PRINCIPLE OF THE EXPERIMENT PRESENT RESULTS see Ref.(5) E 1 PV: : PV E 1 6S-7S amplitude interferes with  E z : Stark induced E 1 amplitude POLARIMETRIC METHOD OF MEASUREMENT... and CALIBRATION Input probe polarisation parallel to  ex, rotates during propagation by an angle k  PV (k : atomic factor) Polarimeter imbalance  left-right asymmetry A LR (  PV )  (S X -S Y )/(S X +S Y ) = 2 k  PV Calibration: rotating  ex by  cal  probe rotation k  cal  A LR (  cal ) = 2 k  cal  PV = [ A LR (  PV ) / A LR (  cal ) ].  cal  IMPLEMENTATION of the EXPERIMENT EXCITATION AND DETECTION 4 Polarization configurations : 0°, 45°, 90°, 135° Selection criteria of the PV rotational invariant 1 PV data 0,4s 0,8s 6s 2 mn 12s   PV exp (µrad) point: 400 PV data 1 point: 200 PV data Excited vapour gain axes are // (and  ), not to  exc but to  exc +  PV  exc ^ z : rotated from  exc by an angle  rad, odd in E z  output probe polar n  pr out =  pr in + k  PV  pr in ^ z atomic factor (Cs density, HFS,..) OUR GOAL: measurement of E 1 PV with 1% precision as a cross check of the Boulder 1999 result  A new independent measur’ of Q W the weak charge of Cs nucleus as a precise test of the electroweak theories (Standard Model and extensions, e.g. extra dimensions, additional gauge bosons..)      8 months 7 weeks cells 2002 EVOLUTION OF THE RESULTS (7 different cells) August 2004 probe beam excitation beam REFERENCES ( 1) "A New Manifestation of Atomic Parity Violation in Cesium: a Chiral Optical Gain induced by linearly polarized 6S-7S Excitation", J. Guéna & al., Phys. Rev. Lett. 90, (2003). (2) "Cylindrical symmetry discrimination of magnetoelectric optical systematic effects in a pump- probe atomic parity violation experiment’’, M-A. Bouchiat & al., Eur. Phys. J. D28, 331 (2004). (3) "Prospects for forbidden-transition spectroscopy and parity violation measurements using a beam of cold stable or radioactive atoms’’, S. Sanguinetti & al., Eur. Phys. J. D25, 3 (2003). (4) "Proposal for high-precision Atomic Parity Violation measurements using amplification of the asymmetry by stimulated emission in a transverse E and B fields pump-probe experiment“, J. Guéna & al., JOSA B 22, 21 (2005). (5) “Measurement of the parity violating 6S-7S transition amplitude in cesium within 2x atomic unit accuracy by stimulated emission”, J. Guéna, M. Lintz, and M- A. Bouchiat, Phys. Rev. A.71, (2005). ArXiv:physics/ (6) “Demonstration of an optical polarization magnifier with low birefringence”, M. Lintz & al., Rev Sci. Instr. 76, 4, (2005), arXiv:physics/ (7) “An alkali vapor cell with metal coated windows for efficient application of an electric field”, D. Sarkisyan & al., Rev. Sci. Instr., 76, ArXiv:physics/ (8) Review Article: “ Atomic Parity Violation: Principles, Recent Results, Present Motivations”, J. Guéna, M. Lintz, and M-A. Bouchiat, Mod. Phys. Lett. A 20,6, 375 (2005). ArXiv:physics/ THE CESIUM PARITY VIOLATION EXPERIMENT IN PARIS: Determination of E 1 PV within 2x ea o J. Guéna, M. Lintz and M.-A. Bouchiat, Département de Physique de l'ENS, 24 rue Lhomond, Paris cedex 05, FRANCE Particle physics......without accelerator! HOW TO AMPLIFY THE PV EFFECTS? cell input S/N now adequate to reach 1% precision by lengthening the acquisition time, using last improved cesium cell (conductive windows, ref.7) Updated average result :  PV =  µrad together with a 1% accurate E z field in-situ determination from atomic signals agrees with  PV =  µrad, at 1.62 kV/cm expected from Boulder result for E 1 PV/ /  We extract a new determination of E 1 PV E 1 PV = (  2.1) x ea o for the 6S,F=3 – 7S, F=4 hyperfine transition PASSIVE AMPLIFICATION How to make a polarisation magnifier ? 6 brewster plates... with no two surfaces parallel ! (interference + linear dichroism  birefringence) Polarisation Magnifier at cell output : Passive Amplification of the Polarisation Tilt   x 3  y x t y = 1/3 t x = 1 But… 9 x less photons detected : photon shot noise also increased X 3 ! To gain in S/N we increase the probe intensity dichroic component with axes x (transmission  1) and y (transmission T y << 1) 6 wedged silica plates see Ref. (6) Excited vapour  anisotropic amplifier (  : gain anisotropy)  exponential growth of both probe intensity and left-right asymmetry vs. optical density A LR  2  PV x [exp(  A ) -1] = 2 ( E 1 PV /  E z ) x [exp(  A ) -1] where A = Ln( I out / I in ) : optical density,  E z 2  Increase E z at will?... Not in practice : high endcap potentials  discharges at E z > 2 kV/cm...by the atomic medium itself! Exploiting further A LR amplification: a new PV proposal in transverse E and B fields Advantages in transverse field configuration: Larger excitation rate (involves scalar polarisability  =10x  ), Longer interaction length possible without discharges New cell design to restore cylindrical symmetry by rotating E and B fields by 45° steps New observable = PV excited-state orientation  probe circular dichroism, detected using circular analyser Predicted quantum-noise limit is reduced by a factor of 10, or even more in the triggered superradiant regime !  possible design for a 0.1% statistical precision ACTIVE AMPLIFICATION -V1 V1 -V1 -V2 V2 0 0 Noise reduction and increased rep. rate 160Hz Dichroic mirror Since first 9% result (cell # 1, Ref. 1), S/N improved by 3.5  acquisition time for S/N = 1 reduced by 12 probe polarimeter see Ref.(4)