Speaker
John Behr
(TRIUMF)
Description
I will discuss backgrounds and possible scenarios using TRIUMF's existing
e-linac to produce and detect MeV-mass particles, assuming the previous
talks and somewhat dated PPAC submission
(daqshare.triumf.ca/~trinat/darkPPAC.pdf).
The recent improved measurement of the fine-structure constant predicts a
different electron g-2 compared to experiment, motivating experimentally
accessible MeV-mass bosons.
Assuming zero background-- essential for sensitivity to increase linearly
with counting time-- the highest-energy electron beam will always win, as
production scales like bremsstrahlung. Yet e-linac experiment backgrounds
have two natural plateaus: pion threshold and (gamma,neutron) threshold.
Thermal neutrons can produce 10 MeV single-gamma events distinguishable
from exotic particles only by direction, so experiments at our low e-linac
energies must face this issue both from the cyclotron (the BGO array at
DRAGON sees those) and the e-linac .
Neutron damage of electronics in the ISAC mass separator room may prove
problematic for that location.
This motivates a scenario that disturbs neither cyclotron beamtime nor
e-linac production of neutron rich nuclei:
two pulsed lasers on a photocathode to independently fill the half of the
buckets left unused by ARIEL;
Doug Storey's resonant chopper after either the 10 MeV injector (below
(gamma,n) threshold on many materials) or the full 35 MeV;
a high-Z detector technology with 10's of psec timing resolution to
utilize the 10 psec/1.5 nsec duty cycle for Mev-mass TOF and suppress
backgrounds;
a detector after 1.5 meters of tungsten-steel shielding, either in the
air in the e-hall to avoid scattered neutrons from the floor or burrowed
west to suppress cosmic rays one order. The 10 MeV version appears
compatabile with a THz radiation source (see workshop July 5)
