Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.
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Transcript of Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.
![Page 1: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/1.jpg)
Status ofMøller Polarimeter
Peter-Bernd OtteSeptember 23, 200812th Collaboration Meeting, Mainz
![Page 2: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/2.jpg)
Why built a Møller Polarimeter?
Aim: measuring electron-beam polarization
Using Møller scattering
![Page 3: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/3.jpg)
What is Møller Scattering? (1/2)
kj
Rk
Bjjk
CMCM
PPad
d
d
d
,
0
1
zyxkj ,,,
Spin component from beam and radiator
Electron-Electron-scattering(Composed of 2 amplitudes in 1st order QED)
cross section:
e-
e-
tensor gives analysis powerMøller c.s. for unpol.
![Page 4: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/4.jpg)
What is Møller Scattering? (2/2)
Key features of this two-electron process: energy sum of both electrons sums up to beam energy:
Angular distributionof scattering angle:
Both electrons are emittedcoincidently
BeamEEE 21
Bremsstrahlung
Møller scattering
![Page 5: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/5.jpg)
BeamEEE 21
Using the tagger: setup:
several pairs of tagger channels with a sum of EBeam
→ coincidental detection of both Møller electrons
measurement:
(arrows indicate spin alignment of beam and target)
Trigger logic
NN
NNA
![Page 6: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/6.jpg)
Background processes
Processes that produce the same footprint on the ladder:
Møller scattering always:
E1+E2 = EBeam
time correlated
Bremsstrahlung accidental coincidences not time correlated
Pair production(3 body process)
sometimes: E1 + E2 = EBeam
time correlated
Reduce bremsstrahlung and pair production events
![Page 7: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/7.jpg)
Better results by…
forcing: …correct energy sum
→ this becomes the trigger condition(reduces pair production events)
…correlation in time→ done in offline analysis usingtime-spectrum(reduces Bremsstrahlungs events)
Possible: attaching additional detectors near the focal plane(→ see Dubrovnik talk)
![Page 8: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/8.jpg)
Why a new Møller Polarimeter?
why demanding a new one? new Tagger gap width (2.5cm) adapt the trigger logic
more easily
The new trigger board: Uppsala board,
FPGA based
faster
smaller
more flexible
![Page 9: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/9.jpg)
Status and Measurements (1/2)
Møller Trigger works fine, test measurement with following logic: 32 low energy channels each with corresponding 17 high energy channels,
centred around (E’1+E’2) = beam energy
low energy channel 17 corresponding high energy channels
Trigger signal
Tagger channels
more…
![Page 10: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/10.jpg)
Status and Measurements (2/2)
First test with unpol. beam: duration: 14 min. 490nA, 1508 MeV 1,5kHz Interrupts 19% Livetime
Uppsala board Level adapters
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Results 1/6
Trigger logic works fine,Multiplicity in tagger:
Within time window of +/- 50ns around trigger signal
All recorded events
multiplicitynum
ber
of r
ecor
ded
even
ts *
104
Only events with multiplicity=2 used for analysis
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Results 2/6
Task: Count the number of events for each channel pair (using time difference)
For example: 15 time difference histograms forchannel 33 and 315..329
no hits
Møller peak
coincident background
time difference in ticks time difference in ticks time difference in ticks
coun
tsco
unts
coun
tsco
unts
coun
ts
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Results 3/6
Doing this for each low energy channel, e.g. 33..35:
no hitsMøller peak
coincidentbackground
coun
ts
energy sum E’1+E’2 in MeV
measuredenergy shift
~17MeVbe
am e
nerg
y
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Results 4/6
Shift of Møller peak
(E’ 1+
E’ 2)
- b
eam
ene
rgy
in M
eV
tagger channel of low energy electron
preliminary
simulation withsimplified field: only 2 MeV shift, but same direction.
Due to bigger scattering angle than bremsstrahl electrons
→ remember Talk from A. Polonskij Dubrovnik
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Results 5/6
All channels combined, rebinned to 2.1MeV
bea
m e
nerg
y =
150
8MeV
measuredenergy shift of Møller peak17,2(4) MeV
coun
ts
energy sum E’1+E’2 in MeV
![Page 16: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/16.jpg)
Results 6/6
Percentage of background under peak? Within 2 around Møller peak: 96(4)% Møller events
coun
ts
energy sum E’1+E’2 in MeV
Møller eventscovered under normal distribution
background events
![Page 17: Status of Møller Polarimeter Peter-Bernd Otte September 23, 2008 12th Collaboration Meeting, Mainz.](https://reader034.fdocuments.us/reader034/viewer/2022051516/56649efc5503460f94c0ecf4/html5/thumbnails/17.jpg)
Outlook
Measuring of Beam Polarisation on Wednesday (tomorrow).
New simulations necessary:for correction due to coincident background
Still current: mounting additional detectors(suppress background)
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appendix
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Simulated Tagger Optic 1/3
Setup with effective magnetic field edgesfocal plane
hom. magnet fieldwith effective edgeselectron trajectory
reference entrypoint
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Simulated Tagger Optic 2/3
Construction of focal- and detector plane (20 cm space to focal plane)
Using crossing point of two electrons trajectories (with +/-small
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Simulated Tagger Optic 3/3
Calculated shift in energy sum
(E’ 1+
E’ 2)
- b
eam
ene
rgy
in M
eV
Møller electron energy in units of beam energy
mean value