A Deuteron Polarimeter for an EDM Search

1
A Deuteron Polarimeter for an EDM Search E.J.
Stephenson, G. Noid Indiana University
Cyclotron Facility C.J.G. Onderwater KVI
Gorningen, the Netherlands
- for the Storage Ring EDM Collaboration
The observation of an electric dipole moment
aligned along the spin axis of a particle would
violate time reversal. At a level within
experimental reach, it would be evidence for
mechanisms not now a part of the Standard Model.
SUSY model predictions are within reach, and
connect to other issues (matter asymmetry of the
universe).
The signal for an EDM is the precession of a
particles spin in response to an imposed, and
strong, electric field.
We propose to conduct such a search on a charged
particle using the electric field induces as a
particle circulates in a ring. The case to be
considered here is the deuteron.
2
Using a storage ring to search for an electric
dipole moment on a charged, polarized particle
Method 2 Oscillate the particle velocity
(synchrotron oscillation) in sync with the spin
precession so that EDM precession does not cancel
but accumulates on each turn.
Method 1 Use a radial electric field to change
the orbit radius without changing the magnetic
field and select the circumference that
freezes the spin.
Every bending magnet has an outward
radial electric field 3.5 MV/m
This weakens the radial Lorentz force and
enlarges the ring.
The deuterons anomalous magnetic moment is
-0.143. Now it has enough time to complete one
rotation with every revolution.
Consider the deuteron
SIGNAL
the spin to precess if the particle has and EDM.
Radial field at particle from v x B causes
Deuteron is captured into orbit by ring magnets.
momentum 0.7 GeV/c (126 MeV) B field 0.21
T radius 13.3 m
Vertical polarization rises with time.
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EDM polarimeter

• IDEA
• make thick target defining aperture
• scatter into it with thin target

lost to ring acceptance (2 kb)
40 MeV 10-5 1 GeV 6x10-4
cross section
(POMME efficiency several percent)
detector system
Coulomb
useful for spin (17 mb)
nuclear
U
defining aperture primary target
angle
L
extraction target - gas
R
D
R
?
D
Target could be Ar gas (higher Z).
Detector is far enough away that
doughnut illumination is not an acceptance
issue ? lt R.
Hole is large compared to beam. Every- thing
that goes through hole stays in the ring. (It
may take several orbits to stop scattered particle
.)
Events must imbed far enough from hole to not
multiple scatter out of primary target, thus ? ltlt
D. ?, which is a large fraction of the deuteron
range, sets scale for polarimeter.
Target extracts by Coulomb scattering
deuterons onto thick main target. Theres not
enough good events here to warrant detectors.
Primary target may need to be iris to allow
adjustment of position and inner radius. It may
also need to be removed during injection.
4
Rainbow scattering
A strong spin-orbit force separates the deuteron
spin projections (perpendicular to scattering
plane) into three very different cross sections.
In this scheme, the analyzing powers can be
calculated as
5
Basic Plan
beam
126 MeV
55 MeV
lower limit without hitting negative
analyzing powers
Take data at two energies 80 and 110 MeV.
CH2 or C target
(typical it11 0.44)
points chosen as polarization reference
A y
KVI in-beam polarimeter with 8 detector arms
Hatanaka, NP A 426, 77 (84)
Sekiguchi, PR C 65, 034003 (02)
all other points AHEAD polarimeter, Witala FBS
15, 67 (93)
6
beam
plastic ?E
NaI (stopping detector)
Temporary detector arrangement using the
horizontal arm position of the KVI in-beam
polarimeter
7
selected particle spectra
Sample spectra (110 MeV, 27)
particle identification
2 4.44
g.s.
triton
?E energy
deuteron
deuteron
proton
NaI energy
breakup
particle identification linearized
3.85 5/2
proton
deuteron
proton
triton
energy of particle emitted from target (MeV)
8
Deuteron elastic scattering angular distributions
A y
80 MeV
70 MeV (data from Kato)
FOM s Ay2
cross section (mb/sr)
goes as 1/error2
figure of merit (mb/sr)
110 MeV
laboratory scattering angle (deg)
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Deuteron elastic scattering angular distributions
A y
80 MeV
Original concept based polarimeter on the use of
this peak in the figure of merit angular dist.
70 MeV (data from Kato)
cross section (mb/sr)
figure of merit (mb/sr)
110 MeV
laboratory scattering angle (deg)
10
Deuteron elastic scattering angular distributions
A y
At the higher energy, another lobe in the
analyzing power is getting larger, making
possible greater efficiency at smaller angles.
This needs more investigation and data.
80 MeV
70 MeV (data from Kato)
cross section (mb/sr)
figure of merit (mb/sr)
110 MeV
laboratory scattering angle (deg)
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Deuterons and protons from the continuum
34.5
s (mb/sr/5 MeV)
s (mb/sr/4 MeV)
The positive analyzing powers from the
spin- orbit interaction extend into the continuum
for both deuterons and protons (neutron transfer
or breakup).
A y
A y
The design should include some of these regions.
FOM
FOM
12
Status
It seems possible to build a deuteron polarimeter
with broad particle acceptance, an efficiency of
about 1, and an analyzing power of Ay 0.3 to
0.4 .
The first round of data on carbon show the
outlines of what should be in the acceptance of
the instrument. More data is needed for forward
angle elastic at the higher energies.
(Meanwhile, studies of the ring design are
underway.)