Ultracold neutrons and Ultracold neutrons and neutron decayneutron decay

Oliver Zimmer

ILL Grenoble / TU München

19th Int. IUPAP Conf. On Few-Body Problems in Physics Bonn, 14 July 2008

Institut Laue-Langevin

Forschungsreaktor FRM II

WWhere do our here do our neutrons come neutrons come

from?from?Reactor sources:

Spallation sources:

58 MW

20 MW

SNS Oak Ridge (ramping up)

PSIVillig

en

reactor core

cold source

Verticalguide

Neutron turbineA. Steyerl (TUM/ILL 1985)

Ultracold neutron production at in Ultracold neutron production at in GrenobleGrenoble

Properties of UCN

900 total reflection angle storage in bottles possible long observation time high precision in experiments

~50 cm-3

Ekin < 250 neV, > 80 nm, v < 7 m/s, “T” 2 mK

The turbine for neutron

decceleration…

…a neutron phase space

transformer

VCN

UCN

A. Steyerl et al., Phys. Lett. A 116 (1986) 347

(50 cm-3)

„„Superthermal“ production of UCNSuperthermal“ production of UCN

• no thermal equilibrium of neutron gas with scattering system

• Conversion of cold neutrons to UCN by a converter (dominantly by emission of single phonon)

• up-scattering suppressed by Boltzmann factor “accumulation” of neutrons as UCN

EUCN

EUCN +

UCNcold neutron Phonon

downscattering

• detailed balance:

for >> kBT >> EUCN up << down

B/UCNup down

UCN

k TEe

E

• two converter materials:

Solid deuterium (SD): abs 0 0.15 s in-pile needed

superfluid 4He (He-II): abs = 0 800 s (<n) beam possible

but in-pile even better

Some projected UCN sources (SD)Some projected UCN sources (SD)

Mainz TRIGA: currently 2×105 UCN/pulse 20/cm3 in V = 10 l,

(after upgrade 2×106 UCN per pulse)

student‘s training and UCN developments

UCND2&Cryo

Mini-D2 source

Mini-D2 UCN source at Munich:104/cm3 in transport tube with V = 30 liters

present UCN density at ILL: 30/cm3

PSI: > 1000/cm3 in V = 2000 liters

• reaction cross section reaction = 0

• 0.7 K: storage 500 s (due to phonon absorption)

0.5 K: storage 800 s

• PI = 14 cm-3s-1 at intense cold beam (for d/d(0.89 nm) = 3109 cm-2s-1nm-1)

UCN 104 cm-3 possible at a cold-neutron guide

„phonon-roton“ dispersionof superfluid 4He

free neutron dispersion

q

7 nm-1

12 K

UCN storageP

R. Golub, J.M. Pendlebury, PL 53A (1975) 133

converter

cold neutron beam

UUCN production in superfluid CN production in superfluid heliumhelium

0 100 200 300 400 500 6000

200

400

600

800 T = 0.82 K

UC

N c

ount

rat

e (s

-1)

time (s)

First successfull extraction of UCN accumulated in superfluid helium

O.Zimmer et al., Phys. Rev. Lett. 99 (2007) 104801

Experiments at FRM II with prototpye He-II UCN source

At the beam (NL1 at FRM II)At the beam (NL1 at FRM II)

Source location Source type UCN density [cm-3]

comment when?

ILL Grenoble, PF2 LD2 + turbine 50 still THE source > 1985

Los Alamos, 2.4 kWav proton

SD2 120 in source now

Mainz TRIGAupgraded

SD2 20 200

in V = 10 l now2009

ILL Grenoble, H172 upgraded + magnetic trap

He-II (0.5 K) > 10002000

polarised

in V = 6.4 lup to 40 l

2009> 2011

PSI, 12 kWav proton SD2 > 1000 in V = 2000 l 2010

North Carolina, 1 MW reactor

SD2 1300 in source 2011

Munich, 20 MW reactor SD2 10000 in source 2011

PNPI, 16 MW reactor He-II (1.2 K) 130007700

in 35 l exp. bottlein 350 l exp.

bottle

2012

TRIUMF, 5 kWav proton He-II (0.8 K) 18000 at exp. port proposal+ insitu He-II UCN sources at ILL (Cryo-EDM), NIST (n-lifetime), and SNS (EDM)

IInternational competition in UCN productionnternational competition in UCN production

A w

orld of matternEDM

neutronlifetime

???

nuclear few-bodyinteractions

Big bang nucleosynthesis and the neutron Big bang nucleosynthesis and the neutron lifetimelifetime

10-6 s (100 MeV): quarks & gluons form nucleons

n + e+ p + , n + p + e, n p + e +

1 s (1 MeV): neutrinos decouple neutrons freely decay

n p + e + , p + n d +

3 min (0.1 MeV): deuterons become stable

p(n,)d, d(d,n)3He, d(d,p)3H, 3He(n,)4He ...

after 30 min: primordial abundances of light elements:

2n pn

expp

m m c

kT

1H 75%4He 25%2H 30ppm3He 13ppm7Li 410-10

G. Mathews et al., Phys. Rev D 71 (2005) 021302

NNeutron eutron decay decay

V1 2

n21 3g A Vg g

in Standard model:

„V-A“ structure with known Fermi- and Gamow-Teller matrix elements

precise determination of gA and gV from two independent n-decay observables

semileptonic weak cross sections

e.g. test of CKM unitarity:

n + e+ p + e n + e p + e p + p d + e+ + e ...

usu bd u

2 2 2 1V VVFV udg G V

+ various other tests of the standard model – listen next talk in this session!

from asymmetry (PERKEO)

H. Abele, Prog. Part. Nucl. Phys. 60 (2008) 1

H. Abele, Prog. Part. Nucl. Phys. 60 (2008) 1

A. Serebrov et al.,PLB 605 (2005) 72

885.7(8) s

878.5(8) s

Experiments

1975 1980 1985 1990 1995 2000 2005865

870

875

880

885

890

895

ne

utr

on

life

time

va

lue

s

year

cold beam UCN

cold neutron beam:

UCN storage:

A. Serebrov et al., Phys. Lett. B 605 (2005) 72

UCN

Neutron lifetime experiment with low-T Fomblin oil coated walls

1storage

1l ssn o

1

878.5(8) s

Frequency of wall collisions (/s)

UCN storage in a trap from permanent magnetsUCN storage in a trap from permanent magnets

(PNPI – ILL – TUM)

V. Ezhov et al., J. Res. NIST 110 (2005) 345

Follow-up trap design (PNPI):

slit for filling

1.2 m

superconducting coilsB 2 T (at wall)

focusing coils

proton detectors

volume ~ 700 l

UCN UCN detector

neutron absorber

UCN = 103 – 104 cm-3 (PSI /FRM II):

Nstored = 107 – 108

– Statistical accuracy:

n ~ 0.1 s in 2-4 days

– Systematics:

• Spin flips negligible (simulation)

• use different values Bmax to check

expected EUCN independence of

PProposed large volumeroposed large volume magnetic storage experimentmagnetic storage experiment

R. Picker et al., J. Res. NIST 110 (2005) 357

no UCN collisions with material walls:

S. Paul et al.

P. Huffman et al., Int. workshop Particle Physics with

slow Neutrons, May 2008 ILL

A superconducting Ioffe trapA superconducting Ioffe trap

UCN production in He-IIand in-situ detection (NIST)

D. Bowman, Int. Workshop UCN Sources and Experiments Sept. 13-14 2007 TRIUMF

Bx

cold neutron beam

beam switched off

we preparewe prepare NNeutron eutron llifetime experimentifetime experiment with with

magneto-peristaltic UCN extraction from superfluid magneto-peristaltic UCN extraction from superfluid 44He into He into

a magnetic trapa magnetic trap

Halbach magnetic octupole (1.3 T) with

V = 5 liters and 106 neutrons per filling

statistical accuracy: 0.1 s in 50 days

O. Zimmer, NIM A 554 (2005) 363K. Leung, O.Z., arXiv:0811.1940

protondetector

Merci!

The end... or rather the beginning