Transcript Michaelson Morley Experiment

Neutron decay data are useful
Many processes have the same Feynman diagram as neutron decay:
νe
d
Primordial element formation
(2H, 3He, 4He, 7Li)
Solar cycle
Neutron star formation
Pion decay
Neutrino detectors
Neutrino forward scattering
W and Z production
n + e+ ↔ p + ν'e
σν ~ 1/τ
p + e− ↔ n + νe
σν ~ 1/τ
n ↔ p + e− + ν'e
τ
p + p ↔ 2H + e+ + νe
p + p + e− ↔ 2H + νe etc. ~ (gA/gV)5
p + e − ↔ n + νe
π− ↔ π0 + e− + ν'e
ν'e + p ↔ e+ + n
νe + n ↔ e− + p etc.
u' + d ↔ W−  e− + ν'e etc.
W
e−
u
e−
u
W
νe
d
e−
νe
W
d
u'
… precision data of weak interaction parameters
today only from neutron decay
Schleching 2008
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.1
ILL-Millenium program
calculated gains in
neutron count rates
Mean gain in ILL total efficiency
18
16
14
12
Instr.+Guide
Renewal
10
8
Instr. Renewal
Only
6
4
2
2009
2007
2005
2003
2001
1999
0
Year
Schleching 2008
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.2
Start-ups
2001 S-DH GmbH: Neutron optics, H. Häse
2006 CASCADE GmbH : large fast n-detectors, M. Klein, C. Schmidt
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Experimente diesseits SM
4.3
History of the universe: a succession of phase transitions
Temperature
kT =
10+19 GeV
10+16 GeV
10-11 GeV
Planck scale
Grand Unification
Inflation ...
... wenn H = å/a ≈ const.
Chiral phase transition
Nucleon freeze out
Electroweak transition
Nuclear freeze out
Atomic freeze out
Galactic freeze out
(T = 2.726 K)
Big
Bang 10-43 s
10-35 s
10-12 s
1s
TP
NP
AP
FKP
105 y 109 y today
Time
t
…
Schleching 2008
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Experimente diesseits SM
4.4
Only few Standard Model parameters in n-decay
n-decay rate:
τ −1 = const (|gV|2 + 3|gA|2) = const GF2 |Vud|2 (1+3|λ|2)
Only 2 parameters needed:
(GF from muon decay)
CKM matrix element Vud,
ratio of c.c. λ = gA/gV
… but many n-decay observables:
decay rate  1  const Vud (1  32 ),   885.7(8) s
1  2
e   e  correl.: a 
 0.103(4)
2
1  3
 (  1)
β  asymmetry: A  2
 0.1173(13)
1  32
 (  1)
ν e  asymmetry: B  2
 0.981(4)
2
1  3
4
p  asymmetry: C  0.2748
 0.238(11)
1  32
 T - Violating triple- correlation D,
 correlations involvingelectronspin : R, N , G, ..., plus n  Hν data?
2
problem is overdetermined: many tests of Standard Model
Schleching 2008
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Experimente diesseits SM
4.5
Many derived quantities from n-decay
Standard model:
axial to vector coupling c.c.
CKM- matrix element
unitarity test of CKM-matrix
weak magnetism
all ν - p, ... weak cross-sections
number of ν-families
baryonic matter in universe
λ = gA /gV
|Vud|
Δ = Vud2 + Vus2 + Vub2  1 = 0 ?
μp − μn
σνp/Eν = 0.67·10−38 cm2/GeV
Nν = 2.5(6)
ρ/ρcrit = 3.3(7) %
beyond Standard model:
mass of right-handed boson
m(WR) > 300 GeV/c2 (90% c.l.)
left-right mixing angle
0.20 < ζ < 0.07
(90% c.l.)
scalar weak interaction amplitudes
gS
tensor weak interaction amplitudes
gT
Fiertz interference amplitude
b
second class amplitudes
neutrino helicity < 1? (semileptonic decays)
T-viol. amplitudes ... and others
Aim: measure all these parameters to the highest precision possible
Schleching 2008
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.6
History of neutron lifetime τ
best measured with stored ultracold-neutrons ('UCN', Tn ~ 1mK)
.
· ·
.
· ·.
. . ·
· .
.
. ·
. ·
. UCN
N = Noexp(– t/τ)
→ decay rate:
τ−1 = const × |Vud|2 (1 + 3λ2)
short history:
neutrons 'in-beam':
stored UCN:
1960: τ = (101030) s
1982: τ = (92511) s
1989: τ = (8883) s
2004: τ = (885.70.8) s
R. Picker, Mo Abend
Schleching 2008
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Experimente diesseits SM
4.7
History: λ = gA/gV:
derived from β-asymmetry A:
λ =gA/gV = −1.19 ±0.02
= −1.25 ±0.02
= −1.261 ±0.004
= −1.2695±0.0039
= −1.2739±0.0015
Schleching 2008
1960
1975
1990
2005
2006
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.8
Unitarity tests of upper row of CKM matrix
|Vud|2 + |Vus|2 + |Vub|2 = 1 − Δ
↑0.0000
i.e. test of cos2θC + sin2θC
Standard Model: Δ = 0
DEVIATION FROM UNITARITY
0,015

0,010
Vud from:
n:
Nucl:
:
0,005
upper row, with:
Vud= 0.9717±0.0013 n
Vud= 0.9740±0.0005 Nuclei
Vud= 0.9728±0.0030 π
Vus= 0.21960±0.0023 K
Vub= 0.0036±0.0009 B
0,000
-0,005
upper row, combined:
Δ = 0.0040 ± 0.0012
if Δ due to right-handed currents:
first column, with Vcd, Vtd:
Δ' = 0.0015±0.0054
Aim: all entries in CKM matrix
from particle decays
Schleching 2008
phase ζ = 0.0020 ± 0.0006
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.9
Nuclear super-allowed 0+→0+ β-transitions
ft 
K
GF2 Vud
2
before nuclear
corrections:
(plus corrections)
with half life t,
phase space factor f
J.C. Hardy, I.S. Towner,
PR C 71, 055501 (2005)
after nuclear
corrections:
1σ band→
Schleching 2008
(from > 100 measurements)
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.10
new neutron lifetime measurement
Neutron Lifetime, recent results
900
neutron lifetime (s)
895
890
all
previous
885
880
new
value
875
870
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
Year
reestablishes unitarity when using old Vus …
Δ ≈ 0 ± 0.001
Schleching 2008
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Experimente diesseits SM
4.11
New Vus value
= by-product of ε'/ε-analysis:
2002↓
↓2005
B.R. KL→ π e ν, π μ ν
reestablishes unitarity when using old τn:
PDG 2006, all measurements:
Δ = 0.0008 (5)ud (9)us
Other strategy: assume unitarity to hold → strong-interaction physics
Schleching 2008
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.12
planned: PERC
collect charged decay products from within a long piece of cold n-guide:
n-guide = source of neutron decay products:
"Proton-Electron Radiation Channel" PERC
B ~Tesla
e−
p+
neutron puls in long piece of n-guide
bright:
clean:
versatile:
Schleching 2008
~ 106 neutron-decays/sec/m of beam
under well defined conditions:
spectral distortions ≤ 10−4, background/signal ≤ 10−4, …
vary width and divergence of emerging p+, e− beam
without change of spectral properties
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.13
example for setup:
ILL user
10m
example: B0=2T, B1=8T, B2=½T:
count rates:
6104 s−1 for a continuous unpolarized n-beam;
1104 s−1 for a continuous beam polarized to 98%;
3103 s−1 for a pulsed unpolarized beam;
3102 s−1 for a pulsed beam polarized to 99.5%.
beam time for ~10−4 statistical error:
½ h
for continuous unpolarized,
3 h
for continuous polarized,
10 h
for pulsed unpolarized,
4 d
for pulsed polarized
Schleching 2008
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Experimente diesseits SM
4.14
Error budget of PERC (not all measurements sensitive to all errors)
correction
in units of 10−4
orifice:
1. non-uniform neutron beam profile over orifice
0.6
2. finite thickness of orifice
3. electron escape from orifice
error
0.2
eliminated
1
0.2
1
0.3
0.5
0.5 (M-C- req.)
4
1
solid angle of p+, e− emission:
4. non-uniformity of B0-field
5. non-adiabatic variation of B1-field; adiabatic decoupling from B2-field
background:
6. from neutron guide
7. from n-beam shutter, pulsed neutron beam
from n-beam shutter, continuous neutron beam
non-existent
1
8. from n-beam stop, pulsed neutron beam
from n-beam stop, continuous neutron beam
1 (exp. study req.)
non-existent
2
1
9. from beam window
1
0.2
10. from electron/proton beam dump
2
0.4
11. from electron/proton detector (user's responsibility)
6
1
5
5
e−/p+ backscattering:
neutron polarization:
12. polarisation measurement
Präzisionsphysik
mit Neutronen / 4.
Schleching 2008
13. depolarisation
in non-magnetic supermirror
guide
Experimente diesseits SM
At present (for β-asymmetry A, total, D. Mund (2005)):
present: 34
≤5
present: 39
4.15
magnetic mirror limits beam divergence:
n-guide
magn. mirror
= 'keyhole'
B0
B1
→ to experiment
θcr
B2
~10m
example:
magnetic field: 2Tesla
gyration radius: 2mm
critical angle:
300
8Tesla
½mm
900
½Tesla
4mm
150
beam width can be traded against beam divergence, with negligible spectral distortion
Schleching 2008
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Experimente diesseits SM
4.16
… of variable beam divergence:
B1
high
divergence
guide field
B0
low divergence
n-decay products
magnetic
mirror field
Schleching 2008
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.17
neutron beamstop:
Charged neutron decay products can be guided anywhere (electro-)magnetically
Example:
10
7.5
5
2.5
0
2.5
5
7.5
M AGNETIC FIELD LINES
B0=2T
B1=8T
50
10
7.5
B =2T
5 0
2.5
0
2.5
5
7.5 ↑ n-guide
B1=8T
B2=0.5T
↑ n and γ
absorbers
↑ n-guide
50 γ
↑ n and
absorbers
0
B2=0.5T
MAGNETIC FIELD LINES
x cm
x cm
cm
0
e and p ↑
window frame
50
100
150
z cm
50
Scale×10
100
200 p ↑
e and
window frame
150
200 cm
z cm
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Experimente diesseits SM
4.18
EXAMPLES
a) e− spectroscopy (from pol., unpol. n's):
B2
orifice
Schleching 2008
e−
energy sensitive
detector
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.19
b) magnetic p+, e− spectroscopy:
MAGNETIC
SPECTROMETER
e−
B2
B3
window- ↑
frame
p+
γ-shielding ↑ ↑ positionsensitive
detectors
Fig. 6: Sketch of a magnetic spectrometer for neutron decay products
installed at the end of the beam line.
Schleching 2008
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Experimente diesseits SM
4.20
c) aSPECT retardation spectrometer:
p+
↑orifice
↑ aSPECT
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Experimente diesseits SM
4.21
d) Mott scattering:
e−
MOTT
SCATTERING
APPARATUS
↑orifice
test of:
electron helicity He ~ υe/c in hadron decay
Schleching 2008
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Experimente diesseits SM
4.22
Error sources
thin orifice: in 1st order no edge effect
orifice→
0.2
0.4
1
n-guide
Te 0.6
B
0.8
FRAM E TRANSM ISSION
1
0.5
0
0.5
1
LATERAL POSITION x x2
Transmission profile
of the absorbing frame:
thin orifice: no angular or spectral distortion of the p+, e− beam
Schleching 2008
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.23
2nd order error sources of orifice:
1. neutron beam not uniform over edge of orifice:
error 6·10−5 at Eβmax for 10% change of n-flux over 1cm width
2. particles hit inner face of orifice:
solution: oblique edge angle >θ2
2mm
3. non-perfect absorption near edges:
error 4·10−3 × 0.1 "active edge"
N.B.: electron scattering effects can be calculated reliably to better than 10%
Schleching 2008
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
4.24
b) effect of mag. mirror field B1 on p+, e−:
a) CRITICAL ANGLE
b) COUNTRATE
1
80
0.8
c
0
N/N0
60
40
20
0.4
0.2
0
0
0
0.2 0.4 0.6 0.8 1
B0/B1
0
c) ASYMMETRY
1
0.2 0.4 0.6 0.8
B0/B1
1
d) EFFICIENCY
1.2
1
0.8
0.8
0.6
NA2
A/A0
0.6
0.4
0.6
0.4
0.2
0.2
0
0
Schleching 2008
0.2 0.4 0.6 0.8
B0/B1
1
0
0.2 0.4 0.6 0.8
B0/B1
Präzisionsphysik mit Neutronen / 4.
Experimente diesseits SM
1
4.25