# Presentation: 723277

## Diamond-like Carbon for                             Ultra-cold Neutrons

- Peter Fierlinger, PSI UCN group

- Collaboration:
- PSI Villigen
- ETH Zürich
- Universität Zürich
- Fraunhofer IWS Dresden

## Ultra-cold neutrons

- 	- Gravity ~ 100 neV / m
- 	- Magnetic field ~ 60 neV / T
- 	- Strong interaction:
- 			„Fermi potential“

- UCN can be stored in traps for ~ 1000 s

- V**┴**

** **

- Spallation target

- Shutter

- n-Guide

- Cold sD2 moderator

- UCN storage volume, 2m3

- UCN tank system
-      (~6m high)

- D2O moderator

- Coated walls

- To experiments

- p beam

**3000 UCN/cm3**

- Talk M. Daum

## Storage materials

- low loss probability per wall collision μ
- 	long storage time
-       μ(E) ~ 
- high Fermi potential
- 	more UCN
- low spin flip probability 
- 	polarized UCN
- 	(e.g. in nEDM)

## Diamond-like Carbon

- „sp2“

- „sp3“

- DENSITY

## Reflectometry

- φ

- φ

- v┴

- Detector

- V┴ ~ < 7 m/s ~ UCN

- Other methods used: XPS, NEXAFS, Raman, LaWAVE, UCN time-of-flight

**DLC foil**

## DLC test experiment

- 1.5 T Magnet

- Gravity

- Material

- polarized
- UCN

## Setup:

- Switch

- Coils (300 A, 200 V)

- Cooling

- Sample (1m)

- Neutrons

- Detector

- n+3Het+p+780keV

- NIMA550(2005)637

## Measurement

- Detector count rate:

- B

**Sample**

- Magnet

- UCN from ILL-turbine

- Detector

- B

- 105
- 1

- 100 %
- 0

- 0	 100	   200	      300          400

- time [s]

## Method I: results

- Wall loss coefficient    [1 / wall collision]

- x 10-4

- DLC is a good choice 

- PLB625(2005)19

## Method I & II: results

- Spin flip probability   [1 / wall collision]

- 	...Method I
- 	...Method II

## Interpretation

- So-called „anomalous losses“:
- (0 K) ~ 2**.**10-7 theor.
- but:     ~ 10-5 exp.

- Hydrogen:  = C + H   	Debye Model

## Outlook

- DLC TESTS: Foilbottle

- DLC PRODUCTION: PLD setup @ PSI

## BACKUP

## DLC Deposition on large foils

- Fraunhofer Institut Dresden, Coating facility in Dortmund

## Vacuum Arc Deposition

**1**...igniting Laser with beam guides**2**...cathode cylinder**3**...anode**4**...filtering electrode**5**...plasma beam**6**...opening to the coating chamber

## Motivation: nEDM

-  ILL-Sussex-RAL (1999):
-  ( -1.0 ± 3.6 ) ·10-26 e·cm

- Theoretical predictions:
- SUSY : 10-25-10-28** **e·cm

- Imagine the neutron were the size of the Earth...

- x  1m

## nEDM measurement

- B0

- B0

- B0

- B1

- B0

- B1

- Free Precession

- /2 Pulse

- Polarized UCN
- in a trap

- /2 Pulse

**100 s**

- +

- +

- ±E

## UCN Transmission

- _EDM-UCN beam at ILL:_
- TOF
- Foil coated with
- Be (black)
- DLC (red)

- UCN

- Chopper

- Sample

- Detector

- 2 m

## UCN Physics in Geant4

- Fermi potential, wall reflections
- Wall losses & spin-flips
- Absorption, scattering
- gravitational &                                                           magnetic fields                                                              (space-, time-dependent)
- Numerical solution of                                                          the Bloch equation

- L/

- from NIM A 457 (2001), 338-346

- components of P after /2 flip at |B| = 1g

- Filling

## RK4

## Low field transitions

- B0

- Bearth

## Spin tracking

- Coupled equations:

- „Bloch“-equation

- Treated classically

## Penetration depth

- .... „Penetration depth“

- Energy inside the barrier

## The Magnet

## Neutron life time

- CKM (quark mixing) matrix is unitary:

-            Vud (neutr)	= 0.9725±0.0013   PDG 2004
-            Vud (nucl)	= 0.9740±0.0005

- Coupling for Leptons = Coupling for Quarks

- (885.7±1 s) PDG 2004

- STATISTICAL LIMIT

## Maxwell spectrum

- v

- vUCN < 7m/s

- vth ~ 2 km/s

- vc ~ 1 km/s

## 4He

## Maxwell Distribution

** **

- Neutron density between v and v+dv at thermal equilibrium** **

- (average velocity)

## A oder  und B 

- A mit den elektronen
- B mit neutrino

## The spectrometer PERKEO II 

*The spectrometer** **P**ERKEO** II** *
*(Heidelberg – ILL)*

- [J. Reich, H. Abele, D. Dubbers *et al.*, NIMA 440 (2000) 535]
-  // [H. Abele, S. Baeßler. D. Dubbers *et al.*, to appear in PRL]:

- [H. Abele, S. Baeßler, D. Dubbers *et al.*, PLB 407 (1997) 212]:

## Maxwell Distribution

** **

- Neutron density between v and v+dv at thermal equilibrium** **

- (average velocity)

##  - decay

- Correlation coefficients:
**A** – parity violation,
-        coupling constant ratio GA/GV
**D** – time-reversal violation
**R** – parity and time-reversal violation

** **

**Superallowed ****β-decays**

**Ft = ft(1 + ****δ****R****)(1 – δ****C****) **
**     ****= K/[2G****V****2****(****1 + Δ****R****)]**
**Universality: ****G****V**** = ****G****μ****•cosθ = ****G****μ****•**** ****V****ud**
**V****ud****2**** = K/[2G****μ****2**** (1 + Δ****R****) Ft]**

**V****ud**** = 0.9740 ******** 0.0005(10)      ****(unitarity value: ~0.9756)**

- Courtesy H.K. Walter

**New  measurements?**

## Angular correlations:

- Differential decay probability:

*p*

*e**-*

## UCN turbine

**Maxwellian distribution**
**2000 UCN/cm****3**

**extracted UCN**
**40 UCN/cm****3**

**1~10**
**UCN/cm****3**
**at experiment**

## Inelastic scattering

## Strategy:
Magneto-gravitational trapping of UCN, avoiding wall collisions
No losses due to depolarisation (?), but:
Control of losses

In-situ measurement of N(t) using proton detectors

- Magneto-gravitational trapping of UCN, avoiding wall collisions
- No losses due to depolarisation (?), but:
- Control of losses
- In-situ measurement of N(t) using proton detectors

- [F.J. Hartmann, I. Altarev, S. Paul *et al*.,
- TU München, E18]

*Setup of the trap with *
* **permanent magnets*

*Magnetic storage *
*(TU München, PNPI)*

- TAKEN FROM O: ZIMMER                                     [O. Zimmer, JP G 26 (2000) 67-77]

* **UCN density at FRM II: 10**4** *cm-3
*                         **(at ILL: 50 *cm-3*)*

## Superthermal converters

- Superfluid He – zero absorption cross section but needs very low temperatures ( ~ 0.5 K) (NIST, ILL, SNS)
- Solid D2 – absorption lifetime 150 ms, 2 orders of magnitude higher production rate as compared with He, temperature of ~ 8K sufficient (Munich, Los Alamos, PSI)
-  Solid CD4 – compared with D2 more low lying rotational states – investigations at the very beginning
- Solid O2 – phonons and magnons excitation but temperatures below 2K needed

## Deuterium

- D2 nuclear spin : S = 0,2 (ortho) and S = 1(para)
- Ortho-D2 : J = 0,2,4 ...(rotational quantum number)
- Para-D2 : J = 1,3,5...
- Energy of the lowest rotational state:
- Para-D2 J =1 E = 7.5 meV
- Ortho-D2 J = 0 E = 0 meV
- Importance of high ortho-D2 concentration

- Additional up-scattering channel !

## sD2 Moderator

**liquid**

**solid**

- Slow freezing around triple point

## UCN Extraction

- mono sD2 crystal

- real sD2 crystal

## Raman spectra

## Fermipot

- ...range          must be small         for f()f

- Many scatterers:

## Reflectivity

- At boundary:

- Outside

- Inside