High energy polarized beams from hyperon decays Page: 4 of 6
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dimension. The beam we are building is mirror symmetric about an
-AO
intermediate focus with a transfer matrix of (O-l) at that focus.
A
In order for the global cancellation of precession in the quad-
rupoles to occur, the spin directions entering one set of quadru-
poles must be the same as the directions exiting the preceding set.
Precessions by bends must cancel between quadrupole sets. Net bends
between quadrupoles can lead to depolarization because rotations
about orthogonal axes do not commute.
SCALING
If we are building a beamline to use transverse mode at a parti-
cular momentum, we can scale the beam length to match the lambda
decay length. The spot size for tagging will be a constant, roughly
3. cm across, depending on the specifics. Once we have this scaling
in length and approximately constant p^ distribution for lambdas, we
can use the same quadrupoles and transport dipoles at any momentum
(e.g. 8.9 GeV and 16 TeV). This ignores the facts that magnet
lengths are a fraction of the beam length at low momentum and that
we might not want a single-momentum beam.
The sweeping magnets do not scale in the same way at all. If we
assume the Fermilab scheme and say that the primary beam must be
bent to an angle greater than lambda production angles in a distance
less than a lambda decay length, the field required in the sweeper
goes roughly as
B
sweep
(kg)
1000
(GeV) • X2p
sec
in this example we need 1 kg at the SSC and 1500 kg at 8.9 GeV. For
a polarized 'p source for a storage ring, we might not sweep but use
a careful acceptance at the image of the virtual spot to avoid the
primary beam and limit the source emittance. (The source emittance
is still too large for existing accumulators, approximately IOOit MM-
MR vs. 20ir MM-MR.)
POLARIMETERS
We are developing two new kinds of polarimeters for the Fermilab
beam. One based on the Primakoff effect®”® (Fig* 4) and one based
Q
on the Coulomb-nuclear interference. The analyzing power foT pure-
ly hadronic elastic scattering at small t is too small to be useful.
Both of the new polarimeters use interactions at t * 10“', and
require precise reconstruction of beam and outgoing tracks. The
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Underwood, D.G. High energy polarized beams from hyperon decays, article, January 1, 1986; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1069293/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.