The physics of elementary particles is explored by colliding particles together and observing the results. Feynman likened this to colliding swiss watches, picking up the pieces and trying to figure how they work. When colliding or scattering particles there are several options: (1) the accelerated particle can be slammed into a collection of stationary particles, (2) particles of equal mass can be collided 'head-on' and (3) unequal mass particles can still be collided 'head-on' but the resulting debris then is no longer symmetrically distributed. This latter case is the method of study at the H1 experiment at Hera, the German electron proton collider in Hamburg. Equal mass collider experiments were done at the electron positron colliders at the Stanford Linear Accelerator Center and at KeK in Tsokuba, Japan. Our other colleagues here at UC Davis are generally pursuing colliders.

Professor Yager's research follows option (1), difficult but rewarding. The old fashioned way of taking the accelerated beam into a 'fixed' target is wasteful and does not gain the relativistic energy saving of the collider experiments. There are however off-setting advantages. Produced particles will travel further allowing detailed study of their lifetimes and decay characteristics in spite of extremely short mean lives. The choice of projectile is far greater - we have done fixed target experiments with Kaons, pions, protons, anti-protons, photons and a proposal is being considered to use neutrinos. These experiments are generally more flexible, allowing the detectors to be changed, re-arranged or replaced to explore un-anticipated areas of physics. Currently, our fixed target research is carried out at the Fermi National Accelerator Laboratory. A recently completed experiment first used a proton beam into a 'live' target composed of photographic emulsion followed by an array of electronic detectors. Data recorded electronically were examined to find where to look in the photographic emulsion for rare and interesting collisions. Particles containing a charm-quark produced in association with anti-charm quark were studied with virtually no background due to the visual information. A second experiment followed this with some modifications to the detector and a change in the beam particle to a negative pion. It was expected that with the pion, the production of beauty particles would occur at a significant enough level to study their production and decay. This expectation was born out. We were the first to find nine pairs of hadronically produced beauty!

Another interesting experiment uses 860 GeV protons to produce pi-zeros which decay immediately to a pair of photons. Other particles (charged) are swept away from the forward direction with magnets. The photons then impinge on a converter making electrons and positrons. In this way (the hard way!) we make an electron beam. It is the only way to get the high energy we want. The electrons and positrons are transported to the experiment, pass through a radiator and are swept aside. The result of their radiator experience is to 'shake-off' a high energy photon which is now used as a projectile to study photo-production of charm. This experiment is currently the world leader in fixed target charm production and a new experiment is approved to increase our charm sample by an order of magnitude using much the same apparatus. We expect to be building our part of the detector in 1993-1994 and taking data in 1995. There will be at least five more years of good fun and good physics!

We have proposed an experiment, now under favorable consideration at the Fermi Laboratory, to study the elusive neutrino and the fundamental question of whether or not the neutrinos have mass. If they do, they can 'oscillate', that is one type of neutrino will transmogrify into a second type as it travels, in much the same way that the celebrated neutral Kaon system behaves. A chance to find this marvelous behavior in the neutrino is possibly the most intriguing aspect of particle physics today.

Memberships
for
Philip M. Yager

  • Phi Beta Kappa
  • Sigma Xi
  • American Physical Society
  • AAAS


    • E-mail yager@physics.ucdavis.edu

    Back to people page.