1. Ramsey Spectroscopy: Search for e- Dipole Moment
Thank you for coming. I am very excited to talk to you about RS and … because it is a really beautiful experiment that brings together knowledge from many different areas of physics
Masha Baryakhtar
Physics 95

2. Introduction
What do thorium monoxide and supersymmetry have in common?
There are experiments going on now in this very building that are

3. Introduction Characterizing the electron electric dipole moment (eEDM)
approaching the problem from a completely different angle!

4. Outline
Why electron EDM?
Ramsey spectroscopy
ACME EDM

5. Outline
Why electron EDM?
Ramsey spectroscopy
ACME EDM

6. - + Why electron EDM? dm molecular dipole moment
What is a dipole moment?
a vector representing the distribution of charge in a dipole : two opposite charges separated by a distance
Units of charge*length
molecular dipole moment

7. - + Why electron EDM? de electron dipole moment
The unexpected: dipole moment in a fundamental particle
electron dipole moment

8. - + Why electron EDM? Violation of Time symmetry
electron dipole moment + -
Time: does not affect location of charges
Spinning backwards
Violation of Time symmetry

9. P - + Why electron EDM? Violation of Parity symmetry
electron dipole moment + -
Parity : flipping all coordinates
Will switch location of plus and minus charges, so flip dipole
Can think of it as mirror image PLUS 180 rotation P
Violation of Parity symmetry

10. Why electron EDM?
Evidence of CP symmetry breaking in leptons  matter – antimatter imbalance + -
T violation is the same is CP violation
Sakharov showed that we need significant CP violation to see matter asymmetry we have today
Haven’t found it yet, especially not in leptons

11. Why electron EDM? Standard Model: |de| < 10-40 e cm
Current limit (Berkeley 2002): |de| < 1.6 x e cm
Beyond Standard Model Theories: |de| ~ to e cm
Getting really close!
Constrain new physics

12. Why electron EDM?
Can really learn about new physics without accelerators, etc.

13. Outline
Why electron EDM?
Ramsey spectroscopy
ACME EDM

14. Ramsey Spectroscopy
Technique for precisely measuring the frequency of precession of a magnetic moment in a B field
Nobel Prize in 1989
Many applications ω

15. Ramsey Spectroscopy ω Magnetic moment precesses in magnetic field
Larmor Frequency ω
ω = μ B/S ω
Measuring frequency can tell us the value of the magnetic moment
Why are we interested in the magnetic moment?
Note: using a semiclassical explanation here – in reality, the expectation value of the spin precesses. This is explained on p of griffiths.

16. Ramsey Spectroscopy
So idea of how to measure magnetic moment can get us closer to measuring dipole
Focus on just magnetic moment for now for conceptual understanding of technique
electron dipole moment changes precession frequency

17. Ramsey Spectroscopy
Use oscillating magnetic field to find Larmor frequency
Flip spins into desired state
Let system evolve for known amount of time
Measure net phase change to get frequency

18. Ramsey Spectroscopy Flip spins into desired state
Apply RF magnetic field pulse
frequency ω
perpendicular to plane of B and J

19. Ramsey Spectroscopy Flip spins into desired state
Apply RF magnetic field pulse
frequency ω
perpendicular to plane of B and J ω ω

20. Ramsey Spectroscopy Flip spins into desired state Rotating frame ω
Go into frame rotating with the spin, at freq omega.

21. Ramsey Spectroscopy Flip spins into desired state oscillating field on
In this frame, the spin is initially stationary. Turn on oscillating field. If field oscillates at the same frequency omega, stationary in this frame. Spin will start to precess around it.

22. Ramsey Spectroscopy Flip spins into desired state spin precesses
After spin rotates by 90 degrees, turn field off

23. Ramsey Spectroscopy Flip spins into desired state
oscillating field off
After spin rotates by 90 degrees, turn field off

24. Ramsey Spectroscopy Flip spins into desired state Lab frame ω
Back in the lab frame, the spin is still precessing around the main field B, but now in the transverse plane

25. Ramsey Spectroscopy Let system evolve for known amount of time ω ω ω ω
As time passes, the phase of the spin will change
time

26. Ramsey Spectroscopy 3. Measure net phase change to get frequency
Apply another pulse and compare ω ω ω
Spin angle changes by π
Second pulse is in phase with the first, so if frequency of B field is the same as Larmor freq, will flip spin in same direction

27. Ramsey Spectroscopy 3. Measure net phase change to get frequency
Apply another pulse and compare ω ω ω
Spin angle changes by 0
If frequency is off by pi/t, then it will flip the other way
Can be anywhere in between
Sense where the final spin ends up, for instance by deflecting with inhomogeneous magnetic fields.

28. Ramsey Spectroscopy Measure net phase change to get frequency
For matching field and Larmor frequencies, get peak, then falls off.
Get frequency information this way.

29. Outline Why electron electric dipole moment? Ramsey spectroscopy
ACME EDM

30. ACME EDM
Non-zero EDM of electron will shift energy levels of molecules
Change frequency of precession in magnetic + electric field

31. ACME EDM
Non-zero EDM of electron will shift energy levels of molecules
Change frequency of precession in magnetic field
Have to measure the difference in frequencies – reduces systematic error

32. ACME EDM E, B Similar to ramsey scheme, but with lasers
Here cold atoms come out of beam source
atoms are put into coherent initial state, like fist magnetic field pulse.
E, B

33. ACME EDM E, B Atoms travel a certain distance
Then are pumped again with a detection laser
Observe the flourescence with pmt, which indicates phase
Compare for positive and negative electric field
E, B

34. ACME EDM Measure 2deE So what about thorium oxide? benefits
Very strongly polar molecule, amplifies electric field: 100 GV per cm
Measure 2deE

35. ACME EDM
Has two closely spaced levels that interact with electron dipole with opposite sign
energy

36. ACME EDM
Don’t have to flip external electric field, which is leading source of systematic error in previous experiments.
energy

37. ACME EDM Expected error: Combining all these technologies
Run time of 1 year gives lower bound of 10-30

38. ACME EDM
The region we can cover after running for a year

39. Conclusion Ramsey spectroscopy precisely measures magnetic moment
Combine spectroscopy, molecules, cryogenics to study particle physics
Expect stringent bounds on beyond Standard Model theories in a few years!
Ramsey spectroscopy works by writing initial coherent state, letting phase accumulate, and measuring phase info to get frequency and then moment

40. Questions?