Polarimeter for dEDM experiment

1
Polarimeter for dEDM experiment

• G. Venanzoni
• Laboratori Nazionali di Frascati
• for the dEDM collaboration

Workshop on Flavour in the era of LHC Cern 9-11
Oct 2006
2
A typical experimental layout contains
(f0)
y
left detector
f
left and right detectors useful for vector
polarization
x
?
z
beam direction
ß
target
right detector
scattering plane
A polarization of the beam (p) causes a
difference in the rates for scattering to the
left compared to the right.
For protons (S1/2)
analyzing power (determined by nuclear effects
in scattering) governs spin sensitivity
vertical component of the polarization
unpolarized cross section (determined by
nuclear effects in scattering) governs efficiency
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A typical experimental layout contains
(f0)
y
left detector
f
left and right detectors useful for vector
polarization
x
?
z
beam direction
ß
target
right detector
scattering plane
A polarization of the beam (p) causes a
difference in the rates for scattering to the
left compared to the right.
For deuterons (S1)
unpolarized cross section (determined by
nuclear effects in scattering) governs efficiency
analyzing power (determined by nuclear effects
in scattering) governs spin sensitivity
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Left-Right and Down-Up Asymmetries

• In dEDM experiment we are looking for an increase
  with time of the vertical polarization (pV,y),
  over the length of a beam store
• By making measurement at f1 and f2 f1p , we
  look at the Left-Right (LR) asymmetry, which is
  sensitive to pV,Y
• In the same way, the Down-Up (DU) asymmetry is
  sensitive to the component in the plane pV,x
• LR Asymmetry due to tensor polarization will have
  other distinctive signature (phase and
  oscillation), and is not expected to increase
  with time

eLR will increase with time
eDU will oscillate with g-2 frequency
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Functional polarimeter elements (must run
continuously)
Up
Iron absorber
Left
Segmented scintillator
Carbon target
Right
Angle range 4 - 15
Carbon target is small.
Down
Left-right asymmetry carries EDM information.

• Two possibilities for the polarimeter
• extract using jet in ring onto annular target
• tune beam onto annular target
• slow extraction into second beam

Down-up asymmetry carries information on g-2
precession.
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Layout of the Polarimeter (if it were situated on
the ring)
detector system
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.
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Polarimeter optimization ingredients

• sunp(b) (largest at forward angle)
• Vector analyzing power iT11(b) (usually increases
  at larger angles)
• The solution is often a compromise between
  sunp(b) and iT11(b). Its common to define a
  figure of merit (FOM)

d error in the measurement of the pV components
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Deuteron data
Current design pd 1.0 -1.5 GeV/c
? Td 250 525 MeV

• Data
• POMME at Laboratoire National Saturne (France)
  (B.Bonin et al. (1990), V.P. Ladygin et al.
  (1998) )
• Td in (0.175 1.8) GeV ? in
  4, 15 per Td lt 300 MeV
• 2, 20 per Td gt 300 MeV
• SMART at RIKEN (Japan) (Y. Satou et al.)
  Td in (200 300) MeV

Previous design pd 0.7
GeV/c ? Td 126 MeV

• Data
• S. Kato et al., NIM A 238 (1985) 453-462
• 
  Td in (35 70) MeV ? in 30, 65

Data also from Test beam at KVI (Groningen, NL)
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Data from Pomme polarimeter at energies gt 200 MeV
iT11(b)
sunp(b)
efficiency ()
average iT11
momentum (GeV/c)
Work here.
An iron absorber was placed to remove non elastic
particles from the scattered flux. At about 700
MeV it loses its effectiveness and iT11 starts
to decline.
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Data from 270-MeV deuteron elastic scattering
RIKEN
Two possibilities
Optimize here favor larger analyzing
power, leverage against systematics
700 MeV
Optimize here favor statistical precision
At this energy (p1 GeV/c) these two choices lead
to different angle covarage. But as momentum
rises FOM and analyzing power peak together.
700 MeV
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Momentum dependence of FOM, iT11 and efficiency
The SOLID dots and lines follow the FORWARD peak
in the FOM curve.
The open/dashed dots and lines follow the
analyzing power peak (where there is enough data
to use).
The AVERAGES shown here integrate over some angle
range that covers the relevant feature in FOM or
iT11.
Satou gets even larger analyzing powers by
cutting out more protons and losing efficiency.
The FOM is down about 30 from the open dots.
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Polarimeter statistical error
p 1.5 GeV/c
At d10-29e?cm
0.36x0.6
5.710-10 rad/s
polarimeter efficiency 2
effective beam use fraction 0.5
particles per fill 1012
run time 6107 s
spin coherence time 1000 s
2 years to arrive to sd 10-29e?cm
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Polarimeter systematic errors (examples of
issues)
(What other sources arise for a left/right
asymmetry?)
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Displacement / angle errors
detectors
?
x
?
angle shift
position shift
Remedy measure on both sides (L/R)
flip initial spin opposite sign for EDM
accumulation
left/right efficiency differences cancel
spin
detector
/ luminosity differences cancel
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Errors that are second-order in ? and upp-
A is the analyzing power q is the difference in
the mean acceptance angle of the detector btw the
a polarization states. For LR asymmetry q is
the angular shift of the detector/target.
Example With ?max ?10-7 and requiring de/e lt
10-5 ? qlt0.02o
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Polarimeter systematic errors (contd)
2
Polarimeter rotation
U
L
R
We are helped by the time dependence of eDU and
f-dependence in analysis of segmented detector.
target
D
f
3
Parity violation
Effects start to appear at e lt 10-6 associated
with px.
We are helped by time dependence.
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Polarimeter systematic errors (contd)
Tensor polarization requires and equal population
of m1 and m-1 deuterons that is different from
m0.
4
For spin 1, tensor contributions (t21)
detectors
The left/right asymmetries oscillate as the spin
rotates in the ring plane. They do not grow with
time. The effect appears at 10-4 with 1 tensor
contamination of the polarized beam.
The left/right asymmetry is maximal along 45 but
reverses sign in the perpendicular direction.
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Conclusion and outlook

• Considerable effort in the past to develop a set
  of data on which to base the design for the
  polarimeter (at p0.7 GeV/c)
• At the current design (1.0-1.5 GeV/c) we need to
  define/study
• extraction of the beam
• operating momentum of the ring
• sensitivity of the polarimeter to different
  error sources
• thickness of the target
• segmentation of the detector
• Readout and DAQ
• Test beam-polarimeter interactions (at COSY), in
  the case we decide to have the polarimeter in the
  ring
• Prepare (and test) prototype