Dark Matter studies at LHC
Dark Matter searches at LHC
A main driving force for scientists is to push our understanding of the universe further and study its composition. Although we have a plethora of scientific achievements, we still can not explain the nature of dark matter (DM). When we observe the rotation of galaxies, they seem to be spinning at an impossible rate. Galaxies should have torn themselves apart long ago! This has led scientists to believe there must be some extra matter at play, giving galaxies the extra gravity generating mass necessary to stay intact. This matter has become known as dark matter. Since this revelation, other evidence has further suggested the existence of dark matter such as gravitational lensing observations and the cosmic microwave background.
The ATLAS Experiment
The ATLAS (A Toroidal LHC Apparatus) Experiment is a particle physics experiment located at the Large Hadron Collider (LHC). The LHC is the world’s most powerful particle accelerator, located at the CERN laboratory near Geneva, Switzerland. ATLAS is one of the four main experiments located at beam crossings along the LHC. It is one of two general purpose detectors at CERN, investigating the largest possible range of physics.
The ATLAS detector is used to explore dark matter interactions with the Standard Model (SM). If such interactions exist, DM particles could be produced at the LHC. However, DM particles would not interact directly with the detector, so we would have to observe them in association with visible SM particles. The hermetic construction of ATLAS makes it possible to search for this missing energy in such a particle-collision event.
The Data
Long-Term
The dataset consists of a series of ROOT-kind ntuples files containing real data recorded by the ATLAS Experiment at a
centre-of-mass energy of 13 TeV. It also includes a set of simulated Monte Carlo (MC) samples ranging from very
well-known Standard Model processes to some hypothetical Beyond the Standard Model (BSM) physics.
Short-Term
We are taking a public ATLAS result, searching for dilepton resonances, and reinterpreting this result in the context of dark matter production. The dataset consists of ROOT-style tuples, containing a summary of the results from the real dilepton resonant analysis. For reinterpretation, we must generate dark matter models in order to compare with the limits set by the analysis. This is done for a number of models, where more could be done by other interested scientists.
The Analyses
Since ATLAS is a general purpose detector, the experiment consists of a very large team in order to analyze the massive amount of data produced. From 2015-2018, we were involved in searches involving $ll + X $ in the final state. Namely, the team was looking for any events containing two leptons and missing energy. In this way more sensitive selections could be made in order to scan the invariant mass, searching for any resonances indicating a new particle (think of the Higgs discovery: $\textrm{H} \rightarrow \textrm{ZZ}$, $\textrm{H} \rightarrow \gamma + \gamma $).
In one part, we wish to reinterpret the results from the dilepton resonant search. The analysis produced the fiducial cross-section limit, so we can:
- Generate different theoretical physics models.
- Apply the same fiducial selections.
- Compare the results.
The inclusive search is particularly sensitive in high mass regions, but as you can see there is a massive amount of background in the lower mass regions. There are a number of Dark Matter models we expect to be sensitive to that could have been hidden by the background.
Look up the CODE
