Fundamentale WechselwirkungNeutronenphysik

W.Heil

Einleitung Präzisionsexperimente mit ultrakalten Neutronen und Perspektiven ß-Zerfall des Neutrons und Tests des Standard Modells Zusammenfassung

NEUTRON discovery 1932 ( J. Chadwick ) + 9Be n + 12C ( via H(n,p)-reaction )

Q < 10-21 e , Baumann et al., ´88

Spin: I = ½ ; n = - 1.913 K

T = 885.7 0.8 s , PDG 2004 ( n p + e + e )

Particle physics at low energies

EDM of the neutron ( CP-violation )

Beta-decay experiments: neutron lifetime measurements angular correlation experiments

Quantum states and gravitation

n-n oscillation, n-n‘ oscillation, …

Neutrons as probe: = h / mv : O(Ǻ)

scattering amplitude:

~ < bc + bi + /2·re · · M⊥( r ) > , bc bi re 3 fm

structure and dynamic of condensed matter

takes part on all four known fundamental interactions ( strong, weak, elmg., gravitative)

Spectrum of

Neutrons

UCN: v < 6 m/s

storageexperiments

Fluence rate (109 cm-2s-1) 4 14 2 (20)

Fluence rate (108 cm-2s-1) 8 (10) (5)

CP-violation and EDM

EDM is a test for flavour diagonal CP- test of structure of vacuum at small distance scales- background free probe for ‚new physics‘

CP in nucleons (neutron) needed for- Baryogenesis problem (matter vs. anti-matter in the universe)- test of CP violating part in QCD ( -term )

EDM can be studied in-Diamagnetic atoms-Paramagnetic atoms, molecules ( CP electron-EDM)-Neutron ( CP in quark sector )

EDM verletzt P und T Symmetrie

Neutron EDM: ˆN Nd d J

dn < 310-26 ecm (90% CL)

[ecm]

The neutron EDM:

Progress at order of magnitudeper decadeStandard Model out of reachstrong contrains on e.g. Super Symmetry

exp. vs theory

Proposed limits on dn

(10-28) e·cm

C.A.Baker et al.,

Ramsey’s Technique

4.

3.

2.

1.

Free precession...

Apply /2 spinflip pulse...

“Spin up” neutron...

Second /2 spinflip pulse.

B B BE E

-+

Apparatus

Neutronstoragechamber

HV

B-fieldcoils

E = 7 kV/cm

B = 1 T

Hg co-magnetometer

Neutron EDM result

dn < 310-26 ecm

Sensitivity figure

at present: visibility: 0.5 ( neutron polarisation ) electric field: E 7 kV/cm ( limited by Hg co–magnetometer ) storage time : T = 130 s ( limited by T2 of Hg co-magnetometer ) Nucn/batch : N 13000 ( ucn 1 cm-3 - UCN density !!! )

1 day of data ( 360 Ramsey-cycles ) : ecmEDMn25

, 104

1 year of data ( 250 days ) : ecmEDMn26

, 105.2

statistically limited !!!

2nd

E T N

Density of neutrons with velocities between v and v+dv at thermal equilibrium

2

2 20 4

2 exp ( / )v

v dv v dv

2 /Bk T m

Density of ultra-cold neutrons: 0 ≤ E ≤ VF

2max

3/ 21/ 2

0

0

2

3

FV mv

FUCN

B

Vv dv

k T

ILL-Grenoble: T0 =300 K

= 2.2x105 cm/s VF = 200 neV 0= 61014 n/cm2/s

UCN 40 cm-3

gain due to cooling

3/ 2

0T

T

UCN production ( conventional )

1000 / cm3liquid D2: 25 lT = 25K

40 / cm3

Superthermal UCN sources

( En= ) >> kBT >> EUCN

exp ( / )Sup thUCN Bk T

3/ 2

0thUCN

TT

R.Golub, J.M.Pendlebury, Phys.Lett. A53,133 (1975)

T 0.5 K

at present : P 1 UCN/cm3/s

Superfluid He ( T 0.5K)

Cryogenic Neutron EDMExperiment at ILL

solid deuterium

Cryostat with neutron detector

research reactorTRIGA-Mainz

UCN TOF-spectrum

200.000 / pulse

Mainz, TUMcollaborationEPJ A (’07) in press

104

102

100

10-2

10-4

10-6

1970 19901980 2000 2010

UC

N d

en

sit

y /

cm

3

Experiments: - nEDM - n-lifetime

- n quantum states in the Earth‘s grav. field - angular correlation coefficents in n ß-decay - ...

Test Newton with Neutrons Quantum states and gravitation

/1 2( ) (1 )rm mV r G e

r

Newton + Yukawa Potential

arising from higher-dimensional gravity,

gauge forces or massive scalar fields

/' 3

2z

E

ge

g R

- strength factor

- Yukawa-length

10 ; 1z m

12' 10gg

Neutron mirror: polished glass plate 10 cm long Nature 415 299 (2002), Phys. Rev. D 67 102002

(2003).

1 peV

2 peV

3 peV

4 peV

UCN

v↑ 1 cm/s6z m

m v

rate: mHz

Baeßler et al. PRD 2007Westphal, Abele, Baeßler

arXiv:hep-ph/0703108

Limits

e

e

e e e en

e e

ee

e

e

1

+ ...

a

A

p p

E E

p p p p p

E E E

mdW E

E

B D

b

RE E

Obserables in neutron ß-decay

pn

e-

e

n

e

dn

21u

2 2e 1 3FE G V Neutron lifetime

Beta-Asymmetry

Jackson et al., PR 106, 517 (1957):

2

2

Re2

1 3A

Neutrino-Electron-Correlation

2

2

1

1 3a

Standard Model

(re-)measured by:

PENELOPE

aSPECT

PDG 2006:

12

ub

2

us

2

ud VVV!

CKM-Unitarity of first row:

( , , )n A a Kaon decay

Neutron lifetime measurements beam experiments

n

dN N

dt

(e-, p)

… register the decay products from a well-defined volume traversedby a beam of well-determined fluence rate (absolute measurement)

storage experiments

…measure the decay product of an ensemble of neutrons as a function of time and determine the slope (relative measurement), but …

0( ) ( ) exp ( )tN t N t

1 11l ssn o

n

MAMPE

Neutron Lifetime versus Year

Serebrov et al.,

Phys. Lett. B 605, 72 (2005)

(878.5 ± 0.7 ± 0.3) seconds

Data points used by PDG 2004 for

averaging

BWF 2005

New approach… magnetic storage

F B

( PNPI, ILL, TUM )

bottle made of super-conducting magnets

measure storage and decay

expected ( FRM II ):108 UCN @ V= 700 L

goal: rel.statistical uncertainty

4/ 10n n

new Vus value

Perkeo II ( Abele et al.)(Wu-experiment)

( ) 1 cosßvW A

c

Perkeo (2002): 1.274(2)

Perkeo (2006): 1.275(1)

corrections to superallowed0+→0+ nuclear ß-decayHardy,Towner, arXiv:0710.3181v1, Oct‘07

lower average Ft-values

higher Vud

… towards a strong source of n-decay products

10 2 10 10 n cm s

cold neutron guideILL, FRM II :

A = 100 cm2

800 /v m s 106 n-decays s-1 m-1

… PERC (Dubbers et al.)

Zusammenfassung:

Neutronenphysik (heute)

- dN < 310-26 e cm- Unitarität der CKM-Matrix ( = 0.0008(14)- Quantenzustände im Gravitationsfeld (peV)- …

Angenommen das Neutronhätte die Größe der Erde...

x 1mNeutronenphysik (morgen) ab 2010: leistungsstarke Quellen ultrakalter Neutronen ( PSI, FRMII, ILL,TRIGA, …) mit Dichten 102 < < 104 cm-3 leistungsstarke Quellen für e-, p aus dem Neutron ß-Zerfall ( PERC,…)

ucn

sensitiv auf dN 10-28 ecmGravitation: E 10-18 eV n-Lebensdauer: nn‘ , nn –Oszillationen ……

0.1n s