Proton Detection in the Spectrometer
aSPECT
M. Simson1,4, H. Angerer1, F. Ayala-Guardia2, S. Baeßler2, M. Borg2, J. Byrne3, K.
Eberhardt2, F. Glück2, M. van der Grinten3, W. Heil2, I. Konorov1, G. Konrad2, R.
Munoz-Horta2, G. Petzoldt1, Y. Sobolev2, H.-F. Wirth1, O. Zimmer1,4
1
2
TU München
Johannes-Gutenberg-Universität Mainz
3 University of Sussex
4ILL Grenoble
[email protected]
Outline
• The “old” Detector
– Setup
– Performance during the
beam times
– Systematic investigations
• A new Detector
– Detection principle
– First results with a test
detector
– Outlook: The “new”
detector
• Conclusion
2
Digital electronics
UHV-gate valve
ExB electrodes
3
Detector & Preamplifier
(~ -30 kV)
The aSPECT Detector
• Si-PIN Diode
– 25 Strips
– Strip size 0.8 x 25 mm2
– Entrance Window 67 nm
(40 nm Si3N4 + 27 nm
SiO2)
4
Readout Electronics
5
Pulseheight Spectra
Detector at 30 kV
Pulseheight Spectra for
50 V and 800 V at the
analyzing plane
6
Background (800 V)
subtracted spectra
Offline Data Analysis
Single proton events: High noise, low signal: background-ratio (~10:1)!
Bad separation of proton- and background-peak in the pulse height spectrum
Fit of the events with theoretical known pulse function
7
Diode Characteristics
Det. 2: Does not detect protons any more
8
Det. 4: Still detecting protons
Proton Source
paff: “proton accelerator with femto ampere flux“
Detector
Specs:
–
–
–
–
9
Proton energy 10-35 keV
Flux: nA to several CPS
Two monitor detectors
Other ions possible
A.R. Müller et al. submitted to NIM A
Between the Strips
Gap between the strips: 200 µm
Î Small, movable aperture ( Ø 0.2 mm) before the detector
10
Submitted to NIM A
Temperature effects
Î Cooling the setup reduces the amount of
noise significantly
11
A new detector type
• New Type: Silicon Drift Detector (SDD)
• Principle:
p-doped backside
p-doped rings
Potential Valley
e- drift to a small
anode in the middle
12
P. Lechner et. al. , XRS 2004 33 256-261
SDD Test Detector
• Supplied by HLL / PNSensor
• Features:
– Active area: 30 mm2
– Integrated FET
– Mounted ready to use
– Mounted on a Peltier
element
– Optimized preamp +
shaper
– Integrated temperature
diode
– Different entrance
windows available
13
First Spectra with the SDD
First protons on the SDD:
Detector at room temperature
Submitted to NIM A
Energy Calibration with
a 55Fe source:
Mn-Kα − FWHM @ -13 °C:
~ 165 eV
14
Submitted to NIM A
First Spectra with the SDD II
Comparison:
protons – electronic noise
Submitted to NIM A
Protons on the cooled detector:
Impact energy 12 keV
Temperature -4 °C
15
Charge Collection Efficiency
• 3 part function
• 4 Parameters
– S : Minimum
(starting point)
– τ : Steepness
– c : Shape
– l : Depth
16
Simulations
Simulations done with SRIM
17
Questions:
How much energy is detected for each proton?
How many protons are backscattered?
Is there an angular / energy dependence?
From Measurement to CCE
EXYZ-File
Calculate ΔE
for each line
Tune the CCE parameters
to fit the measurements
Multiply it
by the CCE
Integrate over the
complete track
Artificially broaden the
simulation by the noise
S = 0.41
τ = 75 nm
c=2
l = 50 nm
18
A new detector for aSPECT
active area: 3 x 100 mm²
14 mm
Temperature diode
34 mm
19
A new detector for aSPECT II
• Advantages:
– Noise performance comparable to the test
detector
– HV only ~ 15 kV
– New (simplified) detector mechanics
– Simplified preamplifier (based on 3 Amptek A250)
• Disadvantages:
– Loss of spatial resolution
– (Slightly) reduced count rate
20
Conclusion
• First beam times with aSPECT completed
• Present detector performance not satisfying
• New SDD detector successfully tested
• SDDs will be ready for the next beam time at
the ILL in autumn
21
Online Trigger
• No external trigger Î self-triggering system
• Signals are shifted through time bins
• Trigger settings:
– W1: Long window
(baseline): 512 bins
– W2: Short Window
(event): 16 bins
– Threshold: 15 ADCChannels
– Delay: 3
22
Magnetic shield
High magnetic field
might disturb other
experiments
-> magnetic shield:
– 4 poles 0.2x0.2x4 m
– 2 plates 1.8x1.8x0.1 m
– ~10 t iron
23
Coupling Constants of the Weak Interaction
Coupling Constants in Neutron Decay
p = (udu)
u
Nucleosynthesis
e-
gV, gA
p
νe
W±
n
Solar cycle
e+
W±
νe
p + p → 2H+ + e+ + νe
24
νe
n
e+
n + e+ → p + νe
Neutrino Detection (SNO, CC)
νe
2H+
p+p
W±
n + ν e → p + e-
n → p + e- + ν e
νe
p
W±
d
n = (ddu)
2H+
e-
W±
p+p
e-
p+p
W±
e-
p + e- + p → 2H+ + νe
2H+
νe
νe + 2H+→ p + p + e-
Standard Model Test
Cabibbo-Kobayashi-Maskawa-Matrix
Condition of Unitarity
• B/D Mesons
• Superallowed Fermi Decays
• Neutron Decay
• Kaon Decays
• Hyperons
• Pion Decay
25
Situation
2004
Ke3
and Lifetime
Kμ2 measurements
New
Neutron
Measurement
0.980
Unitarity
of the2005]
CKM Matrix
Vus [Blucher et al., CKM
2
Vud = 1 − Vus + Vub
2
0.975
Vud
Neutron Measurements needed:
• Neutron lifetime τn
0+→ 0+
[Marciano, Sirlin, 2005]
τn [Serebrov 05]
0.970
(
τ n −1 ∝ GF2Vud2 1 + 3 λ
2
• Beta Asymmetry A(λ)
)
; λ = gA/gV
2
τn [PDG2006]
A [PERKEO
[PERKEO II]
II]
A
0.965
-1.25
-1.26
-1.27
-1.28
λ = gA/gV
Fermi-Transition:
g V = GF ⋅Vud
Gamow-Teller-Transition: g A = GF ⋅Vud ⋅ λ
26
A = −2
λ + Re λ
1+ 3 λ
2
• Neutrino-Electron-Correlation a(λ)
a=
1− λ
2
1+ 3 λ
2
Determination of λ
-1,255
Yerozolimskii,
1997
Stratowa, 1978
Liaud, 1997
Unitarity,
PDG2004
λ
-1,265
PERKEO, 1986
-1,275
PERKEO II, 2002 Unitarity,
PDG2006
Unitarity,
PERKEO II, 1997
Serebrov 05
Byrne, 2002
-1,285
• Different Systematics Î Measurement of a is independent of
possible errors in A
• An accuracy of Δa/a < 1% is needed !
27
Information in the Proton Spectrum
28
The spectrometer aSPECT
SPECTrometer for a
29
30
Properties of the Detector
• Diode Î IV characteristics
• Detection performance
– Different impact angles
– Different proton energies
– Gaps between the strips
• Temperature effects
31
Diode Characteristics
Det. 2: Does not see protons any more
Det. 4: Still seeing protons
32