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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-Ionization Energy of Helium Atom
Level 2 3S1
Calculation 1 152 842 741 ± 6 MHz
Experiment 1 152 842 743 MHz
Gordon Drake, Phys. Scripta (1999)
Helium Atom
fm
3
QCD
q
q
N
N
MesonexchangeN
N
π
Effective Model of Nuclear Interaction
∑ ∑<
+++=i ji
Rijijiji vvvKH πγ
EM 1-π short-range
Coupling parameters fit to NN scattering data
Problem: binding energy of most light nuclei too small
Rijkijkijkijk VVVV ++= ππ 32
Coupling parameters fit to energy levels of light nuclei
Pieper & Wiringa. Ann. Rev. Nucl. Part. Sci. (2001)
Two-body potential: Argonne V18
Three-body potential: Illinois-2
4
Quantum Monte Carlo Calculations of Light Nuclei
Pieper & Wiringa. Ann. Rev. Nucl. Part. Sci. (2001)
5
Halo Nuclei 6He and 8He
Isotope Half-life Spin Isospin Core + Valence
He-6 807 ms 0+ 1 α + 2n
He-8 119 ms 0+ 2 α + 4n
Borromean RingsBorromean Nucleus
4He
8He
6He
QuantumMonte Carlocalculation
Proton
Neutron
6
Hadronic Probe: Scattering of 6He & 8He 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
18O9Be
6He12C
6Heθ1H
6He
7
E&M Probe of Nuclear Charge Distribution
22exp( ) ( ) ( )Mott
d d F qd d
σ σ= ⋅
Ω Ω
2 2 2arg
1( ) 16 ch eF q q r= − < > + ⋅ ⋅ ⋅
( )2 2r r r d vρ< > = ⋅∫mean-square radius
2r< >root-mean-square radius
4He rms charge radius = 1.676 (8) fm [I. Sick Phys Lett B (1982)]
Proton rms charge radius = 0.895(18) fm [I. Sick Phys Lett B (2003)]
electron
q
θ4He
8
Atomic Energy Levels of Helium
23S1
11S0
389 nm
1083 nm
23P0,1,2
19.82 eV
33P0,1,2
He energy level diagram
100 ns
100 ns 1.6 MHz• Single photon kick 0.1 m/s
• Transition rate ~ 4 x 106 /s
• Acceleration ~ 4 x 105 m/s2
Cooling & Trapping at 1083 nm
• Single photon kick 0.3 m/s
• Doppler shift 400 kHz
Spectroscopy at 389 nm
Isotope Shiftδν = δνMS + δνFS
9
10 100 1000 10000
-150
-100
-50
0
δνM
S R
el. t
o M
ass
∞ (G
Hz)
Mass, amu
Mass Shift & Search for Helium-Like Strangelets
1s2s 3S1metastable
1s2p 3P2
1083 nm (1 eV)
1s1s 1S
20 eV
u d s
Strangelet
P. Mueller, Z-T Lu et al., PRL (2004)
Witten, PRD (1984)Jaffe, Busza, Wilczek, Sandweiss, RMP (2000)
1 /e
MSe N
mm M
ν ∝+4He
3He
6He
8He
10
10 100 1000 1000010-20
10-18
10-16
10-14
10-12
10-10
10-8
10-6
IsotopicKlein et al.
SolarVandegriff et al.
SolarThis Work
TerrestrialThis Work
Li
mits
on
Abu
ndan
ce
Mass (amu)
IsotopicThis Work Isotopic “per 4He in
Earth’s atmosphere”
Terrestrial “per atom of all elements on Earth”
Solar “per atom ofall elements in Sun”
Limits on the Abundance of Anomalously Heavy Helium
References:This work -- P. Mueller et al., PRL 92, 022501 (2004)Klein et al. in Proc. of Symp. on Accelerator Mass Spectrometry, ANL/PHY-81-1 (1981)Vandegriff et al., Phys. Lett. B365, 418 (1996)
11
Field (Volume) Shift
AA
FS rZe′
⋅ΨΔ⋅−= 222 )0(3
2 δπδν
1 10 1001E-3
0.01
0.1
1
10
100
| Iso
tope
Shi
ft |,
GH
zAtomic number, Z
rE
s
p
V ~ - 1/r
12
Drake, Can. J. Phys (2006);Pachucki & Sapirstein, J Phys B (2002)
Non-relativistic wave functions fromvariational calculations
Perturbation theory for relativistic corrections, QED,finite nuclear mass and nuclear charge radius
QED terms “cancel” in isotope shift
Atomic Theory of Helium
3PJ
3S1
For 23S1 – 33P2 transition @ 389 nm:6He - 4He : δν6,4 = 43196.207(15) MHz + 1.008 (<r2>He4 - <r2>He6) MHz/fm2
8He - 4He : δν8,4 = 64702.409(74) MHz + 1.008 (<r2>He4 - <r2>He8) MHz/fm2
100 kHz error in IS ~ 1% error in radius
13
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 (<106 atoms/s available)
Metastable efficiency ~ 10-5
Precision requirement (~100 kHz)
16
8He @ GANIL by Antonio Villari et al.
2.15 3.15
1.85 0.75
1.65
5 m
Salle D213C
• He-8: 5 x 105 s-1
• He-6: 1 x 108 s-1
8He+
@ 20 keV
8Hethermal
Laser System
MOT
ECR Ion Source
Massseparator
1 GeV, 400 pnA
17
Atom Trapping of 6He & 8He at GANIL
~1x108 6He+/s~5x105 8He+/s
PMT
Zeemanslower
MOTTransverse
cooling 389 nm1083 nm
Atom Trap Setup
RF -Discharge
Xe
Spectroscopy389 nm
23S1
11S0
2 3P2
3 3P2
Trap1083 nm
He level scheme
Capture efficiency1x10-7
Source6He ~ 5x107/s8He ~ 1x105/s
Trap6He ~ 5 /s8He ~ 1x10-2/s
0 5 10 15 200.0
0.2
0.4
0.6
0.8
1.0
1.2
Pho
ton
coun
trate
/ kH
zTime (s)
One trapped 6He atom
18
He-8 Trapped!
First He-8 AtomJune 15th 2007
t
f
-10 -8 -6 -4 -2 0 2 4 6 8 100
100
200
300
400
500
Cou
nts
per C
hann
el
Rel. Laser Frequency, MHz
-10 -8 -6 -4 -2 0 2 4 6 8 100
20
40
60
80
100
Cou
nts
per C
hann
el
Rel. Laser Frequency, MHz
50 kHz
6He
~30 6He atoms/s
110 kHz60 atoms
8He
~30 8He atoms/hr
19
0.4
0.5
0.6
0.7
0.8
0.9
-0.2
0.0
0.2
0.4
0.6
0.8
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
δν6,
4 - 4
3194
, MH
z
(b)
(a)
δν8,
4 - 6
4701
, MH
z
J = 0 J = 1 J = 2
(c)
6He8He
Fiel
d S
hift,
MH
z
J = 0 J = 1 J = 2
8He
6He
Isotope Shift and Field Shift : J - Dependence?
2 3S1
389
nm
3 3P0,1,2
J=2J=1
J=0
J=1
Wang 04Argonne
J=13 1P1
20
6He & 8He Charge Radii6He 8He
Field Shift, MHz -1.464(34) -0.916(95)
RMS RCH, fm 2.068(11) 1.929(26)Total Uncertainty 0.5 % 1.3 %- Statistical 0.1 % 0.6 %
- Trap Systematics 0.3 % 0.6 %
- Mass Systematics 0.2 % 1.0 %
- He-4: 1.676(8) fm 0.3 % 0.4 %
2
int 2 atom
PE E
Mγ
γ = +Recoil Correction
21
Charge Radius vs. Point-Proton Radius
Theory:mean square
point-proton radius<rp
2>
Experiment:mean squarecharge radius
<rc2>
rp
Z<rc2> = Z<rp
2> + Z(<Rp2>+0.75/Mp
2) + N<Rn2>
Mean square charge radii of nucleons:
Neutron <Rn2> = - 0.116(2) fm2
Proton <Rp2> = 0.769(12) fm2 (I. Sick)
Darwin-Foldy 0.75/Mp2 = 0.033 fm2 (J. Friar)
Rp
rc
Rn
23
He-6 CollaborationP. 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, ArgonneG. W. F. Drake - Univ of Windsor, Canada
He-8 CollaborationP. 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, FranceG. W. F. Drake - Univ of Windsor, Canada L.-B. Wang – Los Alamos Lab