Laboratoire National Champs Magnétiques Intenses, Toulouse, France M. Fouché, Agathe Cadène, Paul...
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Transcript of Laboratoire National Champs Magnétiques Intenses, Toulouse, France M. Fouché, Agathe Cadène, Paul...
Laboratoire National Champs Magnétiques Intenses, Toulouse, France M. Fouché, Agathe Cadène, Paul Berceau, Rémy Battesti, Carlo Rizzo
The QEDVacuum Magnetic Birefringence (BMV)
Experiment
E
Elliptic polarizationLinear polarization
Magnetic Birefringence
Epar
Eperp
x
y
E B
Linear polarization
Induced magnetic birefringence :
n = ( n// – n┴ ) α B2
This effect exists in any medium
n measurement to a few ppm
Pure QED test
Vacuum Magnetic BirefringenceQED theory predicts that this effect also exists in vacuum
• Due to the creation of virtual positron-electron pairs
nonlinear interaction between electromagnetic fields
• Calculated in the 70s :
0
2
54
32
4
251
15
2
B
cmn
e
At the lower orders in
2
24
T 1 10 00000500316994
B
n ..
O(3)
O(4)
O(5)
?
?
Fondamental constants : Codata 2010
Z. Bialynicka-Birula and I. Bialynicki-Birula, Phys. Rev. D 2, 2.34 (1970)V. I. Ritus, Sov.Phys. JETP 42, 774 (1975)
Experimental challenge
• BMV project
Development of a very sensitive ellipsometer in order to be able to observe this fundamental
prediction for the first time
• Extremely small Not yet experimentally observed
2CM Bkn 224
CM T 104 .kwith
The ellipsometer
A
P
It
Iext
BM2
M1
• P and A : polarisers crossed at maximum extinction
• Ellipticity :
• Key elements :
Magnetic field : special magnets developed at LNCMI to have a B2LB as high as possible
Fabry-Perot cavity : to increase the optical path in B
CMkλ
πΨ
π
F2BLB2
laser=1064 nm
LB
R. Battesti et al., EPJD 46, 323 (2008)
Pulsed transverse magnetic field
L = 25 cm
laser beam
Unconventional magnets developed at LNCMI
X coil geometry high transverse magnetic field
I
B1 B2
B
I
laser
R. Battesti et al., EPJD 46, 323 (2008)
Pulsed transverse magnetic fieldB
(T
)
time (ms)
I = 8300 AU = 4000 Vtpulse = 4 ms
B = 14.3 TB²Lmag = 28 T²m
E = 100 kJ
Pulses in vacuum:mT 75
T 5622
max
max
.
.
BLB
B
• Time evolution: • Longitudinal profile:
= 0.137 m
Hole to let the laser in
12mm
Coil in its cryostat
Immersion in liquid nitrogen to avoid consequences of heating
External reinforcement to contain the magnetic pressure
The Fabry-Perot cavity
Finesse :
• photon lifetime in the cavity (Lc = 2.27 m long) : = 1.08 ms
• flight distance in the cavity = 325 km
000 054cL
cF
One of the sharpest cavities of the world
Interferometers in the world
Lc 3 km 6.4 m 4 km 2.27 m
159 ms 442 ms 970 ms 1.08 ms
F = 50 70 000 230 450 000
= 1 kHz 360 Hz 164 Hz 147 Hz
aa
2LcF2LcF
LcLc
c τc τ
c c
high reflectivity mirrors work in a clean room
BMV experimental setup
• Increase of the path of light in the medium : Fabry-Perot cavity
• Pulsed transverse magnetic field B as high as possible
Data acquisition
Alignment of the cavity mirrors
Shot
Data analysis
TEM00 mode
Laser locked on the cavity
Data analysis
Both signals It and Iext are used:
A
P
It
Iext
B M2
M1
Ellipticity to be measured, proportional to B²(t)
polarizers extinction≈ 4.10-7
cavitywithout t
ext2
I
I
Cavity static ellipticity≈ 10-6
)( tI
Ψ2σI
22
t
ext for Ψ
22 ΓΨ(t)σI
t
ext I
Data analysis
)( tI
Ψ2σI
22
t
ext for Ψ
Ψ(t) Y(t) 22
t
e
I
I
with = sign of
CMCM2filteredCM 2
and BFL
ktBY
in T-2
takes into account the first order low pass filtering of the cavity
cutoff frequency: c=1/4 = 75 Hz
2filteredB
Y(t) fitted by tBCM2filtered
P. Berceau et al., Appl. Phys. B 100, 803 (2010)
Magnetic birefringence of nitrogen vs pressure
Results in N2
3.1×10-2
2.2×10-2
9×10-4
< 5×10-4
4×10-2
2×10-2
3.5×10-2
2.2×10-2
3×10-4
type A type B
Relative uncertainties
Pf
Ln
Bb
2sin
1
4 ISLCM
P. Berceau et al., Phys. Rev. A 85, 013837 (2012)
Group
PVLAS
Q&A
BMV
• measurements linear fit 1 confidence level
Results in vacuum
Ψ(t) Y(t)22
t
e
I
I
Pulses realized in same experimental conditions,
at 3 confidence level
Systematic effects
(rad
)
Ox
0
//B
-219CM T 101012 ..k
Systematic effects
Possible Cotton-Mouton effects:
• Residual gaz :
P<10-7 mbar
Gaz analyser: most important contributions come from N2 and O2
• CM effect of cavity mirrors
Bmirror = 150 T
kCM = (2.1 0.1) 10-19 T-2 at 3 confidence level
No Cotton-Mouton systematic effect
-223CM T 1051 .k
-224CM T 101 k
>0, B antiparallel to Ox
New data acquisition procedure
Using symmetry properties of Ψ(t) Y(t)22
t
e
I
I
4 new data series YB
Y(t) >0, B parallel to Ox
Y(t)Y(t)Y(t) <0, B parallel to Ox
<0, B antiparallel to Ox
We then derive a more general expression for Y(t)
SdScSbSa
SdScSbSa
SdScSbSa
SdScSbSa
Y
Y
Y
Y BS = function with a given symmetry
+ even parity- odd parity
Cotton-mouton effect S-+
New data acquisition procedure
• Symmetry functions can be measured with a linear combination of functions Y
• Allow to measure and to overcome systematic effects that might mimic the CM effect
at 3 confidence level
A. Cadène et al., arXiv:1302.5389 (2013)
-221CM T 107847 ..k
Comparison
BFRT Collaboration: R. Cameron et al., Phys. Rev. D 47, 3707 (1993)
PVLAS, 2008: E. Zavattini et al., Phys. Rev. D 77, 032006 (2008)
PVLAS, 2012: G. Zavattini et al., Int. J. of Mod. Phys. A 27, 1260017 (2012)
A. Cadène et al., arXiv:1302.5389 (2013)
Conclusion
Status
• Coupled high magnetic field and one the best Fabry-Perot cavities• Measurements performed on gases and in vacuum
Needed sensitivity improvement: almost 4 orders of magnitude
B2Lmag > 300 T2m
Future• Increase the transverse magnetic field : new XXL-coil
• Improvement of the ellipticity sensitivity (Decrease of 2 and 2 (10-8))