Charged Particle Electric Dipole Moment Searches in Storage Rings
Charged Particle Electric Dipole Moment Searches in Storage Rings J. Pretz RWTH Aachen & FZ Jülich for the JEDI collaboration
Axions and the Low Ener...
Charged Particle Electric Dipole Moment Searches in Storage Rings J. Pretz RWTH Aachen & FZ Jülich for the JEDI collaboration
Axions and the Low Energy Frontier, Bonn, März 2016
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Outline Introduction: Electric Dipole Moments (EDMs): What is it? Why is it interesting? What do we know about EDMs? Experimental Method: How to measure charged particle EDMs? Recent Achievements: Spin-
Coherence Time Tune Feedback Tracking
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What is it?
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Electric Dipoles
~r1 −
Classical definition: ~d =
X
~0
qi~ri
i
+ ~r2
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Order of magnitude
atomic physics charges
e
|~r1 − ~r2 |
1 Å= 10−8 cm
hadron physics
EDM naive expectation
10−8 e · cm
observed
water molecule 2 · 10−8 e· cm
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Order of magnitude
atomic physics
hadron physics
charges
e
e
|~r1 − ~r2 |
1 Å= 10−8 cm
1fm = 10−13 cm
naive expectation
10−8 e · cm
10−13 e · cm
observed
water molecule
neutron
2 · 10−8 e· cm
< 3 · 10−26 e· cm
EDM
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Neutron EDM d~
2 3
2 · rn ≈ 10−13 cm
− 13
− 13
neutron EDM of dn = 3 · 10−26 e·cm corresponds to separation of u− from d−quarks of ≈ 5 · 10−26 cm 7 / 87
~ = q~r Operator d is odd under parity transformation (~r → −~r ): P −1 ~dP = −~d Consequences: In a state |a of given parity the expectation value is 0: D
E D E a|~d|a = − a|~d|a
but if |a =Dα|P =E+ + β|P = − in general a|~d|a 6= 0 ⇒ i.e. molecules
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EDM of molecules z H H x
H
H N
N H
z
y
y x
H
Ψ2
Ψ1
z
z ground state: mixture of
Ψs = Ψa =
√1 2 √1 2
(Ψ1 + Ψ2 ) ,
P=+
(Ψ1 − Ψ2 ) ,
P=− 9 / 87
EDMs & symmetry breaking
Molecules can have large EDM because of degenerated ground states with different parity
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EDMs & symmetry breaking
Molecules can have large EDM because of degenerated ground states with different parity
Elementary particles (including hadrons) have a definite parity and cannot posses an EDM P|had >= ±1|had >
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EDMs & symmetry breaking
Molecules can have large EDM because of degenerated ground states with different parity
Elementary particles (including hadrons) have a definite parity and cannot posses an EDM P|had >= ±1|had > unless P and time reversal T invariance are violated!
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T and P violation of EDM
~d: EDM µ ~ : magnetic moment both || to spin H T :
H
P:
H
= = =
~ ~ −µ~σ · B−d~ σ·E
~ ~ −µ~σ · B+d~ σ·E
~ ~ σ·E −µ~σ · B+d~
−
~s d~
µ ~
P
+
T
+
+ − −
⇒ EDM measurement tests violation of fundamental CPT symmetries P and T ( = CP) 13 / 87
Symmetry (Violations) in Standard Model electro-mag.
weak
strong
C
X
E
X
P
X
E
(X)
T → CP
X
(E)
(X)
CPT
C and P are maximally violated in weak interactions (Lee, Yang, Wu) CP violation discovered in kaon decays (Cronin,Fitch) described by CKM-matrix in Standard Model CP violation allowed in strong interaction but corresponding parameter θQCD / 10−10 (strong CP-problem) 14 / 87
Sources of CP−Violation and connection to EDMs Standard Model Weak interaction → unobservably small EDMs
CKM matrix Strong interaction θQCD
→ best limit from neutron EDM beyond Standard Model
e.g. SUSY
→ accessible by EDM measurements
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Why is it interesting?
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Matter-Antimatter Asymmetry Excess of matter in the universe:
η=
nB −nB¯ nγ
observed
SM prediction
6 × 10−10
10−18
Sakharov (1967): CP violation needed for baryogenesis ⇒ New CP violating sources beyond SM needed to explain this discrepancy They could manifest in EDMs of elementary particles
