Neutron decay data are useful
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Neutron decay data are useful. d ν e W u e −. u e − W d ν e. e − ν e W d u'. Many processes have the same Feynman diagram as neutron decay: Primordial element formation n + e + ↔ p + ν ' e σ ν ~ 1/ τ

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Neutron decay data are useful

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Neutron decay data are useful

Neutron decay data are useful

d νe

W

u e−

u e−

W

d νe

e−νe

W

d u'

Many processes have the same Feynman diagram as neutron decay:

Primordial element formation n + e+↔ p + ν'eσν~ 1/τ

(2H, 3He, 4He, 7Li) p + e−↔ n + νeσν~ 1/τ

n ↔ p + e− + ν'eτ

Solar cycle p + p ↔ 2H + e+ + νe

p + p + e− ↔ 2H + νe etc. ~(gA/gV)5

Neutron star formation p + e− ↔ n + νe

Pion decay π−↔ π0 + e− + ν'e

Neutrino detectors ν'e + p ↔ e+ + n

Neutrino forward scattering νe +n↔ e− + p etc.

W and Z production u' + d ↔ W−  e− + ν'e etc.

… precision data of weak interaction parameters

today only from neutron decay

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Calculated gains in neutron count rates

ILL-Millenium program

calculated gains in neutron count rates

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Neutron decay data are useful

Start-ups

2001S-DH GmbH: Neutron optics, H. Häse

2006 CASCADE GmbH : large fast n-detectors, M. Klein, C. Schmidt

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Neutron decay data are useful

t

History of the universe: a succession of phase transitions

TP NP AP FKP

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Only few standard model parameters in n decay

Only few Standard Model parameters in n-decay

n-decay rate:τ−1= const (|gV|2 + 3|gA|2)= constGF2 |Vud|2 (1+3|λ|2)

Only 2 parameters needed: CKM matrix elementVud,

(GF from muon decay)ratio of c.c. λ= gA/gV

… but many n-decay observables:

problem is overdetermined: many tests of Standard Model

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Many derived quantities from n decay

Many derived quantities from n-decay

Standard model:

axial to vector coupling c.c.λ = gA/gV

CKM- matrix element |Vud|

unitarity test of CKM-matrix Δ = Vud2 + Vus2 + Vub2  1 = 0?

weak magnetismμp−μn

all ν- p, ... weak cross-sectionsσνp/Eν= 0.67·10−38cm2/GeV

number of ν-families Nν= 2.5(6)

baryonic matter in universeρ/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

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


History of neutron lifetime

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':1960: τ = (101030) s

1982: τ = (92511) s

stored UCN:1989: τ = (8883) s

2004:τ = (885.70.8) s

R. Picker, Mo Abend

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


History g a g v

History: λ= gA/gV:

  • derived from β-asymmetry A:

  • λ=gA/gV= −1.19 ±0.02 1960

  • = −1.25 ±0.02 1975

  • = −1.261 ±0.004 1990

  • = −1.2695±0.0039 2005

  • = −1.2739±0.0015 2006

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Unitarity tests of upper row of ckm matrix

Unitarity tests of upper row of CKM matrix

|Vud|2 + |Vus|2 + |Vub|2 = 1 −ΔStandard Model: Δ = 0

↑0.0000

i.e. test of cos2θC + sin2θC

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

upper row, combined:

Δ = 0.0040 ± 0.0012

first column, with Vcd, Vtd:

Δ' = 0.0015±0.0054

if Δdue to right-handed currents:

phase ζ = 0.0020 ± 0.0006

Aim: all entries in CKM matrix from particle decays

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Nuclear super allowed 0 0 transitions

before nuclear corrections:

after nuclear corrections:

1σ band→

Nuclear super-allowed 0+→0+β-transitions

(plus corrections)

with half life t,

phase space factor f

J.C. Hardy, I.S. Towner,

PR C 71, 055501 (2005)

(from > 100 measurements)

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


New neutron lifetime measurement

new neutron lifetime measurement

reestablishes unitarity when using old Vus …

Δ ≈ 0 ± 0.001

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


New v us value

New Vus value

= by-product of ε'/ε-analysis:

2002↓↓2005

B.R. KL→πe ν, πμν

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

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Planned perc

e−

p+

B ~Tesla

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

  • bright:~ 106 neutron-decays/sec/m of beam

  • clean:under well defined conditions:

  • spectral distortions ≤ 10−4, background/signal ≤ 10−4, …

  • versatile:vary width and divergence of emerging p+, e− beam

  • without change of spectral properties

neutron puls in long piece of n-guide

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Example for setup

ILL user

10m

example for setup:

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−1for a pulsed beam polarized to 99.5%.

beam time for ~10−4 statistical error:

½ hfor continuous unpolarized,

3 hfor continuous polarized,

10 hfor pulsed unpolarized,

4 dfor pulsed polarized

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Neutron decay data are useful

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Magnetic mirror limits beam divergence

θcr

magnetic mirror limits beam divergence:

n-guidemagn. mirror→ to experiment

= 'keyhole'

B0

B1

B2

~10m

  • example:

  • magnetic field: 2Tesla 8Tesla ½Tesla

  • gyration radius: 2mm ½mm4mm

  • critical angle: 300 900 150

  • beam width can be traded against beam divergence, with negligible spectral distortion

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Of variable beam divergence

… of variable beam divergence:

guide field

B0

B1

high divergence

low divergence n-decay products

magnetic mirror field

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Neutron beamstop

cm

Scale×10

cm

B0=2TB1=8T B2=0.5T

B0=2TB1=8T B2=0.5T

↑ n-guide ↑ n and γ e and p ↑ absorbers window frame

↑ n-guide ↑ n and γ e and p ↑ absorbers window frame

neutron beamstop:

  • Charged neutron decay products can be guided anywhere (electro-)magnetically

  • Example:

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Examples a e spectroscopy from pol unpol n s

B2

e−

orificeenergy sensitive

detector

EXAMPLESa) e−spectroscopy (from pol., unpol. n's):

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


B magnetic p e spectroscopy

b) magnetic p+, e−spectroscopy:

MAGNETIC

SPECTROMETER

e−

B2 B3

window- ↑

frame p+

γ-shielding ↑ ↑ position- sensitive

detectors

Fig. 6: Sketch of a magnetic spectrometer for neutron decay products installed at the end of the beam line.

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


C aspect retardation spectrometer

p+

↑orifice

c) aSPECT retardation spectrometer:

  • ↑ aSPECT

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


D mott scattering

d) Mott scattering:

  • MOTT SCATTERING APPARATUS

e−

↑orifice

test of:

electron helicity He~ υe/c in hadron decay

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


Error sources

B

Transmission profile

of the absorbing frame:

n-guide

orifice→

Error sources

thin orifice: in 1st order no edge effect

  • thin orifice: no angular or spectral distortion of the p+, e− beam

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


2 nd order error sources of orifice

2mm

2nd order error sources of orifice:

  • 1. neutron beam not uniform over edge of orifice:

  • error 6·10−5 at Eβmaxfor 10% change of n-flux over 1cm width

  • 2.particles hit inner face of orifice:

  • solution: oblique edge angle >θ2

  • 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%

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


B effect of mag mirror field b 1 on p e

b) effect of mag. mirror field B1 on p+, e−:

a)

CRITICAL

ANGLE

b)

COUNT

RATE

1

80

0.8

60

0.6

0

0

N

c

40

N/

0.4

20

0.2

0

0

0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1

B0/B1

B0/B1

c)

ASYMMETRY

d)

EFFICIENCY

1

1.2

1

0.8

0.8

0.6

0

2

A

A

0.6

A/

N

0.4

0.4

0.2

0.2

0

0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1

B0/B1

B0/B1

Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM


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