Making a neutrino beam The neutrinos detected in the MINOS experiment are produced in the Neutrinos at the Main Injector (NuMI) beam line at Fermi National Accelerator Laboratory. First, energetic protons are fired into a graphite target, creating pions. These pions are focused into a beam using magnetic horns. The pions then decay into muons and neutrinos. Undecayed pions and muons are stopped in rock absorbers, and the neutrinos stream through the rock towards the detectors. Main Injector Neutrino Oscillation Search MINOS is a neutrino experiment poised to provide a precision measurement of the parameters governing the mixing among neutrino flavors. One of the fundamental particles of nature, the neutrino comes in 3 “flavors”, called the electron neutrino, the muon neutrino, and the tau neutrino. In the Standard Model of particle physics, each of these neutrinos is masseless; however, new developments indicate that these particles do in fact have mass and each has a different mass. As a consequence of the difference in masses, neutrinos will change flavor as they propagate, a phenomenon called neutrino oscillation. The probability that a muon neutrino changes into a tau neutrino is dependent on the energy of the neutrino and the distance it travels. For a fixed propagation distance, the probability of changing flavor swings up and down as a function of neutrino energy, hence the name neutrino oscillation. By measuring the probability that a neutrino will change flavor at different energies, MINOS will determine the two parameters in the oscillation probability, namely the difference in mass squared between two neutrinos, Δ m 2, and the mixing amplitude, sin 2 (2 θ ). Detector Technology Both MINOS detectors are magnetized calorimeters, made of sheets of steel, with arrays of plastic scintillator strips sandwiched in between. Neutrinos interact in the steel, producing many daughter particles. These resulting particles traverse the scintillator and produce light. This light is collected on fibers embedded in the scintillator, then routed out of the detector via fiber optics where it is incident on photomultiplier tubes. The signals from the phototube indicate how much light was produced and where it was produced. Multi-anode PMT Extruded PS scint. 4.1 x 1 cm WLS fiber Clear Fiber cables 2.54 cm Fe U V planes +/ cm Scintillator Steel Veto Shield Me PMT Boxes The Far Detector Beam Courtesy J. Meyer The MINOS Far Detector is located in the Soudan Underground Laboratory in northern Minnesota. Located half a mile underground to shield it from cosmic rays, the Far Detector is 8 m tall and nearly 30 m long. Weighing in at 5400 tons, the Far Detector has almost half the mass of the HMS Belfast. The detector was brought down from the surface in pieces, then assembled underground; like building a ship in a bottle. The MINOS Near Detector is located at Fermilab, 1 km downstream of the neutrino production target. The Near Detector will record billions of neutrino interactions per year. The picture below shows the traces of several neutrino interactions in the near detector. Patricia Vahle, University College London Expected energy distribution, no oscillations Expected energy distribution, with oscillations Position of dip- Δ m 2 Depth of dip-sin 2 (2 θ ) Dip-signature of oscillations ν μ survival probability, Δ m 2 =0.002 eV 2 Energy (GeV) The Elusive Neutrino Neutrinos have no charge and interact with other particles only weakly; in fact, a neutrino can travel through one light year of lead without interacting. To study neutrino properties, physicists need a lot of neutrinos and a big detector. The MINOS Detectors MINOS measures the properties of neutrinos in two detectors, first, in the Near Detector, close to the neutrino production point and again in the Far Detector, 735 km away. One then compares the measurements taken at the two detectors to see how the neutrinos have changed. CalDet To learn how the big MINOS detectors respond to interactions of different particles with different energies, a small version of the detectors was built and tested in a beam of particles at CERN. While too small to efficiently detect neutrinos, the Calibration Detector, or CalDet, allowed for the study of pions, protons, electrons and muons in a MINOS-like detector. Why study neutrinos? Neutrinos are a fundamental constituent of matter, perhaps the most abundant particle in the universe, yet our understanding of the properties of the neutrino lags far behind our knowledge of the other elementary particles. Non-zero neutrino mass gives an indication of physics beyond the Standard Model of particle physics and has ramifications on the evolution of the universe. Beyond the questions surrounding inner workings of our cosmos, the neutrino’s power of penetration opens an alternate window into the furthest reaches of our universe, our sun, and our earth. Collaborators MINOS is an international collaboration made up of 175 physicists in 32 institutions across 6 nations Coil Hole Scint. Modules PMT+FEE Racks Beam The Near Detector Courtesy Fermilab Visual Media Services A front end view of a beam neutrino in the Far Detector. The long curving track is the trail left by a muon, bending in the magnetic field. In the absence of oscillations, about 1 beam neutrino will interact in the Far detector every 4 hours NuMI Target NuMI Focusing Horn Neutrino interactions come in two types, charged current (CC) and neutral current (NC). A muon neutrino, CC interaction, is characterized by a the presences of a muon along with the remains of a broken nucleus. The muon shows up in the detector as a track, and the remnant of the nucleus shows up as a shower of hits near the beginning of the muon track. The energy of the muon is determined either by how far it travels in the detector or by how much it bends in the magnetic field, while the shower energy is determined from the amount of light produced in the scintillator. The energy of the original neutrino is the sum of the muon and shower energy. The signature of an NC interaction is the presence of a shower without the muon. The primary MINOS measurement amounts to looking for a deficit of muon neutrino CC interactions in the Far Detector relative to what is measured in the Near Detector. What do neutrinos look like? ν μ CC candidate E=3.7 GeV NC candidate E=4.5 GeV The NEMO Detector Other Exciting HEP Projects at UCL While MINOS, and other oscillation experiments, have sensitivity to differences in neutrino masses 100,000 times smaller than the electron mass, they only measure differences in masses, not the actual mass of the neutrino. Other experiments, such as NEMO, and the future SuperNEMO, both being pursued at UCL, aim to measure the absolute value of the neutrino mass. By 2008 NEMO will achieve sensitivy to neutrino masses down to 0.2eV (that’s about grams). Another neutrino project at UCL, ACORNE, proposes to detect ultra-high energy cosmic neutrinos acoustically. Such neutrinos deposit so much energy in the target medium that they actually make audible clicks when they hit. The fact that neutrinos only interact weakly means they travel through the universe almost undisturbed. If these ultra-high energy neutrinos can be detected, they could provide a unique insight into cosmology and astrophysics. Beyond neutrino physics, UCL physicists play a large role in the CDF experiment. Ten years ago, the CDF+D0 experiments discovered the top quark, the heaviest of the predicted quarks. Still taking data at the world’s highest energy collider, CDF is making precision measurements of the top quark mass as well as the W boson mass and cross sections. Such precision measurements provide valuable tests of the Standard Model and constrain new physics models beyond. CDF continues to search for the Higgs particle and strives to provide insight on why the universe is dominated by matter rather than antimatter. UCL is also involved in another on-going experiment, studying the particle reactions in the ZEUS detector. Using the high energy electron-proton beam at the HERA accelerator facility, ZEUS measures electroweak phenomena and extends our understanding of the strong force Looking to the future, UCL is an active participant in ATLAS, one of the two general purpose detectors that will record the collisions of protons at the Large Hadron Collider at CERN. While the neutrino experiments try to measure the neutrino mass, ATLAS will probe the very origin of mass by searching for the Higgs Boson. When the LHC starts running in 2007, ATLAS will shed light on the fundamental questions of particle physics, including the existence of extra dimensions, supersymmetry, and the nature of dark matter. Planning for the longer term, UCL physicists are also involved in the design of next generation accelerators and detectors such as the International Linear Collider. 2 GeV electron 2 GeV pion 2 GeV proton 2 GeV muon ZEUS ILC ATLAS The CDF Detector