The high-energy physics group focuses on two research areas, neutrino physics and the highest energy cosmic rays. Our research is addressing some of the most exciting puzzles that nature has to offer.
Despite the fact that neutrinos are some of the most abundant particles in the Universe they are also some of the most ghostly particles which require very sophisticated detectors to observe and characterize them. Neutrinos can be studied in underground laboratories or at particle accelerators. The latter is not true for the highest energy cosmic rays which are particles arriving on Earth with energies many orders of magnitude larger than what could be accomplished with man-made particle accelerators.
We are involved in a number of experimental projects to collect data on neutrinos
and the highest energy cosmic rays in order to solve the mysteries associated with
Neutrinos are source of mysteries and surprises. Many of their fundamental properties and characteristics remain to be explored. Neutrinos are a challenge to study because they rarely interact with matter and hence are difficult to detect. Experiments provide evidence for the existence of three types of neutrinos. Recent measurements demonstrate that neutrinos can change from one type into another (they 'oscillate') as they travel from their source to a suitably distant detector. The mixing of neutrinos is very different from what has been observed in the quark sector where mixing is comparatively small.
Recently reactor based experiments as well as the neutrino long baseline experiment T2K (Tokai to Kamiokande) have turned the least well measured mixing parameter theta-13 into the best known one. We are actively involved in the T2K experiment which is located in Japan and directs a muon-neutrino beam through a near detector complex and on to the 295 km distant water Cherenkov detector Super-Kamiokande. A comparison of measurements at the near detector, which samples the un-oscillated neutrino beam with observations made by the far detector allows to study neutrino characteristics. Next steps for the T2K experiment include the study of the properties of anti-neutrinos and whether they behave differently from neutrinos.
An asymmetry between matter and anti-matter (charge-parity or CP-violation) in the neutrino sector might provide insight into the origin of our Universe and our very own existence. We are merely at the beginning of what promises to be an exciting exploration of uncharted physics terrain.
The long baseline neutrino experiment (LBNE) which aims to send a neutrino beam from Fermilab, Illinois to the Sanford Underground Research Facility (SURF), South Dakota will have better sensitivity to an asymmetry between neutrinos and their anti-matter partners. In addition, it aims to measure other neutrino properties such as the ordering of neutrino masses (the 'mass hierarchy') and search for nucleon decay. Presently LBNE is in the planning stages and we are conducting research and development to optimize the experiment. A number of smaller projects such as LArIATand CAPTAIN, which employ liquid argon detection technology will serve as important stepping stones towards a large (tens of kilotons) liquid argon detector as anticipated for LBNE.
In previous years we studied neutrinos from the Sun and searched for additional types of neutrinos:
Neutrinos are produced in the fusion reactions that fuel stars. Hence, our Sun is a powerful source of neutrinos. Numerous experiments have observed solar neutrinos but the observed solar neutrino flux was lower than theoretical models predicted; a dilemma that was termed the 'solar neutrino problem'. In the early 2000's the Sudbury Neutrino Observatory (SNO) demonstrated conclusively that the discrepancy between theoretical expectations and data is resolved by the nature of neutrinos themselves. As the neutrinos travel from Sun to Earth they change their type (they 'oscillate') and previous experiments had only been sensitive to one type. The SNO experiment which consisted of 1 kton of heavy water, which was viewed by nearly 10,000 light sensitive photo-sensors was able to distinguish between the different types of neutrinos. We observed the flux of all three known types of neutrinos to agree very well with predictions.
Three types of neutrinos are known to exist but results from the 'Liquid Scintillator Neutrino Detector' (LSND) give indications that a fourth and rather mysterious neutrino might exist. The MiniBooNE experiment at Fermilab explored the open question of the existence of a fourth type of neutrino. The experiment studied neutrinos coming from a man-made neutrino beam with a spherical detector which contains mineral oil and which is viewed by 1,500 photo multipliers.
The highest energy cosmic rays are particles that have been observed on Earth with energies in excess of 1020eV. One of the largest mysteries associated with the highest energy cosmic rays is their origin. Where do they come from ? What astrophysical objects and mechanisms can accelerate particles to energies of 1020eV and above ? What exactly are these particles ?
The Pierre Auger Observatory is a project which is currently taking data to answer the above questions. The observatory is located in Mendoza Province, Argentina. It consists of an array of 1600 regularly spaced water Cherenkov detectors spread out over an area the size of Rhode Island and a series of fluorescence telescopes which monitor the atmosphere above the detector array. The strengths of both detection techniques complement each other and allow to obtain a maximum amount of information on the highest energy cosmic rays. In order to fully study the origin of these particles full sky coverage is mandatory and plans for a second observatory site in the northern hemisphere are currently being pursued.
LSU has been a member of the Auger Project since its inception and continues to be a key contributor to the experiment.