Parity nonconservation in the 6s 2 1 S 0 – 6s5d 3 D 1 transition in Atomic Ytterbium: status of the Berkeley experiments K. Tsigutkin, J. Stalnaker, V. D. Budker K. Tsigutkin, J. Stalnaker, V. Yashchuk, D. Budker Department of Physics,University of California, Berkeley

Weak interaction in Atoms 133 Cs *,** 205 Tl *** QWQWQWQW-72.11(27)-114.2(3.8) sin 2  W (12)0.220(7) Nuclear spin independent contributionNuclear spin dependent term  A -Anapole moment  A -Neutral currents  Q W - Radiative corrections   -Magnetic moment in terms of nuclear magneton g  -Weak coupling constant of the unpaired nucleon C 2  - Coupling constants for the valence nucleon Unpaired neutron:  n =-1.2; g n =-1 Unpaired proton:  p =3.8; g p =5 Unpaired proton 133 Cs I=7/2 205 Tl I=1/2  A  (6.2)-22(30)  2  Anapole moment is much bigger for nuclei with unpaired proton Unpaired neutron  A  100  2  Yb I=5/ *C.Wood et al, Science (Univ. of Colorado, Boulder) ** J. Guéna, M. Lintz, and M. A. Bouchiat PRA 2005 *** P. Vetter et al, PRL (Univ. of Washington, Seattle) Khriplovich & Flambaum

Signature of the weak interaction in atoms H PNC mixes |ns 1/2 > and |n`p 1/2 > states of valence electron  A PNC of dipole-forbidden transition. If A PC is also induced, the amplitudes interfere. Interference E-fieldStark-effect E1 PC-amplitude  E E1-PNC interference term is odd in E Reversing E-field change the transition rate. Transition rate  A PNC A Stark A PC A’ PC interference MUST: Determine A PC with high precision Limit A’ PC

Atomic structure of Yb 3 D 1 By observing the 6s 2 1 S 0 – 6s6p 3 P nm decay the pumping rate of the 6s 2 1 S 0 – 6s5d 3 D nm transition is determined. In addition, the population of 6s6p 3 P 0 metastable level is probed by pumping the 6s6p 3 P 0 - 6s7s 3 S nm transition.

Yb isotopes and abundances C.J. Bowers et al, PRA 1999

Rotational invariant and geometry of the Yb experiment  = 2.24(25)  e a 0 /(V/cm) – Stark transition polarizability (Measured by J.Stalnaker at al, PRA 2006) |  | = 1.08(24)  (Q W /104) e a 0 /(V/cm) – Nuclear spin-independent PNC amplitude (Calculations by Porsev et al, JETP Lett 1995; B. Das, PRA 1997 ) Rotational invariant to which the PNC-Stark interference term is proportional is chosen so that E is along the excitation light axis. This suppresses the interference between M1 and Stark amplitudes emphasizing the PNC-Stark contribution. Reversals: B – even E – odd  – odd  – even

PNC effect on line shapes: even isotopes PNC-Stark interference terms 176 Yb Rate modulation under the E-field reversal yields:

PNC effect on line shapes: odd isotopes PNC-Stark interference terms 171 Yb  NSD  ea 0 for odd Yb isotopes  =10 -9 ea 0  ` must be measured with 0.1% accuracy

Experimental setup Yb density in the beam ~10 10 cm -3 Reversible E-field up to 15 kV/cm, spatial homogeneity 99% Reversible B-field up to 100 G, homogeneity 99% Light collection efficiency: Interaction region: ~2% (556 nm) Detection region: ~25%

Optical system and control electronics Light powers: Ar + : 15W Ti:Sapp (816 nm): 1W Doubler (408 nm): 50 mW PBC: Confocal design, 25 cm; Finesse ~4000 Locking: Pound-Drever-Hall technique

Doppler width and spectral resolution Application of the atomic beam collimator allows to reduce the Doppler broadening by a factor of 10. Spectral lines of closely neighboring isotopes can be clearly resolved. Scanning over 408 nm line, observing 556 nm fluorescence at the interaction region. Observations of the 649 nm line will contribute to a factor of 10 increase in the sensitivity.

Line shapes under the B-field Under application of B-field line profiles demonstrate predicted shapes Signal averaged over 100 scans Scan rate = 1 Hz Ready to collect data with E-field modulation

Systematic effects E-field inhomogeneity B-field inhomogeneity Distortion of linear polarization of the light Residual light propagation in the PBC M1~300  Required: Non-reversing dB x, dE z << 1% Terms having same dependence on the leading E-field reversal and same polarization angle dependence as the Stark-PNC interference term must be limited

Summary The program of measurements needed to understand the system is complete. It is now possible to proceed with confidence towards a first measurement of PNC in Yb The challenge will then be to refine the system to achieve the fractional precision needed to observe NSD effects.