Research activities

Physics program

The ATLAS group at LBNL has a long-standing and strong involvement in a wide variety of physics measurements and searches of physics Beyond the Standard Model (BSM). Each research area sees the involvement of a combination of LBNL senior members, postdoctoral researchers and, often, graduate students.

Research areas include, but are not limited to:

• Studies related to Higgs boson physics.
  In particular we have been working on the properties of the Higgs boson interactions with the Standard Model Vector-Bosons (Z and photons) and Fermions (top, charm and muons). We have been contributing to analyses related to H->ZZ* decays (HZZ group), H->di-photon (HGamma group) including the ttH production measurement, ttH->multi-leptons (HTop group) and searches for the decay of the Higgs boson in muons and charm quarks (second generation Fermions). In addition we are also involved in di-Higgs searches in multi-lepton final states and in the combination of all ATLAS Higgs analyses to derive stringent tests of the Standard Model and put constraints on Beyond the SM interactions of the Higgs boson.
• EWK and QCD Standard Model measurements.
  Studies of processes sensitive to anomalous quartic gauge couplings, e.g. vector-boson-scattering in W^±W^±jj and photon-induced WW final states, differential cross-section measurement of vector boson production in association with light and heavy-flavor jets (including charm), and measurements of properties of jets (Jet and photon group).
• Searches for exotic phenomena predicted by Supersymmetry and other BSM theories.
  We have a long-standing involvement in supersymmetry searches in ATLAS, both using prompt and long-lived particles signatures, especially when connected with advanced usage of the ATLAS inner tracker and calorimeters. Other searches we are involved with include final state with Higgs boson(s) and di-jets (light of heavy-flavored), in the context of various BSM scenarios, including the interface with Dark Matter and searches for flavor-changing neutral currents in top decays.

Such a wide physics program is supported by an equally large involvement in performance studies and development of new event reconstruction algorithms. The group is deeply involved and has a long-standing expertise in charged particle reconstruction algorithms (tracking and vertexing), leveraging its large hardware and computing expertise (see below for a description of the hardware and computing/software activities in the group); other contributions include areas such as jets calibration and sub-structure, flavor-tagging (including charm-tagging) and photon identification.

The group is also active in advancing the development of simulation tools, ranging from event generators to detector simulation, to support the physics program. Synergies with the local theory group include event generators and BSM phenomenology. We are as well involved in assessing the performance and physics potential of the future upgrade of the ATLAS Inner Tracker.

Hardware R&D

The ATLAS LBL group has extensive experience in designing, constructing, commissioning, and operating silicon-based tracking detectors for collider experiments.

Our expertises have been developing over many decades, and are driven by the importance of high energy charged particle trajectory reconstruction to study fundamental particles and their interactions using collider experiment data. They are also essential to search for new phenomena.

At the moment, the group is working on the upgrade of the ATLAS Inner Tracking detector (ITk), needed to take full advantage of the collisions produced by the LHC after its High-Luminosity upgrade, which is expected to start data-taking in 2026.

Members of the groups have played leadership roles in the conceptual design, production and testing of the first silicon tracking detectors for collider experiments in the ‘80s (SVX at CDF – link ). We also played a critical role in the design and testing of the readout integrated circuits for the ATLAS innermost layer (link). Moreover, the ATLAS group has accumulated a lot of experience in the assembly, testing and loading (onto support structures) of detectors modules since the ‘90s. Integral part of the group are the many technicians and engineers that collaborate with the physicists and enable the design and production of these challenging detectors.
For example, the engineering department of LBNL established the LBNL Composite Shop to provide support structures for the ATLAS Pixel System in 2002. Since then it has provided structures to many tracking detectors, and developed unique expertises in design, fabrication and assembly of low-mass mechanical support structures for large tracking detectors.

Software and Computing

Our group has a long-standing involvement in software development within the ATLAS collaboration. Our effort is generally divided between support, maintenance, and evolutionary development of several mission-critical aspects of the ATLAS collaboration’s software, Athena, and research and development towards future hardware and software revolutions. LBL is the host to NERSC, one of the large high-performance computing (HPC) centers in the United States. Our group has collaborated with NERSC on bringing a variety of workflows to HPC systems and on efforts to adapt high-energy physics (HEP) software to new HPC architectures.

Our maintenance and development effort focuses on “core” software in Athena, including the underlying framework (Gaudi) and the basic tools and infrastructure on which all Athena jobs rely. We are deeply involved in efforts to make Athena efficiently multi-threaded, and in the past developed the multi-process approach currently used in production. We also have software responsibilities within the Event Generator group in ATLAS (Pythia8, MadGraph5_aMC@NLO, and EvtGen in particular), as well as the Simulation group (the detailed Geant4 simulation, various fast simulation efforts, and projects related to radiation damage modeling in silicon). We have at various times contributed to analysis software and reconstruction software (particularly for tracking) as well. Our maintenance work includes code modernization, thread safety, and performance optimization.

We lead a robust research program in Computational HEP in collaboration with NERSC, the Computing Research Division, and several institutions in the US, Europe, and Japan. We are currently involved in research towards bringing HEP workflows to accelerators (e.g. tracking on GPUs), applications of quantum computing for HEP, the distribution and scheduling of workloads on HPCs, and applications of machine learning for tracking and fast simulation. We have worked on a variety of other projects, including neuromorphic computing and the porting of data analysis workloads to high-performance computing.

The software and computing group at LBL involves primarily staff scientists and post doctoral researchers focusing on software for HEP. We regularly host visitors to work on all of these topics and others, and are happy to involve undergraduate and graduate students in physics, computer science, or related fields.