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

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

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

Outline Why electron EDM? Ramsey spectroscopy ACME EDM

Outline Why electron EDM? Ramsey spectroscopy ACME EDM

- + 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

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

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

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

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

Why electron EDM? Standard Model: |de| < 10-40 e cm Current limit (Berkeley 2002): |de| < 1.6 x 10-27 e cm Beyond Standard Model Theories: |de| ~ 10-25 to 10-30 e cm Getting really close! Constrain new physics

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

Outline Why electron EDM? Ramsey spectroscopy ACME EDM

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

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 179-180 of griffiths.

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

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

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

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

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

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.

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

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

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

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

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

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.

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.

Outline Why electron electric dipole moment? Ramsey spectroscopy ACME EDM

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

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

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

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

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

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

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

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

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

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

Questions?