The T2K Experiment - From Tokai To Kamioka - Where is the anti-matter?
From the beginning of 2010, the T2K experiment will fire a beam of muon-neutrinos from Tokai on Japan's east coast, 300km accross the country to a detector at Kamioka. It hopes to investigate the phenomenon of "neutrino oscillations" by looking for "muon neutrinos" oscillating into "electron neutrinos". A million pound detector has been built at the University of Warwick as part of a vital experiment to investigate fundamental particles - neutrinos.
The experiment aims to measure neutrinos at the start of their journey and then again at the end 300 kilometres away to see how they've changed. Understanding neutrinos will tell us more about the physics of the universe and help explain why the universe is made of matter rather than anti-matter. Associate Professor, Dr Gary Barker said, "It's thought that in the Big Bang that created the universe, matter and anti-matter were created in equal amounts, but it's clear that everything we observe today is only consisting of matter, so the question is where has the anti-matter gone?" 50 trillion neutrinos from the sun pass through us every single second, but as we do not notice these they are hard for scientists to detect. The T2K experiment generates its own beam of neutrinos rather than relying on studying those from the sun.
Work at Warwick
There are 62 institutes across 12 different countries contributing to the T2K experiment. Within this broad collaboration Warwick has made some important and significant contributions towards construction, quality assurance, calibration hardware and software analysis.
The Near Detectors
Downstream from the target (280m) lie T2K's two near detectors: INGRID and ND280.
ND280 is a hybrid detector, situated off the beam axis, which will be responsible both for measuring the initial neutrino flux from the beam and for making neutrino-nucleon cross-section measurments (essential for predicting the expected flux at the far detector). It is built within the magent originally used in the famous *UA1 experiment.
*The UA1 high energy physics experiment ran at CERN from 1981 until 1993 on the SPS collider. The discovery of the W and Z bosons by this experiment and UA2 in 1982 led to the Nobel Prize for physics being awarded to Carlo Rubbia and Simon van der Meer in 1984. It was named as the first experiment in the CERN "Underground Area", i.e. located underground outside of the two main CERN sites at an interaction point on the underground SPS accelerator which was modified at the same time to convert it into a collider.
The central part of the detector, the "basket", contains multiple tracking modules. The most upstream of these is the Pi-Zero Detector (P0D): X-Y layers of triangular scintillator bars are seperated by either lead sheets or target volumes. These target volumes can be filled/emptied with water to provide a target comparable to that at the far-detector enabling cross-sections to determine the interaction rate at the far-detector. The cross-section for neutral pion production in water is of particular importance to the experiment since this represents the largest background for νe appearance at Super-K. With this measurement in mind, the X and Y scintillator planes are separated by a lead foil to encourage photon conversion.
The T2K ND280 neutrino detector is housed in the bottom of the Neutrino monitor pit at the Japan Proton Accelerator Complex (JPARC) in Tokai, Japan. The video of the neutrino detector was taken from the top of the pit. The detector (silver sections in the center of the pit) is observeable with the magnet (red) open during the installation of the neutrino detectors. The neutrino beam produced by the JPARC accelerator will move from right to left in this video.
INGRID is beam monitoring and profiling detector which consists of seven vertical and seven horizontal modules which combined form a cross centred on the beam axis. Each module is constructed of layers of iron and scintillator, which are read out using the same fibres, photosensors and electronics as the ND280 ECals. It is placed upstream of the ND280.
The current theory of particle physics, known as the Standard Model, includes 12 particles which make up matter (the physical contents of the Universe). Of these 6 are quarks: they combine to form particles such as protons and neutrons, which in turn make up the atomic nuclei found in the periodic table. Then there are the 3 leptons: a family containing the electron, which amongst other things is responsible for electricity, and two identical but heavier particles known as the muon (μ) and tau (τ). Together, leptons and quarks form all the matter which we see around us.
Dim lights Embed Embed this video on your siteThis is a short video of the top of the T2K ND280 detector that will detect neutrinos created in the JPARC accelerator in Japan and are aimed at the Super Kamiokande detector. The detector magnet is open and the covers are removed so the electronics can be seen in portions of the top.
You may be wondering how, if neutrinos hardly interact with matter, we can see them in particle physics experiments.
Dim lights Embed Embed this video on your siteThe T2K long baseline neutrino experiment in Japan includes a sophisticated near detector, ND280, with scintillator detectors and time projection chambers. These detectors are supported in a basket to be enclosed by a large magnet originally built for the UA1 experiment. This video shows the installation of the basket support structure on May 19, 2009.
Neutrinos were first postulated by Wolfgang Pauli in 1930 and first detected in 1956 by Reines and Cowan (a feat for which they received the 1995 Nobel Prize). However it was in the late 1960's that they became the focus of serious research. Theorists modelling how nuclear fusion worked in the Sun had made very specific predictions about the number of electron neutrinos being produced, but experiments designed to measure those neutrinos consistently found around a third of the number they were expecting. Likewise, measurements of muon neutrinos, from cosmic ray collisions in the upper atmosphere, also showed a reduction in the number compared with that predicted.
Solar neutrinos: νe → νμ , ντ
The next step is to look for oscillations from muon neutrinos to electron neutrinos. Measurement of this behaviour would not only complete our picture of how oscillations take place but would also make it possible to investigate how neutrinos can contribute to one of the biggest mysteries in physics: the matter - anti-matter asymmetry of the Universe.
Dim lights Embed Embed this video on your siteT2K Horn 2 installation. Tokai-mura, July 10, 2009