Antihydrogen Spectroscopy and Antimatter Gravity in ALPHA

Chris Ørum Rasmussen

September 26, 2019

C. Ø. Rasmussen Antihydrogen Physics slide 1 of 18 Motivations

C. Ø. Rasmussen Antihydrogen Physics slide 2 of 18 Motivations Spaceships!

(Sadly, not practical)

C. Ø. Rasmussen Antihydrogen Physics slide 2 of 18 Motivations Antimatter allows for direct tests of fundamental symmetries and may hold clues to some of the biggest unanswered questions in physics: Why is there no antimatter in the Universe (Baryon asymmetry) Is CPT symmetry conserved? Does the weak equivalence principle hold for antimatter?

C. Ø. Rasmussen Antihydrogen Physics slide 3 of 18 1S-2S Spectroscopy The 1S-2S transition frequency in hydrogen is one of the most precisely measured numbers in physics: f1S−2S = 2 466 061 413 187 035 (10) Hz

Comparing this value with its equivalent in antihydrogen is one of the most appealing and conceptually simple matter / antimatter comparisons, and one of the main motivations for for building an antiproton decelerator.

C. Ø. Rasmussen Antihydrogen Physics slide 4 of 18 The ALPHA Experiment Antihydrogen Laser PHysics Apparatus

C. Ø. Rasmussen Antihydrogen Physics slide 5 of 18 AD

C. Ø. Rasmussen Antihydrogen Physics slide 6 of 18 Typical Numbers

3 × 107 p delivered by the AD every ∼100s at 5.3 MeV 100,000 p captured and cooled after degrading foil About 50,000 H produced by mixing with ∼ 3 × 106 e+ 30 atoms remain trapped in 0.5 K deep magnetic well Best spectroscopic measurement to date involved 15,000 trapped ground state atoms and a measurement campaign of 10 weeks

C. Ø. Rasmussen Antihydrogen Physics slide 7 of 18 Antihydrogen Trapping in ALPHA

C. Ø. Rasmussen Antihydrogen Physics slide 8 of 18 2016 Result

1.2 Disappearance 2016 Appearance 2016 1000 mW Simulation 1

0.8

0.6

0.4 Normalized signal

0.2

-0.2 -300 -200 -100 0 100 200 300 Detuning, D (kHz @ 243 nm)

C. Ø. Rasmussen Antihydrogen Physics slide 9 of 18 2017 Result

1.2 Disappearance 2016 Appearance 2016 Disappearance, r (D) s 1 Appearance, r (D) l 1000 mW Simulation

0.8

0.6

0.4 Normalized signal

0.2

-0.2 -300 -200 -100 0 100 200 300 Detuning, D (kHz @ 243 nm)

C. Ø. Rasmussen Antihydrogen Physics slide 10 of 18 1S-2S Spectroscopy: Best Result

Transition frequency determined with uncertainty of 2 × 10−12 This is the most precise direct measurement on any antimatter system to date. Excellent agreement with ordinary hydrogen Width is dominated by transit time

1.2 Disappearance, r (D) s Appearance, r (D) l 1 1000 mW Simulation

0.8

0.6

0.4 Normalized signal

0.2

-0.2 -300 -200 -100 0 100 200 300 Detuning, D (kHz @ 243 nm) C. Ø. Rasmussen Antihydrogen Physics slide 11 of 18 Challenges of Antihydrogen Spectroscopy

Few atoms available Detection is diﬃcult Complex apparatus since traps for neutral atoms and constituent charged particles must be superimposed

Design experiments such that resonance leads to annihilation

C. Ø. Rasmussen Antihydrogen Physics slide 12 of 18 Ground State Hyperﬁne Spectroscopy Transition converts atom from trapped to un-trappable

∆ν = 1420.4 ± 0.5 MHz

C. Ø. Rasmussen Antihydrogen Physics slide 13 of 18 ALPHA-g Carefully release magnetically trapped antihydrogen atoms to record their gravitational acceleration The challenge: We trap atoms with EK < 0.5 K ≈ 50 µeV Gravitational potential is about 1.2 mK per meter

C. Ø. Rasmussen Antihydrogen Physics slide 14 of 18 Gravity Measurement Balance the escape by compensating the gravitational potential with magnetic potential

Over-compensated

Un-compensated

Anti-atom potential Gravity gradient

-200 -100 0 100 200 z (mm)

C. Ø. Rasmussen Antihydrogen Physics slide 15 of 18 ALPHA-g New experiment to directly measure the gravitational acceleration of antimatter.

C. Ø. Rasmussen Antihydrogen Physics slide 16 of 18 1S-2P: Laser Cooling! Momentum from absorbed photons slows down atoms Need closed transition (1S-2Pa)

This makes everything better!

C. Ø. Rasmussen Antihydrogen Physics slide 17 of 18 Thank you for your Attention

C. Ø. Rasmussen Antihydrogen Physics slide 18 of 18 backup slides

C. Ø. Rasmussen Antihydrogen Physics slide 19 of 18 Cosmic Event Rejection

C. Ø. Rasmussen Antihydrogen Physics slide 20 of 18 CPT Tests and Relative Precision

prospective recent 3 past H e q/m

deuteron q/m

K0 ∆m

m uon g

e+ g

¯p g

p¯ q/m

H¯ 1S- 2S

HGSHF¯

10-21 10-18 10-15 10-12 10-9 10-6 10-3 100 relative precision

C. Ø. Rasmussen Antihydrogen Physics slide 21 of 18 CPT Tests and Absolute Energy Diﬀerence

C. Ø. Rasmussen Antihydrogen Physics slide 22 of 18 1S-2S Transition in Hydrogen

f1S−2S = 2 466 061 413 187 035 (10) Hz Measured with a cold hydrogen beam

H¨anschet al. 2011

C. Ø. Rasmussen Antihydrogen Physics slide 23 of 18 An Unrealistic Projection Antihydrogen measurements (green) are improving in precision faster than measurements in ordinary matter.

C. Ø. Rasmussen Antihydrogen Physics slide 24 of 18 An Unrealistic Projection Antihydrogen measurements (green) are improving in precision faster than measurements in ordinary matter.

However, no antiprotons available until 2021

C. Ø. Rasmussen Antihydrogen Physics slide 24 of 18 Why Antihydrogen?

Use the toolbox of atomic physics for high precision measurements Antimatter counterpart to the best understood atomic system Electrically neutral for gravity measurements

C. Ø. Rasmussen Antihydrogen Physics slide 25 of 18 Hyperﬁne States in (Anti-)Hydrogen

C. Ø. Rasmussen Antihydrogen Physics slide 26 of 18 CERN Accelerator Complex

C. Ø. Rasmussen Antihydrogen Physics slide 27 of 18 Spectroscopy Apparatus Cavity mirrors are in UHV and at cryogenic temperatures.

C. Ø. Rasmussen Antihydrogen Physics slide 28 of 18