses where high-school students learned how to analyze event displays from real CMS Run 1 datasets. One of these masterclasses was particularly special, as it was organized for the second time exclusively for CERN personnel who are not physicists.

Masterclass,IPPOG,CMS Communications
CERN personnel taking part in the CMS Masterclass. (Image: S.Hurst/CERN)

While students were busy discovering particles, ATLAS and CMS pretended to lose one! Did you have a chance to read the April Fool’s Day announcement? Check it out here. Although it was fake news, we also had some that were very real. Take, for instance, the biggest data deletion campaign in CMS' history, where unusable data was removed to free up storage space! And how about the HGCAL beam tests? That was quite a ride too! However, the team's successful results indicate one thing: the preparation of HGCAL (High Granularity Calorimeter), set to be installed during the next Long Shutdown for the Hi-Lumi LHC, is progressing according to plan.

On a different note, CMS welcomed new members and, as is done every year, organized induction courses and the Upgrade Days. The latter are dedicated to exploring the major changes being prepared for the CMS detector in the High Luminosity (or HiLumi) LHC era in a few years’ time.

Lab tour for the Upgrade days

Image from the Upgrade Days looking at the new work being conducted across the collaboration ready for HiLumi CMS. (Image: N.Stathaki, CERN)

Indeed, together with efficiently taking data during the continuation of Run 3 that started in 2022, CMS has been deep in preparations for the HiLumi era. Major changes to the CMS detector are due to start being implemented in 2026 to take the experiment to a completely new level - but the work for these is already well underway! Across all areas, both these aspects have been progressing excellently and efficiently. Let’s take a look:

L1 Trigger
The Level-1 Trigger has successfully performed more than 10 integration tests connecting several sections of the HiLumi CMS system. These tests are essential to ensure the correct functioning of the foreseen trigger system architecture and to validate the advanced hardware boards' designs prior to production, along with the sophisticated machine learning-based algorithms implemented in their core.

MTD - MIP Timing Detector
MTD has started production for the BTL (Barrel Timing Layer), the central part of the new detector, which will be implemented inside the new Tracker volume. After demonstrating the design performance in test beams earlier in the year, the production of all major detector components is now ongoing. The first LYSO crystals that will detect charged particles have been delivered to CERN just in time for Christmas.  ETL (Endcap Timing Layer) has successfully demonstrated its design performance with their readout ASIC, paving the way for the full detector construction for the endcap portion of the detector as well.

HCAL - Hadron Calorimeter
HCAL implemented several improvements focusing on automation and recovery time that should make 2024 operations even better. In addition, HCAL is on track to be ready for HiLumi CMS, making progress on new firmware to accommodate the planned changes to the backend electronics.

ECAL - Electromagnetic Calorimeter
ECAL successfully commissioned the new surface laser lab to calibrate ECAL crystals with the new configuration, ready to take data in 2024. In parallel, the final productions for the HiLumi CMS electronics are being finalised. In December we also received the second Enfourneur, the large apparatus that will extract half of the ECAL modules during the Long Shutdown 3 and re-insert them in CMS after their refurbishment.

HGCAL - High Granularity Calorimeter
HGCAL has made major progress on all fronts: from mechanics, with the completion of the first absorber plates, to the silicon sensors, with the beginning of the mass-production phase, and not forgetting the front-end and back-end electronics! Indeed most components of HGCAL have now entered the pre-production or production phase. There were also successful beam tests at DESY (of SiPM-on-tile modules) and at CERN (silicon modules). The latter featured complete end-to-end electronic systems for the first time, which performed excellently.

BRIL - Beam Radiation, Instrumentation, and Luminosity
Throughout 2023 LHC operation BRIL provided information to CMS related to the LHC beam conditions: to protect CMS from beam anomalies and to measure accurately the radiation environment and collision luminosity, critical for all physics analyses. In parallel the BRIL team worked on the upgrade projects, designing new detectors and associated electronics for HiLumi CMS.

PPS - Precision Proton Spectrometer
The PPS team successfully installed all detectors, namely silicon pixel trackers and diamond timing detectors, in both LHC arms at 220 m from the interaction point in IP5 at the beginning of the 2023 data campaign. All detectors have now been removed for a global overhaul and will be reinstalled before the 2024 data-taking campaign.

2023 was the first full year of operation with four muon detector types in CMS, with the GE1/1 endcap GEM chambers complementing the existing DTs, CSCs and RPCs. The Muon group has also produced the first GEM and iRPC detectors, which will be respectively installed in the most forward region of the 2nd and 3rd CMS endcap disks. These new muon detectors will take part in the 2024 CMS data taking. In 2023, all Muon sub-systems produced and tested several pre-production electronics boards in preparation for HiLumi CMS.

DAQ - Data Acquisition
A major milestone in the HiLumi CMS DAQ developments was reached this year with the reception of five DAQ800 prototype read-out boards, the first of which has already been successfully tested in the DAQ lab. With the upcoming new CMS control room, the DAQ group has also been preparing the refurbishment of the ‘old’ control room to become part of the online data centre.

Dedicated efforts from the strips and pixel teams reduced deadtime, improving performance. Several Inner and Outer Tracker module prototypes for HiLumi CMS were assembled and tested extensively, and successfully! Moreover, the final version of the pixel chip has been submitted and the assembly of kick-off PS and 2S modules, using pre-production hybrid circuits, has started.

Offline & Computing
The overall performance of the computing infrastructure this year was excellent. CMS Offline & Computing was able to leverage Tier-1 CPU resources for the prompt reconstruction of the heavy-ion data, in order to complete the data processing in record time.

A note from our Technical Coordination team:
2023 started with the end of EYETS (Extended Year-End Technical Stop 2022/2023) and finished with the start of the EYETS 2023/24: the loop is closed. YETS are a period of of intense activity for TC: major maintenance and upgrade works are done on the CMS detector and infrastructure following our leitmotiv “Safety, quality, schedule”. Between the YETS, the TC team helped maintain the excellent operation of the detector and prepared the infrastructure at P5 for further upgrades.

Lastly, CMS recognised some members of the Collaboration with various awards including the CMS Awards, the CMS Young researchers Awards and the CMS Ph.D. Thesis Awards. These awards are a huge honour and recognition considering that the CMS Collaboration keeps getting bigger and by the end of 2023 consists of more than 6000 members from 255 institutes coming from more than 50 countries.

Working in CMS,CMS Week,2023
Group photo of some CMS members, June 2023. (Image: S.Hurst/CERN)

CMS thanks every member and institute of the collaboration and wishes them a happy new year!

That was fun. Same time next year?

Date of publication