Mesure du moment lectrique dipolaire du neutron

1
Mesure du momentélectrique dipolaire du neutron
Institut de Physique Nucléaire d'Orsay Mars 2005
Oscar Naviliat-Cuncic LPC-Caen et Université de
Caen Basse-Normandie
2
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

3
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 !

4
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 lt 10-31 ecm beta decay
  correlations lt10-10)
• 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

5
permanent EDMs

• observables - spin S, unit vector s
• - magnetic dipole moment m m s
• - electric dipole moment (d qr)
• - for an elementary QM system d d s

• classical dipole interaction H - (d E
  m B)

• transformations under T and P
• T (d, m) ? (-d, -m)
  P (d, m) ? (d, m)
• T (E, B) ? (E, -B)
  P (E, B) ? (-E, B)

if d ? 0 then T and P are violated
6
EDM measurements

• upper limits have been obtained for
• e, m,t,
  p, n, L, atoms, molecules
• new projects and approaches are being
  considered for
• e, m, n,
  d, radioactive nuclei, atoms

• very active field !
• complementary systems

7
neutron EDM
(A.P. Serebrov, NIM A440 (2000) 653)

• experimental advantages

• no electric charge
• long lifetime
• storage of UCNs

• Systematic effects have continuously been fought

8
measurement principle
Ramsey method of Separated Oscillating Fields

• prepare a sample of polarized neutrons
• make a p/2 spin flip (start clock)
• allow free spin precession in parallel B
• and E static fields
• make a p/2 spin flip (stop clock)
• analyze direction of neutron spin

energy (frequency) shift under field inversion
De h Dn 4Edn
9
beam technique with cold neutrons

• vn 100 m/s
• Pn 70
• B 10 G

(W.B. Dress et al. Phys. Rev. 170(1968)1200)
10
beam technique result

• 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!
(W.B. Dress et al. Phys. Rev. 170(1968)1200)
11
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)

ln 800 Å vn 5 m/s Tn 2 mK En 130 neV
12
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, 77 cm2,
• (58Ni coated)
• UCN source rotating turbine
• UCN density r 20 /cm3

13
in real life
14
Sussex-RAL-ILL experiment
(P.G. Harris et al. PRL 82(1999) 904)

• V 20 l
• B 10 mG, nL 30 Hz
• E 4.5 - 11.0 kV/cm
• T 120 - 140 s

use of 199Hg co-magnetometer d(199Hg) lt 8.7
10-28 ecm
15
Sussex-RAL-ILL result
(P.G. Harris et al. PRL 82(1999) 904)
dn (-3.4 3.9 3.1)10-26 ecm
16
statistical sensitivity

• ? a slope on resonance curve
• T free precession time
• E electric field strength
• N total number of detected neutrons (N r V
  tmes)

optimal sensitivity (with 50 running efficiency)
? (dn) 510-26 ecm / 50 days cycle
current sensitivity (UCN losses and
depolarization)
? (dn) 1510-26 ecm / 50 days cycle
17
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

18
the Spallation UCN source at PSI
19
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 r 3000 /cm3

20
approach

• 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 polarisation
• UCN detection / polarimetry
• coatings
• double chamber
• magnetometry

21
UCN polarization

• objectives
• improve Pn (0.9 to 1)
• increase available UCN density
• implementation
• separate polarization from analysis
• magnetized foils ? SC solenoid

(measurements by PNPI compare with PSI annual
report)
22
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

23
UCN counters
Si/LiF/Si sandwich 380mm/ 600 mg/cm2/ 380mm
(Gatchina)
hybrid solid/gas detector CASCADE
(Heidelberg)
6Li doped glass scintillator
(Caen)
24
GS10 test and spin analysis
pulse height spectrum
transmission asymmetry
25
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
26
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

27
self-oscillating laser pumped cesium magnetometer
magnetic resonance optical preparation
detection
1 magnetometer (OPM) needs 25 mW
1 laser many sensors
1 laser delivers gt10 mW
28
magnetic field fluctuations in a multi-layer
shield
field not stabilized
- Co-Netic - Mu-Metal
2
1
2 OPMs
OPM 2
field stabilized
OPM 1
1
2
coil current
residual gradient fluctuations gt40 fT
29
multiple field measurement inside the ILL-EDM
setup
vector magnetometers
HV electrode
neutron chamber
30
status and plans

• 2004-2006 RD at ILL and design of new setup
• 2007 start operation of PSI source,
  commissioning
• 2007-2008 measurement (1st phase)
• 2009-2012 measurement (2nd phase)

31
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