John Martin

Professor and IPP Principal Research Scientist

Research Interests

Currently I am working on 2 particle physics experiments, ZEUS in Germany and T2K in Japan. (Previously I was involved with many experiments at the Rutherford Laboratory, Argonne National Laboratory and Fermilab, as well as in test beams at CERN, studying the interactions of pions, photons and neutrinos with protons.)

ZEUS: My interest for many years has been deep inelastic lepton-nucleon scattering, an important process for revealing the structure of the proton and understanding aspects of the gauge theories of particle physics at the quark/lepton level. The latest generation of such experiments has been performed at HERA, a unique high energy electron-proton collider and the world's highest energy "electron microscope". HERA was built by several countries including Canada at the DESY laboratory in Hamburg, and ran from 1992 to 2007. The centre of mass collision energy was 320 GeV, giving a view into the quark and gluon sub-structure of the proton at a distance scale approaching 10-18 cm. The proton is held together by the strong interaction, the theory of which is called quantum chromodynamics or QCD, and HERA has provided a fertile laboratory for critical tests of QCD. Also at this previously unattainable tiny distance scale, hints of the new physics necessary to resolve problems raised by the current standard model of particle physics were anticipated. However, so far the standard model reigns supreme (apart from neutrino oscillation, see T2K below), and the LHC at CERN is taking up the challenge to find new physics at even smaller distance scales for the next decade or two.

Our Canadian group from from McGill, York and Toronto collaborated with other physicists from 12 countries on the design, construction and operation of a huge detector called ZEUS to observe the ep interactions. We designed and built a major part of the 300 tonne high precision calorimeter necessary to measure the energy and direction of the jets of particles emerging along the directions of the quarks and gluons scattered out of the proton by the electron. We also provided the third and highest level of the complex trigger system, which separated interesting physics events from a much greater number of background collisions.

In 1995 we constructed an important upgrade to the ZEUS detector, a 10 tonne calorimeter to detect forward scattered neutrons from the ep collisions. This project was instigated by Dr. G. Levman in our Toronto group and has allowed us to probe the structure of the pion. A useful mental picture to understand this idea is that the proton occasionally "mutates" into a neutron and a positively charged pion. The electron then scatters from the pion rather than the original proton.

For the final years of operation HERA was reconfigured to increase the collision rate by a factor of 5 and to provide longitudinal polarization of the electron beam. ZEUS was also upgraded; we designed and built a new third level trigger system, and collaborated with York University in building and commissioning new tracking detectors to improve particle tracking in the forward region of the experiment. We are currently finishing the analysis of the large data-set from the final years in order to provide the most precise understanding possible of the internal structure of the proton.

T2K: I am also a member of the new T2K neutrino oscillation experiment. The most exciting discovery in particle physics in recent years, by the Super-Kamiokande (SK) experiment in Japan and the SNO experiment here in Canada, has been that neutrinos oscillate or transform from one of the three types (electron-, muon- and tau-neutrinos) to another as they travel. This quantum-mechanical process requires that the neutrinos have mass, a new feature of physics "beyond" the Standard Model of particle physics, in which neutrinos are massless particles.

The T2K experiment will measure the most important remaining parameter of this new neutrino oscillation physics, which involves the transition from muon-neutrinos to electron-neutrinos. The experiment, which started taking data early in 2010, directs a beam of muon-neutrinos from the J-PARC laboratory to SK, a distance of 295 km, where we search for the appearance of electron-neutrinos. If the strength of this transition is non-zero (we know already that it is quite small), T2K will then be able to measure a possible violation of matter - antimatter symmetry in the neutrino sector, by comparing oscillation results from neutrino and anti-neutrino beams. This is vitally important for understanding the deep mystery how the universe became dominated by matter over anti-matter shortly after the BIG BANG. (Fortunately this happened, or we matter creatures wouldn't be here to cogitate upon such profound questions...!)

The large earthquake in March, 2011, interrupted the T2K data-taking and caused some damage to the accelerator complex and the experiment. However, recovery is well underway and neutrino beam operations are expected to resume in December, 2011. The Canadian group on T2K involves physicists from TRIUMF and six universities, Victoria, UBC, Regina, Toronto, York and Montreal. We have designed and built many important parts of the neutrino beam monitoring systems and the "near" detector at 280m from the neutrino production target, which measures the flux and direction of the neutrinos before they have a chance to oscillate. During 2009 we installed and commissioned these detectors in Japan and the first neutrino events were seen on November 22, 2009.

June 2011: T2K released a PRL paper on electron-neutrino appearance based on the data taken so far (see Selected publications). Six events are seen, whereas only 1.5 are expected from background. This gives an exciting indication that the transition strength from muon-neutrino to electron-neutrino is non-zero. This new result is based on only 2 percent of the planned exposure, and more data will be needed to confirm. For more details see this News Article .