Precision spectroscopy of atomic hydrogen and the proton charge radius puzzle N. Kolachevsky MPQ MPQ
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Precision spectroscopy of
atomic hydrogen and the proton
charge radius puzzle
N. Kolachevsky
MPQMPQ
Why proton charge radius is so
important?- needed for accurate Rydberg constant
determination
R
1 2S S
Hydrogen atomic levels
Schrödinger :Schrödinger (atomic units):
Dirac:QED:
recoil:
nuclear size correction:
Fundamental constants
2 , , n e pE R F m M r
Relative uncertainties:10: 3 10 10: 4 10em M
Do not contribute
(small corrections!)
2 : 1%pr Leading uncertainty!
L1Sself-energy vacuum pol. rp
total
e p 8 383 MHz -215 MHz 1.253(50) MHz 8 172 MHz
Method 1: Electron scattering
e p
d
d
Measured
value
Mott cross-section:
ep
Transferred momentum
Non point-like proton:
form-factor
For small q
(0) 1F impact parameter >>
proton size
Form-factor and charge radius
Form-factor is the Fourier transformation of the charge distribution
Mean proton charge radius
0
0 0
/( ) , 0.8 fm
r rr e r
Since proton possesses anomalous magnetic moment :
1F
2F
“Dirac” charge form-factor
“Anomalous” magnetic form-factor
(1 )
2
p
p
p
e
m
1.79p
Electric and magnetic form-factors
Electric Magnetic
2
2 22
2
( )6
0
p
E
r
dG q
dqQ
Derivative at q=0
e-p scattering results
Hydrogen spectroscopy
2 , , n e prE mR F MTwo unknowns
Two equations necessary!
Hydrogen spectroscopy: limitations
Precision spectroscopy in H:
- ALL levels except 2S promptly decay
3 3 (4 ) 10 MHzS P P
- Natural linewidth of Rydberg states reduces, but they become
sensitive to electric fields (Stark effect)
7
DCE n
Scattered electric field at the level of 1V/m is hard to control!
Hydrogen spectroscopy: results
Dominating uncertainty results from spectroscopy of higher excited
states (not 2S)
Muonic hydrogen p
p
Hydrogen Muonic
hydrogen
Bohr radius 50 pm 0.25 pm
Lyman- 121 nm
(10 eV)
2 keV
200
em m
mc
2 23 8mc
L2Sself-energy vacuum pol. rp
total
e p 1 085 MHz -27 MHz 0.14 MHz 1 057 MHz
p 0.1 THz -45 THz 0.93 THz -49 THz
Spectroscopy of 2S-2P transition in p
Transition line width 10 GHzGoal – uncertainty of 1 GHz
(1999)
Target (H2)
Resonance line 2S-2P in p
Where the problem resides ?!
-Errors in QED calculations are
excluded at such level of discrepancy
“New”
physics?
Are
- e-p scatteing experiments
- H spectroscopy results
flawless?
Hydrogen spectroscopy
Measurements of the 1S-2S transition
Hydrogen
Theory
Frequency comb
Mobile fountain clock
Optical fiber link
Christian Parthey
Arthur Matveev
Janis Alnis
Axel Beyer
Nikolai Kolachevsky
Randolf Pohl
Thomas Udem
Theodor Häncsh
Tobias Wilken
Birgitta Benhardt
Ulrich Jents
Brett Altschul
Michel Abgrall
Daniele Rovera
Christophe Salomon
Philippe Laurent
Katharina Predehl
Stefan Droste
Ronald Holzwarth
Harald Schnatz
Gesine Grosche
Thomas Legero
Stefan Weyers
The Team
Prof. T.W. Hänsch’s
group
The BossHydrogen 1S-2S
Frequency Comb & Menlo Systems
The team
2009-A. Beyer,
Ph.D.
J. Alnis
Post. Doc.
A. Matveev
Post. Doc.
K. Khabarova
Post. Doc.
C. Partey
Ph. D.
Th. Udem
T.W. Hänsch
me
N. Kolachevsky et al., Opt. Lett. 36, 4299 (2011)
1.5 cm÷ 3
Standard ECDL
25 cm
EOM
Long cavity ECDL
972 nm diode laser with a 20 cm long external resonator and intra-cavity EOM
Beat note diode - dye laser
Master oscillator
2exp rmsη φ
64
eff IRη η8-photon process =>
at 972 nm
-25 -20 -15 -10 -5 0 5 10 15 20 25
0
1000
2000
3000
Frequency detuning, kHz
Long cavity diode laser
Dye laser
Co
un
t ra
te,
co
un
ts/s
FP1-FP2 Allan deviation
0,01 0,1 1 10 100 1000 10000
1E-15
1E-14
1s Gate time, 5.5 Hours of measurement
10 ms Gate time, 350 s of measurement
gate time, s
Alla
n d
evia
tion
Thermal noise limit
Fiber
Laser
I()
Hydrogen maser
Stabilized
op
tical fiber
FP5
Distributionamplifier
Wenzel Chain 4 5 5
Wenzel Chain 4 5 5
PLL
PLL
I()
temperature stabilized
1GHz
1GHz
Comb-comb comparison setup
250 MHzsystem
100 MHzsystem
1542 nm
17107200/2 THzmHz
Comb-comb comparison: result
The Hydrogen spectrometer1S-2S spectrometer
C.G. Parthey et al., PRL 107, 203001 (2011)
C.G. Parthey et al., PRL 107, 203001 (2011)
C.G. Parthey et al., PRL 107, 203001 (2011)
Uncertainly in the 1S-2S transition
cannot solve the proton charge
radius puzzle
It is desirable to measure
independently other transitions in H
with higher accuracy
We already use a laser to excite 2S-4P
(486 nm) transition in a cold atomic
beam of H
2S-4P transition measurements (Yale’95)
2S-4P spectroscopy at MPQ
Cold beam of metastable atoms
(4 K)
Optically populated only one
hyperfine sublevel 2S (F=0)
Velocity selective detection,
typical velocities down to 100
m/s
Frequency measurement is
reliable
Natural line width of
the 4P level
13 MHz
2S-4P experimental setup
H(2S)
486 nm
Antiparallel BeamsActive fiber-based retroreflector:
Inside the chamber
Gaussian beam
Assembly of spherical lenses
Aspherical lens
4 mm
Data evaluation
Data scattering (polarization dependent?)
Cross damping: coherent and incoherent parts
incoherent
coherent
Cross damping problem in the 2S-4P experiment
P1/2
P3/2
Analysis of systematic
effects is
still in progress
Simple rule: if one wants to split the line by the factor
of N, the perturbing line should be further away as N
Thank you for attention!
MPQ
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