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Cavity-Enhanced Parity-Nonconserving Optical Rotation in Hg, Xe, I (and Cs) T. Peter Rakitzis Department of Physics, University of Crete, & Institute of Electronic Structure and Laser (IESL) Foundation for Research and Technology Hellas (FORTH) Slide 2 Atomic Physics Searches for New Physics 1(a). Anomalous magnetic moment of the muon 3.6 discrepancy between experiment and theory (b) Muonic hydrogen (p + ) experiments proton radius puzzle (proton radius appears to be 4% smaller than in all other experiments) 2. Searches for Electron Dipole Moments (EDM) of electrons and of other particles 3. Time-varying fundamental constants 4. Atomic Parity Non-Conservation (PNC). Slide 3 Parity Violation Parity Violating (Weak force) Slide 4 Slide 5 Only this happens Slide 6 Atomic PNC Parity transformation: [H atomic, P]=0 => Atomic stationary states are eigenstates of Parity Z-boson exchange spoils parity conservation (between electrons and quarks in nucleus) Electromagnetic Electroweak H0 H0H0 H0 HW HWHW HW HWHW Slide 7 P = +1 Parity P (r r) P = -1 P = +1 + + + + + + Slide 8 e e Without PNC o EE What is Atomic PNC? Atomic energy levels have definite parity, even (e) or odd (o) E&M does not violate parity Ground state Excited states H=H 0 S S P Slide 9 S + P S + P WITH PNC P + S EE What is Atomic PNC? Ground state Excited states PNC term in the Hamiltonian mixes states of DIFFERENT Parity, but with same total angular momentum (mixes S and P) ~ EE Z3Z3 (in favorable cases, high Z, small ) H=H 0 + H W mixing Goal to measure this small mixing Slide 10 Considering only the E-M terms in the Hamiltonian, atomic states possess well-defined parity (even or odd). E1 Electric Dipole transition Connects states of OPPOSITE Parity M1 Magnetic Dipole transition Connects states of the SAME Parity o (e) e (o) o (e) o e e o o o e e M1 transition amplitude typically about 10 000 times smaller than E1 Parity selection rules of dipole transitions B E Atomic parity violation Slide 11 6s 7s All other one-photon transitions are forbidden (except a very small M1 from hyperfine n-mixing) Stark-Interference Method in Cesium ( 2 S 1/2 ) E1(PV) Too small to measure directly (either by fluorescence or absorption) The highly-forbidden 6s-7s transition Slide 12 E1( ) 6s 7s An external DC E field mixes s and p states ( 2 S 1/2 + 2 P J ) ( 2 S 1/2 + 2 P J ) E1(PV) |E1( ) E1(PV)| 2 = E1( ) 2 2E1( ) E1(PV) + E1(PV) 2 6p Sign of interference term can be changed by reversing the field polarity Stark-Interference Method in Cesium neglibible 7p E = 3230 cm -1 Slide 13 Stark-Interference Method in Cesium |E1( ) E1(PNC)| 2 E1( ) 2 [1 + 2 E1(PNC)/E1( )] 10 -6 Sign changed by inverting E-field and B-field polarities, and sign of detected m-state (by changing laser frequency). Signal changes by only about 1 in a million, yet Wieman measured this to 0.35% precision! Sensitive to new particles with > 1 eV Slide 14 Stark-Interference Method in Cesium |E1( ) E1(PNC)| 2 E1( ) 2 [1 2 E1(PNC)/E1( )] 10 -6 Sign changed by inverting E-field and B-field polarities, and sign of detected m-state (by changing laser frequency). Signal changes by only about 1 in a million, yet Wieman measured this to 0.35% precision! Sensitive to new particles with > 1 eV Slide 15 Signal Reversals E E B B M M (3 such reversals) |E1( ) E1(PNC)| 2 E1( ) 2 [1 2 E1(PNC)/E1( )] Reversals good to ~10 -4 (uncertainty) PNC Signal ~10 -6 One reversal not enough 2 Reversals good to ~10 -8 (uncertainty) Two reversals are enough 5 Reversals allowed redundancy for finding systematic errors Slide 16 Optical Rotation Method in Thallium M1E1(PV) 6P 1/2 6P 3/2 A = |M1 iE1(PV)| 2 = M1 2 2Im[M1 E1(PV)] + E1(PV) 2 phase difference between right and left circularly polarized light B E Slide 17 Circular Dichroism A + A = A + + A = 2 Im[E1(PV)/M1 ] From dispersion relations (Kramers-Kronig): = (n + n )/(n-1) PNC = ( L (n + n ) = ( L (n-1) Im[E1(PV)/M1 ] PNC ~ L Im[E1(PV)/M1 ] Atom densitypath length Optical Rotation Slide 18 6 x 10 -7 rad Optical Rotation in Thallium with 6 x 10 -9 rad (1%) sensitivity PRL 74, 2654-62 (1995) OxfordSeattle Curves proportional to refractive index Optical Rotation Method in Thallium Slide 19 It took several minutes to replace the vapor cell with the empty cell Thallium Crossed polarizers Problems: Small signals Birefringent backgrounds No Signal reversals Very slow background subtraction Oven at 1000 C Since light with (+) and (-) helicities have different absorption probabilities, they will also have different refractive indices, n + and n , and will, therefore, rotate linearly polarized light Slide 20 Signal + Background Background Signal Weakness of technique: Poor, 15 minute subtraction procedure Slide 21 Background Instabilities over 1 hour Note: PNC signal ~ 1 rad Slide 22 1) Stark Interference Cs, 0.35% Science 275, 1759 (1997) 2) Optical Rotation Tl 1% PRL 74, 2654 (1995) Best atomic PNC measurements Improve this one! Slide 23 Why measure atomic PNC? Slide 24 A PV H W Q W m Z SignalMass of Z boson need precise atomic theory, or isotope ratio measurements where atomic theory cancels Compared to m Z from CERN Found new physics beyond standard model AGREE (within error) DISAGREE Constrain bounds for new physics Currently, agreement (Cs) to within 0.5% Constrains mass of Z bosons, m Z 1.3 TeV. Slide 25 Nuclear Spin Independent Nuclear Spin Dependent (I 0) (Higher order term; contribution about 100 times smaller) Experimentally distinguishable Slide 26 M1E1(PV) o + e Anapole moment Anapole moment appears as a difference in the E1(PV) amplitudes between the hyperfine transitions Hyperfine structure Slide 27 JILA 97 Difference in PNC measured different hyperfine components (4-3 and 3-4) show presence of Anapole moment Average is spin-independent PNC Stark-Interference Method in Cesium Standard Model prediction (with atomic structure) Slide 28 Constraints on PNC meson-nucleon couplings PRC 65, 045502 (2002) Poor agreement Between Cs and Tl Either nuclear theory and/or some experiments are wrong. More experiments needed Cs Tl Slide 29 PNC isotope ratios Slide 30 Atomic PNC measurments needed for: 1) Search for new physics beyond Standard Model. (search for various Z bosons, including Dark-Matter candidates) 2) Strong test of nuclear theory via nuclear-spin-dependent PNC measurements 3) Measurement of neutron distribution of nuclei (neutron skin) through PNC isotope ratios. Summary Slide 31 In progress: PNC experiments on Fr and Ra + High Z (large PNC effect), Radioactive half lives ~20 minutes. Ongoing experiments (~1000 trapped atoms) the past ~15 years, at large collider facilities TRIUMPH (Vancouver) and KVI (Groningen) Experiments at colliders, and are no longer table top Yb PNC signal at Berkeley (18+ years) PNC in state-selected diatomic molecules (anapole moments) Slide 32 Our Goal: The improvement of the optical rotation technique, by investigating cavity-enhancement methods, to see if we can make a PNC experiment that is: Simple and tabletop Can produce results quickly (significantly less than 20 years) Allows reproducibility quickly by other groups Received an ERC grant to do this Slide 33 Cavity Enhancement seems an obvious idea Birefringent Medium N E. Zavattini et al., Experimental Observation of Optical Rotation Generated in Vacuum by a Magnetic Field, Phys. Rev. Lett. 96, 110406 (2006). N 44 000 Birefringence Sensitivity 5 x 10 -13 rad/m Increase path length by N roundtrips and it works very well for linear birefringence HOWEVER, for cavity-amplification of Chiral Optical Rotation, there are many problems Slide 34 Chiral Optical Rotation cancels in Linear Cavity Circularly Birefringent Medium Chiral optical rotation of light polarization cancels exactly with the return trip. To work, this symmetry must be broken Total rotation = 0 Slide 35 Cavity resonance split by B field and Chiral sample C C Solution: Bowtie cavity with counterpropagating laser beams Magnetic field with magneto-optic window Slide 36 Advantages of Cavity Signal enhanced by N > 1000. Birefringent backgrounds suppressed. Two signal reversals (B B, M M) Allows absolute chirality measurements without need to remove sample. Many applications Slide 37 Applications: Atomic PNC Measure atomic PNC in systems that couldnt be done before Analytical chemistry Measurement of chirality of microsamples Use with microfluidic devices Circular dichroism (biomolecule structure, e.g. protein folding) Improve time resolution Much smaller sample concentrations necessary Slide 38 High-finesse optical cavity Experiment is being built, construction should be finished in 2-3 months. Slide 39 We Propose Cavity-Enhanced Optical Rotation in Xe, Hg, Iodine, (Cs) Atoms Room Temperature, instead of 1000 C 200 C cell, or 2-D MOT (High Z + Volatile) Experiments Successful In progress Our proposals Slide 40 Slide 41 High-Density Iodine Atoms from I 2 photodissociation 532 nm, 50W/cm 2 532 nm photodissociation Iodine cell Recombination Slide 42 Optical Rotation around 1315nm in Iodine Advantages: Predicted signals (2-30 Tl) Birefringent background suppression 2 Fast Signal reversals Fast background subtraction All at room temperature L. Bougas et al. PRL 108, 210801 (2012) (Editors choice) Proposals: G. Katsoprinakis et al. PRA 87, 040101(R) (2013) Slide 43 Simulated Iodine PNC signal with hyperfine resolution Differences between predictions from Cs and Tl gives 5% differences in iodine PNC signals 1% precision needed Slide 44 PNC Optical Rotation transitions in metastable Xe and Hg Slide 45 High-density (10 12 cm -3 ) metastable Xe or Hg in a discharge lamp Lykourgos Bougas (PhD student) Slide 46 Simulated optical rotation signals 10 19 cm -3 column density Optical rotation ( rad) Detuning (GHz) Metastable Hg 609 nm 10 18 cm -3 column density Metastable Xe 988 nm Measureable signals for expected conditions (not as large as for Iodine) Slide 47 Advantages of atomic PNC in Xe, Hg, I, (Cs): (1) Odd-neutron nuclei ( 199 Hg, 201 Hg, 129 Xe, 131 Xe) Sensitivity for 199 Hg is 6 times more than Yb (Berkeley). (2) Iodine (and Cs) have odd-proton nuclei (3) PNC measurements on isotope chains is important Xe and Hg have 15 commercially available stable isotopes Iodine has several commercially available radioactive isotopes (4) Cs has this best atomic theory of all high-Z atoms Covers all the advantages of all other PNC experiments We are investigating whether this new direction will yield an inexpensive and easy atomic PNC experiments, which can be reproduced relatively quickly by other groups. Slide 48 Acknowledgements (Crete) Lykourgos Bougas Dr. George Katsoprinakis Dr. Wolf von Klitzing V. Flambaum (UNSW) V. Dzuba (UNSW) J. Sapirstein (Notre Dame) Funding ERC Starting grant ERC Proof-of-Concept grant G.M.E. Herakleitos