Starting as ATLAS Exotics Convener

Image: an overview of some constraints on (some!) of the models featuring new particles which are searched for in ATLAS.

Today I started my new role in ATLAS as the convener of the Exotic physics working group. As I’ve mentioned in previous posts, this is a role which means that, along with my co-convener Dr Dan Hayden of Michigan State University, I’m in charge of coordinating  about 20% of the ATLAS collaboration’s physics output, and about half of the searches for new particles. 

The rest of the ATLAS physics programme involves precision measurements of Standard Model particles, detailed study of the Higgs boson and its properties (including its self-coupling), studies of the Top quark and its properties, Heavy Ion physics, and study of decays of B-hadrons (which can give indirect constraints on new processes at higher scales). I won’t discuss these in detail here although they are all fascinating in their own right.

But let me expand a bit on the searches for new particles. What does that mean exactly?

Well, the new physics programme is broadly divided in two groups (following a recent restructure), on the one hand there is the “Higgs and Multi Boson Searches” group, which looks for exotic Higgs bosons (heavy Higgses, charged Higgses, and similar) and final states involving the W and Z bosons (leading, typically to jets, missing energy and leptons); it includes what used to be the Supersymmetry search group (which often includes missing energy!) but is now much wider in scope. That’s the other group. The group which I now co-lead (“Exotics”) is in charge of searches for other weird and wonderful new particles speculated by various theories. Our activities are categorised into five groups, which in turn are led by subgroup conveners who report to Dan and I:

• Jets, Missing energy and eXtra objects (JMX): this is a subgroup which searches for various dark matter models (which would give missing energy signatures) where the new particles are produces along with regular hadronic activity (jets) and potentially some extra SM particles. It’s also a pioneer in the use of anomaly detection, a machine-learning technique which seeks to identify “weird” activity int he detector in an unsupervised way. It also searches for some so-called Dark QCD models, which could give rise for example to semi-visible jets.
• Leptonic Plus eXtra objects (LPX): this subgroup specialises in searching for new particles which decay to leptons (typically electrons and muons), which are normally cleaner in their final states that hadronic activity such as what is expected in JMX. Typically new-physics models covered here would be vector-like lepton, lepto-quarks, heavy new bosons (Z’, pronounced Z prime).
• Heavy Quarks, Tops and Composite Higgs (HQT): this subgroup investigates the idea that there could be additional quarks which might be heavy, such as predicted in Vector-like quark models, or models where the Higgs boson is not a fundamental particle but composted of other particles. This subgroup focuses typically on final states where a new particle decayed to a top quark.
• Long-lived and Unconventional Physics (LUP): before I become the Exotics group convener, this was my main area of focus… searches for long-lived particles, weird jets and anomalous ionization! Basically anything which didn’t fall into the unusual expectations, or which wouldn’t be picked up by usual techniques. This subgroup resulted from a merger of two similar groups (one hosted in Exotics and the other in the Supersymmetry working group), and is in my view one of the most exciting places to be doing particle physics today.
• Combinations, Cross-talk and Summaries (CCS): this subgroup is cross-cutting and is in charge of bringing together results and activities from across the other subgroups, making summaries, and spotting opportunities and uncovered areas.

My new role involves, basically, project managing all this activity, which is the work of about 500 people and involving dozen and dozens of analyses of the ATLAS data. I will report to the ATLAS Physics Coordinators. I’ll be helping to define our strategy for analysing Run 3 of the LHC data, and setting the scene for Run 4. The first big event of my calendar is the Exotics Workshop (a yearly event, this time hosted in Bologna) at the end of October, where the community gets together to review our position and plan for the future. I’ll be giving a talk there to review the experimental landscape for exotic physics in Run 3: basically a chance to set out my stall and my priorities. I’ll make a future post about what I have to say there. In the meantime, I have a whole new stack of meetings to attend, discussions to chair and paper drafts to review.