Moshe Katz-Hyman with Dan Akerib

Detection and Veto of High Energy Neutrons in the CDMS II Experiment

The cryogenic detectors used in the CDMS (Cryogenic Dark Matter Search) experiment are a novel type of device that can distinguish between nuclear and electron recoils.  The detector accomplishes this by independently measuring both the ionization and phonon energies deposited by the recoils. This method of detection allows photons, electrons, and other charged particles to be distinguished from WIMPs, or Weakly Interacting Massive Particles, the type of dark matter we are searching for. However, neutrons are less distinguishable from WIMPs on an event by event basis because both are massive, uncharged particles which have a large phonon energy to ionization energy ratio.  Great steps have been taken to shield the experiment from extraneous backgrounds.  The CDMS II Experiment is located in the Soudan mine in Minnesota, which provides shielding from direct cosmic rays and other forms of radiation.  Low energy neutrons can be shielded effectively from the detectors by hydrogen rich materials, such as polyethylene. High energy neutrons cannot be effectively shielded because the cross-section and energy deposition is too low in these materials. It is likely that the chief source of high energy neutrons is from hadron showers produced in the surrounding rock by cosmic ray muons. A possible method for detecting these showers and thereby allowing a veto of these high energy neutron events is the instrumentation of the surrounding rock.  By placing an array of streamer tubes in the walls and ceiling of the the cave, it should be possible to detect the charged particles created in the hadron showers.  In this experiment, Monte Carlo simulations of the CDMS II site at the Soudan site will be set up and cross-checked against data taken from the Stanford Underground Facility to confirm their reliability. Simulations will be performed to determine the feasibility of instrumenting the rock using different lattice spacings and pattern-detection algorithms.  If these studies result in a practical design, then prototype tubes will be built and a field test, possibly using Lake Erie as the test site, will be carried out.