Antimatter studies at AEgIS and ASACUSA experiments at ...

SMI – STEFAN MEYER INSTITUTE

Antimatter studies at AEgIS and ASACUSA experiments at CERN

Angela Gligorovaa,b aStefan Meyer Institute for Subatomic Physics - Austrian Academy of Sciences

bExperimental Physics/UAD - CERN

CERN Days in North Macedonia 14.05.2019 MANU, Skopje


Outline

• Matter/antimatter asymmetry in the Universe • The Antiproton Decelerator (AD) at CERN • The AEgIS experiment • Physics motivation, principle • AEgIS apparatus and current status

• The ASACUSA experiment • Physics motivation, principle • ASACUSA apparatus and current status

• Conclusions

2


Brief history of antimatter research• 1928: Theoretically predicted by Dirac in 1928

(quantum mechanics+special relativity). • 1932: Experimentally discovered (positron) by

Anderson (cosmic rays). • 1955: Discovery of the antiproton at the Bevatron at

Berkeley, California. • 1956: Discovery of the antineutron at the Bevatron at

Berkeley, California. • 1995: First antimatter atoms (antihydrogen)

synthesised at LEAR at CERN (9 antiatoms) [Baur G. et al. Phys. Lett. B 368, 251–258 (1996)].

• 2000: Antiproton Decelerator (AD) at CERN starts operation. • 2010: First magnetically trapped anti hydrogen at the

AD [Andresen G.B. et al., Nature 468, 673–676 (2010)]3


Matter/antimatter asymmetry in the Universe• The Big Bang should have created equal amounts of matter and antimatter. • Most of the observable Universe is made entirely of matter; no significant amount of detectable antimatter! • If matter and antimatter were separated, gamma rays from their boundaries in deep intergalactic space. • No gamma radiation coming from the boundary regions between matter-antimatter clusters.

• Prospects for CPT (combination of charge conjugation, parity transformation and time reversal) symmetry tests.

4

AD experiments

• Looking for fundamental asymmetry sources between matter and antimatter, in particular between hydrogen and antihydrogen.


Antimatter research at the AD at CERN• ATHENA (and later ATRAP): first cold antihydrogen atoms in 2002 [ATHENA Collaboration, Nature 419, 2002].

• Current experiments:

• ALPHA • 2016: 1S-2S transition of (compatible with H to 2 × 10−10) [M. Ahmadi et al. Nature 541, 506–510 (2017)]. • 2018: 1S-2S line shape of (resonance frequency agrees with H to ~5 kHz out of 2.5 × 1015 Hz).

Consistent with CPT invariance at a relative precision of 2 × 10-12 [M. Ahmadi et al. Nature 557, 71–75 (2018)]. • 2018: Lyman-alpha (1S-2P) line of (agrees with H to 5 × 10−8 [M. Ahmadi et al. Nature 561, 211–215 (2018)]).

• ATRAP (trapping antihydrogen for spectroscopy measurements).

• ASACUSA (antihydrogen beam for HFS spectroscopy, exotic atoms: antiprotonic helium).

• AEgIS (gravitational acceleration of antihydrogen).

• BASE (high precision measurements of the properties of antiproton, e.g. magnetic dipole moment).5

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The Antiproton Decelerator (AD)

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The antiproton decelerator

• ~3x107 antiprotons delivered every 100 s: • 5.3 MeV (100GeV/c). • 200 ns bunches. 7


AEgIS - Antihydrogen Experiment: gravity, Interferometry, Spectroscopy

8


Physics motivation and goal• Currently no experimental WEP test available for

antimatter. • Normal matter ∆g/g: 10-13 [J.G. Williams et al. Phys.

Rev. D 53, 6730, 1996]. • General relativity is the fundamental theory of the

gravitation. • Differences between matter and antimatter

would violate the weak equivalence principle (WEP), a cornerstone of General Relativity. • It is a non quantum theory (classical).

• Many efforts to get a quantum theory of gravity [T. Goldman et al. Phys. Rev. D, 36,1987], [M. Villata, EPL, 94(2) 2011] .

• Main goal: first direct measurement of the Earth’s gravitational acceleration for antihydrogen, with 1% relative precision (∆g/g). 9


Method• 5.3 MeV antiprotons from the AD → decelerating

down to ~9 keV with degraders. • Positrons from 22Na source; • Formation of positronium (Ps); • Laser excitation of Ps to Rydberg state (n=20-30); • Antihydrogen in Rydberg state by charge

exchange reaction;

• Antihydrogen beam by Stark acceleration (electric field of few 100V/cm); • Detection of free fall antihydrogen with position

detector.

205 nm n=1 → n=3 1650 nm n=2 → n=20-30

[A. Kellerbauer et al. Nucl. Instrum. Meth. B 266 (3), 2008]10


The gravity measurement• Antihydrogen pulsed beam: • velocity of few 100 m/s; • horizontal path of ~ 1 m; • time-of-flight ~ ms;

• Vertical shift due to gravity ~20 µm (for v=500 m/s, L=1 m), time-of-flight ~ ms.

• Non-collimated beam • Maxwell distribution of the radial velocity of antihydrogen at

100 mK: vthermal=300 m/s @ 5 K

vthermal=70m/s @ 0.3 K → beam size of few cm!

• Introducing slits in order to measure the shift of a pattern! 11


The gravity measurement• Moiré deflectometer: 2 gratings + position sensitive detector purely classical effect, d>>ƛ. • Fringe pattern with same period as the gratings, which is shifted due to Earth’s gravity. • Gravity measurement with ordinary matter have been performed with a moirè deflectometer: σ(g)/g = 2x10-4

[M. K. Oberthaler et al., Phys. Rev. A 54 (1996) 3165].

Scheme of the moiré deflectometer with a simulated signal from the antihydrogen detector. 12


The AEgIS apparatus

13


Current status• Proof of principle of the moiré: • Observed shift:

Δy=9.6±0.9 (stat.)±6.4 (syst.) µm. • Corresponds to a mean force of

F = (540 ± 50 ± 340) aN (compatible with a Lorentz force from 1 mT or 30 V/cm).

• Antihydrogen formation • Observed a statistically significant

signal compatible with pulsed formation of antihydrogen. • Analysis from 2018 beam time are in

progress.

[S. Aghion et al., Nature Communication. 5, 4538 (2014)][AEgIS Collaboration, Progress report on the AEgIS experiment (2018)]14


ASACUSA - Atomic Spectroscopy AndCollisions Using Slow Antiprotons

15


Physics motivation and goal (addREFS!)• CPT: and have the same spectrum.

• ν(GS−HFS) of H: ∆ν/ν = 10−12 • Compare GS HFS→yields one of the most sensitive

experimental CPT tests.

• Recently measured with ∆ν/ν=4 × 10-4 [M. Ahmadi et al., Nature 548, 66-69 (2017)].

• Goal: to measure the HS of antihydrogen in a field free region, with Rabi microwave spectroscopy apparatus:

• ∆ν/ν=10−7

16[ASACUSA Collaboration, Proposal CERN-SPSC 2005-002 – P307]

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Method• Three body recombination (mixing) of

antiprotons and positrons → atoms. • Cusp trap (spin-polarized beam): • Magnetic field gradient → spin polarised

beam. • Microwave cavity: • Low-field-seeking states are converted to

high-field-seeking states. • Sextupole magnet: • Defocuses the high field seeking states.

• meV antiatoms → guided to a region with a weak magnetic field. • Detection of the antihydrogen atoms by the

detector.17



The ASACUSA apparatus• In contrast to the table-top matter experiments, antihydrogen spectroscopy requires complex apparatuses

for the production of the elusive antimatter atoms.

18


Current status• First beam of anti hydrogen atoms detected

[N. Kuroda, et al., Nature Comm., 5, 3089 (2014)]

• Quantum state distribution has been measured

[C. Malbrunot et al., Phil. Trans. R. Soc. A 376, 20170273 (2018)] 19


Conclusions• Laboratory studies of antimatter provide key results

in comparing the physics properties of matter and antimatter. • The Antiproton Decelerator (AD) at CERN is a unique

facility which makes possible of studying antimatter in lab. • Experiments at the AD produce antihydrogen by

combining antiprotons and positrons/positronium. • Some transitions of the spectrum of have been

successfully measured. • Agreement to a great extent to those for (~10-10).

• AEgIS experiment aims to measure the gravitational accelerations for . • ASACUSA experiment aims to measure the hyperfine

structure of in a field free region.20


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Physics motivation and goal• Currently no experimental WEP test available for antimatter. • Normal matter ∆g/g: 10-13 [J.G. Williams et al. Phys. Rev. D 53, 6730,

1996]

• Three hypothesis of gravitational interaction of matter with antimatter: • Normal gravity: supported by Einstein Equivalence Principle

and Weak Equivalence Principle. • Antigravity: CPT theorem, assuming its invariance also in

curved space-time, and combining it with General Relativity [M. Villata, EPL, 94(2) 2011]

• Gravivector (spin 1)/graviscalar (spin 0) in quantum gravity theory: interaction with slightly different magnitude [T. Goldman et al. Phys. Rev. D, 36,1987]

• Main goal: first direct measurement of the Earth’s gravitational acceleration for antihydrogen, with 1% relative precision (∆g/g).

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AEgIS gravity measurement

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Antimatter studies at AEgIS and ASACUSA experiments at ...

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