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