Prsentation PowerPoint

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Parity violation on the 6S-7S transition of
133Cs detected by stimulated emission
polarimetric measurement of the electric dipole
transition amplitude with an absolute precision
of ?2 x10-13 ea0
M. Lintz, HDR, 16/11/2005
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? Motivations
Why measure Atomic Parity Violation (APV) ?

• Parity Violation specific of weak interactions

• 1st observation (C.S. Wu, 1956) in ? decay
• (exchange of W / W- bosons )
  AR-L 1

• In the stable atom
• ? exchange of neutral Z bosons
• (" weak neutral current interactions ")

?pv, AR-L ltltltlt 1!
? Mixing of opposite parity states gt gt
i?pv -gt,
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The consequence of APV forbidden transitions
are not strictly forbidden
? Selection rules (ltnS d n'Sgt 0) are violated
the expected APV dipole moment is not
too small (Z3 law) calculations have
reached the 0.5 accuracy level (and may still
improve to 0.1) ? Cs best choice for
stable alkalis
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Outline
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? Motivations
What is at stake in measuring QW(Cs) ?
QW(Cs) provides a determination of sin²qW
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SLAC E158 coll. (PRL, 26 août 2005)
E158
NuTeV
QW(Cs) (Boulder)
13 measurement
0.7 measurement of
Q (GeV)
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? Motivations
What is at stake in measuring QW(Cs) ?
(additive)
(Standard Model)
QW(Cs) provides a determination of sin²qW
but not the most efficient one
Is a 1 APV measurement competitive faced with
(future) measurements at LHC?
no, at least not for the determination of SM
parameters
But APV (e-hadron sector, very low energy)
test of SM complementary to high energy physics

• Z (weak neutral current) physics is critical in
  the (extensions of the) Standard Model
• Kaluza-Klein theories high-energy excitations
  of the "low-energy" bosons
• "U" boson (mU a few MeV) PV couplings strongly
  constrained by APV measurements

APV measurements remain an important test for
non-standard particle physics
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? Principles
Principles of the APV experiment The 6S?7S
transition dipoles
?exc linear
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7S1/2
2.2GHz
3
5
y
)600MHz
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Excitation (540nm) 1.5mJ,15ns
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6P3/2
2
x
z
6P1/2
Ez (longitudinal, 1.6kV/cm)
PV
z
Cs (10mtorr)
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6S1/2
9.2GHz
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6S-7S transition dipoles
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? Principles
?exc
linear
Principles of the APV experiment The angular
observables
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7S1/2
3
x
z
Excitation (540nm) 1.5mJ,15ns
Ez (longitudinal, 1.6kV/cm)
z
6P1/2
PV
Cs (10mtorr)
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6S1/2
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(ALIGNMENT) ?plane dichroism
(ALIGNEMENT) ?dichroisme plan violant la parité
APV tilt (10-6 radian) of the eigen-axes of the
excited vapor
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? Principles
Principles of the APV experiment How to measure
the APV dichroism ?
linear
linear
y
x
z
real-time calibration (?Boulder)
ideal expt. no background, L-R asymmetry is a
P-violating quantity, at each shot (?Boulder)
exact "45"?
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? Principles
The (calibrated) dichroism signal
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? Principles
The (most significant) systematics
The (most significant) systematics (1) defects
that break the cylindrical symmetry
? A transverse electric field Et coupled to a
transverse magnetic field Bt calibrated
plane dichroism
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? Principles
The (most significant) systematics (2) defects
preserving the cylindrical symmetry
? "Bz-" (magnetic field odd in Ez reversal)
Ez-odd Larmor precession of eigenaxes Bz- 50
µG ? systematic ?q pv
Diagnostic/measurement probe the
7S,F4?6P3/2,F'5 (very sensitive to Faraday
rotation) (APV is measured on F4?F'4, almost
insensitive to Faraday rotation). Measuring Bz-
takes ? 40 of the total acquisition time.
Average correction ? 11 of q pv.
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?experimental set-up
Block diagram
excitation laser
P exc
dichroic mirror
P pr
probe laser
stabilization
CCD
position meter
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?experimental set-up
Polarization magnifier
transmission
? transmission
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?experimental set-up
Glass cells
-6kV
-8kV
-4kV
0
4kV
6kV
8kV
reentrant window
reentrant window
Cs metal
9 annular electrodes
10kV
Cesiated glass shows surface conductivity (R ?
10k?) ? The potential has to be applied to the
glass surface (multicontacts) ? Same for the
windows (multicontact bracelet connected to the
electrode)
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? experimental difficulties
Observations with glass cells
7S1/2
2,2GHz
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250MHz
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6P3/2
Bz- field of 100µG (chiral currents at the
inner glass surface) ? systematic effect 2 µrad
on ? pv
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2
540 nm
9,2GHz
6S1/2
1) Cs2 hn (540nm) ? Cs(6S) Cs(5D, t ?1µs)
2) Cs(5D) hn (540nm) ? Cs e- 4) electrons
are ejected towards the window ? e- (and
Cs) impact at the windows ? linear space
charge of Cs ions
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? experimental difficulties
? experimental difficulties
Sapphire cells
- Very low surface conductivity - No more
internal electrodes - High Temp "gluing"
(resists gt1000C!) - no more window damage -
Looks ideal... except for secondary
emission!
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? experimental difficulties
How to prevent secondary emission?
SEE is a problem frequently encountered (and
sometimes hard to prevent) particularly in
accelerators
In our case, secondary emission is enhanced by

• Cs adsorption (2eV drop of the workfunction)
• geometry of the cell
• grazing incidence (?1/cosq dependance)

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?APV measurements
The APV measurements
average 0,950?0,025 µradian
q pv (µradian)

• S/N improved by use of
• polarization tilt magnifier
• temperature control of the reflection at the
  windows
• metal-coated windows for better application of
  Ez field
• control of the probe gate extinction factor

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?APV measurements
The APV measurements

• Chiral optical gain demonstrated in the first
  "grooved" cell
• and confirmed in the subsequent cells (all
  measurements agree, as checked by c² test)
• The average Sxy and Suv isotropic values agree
  (expected cylindrical symmetry)
• Observation of the zero-field (M1²) linear
  dichroism without background (?Boulder),
• ? ?Ez calibrated in terms of M1 , precisely
  known from theory
• ? E1pv extracted from ? pv -E1pv/?Ez

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?Conclusions
Results and conclusions

• Stat. precision has reached 2.6 (including
  stat. error on Bz- correction)
• S/N1 in ?20 min (still 1.5 or 2x shot noise),
  looks appropriate for a 1 measurement
• Systematics are at the level of ?1
• The result agrees with the Boulder measurement
  at 0.5
• Cell operation requires only about 1mg of Cs (?
  Boulder gt0.2kg!) acceptable for 135Cs (lt
  105 Bq)
• Project for 0.1 stat. accuracy measurement

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? Projects
Project use of laser cooling in the detection
of forbidden transitions

• Why?
• helps in confining rare or radioactive atomic
  species
• reduces thermal Doppler widths
• ? low velocity atoms (long interaction
  times),
• in a small region of space, or with a
  given trajectory
• A very convenient cooling method? The pyramidal
  MOT funnel
• requires a single laser beam
• emits a directed, low velocity (10m/s) atomic
  beam
• with low velocity spread 1m/s

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? Projects
Project APV measurements in a highly amplifying
medium

• In the ENS experiment, the atomic medium
  amplifies the APV effect
• ? AL-R increases with an increase of the applied
  E field!
• But too large E may trigger dicharges in the
  vapor (high potentials)
• ? transverse E field to take full advantage of
  the AL-R amplification
• applied potentials are much smaller,
• excitation rates are larger (? ? 10x?)
• cell length can be increased at will
• all regimes accessible, from linear
  amplification to spontaneous superradiance
• cylindrical symmetry can be restored

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Bt
polar. analysis
Et
PV observable probe optical rotation
REVOIR?(kEt Bt xexc
Even at moderate optical gain, photon shot noise
should be improved to 0.1, x10 as compared to
longit. E field configuration Control of
systematics using auxiliary atomic signals
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Related topics

• Spectroscopy with the Cs2 dimers measuring the
  delayed probe absorption

• measurement of the 5D5/2 lifetime
• measurement of the cross sections for
• Cs2 dissociation
• Cs(5D5/2) ionization

5D5/2
7S1/2
6P3/2
PV
6S1/2
Cs atom
Cs2 dimer
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Related topics

• Spectroscopy with the Cs2 dimers measuring the
  delayed probe absorption

• measurement of the 5D5/2 lifetime
• measurement of the two cross sections

• Spectroscopy with the Cs2 dimers near-IR
  Photodissociation of Cs2

D2
D1
Cs2 dissociation efficiency _at_tNcs4.1015/cm3
l (nm)
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Related topics

• Spectroscopy with the Cs2 dimers measuring the
  delayed probe absorption

• measurement of the 5D5/2 lifetime and the two
  cross sections

• Spectroscopy with the Cs2 dimers near-IR
  Photodissociation of Cs2

IR ER Eat²

• "Homodyne" selective reflection spectroscopy

"ordinary", wedged
window
vapor
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Related topics

• Spectroscopy with the Cs2 dimers measuring the
  delayed probe absorption

• measurement of the 5D5/2 lifetime and the two
  cross sections

• Spectroscopy with the Cs2 dimers near-IR
  Photodissociation of Cs2

• "Heterodyne" selective reflection

• Laser diffraction at the monoatomic steps of a
  vicinal surface

2Å
AFM scanning of a 2-inch wafer takes between 1
and 50 years
1mm area investigation
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STAGIAIRES Henri CORBET Antoine HUGUENIOT
Amaury MOUCHET Elisabeth BOERI Pierre ANDREI
Frédéric MASSET Patrice GARNIER Daniel
POMAREDE Nicolas STOJANOVIC Anne MATHIEU
Dominique CHAUVAT Franck PEREIRA DOS SANTOS
Joël PUIBASSET Cyril RENAUD Erwan JAHIER
Julie GROSPERRIN Thomas BADR Erwan JAHIER
Eric GRELET Romain DESROUSSEAUX Demascoth
KADIO Vincent EUZEBY Xuan-Son NGUYEN
Abderrahim BENBOUZIANE Loïc ESTEVE Mourad AÏT
MOHAND
Ont contribué à ce travail M.A. BOUCHIAT J.
GUÉNA Ph. JACQUIER L. POTTIER E. HUGHES S.
REDSUN M. PLIMMER A. WASAN D. CHAUVAT E.
JAHIER S. SANGUINETTI A. PAPOYAN D.
SARKISYAN coups de main INM/CNAM,
IN2P3 CERN
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Photo de famille des cellules VPA