Progress towards a new precise microwave measurement of the 2S-2P - PowerPoint PPT Presentation

Progress towards a new precise microwave measurement of the 2S-2P Lamb shift in atomic hydrogen Eric Hessels York University Toronto, Canada The image cannot be displayed. Your computer may not have enough Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 1

From e-p Hofstadter and McAllister (1955) Phys Rev 98 217; 102 851 scattering, already in in 1955 the proton charge radius was known to one digit: 0.8 fm 59 years later, we still know it to one digit Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 2

In 1956 it was suggested that the proton size should show up in the hydrogen 2S 1/2 -2P 1/2 interval (the Lamb shift) Phys Rev 105 1681 Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 3

Hydrogen n=2 Energy levels QED contributions Lamb shift: (10 GHz) (proton size: 0.5 neV) Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 4

Hydrogen n=2 Energy levels Others here can explain the details Calculated and recalculated by many people over the past 5 decades (proton size: Uncertainty is <1 part per million +0.5 neV) (< 1% of proton size contribution) Theory has been stable at this level of precision for ~20 years Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 5

Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 6

9 part-per-million measurement of Lamb shift Determines the proton size to an accuracy of 3% Still the most precise determination of this interval 33 years between Lamb and Lundeen & Pipkin. Now another 33 years have passed and it is time for another measurement. Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 7

Other precise >14-digits 035(10) hydrogen measurements Cannot be used directly for r p determination (Ry) Combinations of measurements can eliminate Ry dependence and determine r p For example: ν (2S-8D5/2)-(5/16) ν (1S-2S) =5 369 962(6) kHz is independent of Ry and determines r p to 2% Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 8

Ten r p determinations from combinations of H intervals: (0.8%) Average e-p scattering (world data) e-p scattering (Mainz 2011) Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 9

Muonic hydrogen Hydrogen proton size 200 proton size effect is 0.01% effect is 2% of Lamb shift of Lamb shift Lamb shift: Recent PSI measurements in muonic hydrogen: proton charge radius of 0.84087(39) fm (proton size: 200 3 +0.5 neV) Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 10

4.5 s.d. discrepancy (increases to >7 s.d. if scattering measurements are included) Hydrogen Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 11

Comparing muonic hydrogen to the individual measurements makes the conflict seem not as big: all but one agree with µ p to within 2 s.d. We need more measurements in hydrogen Hydrogen Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 12

Our Experiment Remeasure hydrogen 2S-2P intervals in ordinary hydrogen SOF microwave measurements We will start with the 2S 1/2 -2P 1/2 Lamb shift interval And follow up with the 2S 1/2 -2P 3/2 interval 10 GHz Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 13

Our Experiment Remeasure hydrogen 2S-2P intervals in ordinary hydrogen SOF microwave measurements More specifically, we will start with the 2S 1/2 (F=0, m F =0) to 2P 1/2 (F=1, m F =0) m F = -1 m F = 0 m F = 1 F = 2 interval 2P 3/2 F = 1 And later we will measure the 2S 1/2 (F=0, m F =0) to 2P 3/2 (F=1, m F =0) F = 1 interval 2S 1/2 F = 0 rf F = 1 2P 1/2 F = 0 Will form a direct test of proton radius without the need for a 1S 1/2 F = 1 precise Rydberg constant F = 0 Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 14

Our Experiment and progress to Date Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 15

Stable ions source with 10 µ A of 50-keV to 100-keV protons Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 16

10 µ A 50-keV to 100-keV protons protons charge exchange with H 2 gas Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 17

We empty the 2S 1/2 F=1 states using 2 rf cavities Charge that drive them down to short-lived 2P 1/2 states exchange 2% H(2S) With F=1 states empty, can make a measurment of the isolated transition from the 2S 1/2 F=0 transition 10 µ A m F = -1 m F = 0 m F = 1 50-keV to F = 2 2P 3/2 F = 1 100-keV protons F = 1 2S 1/2 F = 0 F = 1 2P 1/2 F = 0 1S 1/2 F = 1 F = 0 Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 18

Charge exchange 2% H(2S) 10 µ A 50-keV to 100-keV protons Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 19

Charge exchange 2% H(2S) 2S(F=1) quench 10 µ A 50-keV to 100-keV protons Amplified diode 2S-3P 656-nm laser system To measure the speed, direction and angular spread of the H(2S) beam Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 20

low-Q microwave cavities to create standing waves which drive the main SOF fields 2S(F=1) quench Critical parameter for the SOF measurement is the relative 10 µ A phase of the microwaves in 50-keV to the two cavities 100-keV protons Relative phase is measured by a pickup observing small interference signal in a tube connecting the two regions Any unanticipated error in relative phase is reversed by rotating entire microwave system by 180 O – all in situ Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 21

a 2nd 2S(F=1) quench region assures that atoms that cascade into the 2S(F=1) atoms that decay from Rydberg states do not contribute to the signal m F = 0 m F 1 m F = -1 F = 1 2S 1/2 F = 0 10 µ A 2P 1/2 F = 1 F = 0 50-keV to 100-keV protons Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 22

We detect the 2S atoms that remain by mixing 2S with 2P with a DC electric field and resulting Ly- α is 2S(F=1) detected by ionizing CS 2 gas – quench almost 4 π ~50% Ly- α detection 10 µ A efficiency 50-keV to 100-keV protons Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 23

Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 24

Noise-to-signal ratio (per root Hz) of detected 2S hydrogen atoms Very good signal-to-noise ratio (approaching 10 4 in 1 second) at most frequencies between 100 Hz and 10 kHz Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 25

Diffference in phase between beat signal and SOF signal is zero if rf frequency (f) is in resonance with the atomic transition. We are using a new beat-frequency SOF technique | δ f | =~100 Hz rf in two SOF regions oscillate f f+ δ f between being in phase and out of phase at δ f beat frequency If there is a phase difference, it predicts the difference between the applied frequency f and the atomic resonance frequency. SOF signal δ f =100 Hz PRELIMINARY Signal-to-noise ratio is sufficient to determine atomic frequency to <9 kHz (Lundeen and Pipkin accuracy) in 20 minutes. Note excellent signal-to-noise ratio (uncertainty is indicated by size of data point) Need to do extensive systematic studies. Vary f, P, T, δ f, rotate, etc. Still need to do the hard work of a precision measurement. This data was acquired in 6 minutes Proton Puzzle Mainz June 3, 2014 Eric Hessels York University Toronto Canada 26