The A2 recoil nucleon polarimeter Daniel Watts University of Edinburgh, UK.
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Transcript of The A2 recoil nucleon polarimeter Daniel Watts University of Edinburgh, UK.
The A2 recoil nucleon polarimeter
Daniel Watts
University of Edinburgh, UK
Why nucleon polarimetry?
Would add a unique capability to the MAMI setup – Valuable compliment to circularly and linearly polarised photon beams and polarised target systems.
Observables from recoil group will allow MAMI to make the first complete measurement in pion/eta photoproduction
(Nucleon polarimetry proposal approved by last MAMI-ELSA PAC)
Double-polarisation in pseudo-scalar meson photoproduction
Polarisation of
target recoil
Observable
Nucleon Scattering and polarisation
Analysing power of scatterer
Polar angle distributionfor unpolarised nucleons
x and y (transverse) components of nucleon polarisation
Number of nucleons scattered In the direction
n() =no(){1+A()[Pycos()–Pxsin()]
Simulate p()p channel – realistic beam/target & detector parameters
New routines written for GEANT3 – introduced modulation of for hadronic interactions (take A=1)
All other processes left in. e.g. coulomb scattering, nuclear de-excitations …
Explore possible designs for polarimeter
New GEANT simulations incorporating polarimetry
0
p/
p
x p defines plane
Reconstructed Phi in incident nucleon frame (deg)
E(MeV)
A =
(+
- - ) /
(++
- )
Design 1: Graphite at CB exit
~32% reduction in Apol ~ 2.4% (E=0.3-0.6 GeV, scat>20)
(cm) > 130
Graphitescatterer
TAPS
Target
CB skirt
Analyser efficiency(7cm graphite)
Yie
ld (
a.u
)
COM (Deg)
Yie
ld
(a.u
)
Design 2: Graphite in CB tunnel
~45% reduction in Apol ~ 3% (E=0.3-0.6 GeV, scat>15)
(cm) > 130
Graphitescatterer
Target
Analyser efficiency(7cm graphite)
Reconstructed Phi in incident nucleon frame (deg)
A =
(+
-- ) /
(+-
- ) Yie
ld (
a.u
)
Yie
ld (
a.u
)
E(MeV)COM (Deg)
Design 3: Graphite Near Target
~46% reduction in Apol ~ 3 % (E=0.3-0.6GeV, scat>15)
Graphitescatterer
Target
Analyser efficiency(7cm graphite)
(cm) > 90
Reconstructed Phi in incident nucleon frame (deg)
A =
(+
-- ) /
(+-
- ) Yie
ld (
a.u
)
Yie
ld (
a.u
)
COM (Deg) E(MeV)
• ~35% dilution of analysing power
• Acceptance X%
• If proves worth can move more upstream to greatly increase acceptance
Design 4: Graphite Near Target+ subsequent CB detection!!
(cm) > 60o
~53% reduction in Apol ~ 2.6% (E=300-600 MeV, scat>20)
Graphitescatterer
Target
Analyser efficiency(7cm graphite)
Reconstructed Phi in incident nucleon frame (deg)
A =
(+
-- ) /
(+-
- )
Yie
ld (
a.u
)
Yie
ld (
a.u
)
COM (Deg) E(MeV)
Test polarimeter
• Polarimeter with adjustable thickness and hole diameter
• Will fit in “orange pipe” used in PID tests
• Polarimeter presently being machined in Edinburgh
• Ready for use in tests from late Oct
Tracker detector(s)
First polarimetry measurements on proton target do not need tracker – BUT tracker necessary for neutron target measurements (Fermi motion)
Need to finalise polarimeter design before can finalise tracker design – need test beam time
Tracker Possibilities - Si detectors on face(s) of graphite - Wire chambers - Scintillating fibre
Money already available – Edinburgh £120k GWU £50k
Also Mainz, UCLA , …
Conclusion
Simulations give good indication that we can start testing nucleon polarimeter (and getting first data!) now.
Test polarimeter module ready this month - need test beamtime with prototype to move the project forward
Forward angle tracker pre-requisite to allow neutron target measurements in the longer term
• ~35% dilution of analysing power
• Acceptance X%
• If proves worth can move more upstream to greatly increase acceptance
Reconstructed Phi in incident nucleon frame
Egamma (MeV)
A =
(+
-- ) /
(+-
- )
GraphiteCB tunnel
Design 4: Graphite Near Target+ subsequent CB detection!!
(cm) > 60
~50% reduction in Apol ~ X%
Reconstructed Phi in incident nucleon frame
Egamma (MeV)
A =
(+
-- ) /
(+-
- )
GraphiteCB tunnel
Design 1: Graphite at CB exit
~32% reduction in Apol ~ 2.4%
(cm) > 130
• ~35% dilution of analysing power
• Acceptance X%
• If proves worth can move more upstream to greatly increase acceptance
Reconstructed Phi in incident nucleon frame
Egamma (MeV)
A =
(+
-- ) /
(+-
- )
GraphiteCB tunnel
Design 3: Graphite Near Target
~46% reduction in Apol ~ X %
Reconstructed Phi in incident nucleon frame
Egamma (MeV)
A =
(+
-- ) /
(+-
- )
Design 2: Graphite in CB tunnel
GraphiteCB tunnel
~35% reduction in Apol ~ 3%
(cm) > 130
Nucleon polarimetry concept
Graphite sheet
TAPS
Crystal Ball
beam
Hydrogen target cell
Useful scattered eventSelect events with scattering angleslarger than ~10 degrees : arising from nuclear interaction
n() =no(){1+A()[Pycos()–Pxsin()]
Design 3 – 7cm Graphite 8cm from target
~30% dilution of analysing power
Acceptance X%
If proves worth can move more upstream to greatly increase acceptance
Reconstructed Phi in incident nucleon frame
Egamma (MeV)
A =
(+
-- ) /
(+-
- )
P
T
Previous experimental data – SAID database
Data for all CM breakup angles
Ox’ Cx’
Recent JLAB datanot in database
GEANT simulation of polarimeter
No GraphiteWith Graphite scatterer
• Simulation includes realisticsmearing of energy deposits due to experimental energy resolutionand proper cluster finding algorithms
• Finite target size and E resolution included
Angle between N(E,) and TAPS hit
• ~30% dilution of analysing power
• Acceptance X%
Reconstructed Phi in incident nucleon frame
Egamma (MeV)
A =
(+
-- ) /
(+-
- )
Design 1: Graphite in CB tunnel
GraphiteCB tunnel
CM) >~130o
E=150 MeVE=200Eg=300E=500E=750E=1000E=1500
Polarimeteracceptance
Nucleon angle in lab (deg)
Pio
n a
ngle
in C
M (
deg)
Kinematic acceptance of polarimeter
p()N
• More forward recoils than for pion production.
• Almost all recoils are incident on polarimeter up to ~0.8 GeV
Eg=720Eg=820Eg=920Eg=1520
Lab nucleon angle (degrees)
CM
a
ng
le (
deg
rees)
Polarimeter acceptance
Kinematic acceptance of polarimeter
p()N
MAID predictions and expected data accuracy - p()N
300 hrs MAMI B
500 hrs MAMI C
New GEANT simulations
Simulate New routines added to GEANT – introduced modulation for hadronic interactions (take A=1)
Simulated p(,p)0 data. Run through AcquRoot analysis. Accurate description of target size, beam properties, CB & mini TAPS. E=300-600 MeV
All other processes left in. Explore possible designs for polarimeter without
need for tracker
p
MAID predictions and expected data accuracy - p()N
300 hrs MAMI B
Full MAID
No P11(1440)
Cx’ – Extraction and expected accuracy
Plot difference in distributions for two helicity states (cut on region of with reasonable A())
Left with simple sin() Dependence. Extract Px
0 180 360
Photon energy (MeV)
Cx’
P=0.7, E=±25MeV, =130±10
~ 1 b/sr → Cx ~ 0.015
~ 0.1 b/sr → Cx ~0.05
Greatly improved data quality
-
Expected data accuracy
Common parameters:
Photon beam: 2.5x105 sec-1 MeV-1 Bin ±12.5 MeVTarget: 2.11023 nuclei / cm2
Meson: Bin ±10o
Polarimeter: 3% probability for a (detected) nuclear scatter Average analysing power ~0.4
Principles of nucleon polarimetry
Well established technique – relies on spin-orbit interaction in Nucleon-Nucleon interaction
Polarimeters - exploited nucleon or nuclear targets (2H, 4He, 12C, 28Si) – tended to use materials with well known analysing powers
pomme
A1 FPP
GEn Polarimeter
Kent state
Measure direction of nucleon before and after the scatterer with sufficient accuracy to determine an analysing reaction has taken place.
Polarimetry basics
For incident protons also have multiple (coulomb) scattering
scat=5-20o
scat
Scattered nucleon detection in TAPS
1 TAPS block ~ position resolution for hit TAPS~0.9m from scatterer
N
Straight through10o scatter20o scatter