While the work on improvements on the detector continues during the Long Shutdown 2, physicists are starting to reap the rewards of the LHC dataset collected in LHC Run 2. The dataset is the largest sample ever collected at a collider and equivalent to an integrated luminosity of about 140 inverse femtobarns, equivalent to about 5% of the total data that LHC is expected to deliver in its lifetime. At the 66th Rencontres de Moriond conference, the Compact Muon Solenoid collaboration has presented over 36 new results, of which 7 are using analysis of data collected in 2018 in combination with earlier collected data to amount to the largest datasets ever analysed.

The world-class precision of the Compact Muon Solenoid experiment is taken advantage of in both measurements and searches. Other studies are currently based on smaller datasets while work is proceeding on calibrations with ultimate precision for the most recent data.  But even in the analyses that already exploit this very large dataset, many analyses pursue novel strategies that have not been used before at the large hadron collider. The results cover a wide assortment of topics and range from precision measurements of the Higgs boson and Standard Model processes to searches for rare decays and exotic phenomena.
 

Since its discovery in 2012 the Higgs boson has become one of the focuses of the essential tests of the Standard Model. New results were presented on the production of Higgs bosons when the Higgs boson decays to two Z bosons, one of the most important ways to observe the Higgs boson and the easiest way to study its properties. It is also possible to use the production of two Z bosons to investigate if there are further subtle changes compared to the Standard Model prediction. The new study of ZZ production provides unprecedented experimental precision on the production probability of about 3%, of similar size as the theoretical predictions. Both analyses use the data collected by the CMS experiment in 2016, 2017 and 2018. [Read more: CMS-PAS-HIG-19-001 - CMS-PAS-SMP-19-001 ]

The CMS collaboration also presents new results on the search for the production of four top quarks. The production is a rare process that is about a factor ten less likely to be produced than Higgs bosons together with two top quarks, and about factor ten thousand smaller than the production of just a top quark pair. The analysis has indirect sensitivity to the strength of the interaction between the Higgs boson and the top quark, called the Yukawa coupling, and shows the currently best sensitivity to the process. As four top quark production can be predicted by calculations in Quantum Chromodynamics, it is possible to test for any deviations from the Standard model production. A complementary and novel approach where the Yukawa coupling is directly measured from the behaviour of top quark pairs is now also available, and this is the first time this model-independent approach is used at a hadron collider. [Read more: Physics summary four tops soon - Physics summary top yukawa from top quark pairs - CMS-PAS-TOP-18-003 - CMS-PAS-TOP-17-019 - CMS-PAS-TOP-17-004 ]

Searches for new, long-lived particles with decay lengths of the order of centimetres have been one of the most active research areas in the past years and require specialised reconstruction techniques. The precise time information obtained in the electromagnetic calorimeters had already been used to search for photons originating from delayed decay. For the first time at the LHC, this technique is applied to jets, leading to the most stringent limits to date for some of the models predicting long-lived particles decaying to jets. [ Read more: physics summary - CMS-PAS-EXO-19-001 ]

The very large new dataset has also been used to extend the sensitivity to the production of strongly interacting supersymmetric particles. This search used the established signature of multiple jets and missing transverse momentum, but has been extended to cover cases where a long-lived, charged particle decays within the tracker volume to soft and invisible products, leading to a signature of a “disappearing” track that would only be identified with dedicated algorithms. Such long-lived, charged particles are predicted by many supersymmetric models. The power of the analysis is illustrated for the case when supersymmetric partners of the gluon (gluino) would produce long-lived particles in their decay chain, and the inclusion of the signature in the analysis significantly increases the sensitivity in terms of the gluino mass. [Read more: physics summary - CMS-PAS-SUS-19-005 ]

Another scenario for physics beyond the Standard Model is the existence of vector-like quarks. Here the data are examined for evidence of these particles using a novel machine learning technique to simultaneously identify and classify jets coming from Higgs, W and Z bosons and top quarks, yielding the strongest limits to date for these particles. [Read more: physics summary - CMS-PAS-B2G-18-005 ]

These results show that the CMS collaboration is not only able to analyse the very large data sample that was only collected recently but also could include many novel techniques that have not been used before. There are many more results in preparation on this dataset, using the large dataset to its full potential.

List of new CMS results for conferences in the winter of 2019:

All CMS preliminary results - All CMS journal papers