In July 2012, the Higgs Boson was discovered at the Large Hadron Collider (LHC) at CERN (Switzerland) by both the ATLAS and CMS collaborations. It has been studied in greater detail since then. It is responsible for the breaking of the SU (2)×U(1) electroweak (EW) symmetry, and for the masses of the W and Z bosons, as well as of the known quarks and leptons. One of the main goals of the ATLAS and CMS physics programs is to extend the measurements of the Higgs properties and to reach a precision in the range of a few percent. With such precision, it should be possible to infer signs of new physics appearing at the TeV scale.

In order to achieve these measurements, the accelerator (LHC) and the large multipurpose ATLAS and CMS detectors are being upgraded and enhanced. The U.S. Department of Energy is helping to fund these upgrades. The High Luminosity LHC (HL-LHC), starting in 2027, will run at five times higher p-p collision intensity than today’s LHC. These higher instantaneous luminosities together with improvements in the experiments detectors and data processing capabilities will increase the experiment’s sensitivity by one order of magnitude.

While the breadth of coverage of measurements and searches is fundamental to the motivation for the HL-LHC dataset, there are a number of high-priority analyses that are seen as important drivers of the physics motivation for the program. A few examples include access to the Higgs boson self-coupling (HH channels), precision in measurements of the Higgs boson branching ratios, and mass reach in searches for new physics.

The ATLAS and CMS collaborations are in the process of writing Technical Design Reports associated with HL-LHC upgrades to both the detectors and the trigger – data acquisition system. A significant amount of simulated data is required in preparation for these reports. This data will need to be produced across a wide range of HL-LHC beam conditions. The HL-LHC simulated events are much more complex compared to current simulated data. Many parts of the ATLAS and CMS HL-LHC detectors will be new and new reconstruction algorithms will need to be developed. The simulated data samples produced from this ALCC project will be highly valuable for the collaborations and instrumental in the development of new reconstruction algorithms. This simulated data will be produced using both parameterized models and Geant4 simulation software and digitized/reconstructed if necessary. This software has been used at both NERSC (Cori) and ALCF (Theta) by both collaborations.