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CKM Unitarity and Neutron Beta DecayMeasuring Vud in Neutron Beta Decay
Bastian Märkisch
Physik-Department
Technische Universität München
CKM Matrix Element Vud
Effective CC Couplings
Neutron Lifetime
Neutron Decay Corellations
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Low energy
Long lifetime
τ = 880.3(1.1) s
Only small, precisely known radiative
corrections
Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Neutron Beta-Decay
Two free parameters within SM (GF from muon decay)
Ratio of coupling constants Quark mixing
Axial-vector gA und vector gV Cabibbo-Kobayashi-Maskawa
matrix element
V
A
g
g
udV
73
45
2
2221 )31(
cmf
udFe
R
VG
Ee,max = 782 keVEp,max = 752 eV
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Vud from Neutron Decay
from D. Pocanic arXiv:1704.00192v1Marciano , Sirlin PRL 96 (2006)
|Vud| = 0.97585 (18)RC(55)τ(146)λ
|Vud| = 0.97xxx (18)RC(11)τ(8)λ
|Vud| = 0.97xxx (18)RC(2×22)τ(2×40)λ
(new avg lifetime & upcoming PERKEO III result)
Status today:
(using PDG 2016 averages)
Near future (this year‘s results):
aCorn, aSpect?, UCNA, PERKEO III
Future prospects:
New experiments: Nab, PERC
Penelope / HOPE / τSpect / UCNτ / BL3
For comparision:
average of 14 nuclei (0+ → 0+):
|Vud| = 0.97417 (18)RC(9)NS(6)expJ.C. Hardy & I. S. Towner, PRC91, 025501 (2015)
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Neutron Classification
Cold neutrons
moderated in thermal bath (e.g. liquid D2)
E ~ 3 meV, T ~ 40 K, v ~ 800 m/s, ~ 0.5nm
high flux densities: 2·1010 s-1 cm-2
density ~105 cm-³
decay rate of up to 10 6 s-1 per metre
(typ. correlation measurements)
Ultracold neutrons (UCN)
E < 300 neV, T ~ 1 mK, v < 7 m/s, > 60nm
reflect from surfaces under any
incident angle : storable
moderate densities: ~30 cm-3
(typ. neutron lifetime, EDM)
Fermi potential ~ 100 neV
Gravity
ΔE=mn g Δh
~ 100 neV / m
Magnetic field
ΔE= μn B
~ 60 neV / Tesla
Vn
Vn < Vcrit
Vn > Vcrit
UCN UCN „bottle“
Material storage
and gravity!
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Storage experiments with UCN
“counting the survivors”
0 (extrapolation)
)t(N
)t(Nln
t-t
1
τ
1
2
1
12
m
...τ
1
τ
1
τ
1
τ
1
τ
1
vacuumleakwallβ
m
0 (experiment)
eff
wall
vμτ
1
βτ
1
τ
1
m
N(t1), N(t2)
relative measurements absolute measurements
nτv
n
0β
τdt
d
l
eNN
n
nβ
“counting the dead”
e,p
N0
l
In-beam experiments with
cold neutrons
Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Measurement of the neutron lifetime τn
UCN
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Gravitrap at ILL
Previous most precise measurement
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Neutron Lifetime Measurements
877.7(7)stat(3)sys
878.5(7)stat(3)sys
887.7(12)stat(19)sys
880.5(7)stat(8)sys
New avg?
879.4(8) S=1.9S=1.9
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
New Gravitrap II
Lifetime measurement by fill-and-empty.
Massively larger than previous experiment.
Running at ILL, Grenoble.
Many systematic studies (coating, losses,
temperature)
Next: Change from LN temperature to LHe
cooling (10K) to reduce wall losses.
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
UCN Magneto-gravitational trap
~5500 permanent magnets
Operated at LANL
Material: C.-Y. Liu
EXA2017
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R. W. Pattie, et al.,
arXiv 1707.01817:
877.7(7)stat(3)sys
UCN Magneto-gravitational trap
Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Hallbach
array
Material: C.-Y. Liu
EXA2017
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
More Neutron Lifetime Exp.
TRIGA
Mark II
permanent magnet multipole + SC magnet,
8l volume, new UCN source
short term goal 2s, long term < 0.3s
running at Mainz
HOPE
permanent magnet octupole + SC magnet,
2l volume, new UCN source
Goal: 1s -- running at ILL, Grenoble
J-PARC TPC
Pulsed beam
Status: 1%
Goal 0.1%
NIST BL2: goal 1s
BL3: new magnet; goal < 0.3s
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
PENeLOPE (TUM)
PENeLOPE aims at a precision of ± 0.1 s
Measure protons and neutrons directly from
decay. Also fill-and-empty.
proton detector
absorber
movement
mechanism
outer pressure
vessel
helium vessel
storage walls
(electropolished)
2.5
m
Magnetic & Gravitational trapping avoids material losses altogether!
(HOPE/ILL, Ezhov/ILL, τSpect/Mainz, UCNτ/LANL,
PENeLOPE/TUM): store only one spin-direction
PENeLOPE light
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Neutron Decay Correlations
Electron pe σe
Proton pp
Neutrino pν
Neutron Spin J
A
B
C
Naviliat-Cuncic and Gonzalez-Alonso, Ann. Phys. 525, 8–9,
600–619 (2013)
Dubbers and Schmidt, Rev. Mod. Phys (2012)
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Correlation Coefficients
322 22
F ud e e 0 e5
e e
d 11 3
d d d 2 2p E E E
EG V
ne e e
e n e
e
ee
1p p p p p p
E E E E E Ea A B D
m
Eb
Jackson, Treiman, Wyld,
Nucl. Phys. 4, 1957
1.2(2.0) 10-4
Typical current relative precision
O(10-2 - 10-3)
Goal of next generation PERC:
O(10-3 - 10-4) for some observables
Electron pe σe
Proton pp
Neutrino pν
Neutron Spin JA
B
C
PERKEO IIPERKEO III / PERC
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Determination of = gA/gV
= gA/gV
rela
tive c
hange
.00100 -0.1184APDG .00300 0.9807BPDG
.0040 0.103aPDG .00260 0.2377C
1.1%
0.3%
1.1%
3.9%
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Current Neutron Decay ExperimentsPERKEO III
A, B, C, b
Heidelberg,
TU Wien,
TU München,
ILL
aCORN
a
NIST
UCNA / UCNB
A, B, b
Los Alamos
aSpect
a
Mainz,
TU Wien,
ILL
Nab
a, b
SNS
… and PERC
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Experimental asymmetry, polarisation P
Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
PERKEO: Measuring Beta Asymmetry A
cos1),( Ac
vEW
Electron angular distribution:
Magnetic field to as quantisation axis
V
A
g
g
Within Standard Model:
Integration over hemispheres:
2 × 2π detection
Polarised
Neutrons
Electron
Detector 1
Detector 2
21cos
APNN
NNA
cv
21
exp
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Detector
1
Detector 2
Beamstop
electrons
Active volume
(~2m)
B = 150 mT
(homogeneous
)
B = 90
mT
Total length: 8 m
~50.000 decays / sec in the continuous beam
Beam preparation
Mechanical
disc chopperAdiabatic Fast
Passage Spin Flipper
Supermirror
Polarizer
Velocity
Selector
Pulsed
Neutron
Beam
Duty cycle:
~7%
Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Spectrometer PERKEO III
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
PERKEO III: Pulsed Neutron Beam
Sacrifise ~2 orders of magnitude in statistics to address important systematic:
background; continuous beam 50.000 s-1 ; pulsed 250 s-1
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
PERKEO III: Calibration Fits
114 full calibrations in
(twice per day)
Simultaneous Fit:
Χ²/NDF = 1.0 – 1.3
Free parameters:
Non-linearity, gain,
PE + norms
In addition:
Hourly drift
measurements
~weekly 2D uniformity
scan
Green bars indicate fit region
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Asymmetry Extraction
3109.1
A
A
4108.4
Result (still blinded):
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
PERKEO III Error budget
Finally, close to being unblinded
(inconsistencies in indep. analyses
resolved)
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
PDG 2016
-1.2723(23)
Electron-Neutroino
Correlation „a“:
Results soon from
aSpect, Mainz
Nab goal:
competitive with „A“
New UCNA result
New: aCorn, NIST
Goal of Nab, PERC
Δλ/λ ~ O(10-4)
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Proton Electron Radiation Channel (PERC)
Cryostat
Active volume in a 8 m long neutron-guide, B0 = 1.5 T:
phase space density and statistics
Magnetic Filter, B1 = 6T: phase space, systematics
(solid angle, backscatter suppression)
Source for specialised spectrometers
Aims to improve results by an order of magnitude: 10-4. New Observables.
1220
1 B
B
Nucl. Instr. Meth. A 596 (2008) 238 and
arXiv:0709.4440
B0
B1
B2
Magnetic Filter B1
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Beam Site Mephisto, FRM II
FRM-II, Garching
“Empty” new hall
Neutron guide: length 40 m, R = 3000 m, m = 2.5
Expected intensity equal to PF1B at ILL (2×1010 s-1cm-2)
Only very few neighbours: low ambient background
Easy ground level access, Fixed installation
Status: All major components of the beam line
ready or in production
New hall east Reactor„Atomic egg“
Guide hall
Reactor Core
PERC
Intermediate
Structure
New hall
east
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
PERC: Neutron Spin Control
O(10-4) precision requires neutron spin control on the same level:
- polarisation 99.7%: FeSi polarisers – Soldner / Petoukhov et al. (ILL)
- spin flipper: AFP 100.00%
- guide in strong magnetic field: only 10-4 depolarization per bounce allowed
- measurement with 3He spin filters – Soldner et al. (ILL)
Non-magnetic CuTi mirror m=2
preserves spin direction Production quality(except for the too thin top layer)
Large maximum angle of reflection,
high reflectivity
Reduces neutron losses in PERC by
factor > 2: background!
(Mildly) backable (>80°C). Beneficial for
vacuum conditions.
Hollering (TUM), Rebrova / Schmidt (HD)
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27SPP 1491 Closing Convention - B. Märkisch
Status of the PERC Magnet
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
PERC is a Facility
MAC-E filter
(“aSPECT”)
Magnetic
spectrometer
Electrostatic
chopper & p
detector
R×B
spectrometer
Electron
or proton
detector
Wien filter for
protons
User
System
Clean source of electrons and protons from neutron decay
Scintillator,
Silicon, …
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Prospects
Tremendous ongoing efforts to improve Vud from neutron decay
Lifetime τ
Potential new average (including UCNtau + Gravitrap2 results)
τ = 879.4(8) s; S = 1.9
Many new experimental results to be expected:
UCNtau, HOPE, tauSpect, PENeLOPE, Gravitrap2
Current Goal: O(0.1s)
Ratio of coupling constants λ
New (upcoming) results by
aCorn, UCNA, PERKEO III, aSpect
Next generation
Nab a 0.1% PERC A 0.05%
Long-term future (next decade): cold beam line
ANNI at ESS (more than order of magnitude
More statistics in pulsed beam)
Aerial view ESS
construction site
September 2015
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PERC (Proton Electron Radiation Channel) at FRM II / MLZ
W. Heil
U. SchmidtH. Abele
E. Jericha
O. Zimmer
T. Soldner
J. Klenke
B. Märkisch
G. Konrad
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Wilhelm und Else Heraeus-Seminar
„Particle Physics with Cold and Ultra-Cold Neutrons“
Scientific Organizers:
Hartmut Abele, Atominstitut, TU Wien
Bastian Märkisch, TU München
Physikzentrum Bad Honnef
Wednesday 24th – Friday 26th October 2018
Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
from D. Pocanic arXiv:1704.00192v1
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Beam Method: NIST Experiment
S. Dewey
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Measurement cycle measures
UCN spectral dependenceSmall final extrapolation
878.5(7)stat(3)sysResult:
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Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Observables and Statistics
Unpolarised neutrons
Correlation a ∆a ~ 5 ∙ 10-3
from proton spectrum
Fierz coefficient b ∆b ~ 1 ∙ 10-3
from electron spectrum or
β-asymmetry
Electron helicity h
Time for 109 events
• 5 hours (unpolarised)
• 1 day polarised 98%
• 2 days polarised 99.7%
• ×25 for pulsed mode
Polarised neutrons
• β-asymmetry A ∆A ~ 5 ∙ 10-4
• Proton asymmetry C ∆C ~ 3 ∙ 10-4
Neutrino asymmetry B ∆B ~ 1 ∙ 10-3
• Weak magnetism fWM > 3 σ
from β-asymmetry or
polarised spectra
Electron
Proton
Neutrino
Neutron Spin
A
B
C
a
Focus on non-coincident measurements due to high count rates:
![Page 36: CKM Unitarity and Neutron Beta Decay · Neutron Beta-Decay Two free parameters within SM (G F from muon decay) Ratio of coupling constants Quark mixing Axial-vector g A und vector](https://reader033.vdocuments.mx/reader033/viewer/2022060808/608ce1a4d5a00879f04cb904/html5/thumbnails/36.jpg)
Sensitive to scalar and tensor couplings
within SM: b = 0
Enters decay rate / spectra and
asymmetries:
Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017
Fierz Interference Term b
Requirement:
Calibration etc. independent of neutron data
Reach of existing PERKEO III data
Δb ≈ 3×10-2 from asymmetry.
Pending approval by the collaboration.
Only 1 out of 4 datasets.
![Page 37: CKM Unitarity and Neutron Beta Decay · Neutron Beta-Decay Two free parameters within SM (G F from muon decay) Ratio of coupling constants Quark mixing Axial-vector g A und vector](https://reader033.vdocuments.mx/reader033/viewer/2022060808/608ce1a4d5a00879f04cb904/html5/thumbnails/37.jpg)
Extra
Bastian Märkisch (TUM) | BEYOND 2018 | 29.11.2017