The NuMI Neutrino Beam
How do we make a Neutrino Beam?
At 700kW power, the NuMI neutrino beam is currently the world's most powerful neutrino beam. It sends trillions and trillions of neutrinos towards the NOvA detectors. Unfortunately, due to the neutrinos' elusive nature, only few of those ever interact in our detectors. To make the NuMI beam, 120GeV protons from the Main Injector are fired into a graphite target which produces hadrons, mainly Pions and Kaons. Those hadrons are then focused in the forward direction by two magnetic horns and continue to travel towards the NuMI decay pipe, a 2m diameter, 675m long volume filled with Helium gas at 0.9atm pressure. There the hadrons decay into secondary particles and neutrinos. A concrete and Aluminium hadron absorber at the end of the decay pipe absorbs any remaining secondaries apart from muons, which may travel a bit further into the rock underground at Fermilab. The rock stops the remaining muons leaving a pure neutrino beam to travel to the NOvA Near detector a little further away, and through the Earch to the NOvA Far detector at Ash River in Minnesota.
The Neutrino Beam Flux
One area the UCL group has historicaly been very active in, already on NOvA's predecessor experiment MINOS, is to work to understand the neutrino flux from the NuMI beam. In order to correctly predict what should be seen for the NOvA Far detector, the neutrino flux must be well understood. We are continuing with our work in this area on NOvA.