The ATLAS Experiment presented its latest results at the Hadron Collider Physics Symposium 2011 in Paris, France (14-18 November). Many of the most recent searches and analyses are based on more than double the data available at the last big conference in August.
Highlights include the latest searches for the famous Higgs boson, which delve deeper into those mass regions where the Standard Model predicts the Higgs is hiding. There was also news of searches for Supersymmetry in the third generation of particles, a current 'hot topic' amongst theoretical physicists. A plethora of searches for new exotic particles were reported, reflecting ATLAS' accelerated pace of searches, as it continues to increase the range of new physics scenarios it probes.
Keep an eye on Twitter for news from the conference.
ATLAS Supersymmetry searches at HCP11
Only 5 per cent of the universe is made of ordinary matter (atoms), and current theories do little to describe the remaining 95 per cent that is called Dark Matter and Dark Energy. Supersymmetry proposes to solve the Dark Matter part of this problem. In doing so, it postulates a new particle partner (called a sparticle) for each known particle. Amongst these are the supersymmetric partners of the top and bottom quarks, which are called "stops" and "sbottoms". In some supersymmetry models, stops and sbottoms are light in comparison to some other supersymmetric particles. This means that, if they exist, we may be able to produce them at the LHC and observe them within the ATLAS detector. We expect sbottoms to decay far too quickly to be observed directly, so instead we look for the bottom quarks that are produced in the decays. This has been done for the very first time at the LHC, with data taken by ATLAS in 2011. So far, however, the observations match up with what is expected from the Standard Model, which means within some of these supersymmetric models that the sbottom has to be at least 400 times heavier than a proton. More data will be analysed over the winter to hopefully unveil the mysteries of Supersymmetry.
ATLAS searches for exotic new physics at HCP11
One of the most fascinating challenges of our field is the hunt for new phenomena not predicted by the Standard Model of Particle Physics, such as those proposed by other theories and models. Physicists label these searches 'exotic'. Studying high-energy proton collisions at the LHC, ATLAS is beginning to extend the frontiers of our knowledge by performing searches for exotic particles and processes in regions never before explored. At HCP 2011, ATLAS presented:
- A search for a new quark that decays into a quark and a Z or W boson;
- A search for a compound state of quarks and leptons;
- A search for 'leptoquarks' composed of an electron and a quark;
- A search for excited quark states decaying to photons-jet pairs;
- A search for extra-dimensions by looking at photon-pair production;
- A search for graviton particles and extra dimensions of space by looking at pairs of WZ/ZZ bosons;
- A search for a light Higgs decaying to the long-lived neutral particles predicted by one exotic scenario to be the mediators between Standard Model particles and another hidden sector of particles;
- A model-independent search for the anomalous production of same-charge muon pairs (which could appear in such exotic phenomena as microscopic black hole production).
Exotic searches play an exciting and essential role in the analysis of LHC data, in that non-discovery serves to tighten the boundaries of our current theoretical models. And discovery? That's even more fun!