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Hartmut Abele, Technische Universität Wien
Bastian MärkischHartmut AbeleCKM2014
Neutron Beta Decay:
Determination of the Weak Axial Vector Coupling
2
Neutron -decay
lifetime ~ 15 min
-endpoint: Emax = 782 keV
V-A Theory: Vector coupling: gV = GF Vudf1(q2→0)
Axial vector coupling: gA = GF Vud g1(q2→0)
ratio = gA/ gV = -1.276
Standard Model: Vud, , ei= -1
en p e
Standard Model and Neutron Decay
ud us ub
cd cs cb
td ts tb
CKM-Matrix: V V VV V VV V V
d d
s s
b b
3
Parameters• Strength: GF
• Quark mixing: Vud
• Ratio: = gA/gV
5 41 2 2 2
3 7(1 3 )2ud
Re
F
fV
mG
ch
ObservablesLifetime Correlation A
Correlation B
Correlation C
Correlation a
Correlation D
Correlation N
Correlation Q
Correlation R
Beta Spectrum
Proton Spectrum
Beta Helicity
Electron
Proton
Neutrino
Neutron Spin
A
B
C
a
D
R N
Neutron Alphabet deciphers the SM
High Precision - Low Energy• Hartmut Abele, Atominstitut, TU Wien
RQ
4
a,A = gA/ gV
A + t Vud from CKM matrix
A + B + t Right Handed Currents (RHC)?
WL WR
Neutron Alphabet deciphers the SM
H. Abele, NIM A 611 (2009) 193–197
5
D, R ? T-odd CP-violation
CP
See P. Herczeg, Prog. Part. Nucl. Phys. 46 (2001) 413.See P. Herczeg, Prog. Part. Nucl. Phys. 46 (2001) 413.
Candidate models for scalar couplings (at tree-level): Charged Higgs exchange Slepton exchange (R-parity violating super symmetric models) Vector and scalar leptoquark exchange
The only candidate model for tree-level tensor contribution (in renormalizable gauge theories) is: Scalar leptoquark exchange
Courtesy of K. Bodek
Neutron Alphabet deciphers the SM
6Hartmut Abele, Technische Universität München
Characteristics of Experiments
Using Magnetic Fields
(Dubbers 1980s)
A, B, C
PERKEO I
Method: P. Bopp et al., NIM A 267 (1988) 436.
7
Why ratio = gA/ gV from Neutrons?
Processes with the same Feynman-Diagram
Courtesy of D. Dubbers
PERKEO II Spectrometer
8.9.2014 CKM 2014, Vienna - Bastian Märkisch 8
• X-SM crossed polariser geometry: Kreuz et al., NIM A 547, 583 (2005) Neutron polarisation P = 99.7(1)%
• Largely reduced background (Mund et al., PRL 110 (2013))Improved beam line setup and shielding, Overall S:B = 8:1 Beam related background : 1/1700 in signal region (previous:1/200)
3rd run (beta asymmetry), major Improvements:
Magnetic field:
• alignment of neutronspin
• guide e, p onto detectors
• separation into hemispheres
2 x 2 detector
• backscatter suppression
Error Budget A
9
10
-1.1900(200), PDG (1960)
-1.2500(200), PDG (1975)
-1.2610(40), PDG (1990)-1.2594(38), Gatchina (1997)
-1.2660(40), M, ILL (1997)
-1.2740(30), PERKEO II (1997)-1.2686(47), Gatchina, ILL (2001)
-1.2739(19), PERKEO II (2002)−1.27590(+409)(−445), UCNA (2011) -1.2756(30), UCNA (2013) -1.2748+13
-14 PERKEO II (2013)
a bit history: l from neutron b-decay
PERKEO II: Combined Result
8.9.2014 CKM 2014, Vienna - Bastian Märkisch 11
Combine all PERKEO II results:
H. Abele et al., Phys. Lett. B 407, 212 (1997) A = - 0.1189(12)H. Abele et al., PRL 88, 211801 (2002) A = - 0.1189(8)D. Mund et al., PRL 110, 172502 (2013) A = - 0.11972(+53
-65)
Final Perkeo II result:A = - 0.11926(+47
-53) ΔA/A = 4.2 ∙ 10-3
λ = - 1.2748(+13-14) Δ λ / λ = 1.1 ∙ 10-3
Conservative treatment of correlated errors:detector calibration and uniformity, background determination, edge effect, radiative correction
Vud = 0.97449(18)RC(40)tau(80)AVud = 0.97449(18)RC(40)tau(80)A
Vud = 0.97425(8)exp.(10)nucl.dep.(18)RC (superallowed)Vud = 0.97425(8)exp.(10)nucl.dep.(18)RC (superallowed)
12
-1.1900(200), PDG (1960)
-1.2500(200), PDG (1975)
-1.2610(40), PDG (1990)-1.2594(38), Gatchina (1997)
-1.2660(40), M, ILL (1997)
-1.2740(30), PERKEO II (1997)-1.2686(47), Gatchina, ILL (2001)
-1.2739(19), PERKEO II (2002)−1.27590(+409)(−445), UCNA (2011) -1.2756(30), UCNA (2013) -1.2748+13
-14 PERKEO II (2013)
a bit history: l from neutron b-decay
13 = l -1.2756(30), UCNA (2013)
UCNA (2013)
Recent Results: PERKEO Collaboration
14 14
A =-0.1197(6)
APII = 0.1193(5)PII = 1.2748(13)
error: 1×103
Electron Asymmetry A:
PRL 110, 172502 (2013)
Proton Asymmetry C:
Neutrino Asymmetry B:
B = 0.9802(50)Schumann et a.PRL 99, 191803 (2007)
PERKEO II combined:
first precision measurement
C = 0.2377(36)Schumann et al.,PRL 100, 151801 (2008)
15
Coefficient B,C Proton detector
H. Abele, NIM A 611 (2009) 193–197
C foil ScintillatorProton
Proton detection:• Measure electron energy• Wait for proton• Convert proton into electron signal
Proton detection:• Measure electron energy• Wait for proton• Convert proton into electron signal
n-Spin
16
M. Schumann: The Neutrino-Asymmetry B
M. Schumann,M. Kreuz, M. Deissenroth,F. Glück,J. Krempel, B. Märkisch,D Mund, A. Petoukhov, T. Soldner, H. Abele, PRL 100, 151801 (2008)
• Electron and Proton in same hemisphere
low dependence on energy calibration and energy resolution higher sensitivity due to larger exp. asymmetry
• Electron and Proton in opposite hemispheres
more statistics since this case occurs for ~78% of the events
Electron Proton
Neutron Spin
Neutrino
Electron
Proton
Neutrino
Neutron Spin
NN
NNBexp
NN
NNBexp
Systematically clean method: Integration over two hemispheres
17
Coefficient B, Serebrov et al.
H. Abele, TU Wien
P E R K E O I I IB. Märkisch:Spectrometer PERKEO III
8.9.2014 18
Magnetic field :• alignment of nspin• guide e, p onto detectors
2 x 2 detector
• separation into hemispheres
detector
detector
neutron beam
electron tracks
B = 150 mT
active volume ~2m, 15x15cm²
B = 90 mT
• decay volume 10x longer: ~50.000 events/s in cont. Beam• B = 0.15T
CKM 2014, Vienna - Bastian MärkischB. Maerkisch et al., NIM 611 (2009) 216–218
P E R K E O I I I
velocity selectorl=5.0Å∆ / = 10%l l
~2m, 150mTbeam dump, enriched 10B
homogeneous fieldContinuous,“monochromatic”neutron beam
chopper (6LiF)@ 94Hz
magnetic field
Pulsed Cold Neutron Beam
8.9.2014 19
electron detector
• Edge-free projection onto detectors: full 2 x 2 p detection without distortions
• Background can be fully measured and subtracted
D. Werder, UHD
• Magnetic mirror effect controlled
Benefits:
CKM 2014, Vienna - Bastian Märkisch
P E R K E O I I IPulsed Neutron Beam
8.9.2014 CKM 2014, Vienna - Bastian Märkisch 20
time for signalmeasurement
neutrons hitbeam dump
time forbackgroundmeasurement
slopes due tomagnetic mirror
Signal region 300 keV < E < 700 keV
upstreamdownstream
P E R K E O I I IBackground Subtraction
8.9.2014 21
Time variation of background signal consistent with zero!
Signal region 300 keV < E < 700 keV
Additional background tests:Background monitors (NaI and He), control measurements with blocked beam
Chopper83 Hz
Chopper94 Hz
4101 A
A
CKM 2014, Vienna - Bastian Märkisch
coun
ts (a
.u.)
coun
ts (a
.u.)
P E R K E O I I IInstallation at PF1B, ILL
8.9.2014 22
One of two trucks
Plastic scintillator
Experimental Zone
96% of data acquired in analysis6 10∙ 8 neutron decay events
P E R K E O I I IBeta Asymmetry, Chopper 94 Hz
23
Raw Signal + Background Signal, Background Subtracted
Sum and Difference Experimental Asymmetry
preliminary
preliminary
preliminary
preliminary
NN
NNAexp
P E R K E O I I I
Source Correction ∆A/A (10-4)
Uncertainty ∆A/A (10-4) Predecessor
Neutron beam Polarisation < 10 / 1.4Spin flip efficiency
Background / 7Undetected 1Time variation -1 1
ElectronsMagnetic mirror effect 4Lost backscatter energy 1.4
DetectorDeadtime * -5 2Non-linearity 4 / 4.6Non-uniformity 3Stability * 2Calibration 0.5
Theory Radiative corr. * -1.1 2Total Systematics 12.4 / 3.2Statistics 13.9 / 2.7Total 18.6
Error Budget
24
separate analysis
3109.1 A
A
4108.4
Result (still blinded):separate analysis
2.3x better than Perkeo II
P E R K E O I I IPERKEO III Team
8.9.2014 25
D. Dubbers, B. Märkisch, H. Mest, C. Roick, D. WerderHeidelberg University
H. Abele, H. Saul, X. Wang
Institut Laue Langevin, GrenobleT. Soldner, A. Petoukhov
TU Vienna, TU Munich
PERKEO III Team, ILL
Source Correction ∆A/A (10-4)
Uncertainty ∆A/A (10-4) Predecessor
Neutron beam Polarisation < 10 / 1.4Spin flip efficiency
Background / 7Undetected 1Time variation -1 1
ElectronsMagnetic mirror effect 4Lost backscatter energy 1,4
DetectorDeadtime * -5 2Non-linearity 4 / 4.6Non-uniformity 3Stability * 2Calibration 0,5
Theory Radiative corr. * -1,1 2Total Systematics 12,4 / 3.2Statistics 13,9 / 2.7Total 18,6
Error Budget Uni HD Maerkisch et al., ILL: Soldner et al. TU Wien: Wang et al.
26
separate analysis
3109.1 A
A
4108.4
Result:
separate analysis
Factor 4 improvement over PDG 2013 average
Close to Publication
aCORN @ NISTaSPECT @ Mz, ILL, TUWPERKEO III @ UHD, ILL, TUW: A (B,C not so close)
New InstrumentsNab, PERC
Hartmut Abele, Atominstitut, Vienna University of Technology 27
R. Feynman
Hartmut Abele, Helmut Leeb, Technische Universität Wien
28
30
Standard Model of Particle PhysicsInput: Principia: - Gauge principle U(1) x SU(2) x SU(3)- Lorentz invariance : x‘ = Lx- CPT, ...Invariance
Output: - Interactions- Equation of motion Maxwell, Schrödinger, Dirac- Existence of Photons, Gluons, W±, Z0
(carriers of interaction)- Charge conservation (Source of interaction)
Conclusion: SM very successful- e.g. as basis for technology, chemistry, biology, mol.biologie
D. Dubbers 2007
31
Weak Magnetism form factor f2
Neutron Decay Transition Matrix:
Electron Asymmetry:
f2 Weak Magnetism Form Factor
(SM prediction)
2 % additional Edependence of A
2 21 3
22[ ( ) ( ) ]|2
( )
p
V p f k k if k k nf k
m
Ffi 5 5
GT | (1 ) | ( (1 ) )
2udV p n e
Beyond SMA search for - right-handed admixtures to the left-handed feature of the Standard model. They
are forbidden in the Standard-Model, but, as a natural consequence of symmetry breaking in the early universe, they should be found in neutron-decay. Signatures are a WR mass with mixing angle z.
- scalar and tensor admixtures gS and gT to the electroweak interaction. gS and gT are also forbidden in the Standard model but supersymmetry contributions to correlation coeffi cients or the Fierz interference term b can approach the 10−3 level.
A precision measurement of - the weak-magnetism form factor f2 prediction of electroweak theory. Such an
experiment would be one of the rare occasions, where a strong test of the underlying structure itself of the Standard model becomes available.
Supersymmetry search in the LHC era: - one could expect small deviations in the low-energy tests, such as deviations from
CKM unitarity, but no effect at the LHC, especially if the supersymmetry spectrum is below one TeV, but the spectrum is compressed, or if some of the superpartners are light and others are heavy (a variant on the “split-SUSY” scenario)
Hartmut Abele, Atominstitut, TU Wien 32
Participating Institutions:
• IST Braunschweig
• Univ. Heidelberg• ILL
• Univ. Jena
• Univ. Mainz
• Priority Areas• CP-symmetry violation and particle physics in the early universe. • The structure and nature of weak interaction and possible extensions of
the Standard Model. • Tests of gravitation with quantum objects • Charge quantization and the electric neutrality of the neutron.
• New Infrastructure (UCN-Source, cold Neutrons)- * Coordinators first round (S. Paul, H.A. )
DFG/FWF Priority Programme 1491 : Precision experiments in particle- and astrophysics with cold and ultracold neutrons,
• Exzellenzcluster ‚Universe‘ München
• Techn. Univ. München*
• PTB Berlin
• Vienna University of Technology*
Priority Programme 1491
Research Area A: CP-symmetry violation and particle physics in the early universe- Neutron EDM E = 10-23 eV
Research Area B: The structure and nature of weak interaction and possible extensions of the Standard Model - Neutron b-decay V – A Theory
Research Area C: Test of gravitation with quantum interference - Neutron bound gravitational quantum states
Research Area D: Charge quantization and the electric neutrality of the neutron- Neutron charge
Research Area E: New measuring techniques- Particle detection- Magnetometry- Neutron optics
Experiment PERC- PERC, a clean, bright and versatile source of neutron decay products
(Maerkisch) - Proton spectroscopy (Heil, Zimmer)- Electron spectroscopy (Abele)- Neutron polarisation + analysis with 10-4 accuracy (Soldner)- design of the beam line for PERC (Soldner, Jericha)- Development of a non-depolarising neutron guide needed for PERC
(Schmidt)
Measurement of the neutron lifetime- O. Zimmer et al.
Measurement of n -> H- S. Paul et al.
Priority area B (first 3 years round):Novel experiments on neutron beta-decay
SM tests on 10-4 level
Theory- Recalculation of corrections induced by the “weak magnetism”, the
proton recoil and the radiative corrections.- A. Ivanov, M. Pitschmann, and N. Troitskaya, Phys.Rev. D88, 073002 (2013),
1212.0332.
Experiment PERC- High statistic measurements: - Today: High Average Flux: = 2 x 1010 cm-2s-1
- Decay rate of 1 MHz / metre- Thesis C. Klauser (2013) Polarizer P/P = 10-4 , Spin Flipper f/f = 10-4
Hartmut Abele, Atominstitut, Vienna University of Technology 36
Proton Electron Radiation Channel: B. Maerkisch
D. Dubbers et al., NIM A 596 (2008) 238 and arXiv:0709.4440G. Konrad et al. (for the PERC collaboration), J. Phys.: Conf. Ser. 340 (2012) 012048
=0.5T
cold
Versatile: A, B, C, a, b, κ, …
Sensitivity: • improved by up to 2 orders of magnitude
• high phase space density
Systematics: • 10-4 (for e-)
• precise cuts in dΩe:
Requirements: • no local field minima
• adiabaticity criterion
• B1 homogeneity 10-4 in e/p beam
0 0
sin
sin
B
B
Superconducting Magnet
8.9.2014 38
Preliminary Magnet Design
L = 11.3m
Precision experiments in particle and astrophysics with cold and ultracold neutronsPriority Programme 1491
6 T
1.5 T
Status:Magnet in productionInstallation in 2016
Physikalisches InstitutUniversität Heidelberg
1220
1 BB
39
G. Konrad: R x B Spectrometer
R×B Drift Momentum Spectroscopy
- Small drift distances (cm)
Xiangzun Wang, G. Konrad et al., NIM A (2012), DOI 10.1016/ j.nima.2012.10.071
+ Adiabatic transport of particles+ Low momentum measurements+ Large acceptance of θ0
+ Small corrections for θ0
Last Coil of PERC
Tilted Coils
e-/p+ beam
Detector
Aperture
y
z
x
y
xz
RxBvd qR²B²
B3=0.15T
B2=0.5T
ElectronsProtons
D
1 1(cos )
2 cod
sdT
pD
qBv t
D
RB
α
Hartmut Abele, Technische Universität München 41
SOURCE OF ERROR COMMENT SIZE OF CORRECT.
SIZE OF ERROR:
non-uniform n-beamfor ΔΦ/Φ = 10 % over 1 cm width
2.5·10−4 5·10−5
other edge effects on e/p-window for worst case at max. energy 4·10−4 1·10−4
magn. mirror effect, contin's n-beam 1.4·10−2 2·10−4
magn. mirror effect, pulsed n-beam for ΔB/B = 10 % over 8 m length 5·10−5 <10−5
non-adiabatic e/p-transport 5·10−5 5·10−5
background from n-guide}is separately measurable
2∙10−3 1·10−4
background from n-beam stop 2·10−4 1·10−5
backscattering off e/p-window 2·10−5 1·10−5
backscattering off e/p-beam dump 5∙10−5 1∙10−5
backscatt. off plastic scintillator}for worst case
2∙10−3 4·10−4
~ same with active e/p-beam dump − 1·10−4
neutron polarisation present status 3·10−4 1·10−4
Dubbers, Baessler, Märkisch, Schumann, Soldner, Zimmer, H.A., arXiv 2007
PERC Collaboration
B. MärkischU. SchmidtD. DubbersH. MestL. RaffeltC. RoickN. RebrovaC. ZienerR. MaixB. Windelband
H. AbeleE. JerichaG. KonradJ. ErhartC. GösselsbergerX. WangH. FillungerM. HorvathR. Maix
J. KlenkeT. LauerH. SaulK. Lehmann
T. SoldnerO. ZimmerC. Klauser
W. HeilM. Beck
Heidelberg Vienna
FRM II, MunichGrenoble
8.9.2014 42CKM 2014, Vienna - Bastian Märkisch
Reserva
Hartmut Abele, Atominstitut, Vienna University of Technology 43
PERKEO II: Polarisation
44
Single Polariser: X-SM Geometry:
New polarisation technique: X-SM (crossed super mirror) polarisers Kreuz et al., NIM A 547, 583 (2005)
New analyser technology: 3He Spin Filters
Average polarisation: 99.7(1)%, spin flip efficiency 100.0(1)%Correction 4 times smaller, uncertainty 3 times smaller
wavelength
8.9.2014 CKM 2014, Vienna - Bastian Märkisch
PERKEO II: Background
8.9.2014 45
shutter up
shutter down
closed closed
Shutter Down – Shutter Up, Detector 1
• Overall S:B = 8:1 in fit region• Background variation due to changes
of neighbouring instruments: reduced data set (70%)
• Beam-related background determined by extrapolation procedure, Reich al., NIM A 440.
Only 1/1700 of the electron rate in signal region (previous: 1/200)
PERKEO II: Error Budget
8.9.2014 CKM 2014, Vienna - Bastian Märkisch 46
AA /Mund et al., PRL 110 (2013)
PERKEO II Result, 2013
8.9.2014 CKM 2014, Vienna - Bastian Märkisch 47
APNN
NNA c
v21
exp
Combined, including corrections:A = −0.11972 (45)stat(+32
-44)sys = −0.11972(+53-65); = −1.2761(+14
-17)
Fit: Adet 1 = −0.11846(64)stat Fit: Adet 2 = −0.12008(64)stat
Difference in results for both detectors in agreement with expectation from magnetic mirror effect.
PERKEO II: Combined Result
8.9.2014 CKM 2014, Vienna - Bastian Märkisch 48
Combine all PERKEO II results:
H. Abele et al., Phys. Lett. B 407, 212 (1997) A = - 0.1189(12)H. Abele et al., PRL 88, 211801 (2002) A = - 0.1189(8)D. Mund et al., PRL 110, 172502 (2013) A = - 0.11972(+53
-65)
Final Perkeo II result:A = - 0.11926(+47
-53) ΔA/A = 4.2 ∙ 10-3
λ = - 1.2748(+13-14) Δ λ / λ = 1.1 ∙ 10-3
Conservative treatment of correlated errors:detector calibration and uniformity, background determination, edge effect, radiative correction
49M. Pitschmann, A. Ivanov, Atominstitut, Vienna University of Technology
50M. Pitschmann, A. Ivanov, Atominstitut, Vienna University of Technology
51M. Pitschmann, A. Ivanov, Atominstitut, Vienna University of Technology
52
53
54
Coefficient A
55Hartmut Abele, Vienna University of Technology
Coefficient C
56Hartmut Abele, Vienna University of Technology
Error budget B
Error Budget C
58
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