UCN magnetic storage and neutron lifetime

V.F.Ezhov

Petersburg Nuclear Physics Institute, Gatchina, Russia.

(ITEP - 2007)

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.

CKM mixing matrix:

V F udG G V

A0 2

V

1G A 2

G 1 3

2

ud 2n

4908.7 1.9 sV

1 3

R R 2 2 2

ud F

kft 1 1

V G 1 3

Required experimental accuracy for n and A has to be about 10-3 and better.

Neutron decay and Standard Model

~1.5 % ~2.4 %

u

n d

d

u

d p

u

e-

eW-

GA

GV

u

n d

d

u

d p

u

e-

eW-

u

n d

d

u

d p

u

e-

eW-

GA

GV

GA

GV

W.MarcianoA.SirlinPRL 96, 032002 (2006)

ud us ub

cd cs cb

td ts tb

d V V V d

s V V V s

b V V V b

The best results for neutron lifetime

N beam:• 886.8±1.2±3.2 (NIST, 2003)• 889.2±4.8 (Sussex-ILL, 1995)

UCN storage in 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)

Particle data 2003 (without PNPI - ILL,2004):

n = (885.70.8) s

Neutron decay and Standard Model (status in 2003)

2 2 2nud us ubV V V

1 0.9924(28)

0.0076(28) 2.7

nud

00ud

us

ub

V 0.9717(13)

V 0.9738(5)

V 0.2196(23) PDG(2003)

V 0.0036(9) PDG(2003)

nA,

00ft

2us1 V

n 00ud udV V 0.0021(26)

0.8

n

A=-0.1189(8) PERKEO 2002

885.7 0.8 s PDG(2003)

Data analysis with the most precise measurements of neutron decay

2 2 2nud us ubV V V

1.0038 28 = 1.4 -

2 2 200ud us ubV V V

0.9992 15 = 0.5 +

n 00ud ud

3

However

V V

2.4 1.0 10

2.4Δ=2.4σ

ΔV

ud=

2.4σ

nVud

00Vud

n 878.5 0.8 s (A.Serebrov et al. 2005)

A=-0.1187(5) (PERKEO 2005)

=-1.2733(13)

nud

2ud us

us

00ud

ub

V 0.97614(95)

V 1 V 0.97420(47)

V 0.2257(21) PDG06

V 0.97377(27) PDG06

V 0.0043(3) PDG06

The improvement of the accuracy of A-measurements (factor of 3 or more) is extremely important.

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

BU

17106.0 TeVU

eV7105.2

BBUF

)(

B

B

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:• 1.83108 >> 3.4103.

Bdt

dn

1181083.1 Tsn

BBvBdtdBBn /

v

=25±2 sec

“UCN storage in the vessel with magnetic wall.” JETP Letters 23(3), 1976

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

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

Y.G.Abov, V.V.Vasil’ev, V.V.Vladirski, I.B.Rozhnin JETP Letters, 44(8), 369, (1986)

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

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

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

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. Doyle Nature 403, 62, 2000

τ = 750+330−200 s.

The trapping region is filled with superfluid 4He, which is used to load neutronsinto the trap and as a scintillator to detect their decay. Neutrons have a lifetimein the trap of

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

Magnetic wall

1 – permanent magnet2 – magnetic field

guide

2004

Detector of both polarization

• 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

Experimental advantages

0 20 40 60 80 100

-20

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

Lift is out of trap

Lift is opened & magnetic shutter is switched on

Lift is moved

Shutter is opened

Inte

nsi

ty (

n/s

)

Time (s)

Filling with magnetic shutter on(1) Filling without magnetic shutter(2) Stored UCN (3)

Problems

• Cleaning. Magnetic wall is an ideal mirror, as a result there are stationary trajectories.

• Efficiency of depolarized neutrons collection.

First stage: (2006)Neutron guide diameter 20 mmWithout forced spin-flip

Second stage: (2007)Neutron guide diameter 60 mmForced spin-flip is switched on

00

0 0

trap decay trap dep trap

leak dep trap

trap

leak

dN t N t N t dt

dN t N t dt

N N

N

0

0

( )

( ) 1

decay leak

decay leak

t

trap

tleakleak

decay leak

N t N e

NN t e

00

0

0

0

ln

ln

traptrap leak

decay

trap

trapleak

dep

trap

N TN N T N T

N

T N N T

N TN T

N

T N N T

1 10 0 1 1 1 1

0 0

0 1 0 1 1

ln lntrap traptrap leak trap leak

trap trap

N T N TN N T N T N N T N T

N N

T N N T T N N T

Lifetime no depended method of efficiency measuring

400 600

-0,4

0,0

0,4

Inte

nsi

ty n

/s

Time (s)

CDepolarization on and off

1020

0

20

Inte

nsi

ty n

/s

Time (s)

CDepolarization on and off

1000 301

1 2

3011100 301

2 1

1001

( ( ) ( ))

( ( ) ( ))

t

t

f t f t e dt

f t f t e dt

decay = 878.4 1.8 s.

ε = 0.90±0.02

2005-2006Volume 15 lNeutron elevator Storage time 874.6 -1.6

+4 sec.

0 500 1000 1500 2000 2500

-5

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75In

ten

sity

Time

2200 2300401 401

401 2201

(400) 1/ ( ) ( )t t

N f t e dt f t e dt

1800 1900401 401

401 1801

(400) 1/ ( ) ( )t t

N f t e dt f t e dt

500 600401 2201

401 501

(400) 1/ ( ) ( )t t

N f t e dt f t e dt

…………………………………………………….

860 865 870 875 880 885 890195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

UC

N

decay

(s)

1000 s 1300 s 1800 s 2200 s 400 s

Convolution of different storage function to 400 s depended on neutron lifetime

877.4±1.7 s.

300 600 900 1200 1500 1800 2100 2400

16

32

64

128U

CN

Time (s)

22012300

2200 2200

2201

( ) decay

t

N f t e dt

1801 18011900 2200

1800 1800

1801 1801

( ) 1/ ( )decay decay

t t

N f t e dt f t e dt

878.6±1.8 s.

The best results for neutron lifetime

N beam:• 886.8±1.2±3.2 (NIST, 2003)• 889.2±4.8 (Sussex-ILL, 1995)

UCN storage in 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)

Particle data 2003 (without PNPI - ILL,2004):

n = (885.70.8) sMagnetic trap (2007)

878.2 1.6 s.Preliminary

Our plans

1. 2008 – increasing the volume to one order and increasing of magnetic barrier to 2 times

2. 2009 – run with new trap

• 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

4x10-4 8x10-4 1,2x10-3 1,6x10-3 2x10-3

22

24

26

28

30

32

34

36

B Linear Fit of Data1_B

Qu

an

tity

of n

eu

tro

ns

afte

r 2

20

0 s

of s

tora

ge

tim

e

Vacuum (torr)

Vacuum dependence

1

1

1

0ln

0ln

ppt

NtN

NtN

p

torrsp 1 04.015.0

1/s 0.001131/880 decay

torr10 6p

))exp((0)( tpNtN pdecay

877.4±1.7 s.

878.6±1.8 s.

decay = 878.4 1.8 s.

decay = 878.2 1.6 s. Preliminary

ε = 0.90±0.02 2006-2007 Small diameter of neutron guide

Increased diameter of neutron guide