Simple Atom, Extreme Nucleus: Laser Trapping and Probing of He-8 Zheng-Tian Lu Argonne National Laboratory University of Chicago Funding: DOE, Office of Nuclear Physics

2 Å e-e- Ionization Energy of Helium Atom Level 2 3 S 1 Calculation ± 6 MHz Experiment MHz Gordon Drake, Phys. Scripta (1999) Helium Atom fm

3 Quantum Monte Carlo Calculations of Light Nuclei Pieper & Wiringa. Ann. Rev. Nucl. Part. Sci. (2001)

4 Halo Nuclei 6 He and 8 He Borromean RingsBorromean Nucleus 4 He 8 He 6 He Quantum Monte Carlo calculation Proton Neutron

5 Hadronic Probe: Scattering of 6 He & 8 He Beams Tanihata et al, Phys Lett (1985) LBNL Alkhazov et al, Nucl Phys (2002) GSI Elastic and inelastic collision: He on C, B Elastic collision: He on H, 700 MeV/u Matter distribution, matter radii 18 O 9 Be 6 He 12 C 6 He  1H1H

6 Atomic Energy Levels of Helium 23S123S1 11S011S0 389 nm 1083 nm 2 3 P 0,1, eV 3 3 P 0,1,2 He energy level diagram 100 ns 100 ns  1.6 MHz Single photon kick  0.1 m/s Transition rate ~ 4 x 10 6 /s Acceleration ~ 4 x 10 5 m/s 2 Cooling & Trapping at 1083 nm Single photon kick  0.3 m/s Doppler shift  400 kHz Spectroscopy at 389 nm A glow discharge He gas cell

7 Field (Volume) Shift Mass shift Field shift r E s p V ~ - 1/r

8 Laser Cooling and Trapping Magneto-Optical Trap (MOT) Cooling: Temperature~ 1 mK,  avoid Doppler shift / width Long observation time: 100 ms Spatial confinement: trap size < 1 mm  single atom sensitivity Selectivity:  no isotopic / isobaric interference Technical challenges: Short lifetime, small samples (10 6 atoms/s available) Metastable efficiency ~ Precision requirement (~100 kHz)

9 8 GANIL by Antonio Villari et al. Salle D2 13 C He-8: 5 x 10 5 s -1 He-6: 1 x 10 8 s -1 8 He 20 keV 8 He thermal Laser System MOT ECR Ion Source Mass separator 20 keV He + 1 GeV, 400 pnA

10 Atom Trapping of 6 He & 8 He at GANIL ~1x He + /s ~5x He + /s PMT Zeeman slower MOT Transverse cooling 389 nm 1083 nm Atom Trap Setup RF - Discharge Xe Spectroscopy 389 nm 23S123S1 11S011S0 2 3 P P 2 Trap 1083 nm He level scheme Capture efficiency 1x10 -7 Source 6 He ~ 5x10 7 /s 8 He ~ 1x10 5 /s Trap 6 He ~ 5 /s 8 He ~ 1x10 -2 /s One trapped 6 He atom

11 He-8 Trapped! First He-8 Atom June 15 th 2007 t f 50 kHz 6 He ~30 6 He atoms/s 110 kHz 60 atoms 8 He ~30 8 He atoms/hr

12 8 He 6 He Isotope Shift and Field Shift : J - Dependence? 2 3 S nm 3 3 P 0,1,2 J=2 J=1 J=0 J=1 Wang 04 Argonne J=1 3 1 P 1

13 6 He & 8 He RMS Charge Radii 6 He 8 He Field Shift, MHz-1.464(34)-1.026(63) RMS R CH, fm2.072(9)1.961(16) Total Uncertainty0.4 %0.9 % - Statistical0.1 %0.6 % - Trap Systematics0.3 %0.6 % - Mass Systematics0.1 %0.0 % - He-4: 1.681(4) fm0.1 % Mueller et al., PRL (2007) + Ryjkov et al., PRL (2008): He-8 mass + Sick PRC (2008): He-4 Charge Radius RpRp rcrc RnRn -  SO - MEC = 0.766(12) fm 2 = (5) fm 2

14 6 He & 8 He RMS Point Proton and Matter Radii Wang et al., PRL (2004) Mueller et al., PRL (2007)

15 He-6 Collaboration P. Mueller, L.-B. Wang, K. Bailey, J.P. Greene, D. Henderson, R.J. Holt, R. Janssens, C.L. Jiang, Z.-T. Lu, T.P. O’Conner, R.C. Pardo, K.E. Rehm, J.P. Schiffer, X.D. Tang - Physics, Argonne G. W. F. Drake - Univ of Windsor, Canada He-8 Collaboration P. Mueller, K. Bailey, R. J. Holt, R. V. F. Janssens, Z.-T. Lu, T. P. O'Connor, I. Sulai - Physics, Argonne; M.- G. Saint Laurent, J.-Ch. Thomas, A.C.C. Villari - GANIL, Caen, France G. W. F. Drake - Univ of Windsor, Canada L.-B. Wang – Los Alamos Lab