Laser Trapping and Probing of Exotic Helium Isotopes. Peter Müller

Transcription

1 Laser Trapping and Probing of Exotic Helium Isotopes Peter Müller

2 Outline Nuclear Charge Radii of 6 He and 8 He -Neutron Halo Isotopes 6,8 He - Charge Radii and Isotope Shift - Atom Trapping of Helium - 8 He Experiment at GANIL Laser Spectroscopy of Light Isotopes (@ Mainz University) - 11 Li with Two-photon Spectroscopy ( + TRIUMF) - 11 Be with Collinear Spectroscopy ( + ISOLDE/CERN) Beyond Halo Isotopes - Neutron Rich Isotopes at CARIBU/FRIB - 6 He beta-neutrino correlation 2

3 Laser Spectroscopy of Radioactive Isotopes Nuclear charge radii + nuclear moments >30 years of effort W. Nörtershäuser 3

4 Light Nuclei & Neutron Halos I. Tanihata et al. ( 85) 1-n halo 6 He 2-n halo 4-n halo Charge Radius Measurement 4

5 Green s Function Monte Carlo 2010 Tom W. Bonner Price Pieper & Wiringa (2006) 5

6 GFMC Neutron and Proton Densities in 4,6,8 He n or p 4 He 6 He 8 He Borromean Nucleus Borromean Rings Neutron Proton 6

7 Neutron Halo Nuclei 6 He and 8 He Isotope Half-life Spin Isospin Core + Valence He ms α + 2n He ms α + 4n Borromean 3.0 I. Tanihata et al., Phys. Lett. (1985) Core-Halo Structure Interaction Radius (fm) ( 6 H e ) ( 4 H e ) = ( 6 H e ) σ σ σ I I 2 n I. Tanihata et al., Phys. Lett. (1992) 6 He Helium Mass Number A 7

8 Helium Atom fm Ionization Energy of Helium Atom Å e - Level 2 3 S 1 Calculation Experiment ± 6 MHz MHz Gordon Drake, Phys. Scripta (1999) 8

9 Atomic Energy Levels of Helium He energy level diagram He discharge 3 3 P 0,1,2 2 3 P 0,1,2 3.2 ev 389 nm 2 3 S S ev 1083 nm metastable 19.8 ev, e-collision in discharge 9

10 Field (Volume) Shift E δν FS = 2π Ze 3 r 2 Ψ(0) 2 δ r 2 AA s p V ~ - 1/r Isotope Shift, GHz Mass shift Field shift 1E Atomic number, Z 10

11 Atomic Isotope Shift Isotope Shift Mass shift: due to nucleus recoil A A' δν MS AA ' δν = δν MS + δν δν FS Field shift: due to nucleus size δν FS Ζ [Ψ(0)] 2 δ<r 2 > For 2 3 S P nm: δν = δν MS + C FS δ<r2 > 6 He - 4 He : δν 6,4 = (16) MHz (<r 2 > He4 - <r 2 > He6 ) MHz/fm 2 8 He - 4 He : δν 8,4 = (1) MHz (<r 2 > He4 - <r 2 > He8 ) MHz/fm 2 G.W.F. Drake, Univ. of Windsor, Nucl. Phys. A737c, 25 (2004) 100 khz error in IS ~ 1% error in radius 11

12 Laser Cooling and Trapping Technical challenges: Short lifetime, small samples (<10 6 atoms/s available) Low metastable population efficiency (~ one in ) Precision requirement (100 khz = Doppler 4 cm/s ) 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 12

13 Where to find 8 He? GANIL Caen, France 13

14 GANIL 75 MeV/u, 0.4 pµa 13 C beam on 12 C target 14

15 8 GANIL Salle D2 ECR Ion Source 13 C Mass separator 6,8 He 20 kev 6,8 He 5 m thermal 1.65 MOT Laser System 15

16 Atom Trapping of 6 He & 8 He at GANIL He level scheme Atom Trap Setup 389 nm Spectroscopy 389 nm 3 3 P P 2 Trap 1083 nm 2 3 S S nm Helium Rates 6 He 8 source 5x10 7 s -1 1x10 5 s -1 Efficiency = trap 5 s hr -1 Photon countrate/ khz Single atom signal One 6 He atom Time (s) 16

17 Jan. 26 th

18 Source & Zeeman Slower 18

19 June 12 th - 20 th

20 June 14 th. Trip to Brittany? 300 km 20

21 June 15th. 6 He + 8 He Sample Spectra 6 He 8 He 100 Counts per Channel khz Counts per Channel khz Rel. Laser Frequency, MHz Rel. Laser Frequency, MHz ~ 5 6 He atoms/s 2 minutes ~ 30 8 He atoms/hr 2 hours 21

22 Experimental Uncertainties and Corrections 6 He 8 He Statistical { Photon Counting Laser Alignment 8 khz 2 khz 32 khz 12 khz Reference Laser 2 khz 24 khz Systematic { Probing Power Shift Zeeman Shift 0 khz 30 khz 15 khz 45 khz Nuclear Mass 15 khz 74 1 khz TOTAL 35 khz khz Corrections Recoil Effect Nuclear Polarization +110(0) khz -14(3) khz +165(0) khz -2(1) khz TITAN Penning TRIUMF, V. L. Ryjkov et al., PRL 101, (2008) 22

23 6 He & 8 He RMS Charge Radii R p 6 He 8 He r c Field Shift, MHz (34) (63) RMS R CH, fm 2.072(9) 1.961(16) Total Uncertainty 0.4 % 0.9 % R n - Statistical 0.1 % 0.6 % - Trap Systematics 0.3 % 0.6 % - Mass Systematics 0.1 % 0.0 % - He-4: 1.681(4) fm 0.1 % 0.1 % - δ SO - MEC P. Mueller et al., PRL 99, (2007) + V. L. Ryjkov et al., PRL 101, (2008): He-8 mass + I. Sick PRC 77, (R) (2008): He-4 Charge Radius <R P2 > = 0.766(12) fm 2 <R N2 > = (5) fm 2 23

24 6 He & 8 He RMS Point Proton and Matter Radii 4 He rms point-proton matter Experiment Theory 6 He 8 He 6 He Field Shift, MHz (34) (63) RMS R pp, fm 1.930(9) 1.843(16) Total Uncertainty 0.4 % 0.9 % - Statistical - Trap Systematics 0.1 % 0.3 % 0.6 % 0.6 % 8 He - Mass Systematics 0.2 % 0.0 % - He-4: 1.465(4) fm 0.1 % 0.1 % Nuclear Radii, fm 24

25 RMS Charge Radii : 4 He - 6 He - 8 He 1.681(4) fm 2.072(9) fm 1.961(16) fm 25

26 Resonance Ionization of Lithium Lithium atomic levels Experimental setup 5.4 ev Ion Signal CO-Laser 2 τ = 30 ns 3d 2 D 3/2,5/2 3s 2 S 1/2 735 nm 610 nm 2p 2 P 1/2,3/2 735 nm 610 nm Electrostatic Lenses PZT 735 nm 2s 2 S 1/2 6,7,8,9,11 Li Magnet Courtesy of W. Noertershaeuser, Mainz University 26

27 Nuclear Charge Radii Comparison with Theory r c (fm) r c ( 7 Li) = 2.39(3) fm Suelzle et al, PR 162,992(1967) Pachucki LBSM SVMC DCM AV18IL2 NCSM FMD SVMCFC Li Isotope R. Sánchez et al., PRL 96, (2006) Nature Physics 2, 145 (2006) M. Puchalski et al., PRL 97, (2006) Three body model: 27

28 Limitations for Light Elements The Solution ion beam E kin ~60 kev + collinear laser beam fixed frequency CONVENTIONAL SETUP ( β ) ν = ν γ 1 + c 0 Doppler-tuning Acceleration / NEW APPROACH anticollinear laser beam fixed frequency ( β ) ( β ) ν = ν γ 1 + ν c a 0 = ν γ 1 Deceleration ( ) 0 ν = a ν c = ν 0 γ 1 β ν 0 Completely independent of U! γ= γ(u,m), β = β(u,m), U/U 10-4 δν IS ( 9 Be, 11 Be) = 14 MHz Photomultiplier Impossible for Light Elements (Z<10)!! Requirements: Measure absolute frequencies Accuracy: ν/ν < 10-9 Dedicated Laser System for absolute Frequency Measurements 28

29 9 Be + l 313 nm Experimental Setup 2p 3/2 2p 1/2 F=0,1,2,3 F=1 F=2 2s 1/2 F=1 F=2 Collinear Anticollinear 29

30 Nuclear Charge Radius (fm) Beryllium: Nuclear Charge Radii Electron Scattering: r c ( 9 Be) = 2.519(12) fm, J.A. Jansen et al., Nucl.Phys.A 188, 337 (1972). Muonic Atoms: r c ( 9 Be) = 2.39(17) fm, L.A. Schaller, Nucl.Phys.A 343, 333 (1980). 2,8 2,7 2,6 2,5 2,4 2, Be Isotope W. Nörtershäuser et al., PRL 102, (2009). + References: Experiment Interaction cross section (Tanihata) Greens-Funct. Monte-Carlo Calcul. Fermonic Molecular Dynamics No-Core Shell Model Thanks to R.Torabi, Th. Neff, H. Feldmeier and P. Navratil for providing unpublished data! 30

31 Berylium Charge Radii in FMD Calculations FMD: Fermionic Molecular Dynamics M. Zakova, Th. Neff et al., J.Phys.G, in print (2010). Calculations by Thomas Neff, GSI 10 Be α-α R pp = Charge radius with respect to the center-of-charge α- α Distance. 31

32 Laser CARIBU Cf-252 source 80 mci -> 1Ci Gas catcher Laser Enclosure (~ 6 x 10 ) AC Laser Table (~ 3 x 7 ) HEPA Tape Station High-resolution mass separator δm/m > 1/20000 Ion Trap / Cryostat RF Cooler & Buncher Collinear Beamline To ATLAS 32

33 Laser CARIBU concentrate on developing new techniques extend isotopic chains to more neutron rich isotopes access to refractory elements -> techniques applicable to FRIB setup Low-energy yield, s -1 > < 1 33

34 Laser Spectroscopy of Radioactive Isotopes Charge radii + moments The next 30 years FRIB - more neutron rich - refractory elements W. Nörtershäuser 34

35 Stopped Beams Area at FRIB collinear trap / cryostats laser table ~2m x 2m floor space for traps or cryostat use mass separated beams after RF cooler/buncher charge-exchange cell Ti:Sa laser system w/ frequency doubler 4 x 8 laser table fiber coupling ok 35

36 Beta-Neutrino Correlation in the Decay of 6 He t 1/2 =0.808 sec 6 He 0 + β 100% E 0 = MeV 6 Li 1 + Correlation Coef. a T A V ( θ ) N E C C, 1 a p β + cosθ E β βν βν β Best experimental limit: a = ± T A C T 0.4% C A a(exp) - a(sm) x He n Na 21 Na S Ar 38m K Johnson et al., Phys. Rev. (1963) Fermi fraction

37 Beta-Decay Study with Laser Trapped 6 He Simple atom, nucleus, decay mode Sensitive to tensor couplings MCP Detector Beta-Detector Counts Simulated time-of-flight signal a = +1/3 a = -1/3 New Physics Standard Model 6 Li + β He atom trap Time of Flight (ns) He yields: ATLAS: s -1 with 12 C( 7 Li, 6 He) pna CENPA: ~ s -1 with 7 Li(d, 3 Ηe) 6 1 pµa Assume 6 He trapping rate of s -1, with trapping efficiency 15 minutes, coincidence events, δa = ± (δa/a = 0.1% in ~1 week) 37

38 Thank You! 8 He Collaboration K. Bailey, R. J. Holt, R. V. F. Janssens, Z.-T. Lu, P.M., T. P. O'Connor, I. Sulai Physics Division, Argonne National Laboratory, USA M.-G. Saint Laurent, J.-Ch. Thomas, A.C.C. Villari, J.A. Alcantara-Nunez, R. Alvez-Conde, M. Dubois, C. Eleon, G. Gaubert, N. Lecesne GANIL, Caen, France G. W. F. Drake - University of Windsor, Windsor, Canada L.-B. Wang Los Alamos National Laboratory, USA Argonne Atom Trappers 38

39 GFMC What happens to the α-core? AV18 + IL2 GFMC proton-proton distributions 39

40 GFMC Binding Energy vs. Charge Radius 40