Argonne National Laboratory

ANL extended barrel number 4, being inspected during its instrumentation with scintillating tile and wavelength-shifting fibers. Image courtesy of Argonne National Laboratory

The Argonne National Laboratory is in Argonne, Illinois and collaborates with the ATLAS experiment at the LHC.  At the present time, the High Energy Physics group collaborating with ATLAS comprises 9 physicists, 3 postdoctoral fellows, 1 technical staff and 5 computer professionals.

Contributions to ATLAS Construction
Argonne National Laboratory High Energy Physics Division has been a collaborator on ATLAS since 1994. We brought our technical expertise to the design and construction of the 2600 tonne scintillator-tile hadronic calorimeter and to the Region of Interest Builder – a hardware device essential to the ATLAS Level 1 trigger system and to core software development.

The calorimeter was a major engineering challenge, and engineers at Argonne contributed to the design of the structure. The modest-looking Region of Interest Builder must filter the huge volume of information streaming from the detector into small packets so that the data can travel as quickly as possible. The event selection and I/O framework, for which we have lead responsibility, must provide efficient and reliable access to ATLAS data.

Current Projects and Future Goals
We are now bringing our technical and scientific expertise to the operation of one of the three Analysis Support Centers of US-ATLAS and in addition have developed a cost effective multi-core computing cluster for use in general physics-level analysis.

The ATLAS group and technical staff with the first extended barrel module. Image courtesy of Argonne National Laboratory

Our contribution to detector performance activities in ATLAS is closely aligned with our detector construction activities. One of these areas is jet energy reconstruction, which is one of the two main functions of the hadronic calorimeter and optimization of the response of the calorimeter to jets using software weighting techniques.

Our other interest lies in the physics of processes involving jets. Understanding these processes is crucial to recognizing whether we have evidence of physics beyond the Standard model. Based on expertise in other experiments, we are also investigating processes which produce prompt photons. Pair production of prompt photons is one of the clearest signatures for Higgs production. To identify the Higgs signature, we'll need a full understanding of all processes that result in these pairs of prompt photons.

Our ongoing responsibilities include the maintenance and operation of elements of the detector systems that we constructed – the core software for the I/O framework and databases, the tile calorimeter and trigger hardware. This is most evident in our support of the tile calorimeter where several of the physicists in the group are active now during detector commissioning. A similar, though slightly smaller, effort is being assigned to commissioning the ATLAS L1 trigger.

The efficient access to data will be critical to analyzing the many petabytes of data recorded to identify those few events which reveal something new in nature, for example, the decay of a Higgs boson. The software group has key responsibilities with the I/O framework and in the development of a "TAG database" to expedite access to ATLAS data. Members of the group have held ATLAS leadership positions: Tile Calorimeter Project Leader, co-convener in the Standard Model physics group and co-convener in the JetEtmiss performance group. The current ATLAS Physics Coordinator is from the Argonne group.