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UCN magnetic storage and neutron lifetime. V.F.Ezhov Petersburg Nuclear Physics Institute, Gatchina, Russia. ( ITEP - 2007 ).

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ucn magnetic storage and neutron lifetime
UCN magnetic storage and neutron lifetime

V.F.Ezhov

Petersburg Nuclear Physics Institute, Gatchina, Russia.

(ITEP - 2007)

slide3

After neutrino decoupling and electron-positron annihilation, neutron decay (lifetime ~ 880 sec) begins to deplete neutrons. Once temperature drops below 1.3·109 K, at t ~ 98 s, the rate of two-body and three-body reactions become negligible compared to the one-body reaction. Only neutron decay then dominates.

slide6

Neutron decay and Standard Model

CKM mixing matrix:

W.Marciano

A.Sirlin

PRL 96, 032002 (2006)

Required experimental accuracy for n and A

has to be about 10-3 and better.

the best results for neutron lifetime
N beam:

886.8±1.2±3.2 (NIST, 2003)

889.2±4.8 (Sussex-ILL, 1995)

UCN storagein material trap:

878.5±0.7± 0.3 (PNPI-ILL,2004)

885.4±0.9±0.4 (KI-ILL, 1997)

882.6±2.7 (KI-ILL, 1997)

888.4±3.1±1.1 (PNPI, 1992)

887.6±3.0 (ILL, 1989)

The best results for neutron lifetime

Particle data 2003

(without PNPI - ILL,2004):

n = (885.70.8) s

slide10

Data analysis with the most precise measurements of neutron decay

nVud

ΔVud=2.4σ

00Vud

Δ=2.4σ

The improvement of the accuracy of A-measurements

(factor of 3 or more) is extremely important.

slide11

Reflection of UCN by magnetic barrier W. Paul, in Proc. Int. Conf. on Nuclear Physics and Physics of Fundamental Particles, Chicago, 1951. V.V. Vladimirskii, Sov.Phys. - JETP 12, 740, 1961

  • Magnetic potential
  • For magnetic moment of neutron
  • Nuclear potential of Be
  • Magnetic field 1 T reflects neutrons up to 3.4 m/s, as Al.
  • + for and
  • – for
probability of depolarization
Probability of depolarization
  • Precession of magnetic moment
  • Adiabatic condition
  • ( -- is the velocity of neutron)
  • For case of strong field
  • (B = 1T), B = 1T/mm and velocity v = 3.4 m/s one can receive next relation for adiabatic condition:
  • 1.83108 >> 3.4103.
slide13

“UCN storage in the vessel with magnetic wall.”

JETP Letters 23(3), 1976

Y.Y.Kosvintsev, Y.A.Kushnir, V.I.Morozov

=25±2 sec

44 8 369 1986

Y.G.Abov, V.V.Vasil’ev, V.V.Vladirski, I.B.Rozhnin

JETP Letters, 44(8), 369, (1986)

Ю.Г.Абов, В.В.Васильев,В.В.Владимирский, И.Б.РожнинПисьма ЖЭТФ, т.44(8), 369, (1986).

Main problem of the current systems is too large electric power (about 100 kWt)

Main result:

It was shown firstly that it’s possible to obtain τ > 700 sec in the magneto-gravitational trap.

w paul f anton l paul s paul and w mampe z f physik c 45 25 1989
W. Paul, F. Anton, L. Paul, S. Paul, and W. Mampe, Z. f. Physik C 45, 25(1989).

Sextupole torus. Rs orbit of circulating neutrons.

τ= 877 ± 10 s

The achieved usable fieldof 3.5 T permits the confinement of neutrons in the velocity range of 5 – 20m/s corresponding to a kinetic energy up to 2 * 10-6 eV.

slide17

P.R. Huffman, C.R. Brome, J. S. Butterworth, K. J. Coakle,M. S. Dewey, S.N. Dzhosyuk, R. Golub, G. L. Greene, K. Habicht,S.K. Lamoreaux, C.E.H. Mattoni, D.N. McKinsey, F. E. Wietfeldt,& J.M. DoyleNature 403, 62, 2000

The main problems:

1. Filling and empting. If one use superconducting system, then he can’t switch on field too fast.

2. Huge setup and small storage volume

The trapping region is filled with superfluid 4He, which is used to load neutrons

into the trap and as a scintillator to detect their decay. Neutrons have a lifetime

in the trap of

τ = 750+330−200 s.

magnetic wall
Magnetic wall

1 – permanent magnet

2 – magnetic field guide

experimental advantage s
Experimental advantages
  • To control the depolarization of UCN we cover the inner trap walls with thin lay of fomblin that reflects depolarized UCN. In this case the depolarized UCN penetrate the magnetic barrier inside the solenoid and are measured by the UCN detector installed below the solenoid. Hence this detector may be used as monitor for depolarization losses during neutron storage.
  • Monitor of trap filling
  • Preliminary neutron spectrum preparation
  • Absence of neutrons heating at the moment of magnetic shutter switching on.
  • Possibility to divide fast and spin-flipped neutrons
problems
Cleaning. Magnetic wall is an ideal mirror, as a result there are stationary trajectories.

Efficiency of depolarized neutrons collection.

Problems
slide25

First stage: (2006)

Neutron guide diameter 20 mm

Without forced spin-flip

Second stage: (2007)

Neutron guide diameter 60 mm

Forced spin-flip is switched on

slide29

2005-2006

Volume 15 l

Neutron elevator Storage time

874.6 -1.6 +4 sec.

decay = 878.4  1.8 s.

ε = 0.90±0.02

slide30

…………………………………………………….…………………………………………………….

the best results for neutron lifetime1
N beam:

886.8±1.2±3.2 (NIST, 2003)

889.2±4.8 (Sussex-ILL, 1995)

UCN storagein material trap:

878.5±0.7± 0.3 (PNPI-ILL,2004)

885.4±0.9±0.4 (KI-ILL, 1997)

882.6±2.7 (KI-ILL, 1997)

888.4±3.1±1.1 (PNPI, 1992)

887.6±3.0 (ILL, 1989)

The best results for neutron lifetime

Particle data 2003

(without PNPI - ILL,2004):

n = (885.70.8) s

Magnetic trap (2007)

878.2  1.6 s.

Preliminary

our plans
Our plans
  • 2008 – increasing the volume to one order and increasing of magnetic barrier to 2 times
  • 2009 – run with new trap
slide36
V.F.Ezhov,1 B.A.Bazarov,1 P.Geltenbort,2 F.J.Hartman,3 N.A.Kovrizhnykh,4 A.Z.Andreev, 1 G.Ban5, A.G.Glushkov, 1 M.G.Groshev, 1 V.A.Knyazkov, 1 G.D.Krygin, 1 A.R.Muller, O.Naviliat-Cuncic5 S.Paul, 3 R.Picker, 3 V.L.Ryabov, 1 A.P.Serebrov, 1 O.Zimmer3,2

1 - Petersburg Nuclear Physics Institute, Gatchina, Russia.

2 - Institut Laue-Langevin, Grenoble, France.

3 - Technical University, Munich, Germany.

4 - Reseach Institute of electrophysical apparatus,

S-Petersburg, Russia.

5 - Caen University, France

slide39

2006-2007

Small diameter of neutron guide

ε = 0.90±0.02

decay = 878.4  1.8 s.

877.4±1.7 s.

Increased diameter of neutron guide

878.6±1.8 s.

decay = 878.2  1.6 s.

Preliminary

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