mesure du moment électrique dipolaire du neutron oscar naviliat-cuncic lpc-caen et université de...

Mesure du momentélectrique dipolaire du neutron

Oscar Naviliat-CuncicLPC-Caen et Université de Caen Basse-Normandie

Institut de Physique Nucléaire d'Orsay

Mars 2005

2 IPN - Orsay, 7 février 2005 O.Naviliat-Cuncic: [email protected]

plan

• context and motivation

• measurement principle

• the neutron beam technique

• UCNs and their sources

• present limit on the nEDM

• the new UCN source at PSI

• towards and improved nEDM measurement


context and motivation

• CP is known to be violated (K and B decays)

• The experimental results can (so far) be accommodated within the SM: quark flavor mixing

(complex phase e-i in CKM-matrix)

• The CKM mechanism is too weak to account for the cosmological CP-violation

(matter/anti-matter asymmetry of the Universe)

• At least one other mechanism EXISTS

• Our job (and duty) is to find it !


general principle

• Assuming CPT: CP-violation = T-violation

• In systems or processes without strangeness, the effects due to the CKM CP-violation are strongly suppressed (nEDM < 10-31 ecm; beta decay correlations <10-10)

• New (e.g. SUSY) CP-violating mechanisms are generally enhanced

• Huge window to search for new physics!

• EDMs of quantum systems are very sensitive probes


permanent EDMs

• classical dipole interaction H = - (d ·E + ·B)

• observables - spin S, unit vector ŝ

- magnetic dipole moment: = ŝ

- electric dipole moment (d = qr)

- for an elementary QM system: d = d ŝ

• transformations under T and P

T: (d, ) → (-d, -) P: (d, ) → (d, )

T: (E, B) → (E, -B) P: (E, B) → (-E, B)

if d ≠ 0 then T and P are violated


EDM measurements

• upper limits have been obtained for:

e, ,, p, n, , atoms, molecules

• new projects and approaches are being considered for: e, , n, d, radioactive nuclei, atoms

• very active field !

• complementary systems


neutron EDM(A.P. Serebrov, NIM A440 (2000) 653)

• Systematic effects have continuously been fought

• experimental advantages:

• no electric charge

• long lifetime

• storage of UCNs


measurement principle

Ramsey method of Separated Oscillating Fields

• prepare a sample of polarized neutrons

• make a /2 spin flip (“start clock”)

• allow free spin precession in parallel B

and E static fields

• make a /2 spin flip (“stop clock”)

• analyze direction of neutron spin

4

3

2

1

Free precession...

Apply /2 spin flip pulse...

“Spin up” neutron...

Second /2 spin flip pulse.

B

E

energy (frequency) shift under field inversion: = h || = 4Edn


beam technique with cold neutrons

(W.B. Dress et al. Phys. Rev. 170(1968)1200)

• vn ≈ 100 m/s

• Pn ≈ 70%

• B ≈ 10 G


beam technique result

(W.B. Dress et al. Phys. Rev. 170(1968)1200)

• final:

dn = (0.4 ± 1.5) × 10-24 ecm

(W.B. Dress et al. Phys. Rep. 43(1978)410)

new techniques required for further improvements!


what are Ultra-Cold Neutrons ?

• definition:

neutrons which are reflected at any angle of incidence

(the neutron kinetic energy is smaller than the “Fermi potential” of the surface)

n ≈ 800 Å ; vn ≈ 5 m/s

Tn ≈ 2 mK ; En ≈ 130 neV


the UCN source at ILL

• the only operating source in the world

• high flux reactor (thermal power: 58.3 MW)

• thermal n-flux: 1.5 × 1015 n/s/cm2

• cold neutron source: 20 l of LD2 at 25K

• vertical neutron guide 13m, 7×7 cm2, (58Ni coated)

• UCN source: rotating turbine

• UCN density: = 20 /cm3


…in real life


Sussex-RAL-ILL experiment(P.G. Harris et al. PRL 82(1999) 904)

• V = 20 l

• B = 10 mG, L = 30 Hz

• E = 4.5 - 11.0 kV/cm

• T = 120 - 140 s

use of 199Hg co-magnetometer

d(199Hg) < 8.7 × 10-28 ecm


Sussex-RAL-ILL result

(P.G. Harris et al. PRL 82(1999) 904)

dn = (-3.4 ± 3.9 ± 3.1)×10-26 ecm


statistical sensitivity

(dn) = 5×10-26 ecm / 50 days cycle

optimal sensitivity (with 50% running efficiency)

(dn) = 15×10-26 ecm / 50 days cycle

current sensitivity (UCN losses and depolarization)

NETdn

2

)(

●: slope on resonance curve

• T : free precession time

• E : electric field strength

• N : total number of detected neutrons (N ~ V tmes)


towards a new experiment

• larger UCN densities will be available at the PSI UCN source (more than two orders of magnitude)

• a sensitivity improvement of the nEDM at the level of 10-27 ecm is realistic

• systematic effects must be suppressed below the sensitivity level

• improved magnetometry for control of fields and gradients

• resonance frequency derived from active magnetometry

• build a multiple chamber system

• develop a UCN velocity dependent detection system

under construction

the Spallation UCN source at PSI


UCN source at PSI

• 590 MeV, 2 mA, proton beam

• pulsed: 4 s ON/ 600 s OFF (low duty cycle)

• spallation target: Pb

• moderators: D2O (20-80 K)

• UCN source: SD2 (30 l, 8K)

• volume: 2 m3 (Be coated: vL = 6.9 m/s)

• expected density: = 3000 /cm3


approach

• UCN polarisation

• UCN detection / polarimetry

• coatings

• double chamber

• magnetometry

• study performance and operate the Sussex-RAL-ILL apparatus

• implement improvements including magnetometry

• upgrade apparatus to accommodate a multiple chamber

• design a new spectrometer best adapted to the PSI UCN source


UCN polarization

(measurements by PNPI; compare with PSI annual report)

objectives:

• improve Pn : (0.9 to 1)

• increase available UCN density

implementation:

• separate polarization from analysis

• magnetized foils → SC solenoid


UCN detectors and spin analysis

objectives:

• improve detection efficiency / measurement duty cycle

• improve analyzing powers

• implement velocity selectivity

tests and implementation:

• compare performance of alternative detectors with 3He

• develop spin analyzers


UCN counters

)48.0()83.0()47.1(

)01.1()78.1(710

710

MeVMeVLiMeVBn

LiMeVBn

)74.2()05.2(6 MeVtMeVLin Si/LiF/Si sandwich: 380m/ 600 g/cm2/ 380m

(Gatchina)

(Heidelberg)

hybrid solid/gas detector: CASCADE

6Li doped glass scintillator

)74.2()05.2(6 MeVtMeVLin

(Caen)


GS10 test and spin analysis

pulse height spectrum transmission asymmetry

Detectorturbinespin flipper

polarizer analyzer

chopper

GS10


coatings (DLC)

• developed reliable DLC characterization

• large area coatings with high critical velocity, low losses and depolarization

• Pulsed Laser Deposition (PLD) of DLC presently being optimized

• PLD for UCN guide tubes under construction

UCN transmission through coated Al foil


magnetometry

objectives:

• measure magnetic field and magnetic field gradients

• active internal/external field stabilization

• generation of resonance frequency

tests and implementation:

• compare Cs LOPMs with 199Hg vapor magnetometers

• develop OPMs sensitive to field components


self-oscillating laser pumped cesium magnetometer

magnetic resonance +

optical preparation & detection

1 magnetometer (OPM) needs 25 W

1 laser delivers >10 mW1 laser = many sensors


magnetic field fluctuations in a multi-layer shield

field not stabilized

field stabilized

residual gradient fluctuations >40 fT

coil current

12

1 2OPM 1

OPM 22 OPMs

- Co-Netic

- Mu-Metal


multiple field measurement inside the ILL-EDM setup

HV electrodevector

magnetometers

neutron chamber


status and plans

• 2004-2006: R&D at ILL and design of new setup

• 2007: start operation of PSI source, commissioning

• 2007-2008: measurement (1st phase)

• 2009-2012: measurement (2nd phase)

G. Ban, X. Fléchard, M. Labame, Th. Lefort, E. Liénard, O. Naviliat-Cuncic, G. Rogel

Laboratoire de Physique Corpusculaire, Caen, France

K. Bodek, St. Kistryn, M. Kuzniak, J. Zejma

Institute of Physics, Jegellonian University, Cracow, Poland

D. Mzhavia, B.M. Sabirov

Joint Institute of Nuclear Reasearch, Dubna, Russia

S. Gröger, P. Knowles, M. Rebetez, A. Weis

Departement de Physique, Université de Fribourg, Fribourg, Switzerland

C. Plonka

Institut Laue-Langevin, Grenoble, France

G. Quéméner, D. Rebreyend, Ch. Sage, U.C. Tsan

Laboratoire de Physique Subatomique et de Cosmologie, Grenoble, France

T. Brys, M. Daum, P. Fierlinger, R. Henneck, S. Heule, M. Kasprzak, K. Kirch, A. Pichlmaier

Paul Scherrer Institute, Villigen, Switzerland

mesure du moment électrique dipolaire du neutron oscar naviliat-cuncic lpc-caen et université de...

Documents

ipn orsay

phase slide

metal slide

ckm cpviolation

multiple field measurement

motivation cp

magnetic field fluctuations

physique corpusculaire