People
The Animation
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The NeO java application by Victoria Hamilton-Morris and Paul Harrison. This animation visualises neutrino flavour oscillations, in terms of a set of rotating quantum mechanical amplitudes. (Note - it may take a few minutes to download, the first time). |
The Experiment
One of the fundamental questions in physics is why there is more matter than anti-matter in the Universe. This asymmetry could be explained by a difference between neutrinos and their anti-matter partners, both of which are a part of a family of particles known as
leptons. If neutrinos have mass, which is not predicted by the
Standard Model of particle physics, then they could oscillate between three different flavours - electron, muon and tau - as they propagate through space. The oscillations could then produce
CP-violation effects, which will generate an asymmetry between matter and anti-matter. Recent measurements of neutrino oscillations by
Super-Kamiokande and other experiments imply that neutrinos have mass, and further measurements are required to fully explore the physical properties of the neutrino. The ideal way to do this is to use a
Neutrino Factory, which will produce an intense beam of neutrinos which will be used to make precise measurements of the parameters describing neutrino oscillations and CP-violation for leptons. These measurements, together with results from other experiments such as
BaBar,
T2K and
Cobra will give a more complete picture of CP-violation and how it can generate the observed matter - anti-matter asymmetry in the Universe. The UK is taking a prominant role in research and development (R&D) activities for a
Neutrino Factory, which could be built in the UK at the
Rutherford Appleton Laboratory (RAL). A possible layout of the facility would be that shown
below, in which the intense neutrino beam would be produced from the decay of muons in the last element of the accelerator complex. The design would involve the following elements:
The first stage of the factory design involves a
proton driver system, in which negative hydrogen ions (H
-) are produced by a thermionic emission source and then passed through an early acceleration stage to produce a beam of ions with energies of approximately 0.15 GeV every 50 seconds (frequency of 50 Hz). The ions pass through a thin carbon or aluminium oxide foil to strip two electrons to create protons. The protons are then passed through
rapid cycling synchrotons (RCS) until they reach an energy around 5 GeV, in bunches with an average time duration of 2 nanoseconds. The 4 MW proton beam is smashed against a
target to produce pions. The target needs to be robust enough in order to withstand the extremely high power density of the proton beam. The efficiency of capturing pions from the target relies on precise knowledge of their momentum distribution from the proton-target collision. The
HARP hadron production experiment at
CERN, of which the UK is a major contributor, was conceived to measure these distributions. The pions then decay to muons, which is controlled by the
muon cooling system. The muons need to be cooled so that the muon beam is reduced in size to fit inside the accelerator components further downstream. The
Muon Ionisation Cooling Experiment (MICE) is being constructed at RAL to demonstrate that muon cooling will be possible for a Neutrino Factory. The muons are then
accelerated and stored. The acceleration involes the use of
linear accelerator sections (linacs). Finally, the muons are placed inside a triangular-shaped storage ring. They will travel around the ring, and will eventually decay into electrons and neutrinos after a thousand turns or so. The neutrinos that are produced will travel along the straight sections of the storage ring (represented by the green dotted arrows in the above figure), essentially at the speed of light. These sections need to point to the underground laboratories where the neutrino detectors would be housed. Possible sites for these detectors are
Japan (Kamioka), the USA (
Soudan mine in Minnesota or the
Homestake mine in South Dakota), or Europe (
Gran Sasso in Italy or
Boulby in England). Studies indicate that approximately 10
21 muon decays per year are required to deliver the physics programme, which in turn requires that the Neutrino Factory contain technologies beyond what is presently available, creating the need for an extensive period of R&D.
Research activities
The research that Warwick University is directly involved in is the design of the
front-end test stand, which is being built at
RAL to test the chosen technologies for the
proton driver, as well as optimising the production
yields of pions and muons for a Neutrino Factory
solid target system. The Warwick group is also working on end-to-end simulations of the
Muon Ionisation Cooling Experiment so that these can be compared with measurements to verify whether the muon beam does get cooled (reduced in size) as it passes through the absorbers and radio-frequency (RF) accelerator sections.
