Measuring the gravitational acceleration of antimatter with

9.8 ms-2

Matter Antimatter

???

James Storey

Albert Einstein Center for Fundamental PhysicsLaboratory for High Energy Physics, University of Bern

Measuring the gravitational acceleration of antimatter with antihydrogen

Swiss National Science Foundation (SNSF)

LPHE Seminar, 17th March 2014

James Storey

Outline

2

+

-pe+

1. Why study the gravitational behaviour of antimatter?

2. Background: from the first anti-atoms to “cold” antihydrogen.

3. Trapped antihydrogen & the first direct antimatter gravity measurement.

4. (Near) future measurements with an antihydrogen beam.

James Storey

Acknowledgements

3

Colleagues from AEgIS and ALPHA.Material from many sources (too many to list!).

James Storey 4

1. Why study the gravitational behaviour of antimatter?

James Storey

Antimatter and Gravity:A bit of History

5

Discovery of antimatter (1932) → raised question of its reaction to a gravitational field.

Big Bang model (1948). Number of variants proposed:

1) Matter and antimatter symmetric universe• mechanism for their separation,• antigravity → repulsion between matter & antimatter.

2) Asymmetry of matter & antimatter.

Discovery of CP-violation (1964) → 1) forgotten about...

James Storey

Standard Model of Big-Bang Cosmology

6

Inflationary universe dominated by Dark Matter & Dark Energy

Lambda-CDM model:• Structure of the CMB• Abundance of H,D,He,Li• Accelerating expansion of the universe

James Storey

Problem with Lambda-CDM Model

7

Dark Energy:• Required to explain accelerating expansion of space. But what is it?!• Cosmological constant: why this value?• Vacuum energy: 10120 smaller than expected from QFT.

Excellent parametrisation of current data, but requires 2 ingredients which are undetected and/or not understood.

Dark Matter:• Required to explain gravitational effects observed in large scale structures.• But still escapes direct detection...

James Storey 8

The Dirac-Milne Universe:Renewed interest as an alternative to Lambda-CDM

• What happened to the antimatter?• What is dark energy?• What is dark matter?

Matter - antimatter symmetric universe.Antimatter has a negative active gravitational mass.

A. Benoit-Lévy, G. ChardinA&A 537 A78 (2012)

matter antimatter?Type 1a Supernova distancesAbundance of light elementsCMB acoustic scale

James Storey

What do we currently know about the gravitational behaviour of antimatter?

9

Direct evidence

Indirect evidence

• Quark fraction,

• Torsion balance experiments,

• Cyclotron frequencies of p/pbar,

• CP-violation in neutral Kaons.

James Storey

Indirect evidence:Quark fraction

10

Large fraction of the inertial mass of a proton or antiproton comes from its binding energy.

Assuming quark mass is 1% of the overall mass, then even if g/gbar = -1 : antiproton would not “fall-up”.

Maximum observable effect at the 1% level.

James Storey

Indirect evidence:Torsion balance experiments

11

"Torsion-balance tests of the weak equivalence principle", T.A. Wagner, S. Schlamminger, J.H. Gundlach, and E.G. Adelberger, Class. Quantum Grav. 29, 184002 (2012).

T = k

✓miA

mgA� miB

mgB

◆

James Storey


12


Copper

Beryllium

• |Δa/a| < 2.5 x 10-12

• Binding Energy fraction for Be = 0.995 Binding Energy fraction for Cu

Difference in gravitational attraction for ordinary mass compared to nuclear binding energy < 5 x 10-10.

James Storey


13


Difference in gravitational attraction for ordinary mass to nuclear binding energy < 5 x 10-10.

Direct measurement.

• Suppose some fraction of proton mass attributable to the masses of (virtual) anti-quarks.

• Different elements (may) have different virtual antimatter proportions.

But what does this say about antimatter?!

• However, coupling strength of gravity to virtual particles is not known (Vacuum Catastrophe).

Can’t say much about the gravity of antimatter here.

James Storey

Indirect evidence:Cyclotron frequencies

14

proton

proton

f =qpB

2⇡mi,p

f =qpB

2⇡mi,p

antiproton

antiproton

Test of the weak equivalence principle from particle-antiparticle frequencies.R.J.Hughes and M.Holzsheiter; PRL 66 (1991).

James Storey


15

proton

proton

f =qpB

2⇡mi,p

f =qpB

2⇡mi,p

antiproton

antiproton

R

M M

R

Local time of proton sped up by 1+ GM/Rc2

Local time of antiproton sped up by 1+ (g/g)GM/Rc2

Test of the weak equivalence principle from particle-antiparticle frequencies.R.J.Hughes and M.Holzsheiter; PRL 66 (1991).

James Storey


16

• Observed by us (matter!) people, cyclotron frequency of antiproton will be different to an amount proportional to (1- g/g)GM/Rc2.

M. Gabrielese et al, Phys. Rev. Lett. 82 No. 16, 3198 (1999);

• Antiproton and proton cyclotron frequency measured to be the same to part in 1010.

• Bound on antigravity depends on choice of R and M, i.e. choice of the absolute gravitational potential.

• Assume gravitational potential from local supercluster

��1�g

g

�� < 5⇥ 10�4

James Storey

Indirect evidence:Kaon Oscillations

17

• But, must assume an absolute gravitational potential...

• Neutral kaons are a mixture of matter and antimatter.

CPLEAR Collaboration “Tests of the Equivalence Principle with Neutral Kaons,” Phys. Lett. B 452, 425 (1999).

• Uses same gravitational redshift effect arguments.

• Look for annual / monthly modulations of CP-violating observables, e.g.

•S. G. Karshenboim, preprint 0811.1009v1 [gr-qc] (2008):

James Storey

Indirect evidence:Kaon Oscillations

18

Observed CP-violation consistent with g = -g i.e. antigravity!

James Storey

Motivation:Personal view...

19

• Indirect evidence: Δg/g between 10-13 and 100% → Worth doing a direct measurement!

•Techniques developed to do the experiment, are also applicable for spectroscopy experiments (CPT tests).

•New field of research combining particle, atomic, plasma & laser physics to test fundamental physics.

•Experimentally possible (as I’ll show in a moment).

James Storey

Direct Gravitational Tests of Antimatter:Free-fall Measurements of Neutral Antimatter

20

Hbar, Pbar@ CERN

Ps @ ETH

M @ PSI

James Storey

Antimatter gravity experiments at Cern:Growing competition

21

First experimental limits

Current & future experiments

ALPHA 1 (April 2013): Free-fall style measurement with trapped antihydrogen.

AEgIS (2011-): Free-fall style measurement with an antihydrogen beam.

Gbar (2012-): Free-fall style measurement with laser ionised Hbar+.

ALPHA II (2012-): Improved measurement by laser cooling trapped Hbar.

AEgIS

ALPHA

ALPHA

James Storey

Why antihydrogen?

22

Free-fall experiments with charged antimatter ( e+, p ) failed:

+

-pe+ Antihydrogen: simplest

neutral anti-atom.

Earth

- p

drift tube

Fgravity << Felectromagnetic

Requires:+

e+ E < 10-12 V/mE < 10-7 V/m-p

Not possible: due to patch effect.

patchpotentials

James Storey

Why now?

23

14 orders of magnitude drop in energy in 13 years (1997-2010)!

PS210 (CERN, 1997): First H anti-atoms.

ATHENA (CERN, 2003):First cold H production.

ALPHA (CERN, 2010):Trapped H.

H/p kinetic energy(temp.) eV

(103 K)

eVμ(sub-K)

eV G(1012 K)

Gravity experiments require ultra-cold H ( sub-Kelvin ).

eV M(109 K)

Antiproton Decelerator (CERN, 1999):Low energy antiproton facility.

James Storey

2. Background: From the first anti-atoms to “cold” antihydrogen.

24

James Storey

First antihydrogen atoms

25

First atoms of antihydrogen created by PS210 at CERN’s Low Energy Antiproton Ring (LEAR) in 1995.

p + Z ! p + e+e� + Z ! H+ e� + Z

Xenon clusters H detectordipole magnet

p

Ref: http://ikpe1101.ikp.kfa-juelich.de/ps210/

9 H atoms!

But, 2 GeV/c (1013 K) not useful for precision studies.

http://ikpe1101.ikp.kfa-juelich.de/ps210/

http://ikpe1101.ikp.kfa-juelich.de/ps210/

James Storey

Why do we need cold antihydrogen?

26

Need to produce “cold” (<1K) antihydrogen!

Spectroscopy requires “long” interrogation times.

Require an atom trap, which are typically very shallow (few K).

AEgIS will measure gravitation attraction by creating an antihydrogen beam.

Require antihydrogen atoms < 0.1 K.

James Storey

Energy scales

27

eV(103 K)

eVμ(sub-K)

eV G(1012 K)

eV M(109 K)

GeV/c p

μeV/c H

eV T(1015 K)

T eV/c LHC p

eV/c p

Antihydrogen Experiments LHC

James Storey

Energy scales

28

eV(103 K)

eVμ(sub-K)

eV G(1012 K)

eV M(109 K)

eV T(1015 K)

Antihydrogen Experiments LHC

James Storey

Cern’s Antiproton Decelerator (AD):The world’s only source of cold antiprotons

29

James Storey

Antiproton production

30

p + p → p + p + p + p

26 GeV/c p

p

p

pp 3.5 GeV/c

Air cooled Iridium target

James Storey

Antiproton Decelerator (AD)

31

AEGIS

2. Inject 3.5 GeV/c p

3. Deceleration & cooling to 100 MeV/c

4. Extract 100 MeV/c p

stoc

hast

ic c

oolin

ge- cooling

RF cavities

1. 26 GeV/c p on Iridium pp → pp + pp

ALPHA

James Storey 32

Antiproton Decelerator (AD)

James Storey

Antihydrogen experiments at CERN's Antiproton Decelerator (AD)

33

James Storey 34

Image by E.Butler, CERN.

Axial confinement: static electric fields.

Radial confinement: Lorentz force in solenoidal B-field.

Trapping antiprotons

James Storey

Catching antiprotons

35

Passed through 100 μm foil: ∼ 105 below 4 keV.Catch antiprotons by switching on high voltage.

James Storey

What about positrons?

36

Potassium-40 in bananas: 1 e+ every 75 minutes

Sodium-22 isotope (made with p accelerator): ~10M e+ every second.

22Na → 22Ne + e+ + νe +γ

James Storey

N2N2N2

Positron accumulation

37

T.J. Murphy, C.M. Surko, Phys. Rev.A 46 (1992) 5696.

N222Na e+ e+

e+

e+

e+

electric potential

Neon moderator

~0.2 MeV

~25 meV

~300M e+ every few minutes.

James Storey

Producing antihydrogen

38

Gabrielse, et al. Phys. Lett. A 129 (1988)

Confine antiprotons and positrons in the same region of space with a “Nested Penning Trap”

p

e+

trap potential

-75 V

-125 V

p + e+ + e+→ H + e+

James Storey

θγγ

ATHENA (2002):First production of cold H

39

CsI crystals

Si strip detector

Penning trap

π+/-

π+/-

π+/-

γ

γ

James Storey

First production of cold H

40

cos(!"")

-1 -0.5 0 0.5 10

20

40

60

80

100

120

140

160

180

200

Cold mixing

Hot mixing

131± 22 Golden events!

Amoretti et al., Nature 419 (2002) 456

James Storey

3. Trapped antihydrogen & the first direct antimatter gravity

measurement. 41

James Storey

Why trap antihydrogen?

42

Goal of ALPHA & ATRAP collaborations at Cern’s AD since 2006.

• Penning traps only confine charged particles. Neutral H annihilates < 1 μs after creation.

• Spectroscopy → keep the H for “some time” ( > 1 ms).

• Solution: trap H in a magnetic atom trap.

• Later realised that the release of antihydrogen from the neutral trap could be used for gravity measurement!

James Storey 43

Why is this difficult?

• Magnetic atom trap: uses a magnetic field gradient to trap “low-field-seeking” atoms.

• (Anti-) atom is trapped if H kinetic energy is less than the magnetic well depth, i.e. kB T < μ.ΔB

For ΔB =1T → T < 0.7 K!

• p extracted at 5 MeV, require 0.1 meV H: 10 orders magnitude reduction in temperature!

James Storey 44

ALPHA collaboration (~40 authors)

James Storey

ALPHA I Apparatus (2006-2012)

45

Image by E.Butler, CERN.

2 mirror coils + octupole → 3D magnetic minimum.

James Storey 46

ALPHA:Producing, Trapping & Detecting Antihydrogen

James Storey 47

James Storey 48

10

100

1000

0 10 20 30 40 50

Curr

ent [

A]

Time [ms]

Detection window

OctupoleUpstream Mirror

Downstream Mirror

1. Cool e+ by means of evaporative cooling.

2. Autoresonantly inject antiprotons into positrons.

3. Remove charged particles.

4. Wait 173ms (later 100+ s) → turn off neutral atom trap.

5. Identify trapped antihydrogen!time (ms)

current(A)

Typical trapping experiment

James Storey 49

Magnetic atom trap material → too much multiple scattering to identify location of the e+e- annihilation.

Reconstruct annihilation vertex with 3 layer double sided silicon strip detector.

e+ γ

γe-511 keV

p

p/n

π+

π-

π0

150 MeV

Identifying antihydrogen atoms

University of Liverpool

James Storey 50

• If all charged particles are removed: annihilation after turning off the neutral trap → trapped antihydrogen.

• Complication: magnetic gradients of the atom trap can also trap uncombined antiprotons (“mirror-trapped antiprotons.”)

Is it trapped H or mirror-trapped p ?

Identifying trapped antihydrogen

James Storey 51

left biasright bias

potential(V)

magnetic field (T)

time(ms)

axial position (m)

axial position (m)

Identifying mirror-trapped antiprotons

James Storey 52

time(ms)

axial position (m)

time(ms)

grey dots: simulated H atoms

blue, green, red “clusters”: simulated

mirror-trapped p

38 antihydrogen atoms trapped! Background 1.4±1.4

November 2010: Trapped antihydrogen!

ALPHA, Nature 468 (2010) 7324

James Storey

Recent progress

53

June 2011: Confinement of antihydrogen for 1,000 seconds(ALPHA, Nature Physics 7, 558–564).

March 2012: Resonant quantum transitions in trapped antihydrogen atoms(ALPHA, Nature 483, 439-44).

April 2013: Description and first application of a new technique to measure the gravitational mass of antihydrogen(ALPHA, Nature Communications 4, 1785).

James Storey

Gravity measurement with trapped antihydrogen:Simulation of annihilation locations

F = M_gravitational / M_inertial

F=100

F=1

Simulation: F=100 Data: 434 annihilations

54

(ALPHA, Nature Communications 4, 1785).

James Storey

Average position of y-annihilations: Event data vs. simulation for F=1, 60 & 150

Reverse cumulative average: average of the y positions of all annihilations that occur at time t or later.

Red circles: y-annihilation positions.

Green triangles: x-annihilation positions.

Black line: average y of simulation.

Grey band: 90% confidence region.

55


James Storey

Gravity measurement with trapped antihydrogen:ALPHA result

56

Exclude with 95% confidence:

F>110 (normal gravity), &

F<-65 (antigravity).

First free-fall style, model independent measurements of antimatter gravity.

Prospects for the more interesting F = +/- 1 regime?


James Storey 57

F=-1

F=1

F=0

Gravity measurement with trapped antihydrogen:Future prospects

Grey band: 90% confidence region. (ALPHA, Nature Communications 4, 1785).

James Storey

4. Antimatter gravity measurements with

an antihydrogen beam

58

James Storey

Antimatter gravity experiments at CERN:Expanding programme

59

New antiproton decelerator: Extra Low ENergy Antiproton (ELENA) ring.

Slows AD antiprotons to 100 keV + electrostatic extraction.

AEgIS

ALPHA

James Storey

AEgIS

Antimatter gravity experiments at CERN:Expanding programme

60

New antiproton decelerator: Extra Low ENergy Antiproton (ELENA) ring.

Slows AD antiprotons to 100 keV + electrostatic extraction.

ALPHA

Start operation in 2017.

ELENA project ensures antiproton physics for the next ~20 years.

James Storey

AEgIS collaboration (~70 authors)

61

CERN, Switzerland

INFN Genova, ItalyINFN Bologna, Italy

Kirchhoff Institute of Physics, Heidelberg, Germany

Max-Planck-Insitut für Kernphysik Heidelberg, Germany

INFN, Università degli Studi andPolitecnico Milano, Italy

INFN Pavia-Brescia, Italy

INR Moscow, Russia

Université Claude Bernard, Lyon, France

University of Oslo and University of Bergen, Norway

Czech Technical University,Prague, Czech Republic

INFN Padova-Trento, Italy

ETH Zurich, Switzerland

Laboratoire Aimé Cotton, Orsay, France

University College, London, United Kingdom

Stefan Meyer Institut, Vienna, Austria

University of Bern, Switzerland

James Storey

Principle of the experiment

62

01

2

3

y

Earth

Antihydrogen beam(uncollimated)

moiré deflectometer

Free-fall detector(position, time)

counts vs.Hvertical co-ordinate

James Storey

The AEgIS apparatus

63

5T1T

p

e+

James Storey

The AEgIS apparatus

64

H

catching traps

H production traps

flight region

James Storey

Antihydrogen production & beam creation

65

1. Load & cool antiprotons

2. Trap & then “fire” 500M e+ onto convertor

3. Laser excite Ps → Ps*

Ps* + p →H* + e- 4.

5. Accelerate H

James Storey

Current status

66

catching traps

Ps production target, fiber for laser excitation, & antihydrogen

production traps

antihydrogen detector

positron accumulator & transfer line

James Storey

Experimental challenges

67

Experimental approaches:

1. Produce cold antihydrogen (resistive, evaporative, laser cooling).

2. Produce more antihydrogen (Ps production, enhance Ps overlap).

and/or

3. Minimise the number of antihydrogen atoms that need to be detected on the free-fall detector for a Δg/g = 1% measurement.

Antihydrogen beam



1m

0.1m

vhorizontal = 500 m/sSolid angle → vradial ≦ 100mK

For all Hbar to reach free-fall detector:

James Storey

How much flux(*) do we need?Δg/g dependancy on vertex position resolution

68

Entri

es

2513

68

01

23

45

60

0.050.

1

0.150.2

0.250.3

0.35

Entri

es

2513

68

Antihydrogen beam



pitch p = 40 μm

Hbar100 mK

velocity = 600 m/s

relative intensity

phase shift 2π/p * Δx=

gT2

resolution

James Storey

How much flux(*) do we need?Δg/g dependancy on vertex position resolution

69

Particles0 1000 2000 3000 4000 5000 6000 7000

g/g

6

-310

-210

-110

mµ1 mµ3 mµ5

mµ7

mµ10

mµ13

mµ15

number of fully reconstructed and time tagged hbar atoms

Δg/g

Higher resolution → fewer Hbar atoms required for the measurement.

James Storey

What tracking detector technology has the highest position and angular resolution?

70

emulsion layer (44 microns)

Nuclear emulsion based detectors (*)

emulsion layer (44 microns)

(*) Integrating detector, no timing information.

base layer (200 microns)

SEM cross sectional view of standard film

by FUJI film

0.2 microns

AgBr crystal suspended in a gelatine matrix.

James Storey

Emulsion detectors:Intrinsic resolution

71

56nm intrinsic resolution

-200 -100 0 100 2000

10

20

30

40

50

60

10 GeV/c pion beam

residuals / nm

num

ber

of g

rain

s

100

mic

rons

James Storey

Emulsion detectors:Current state-of-the-art

72

100cm2 emulsion film →1014 channels of AgBr crystal detectors,

each with a detection efficiency of 16% for a MIP.

Long history of use in particle physics e.g.

discovery of the antiproton. 1st observed annihilation star (Bevatron)

Automated scanning (Univ. Nagoya) → 20 cm2/hour (European Scanning System at Bern)

Graphical Processor Unit (GPU) based track reconstruction algorithms (Bern)

AEgIS raw image data → 1 TB/hour

James Storey

Emulsion based free-fall detector:How will it work?

73

π-

p

π+

10-11 mbar

H

Emulsion

( 50 μm )Emulsion

( 50 μm )Plastic/Glass base ( 200-1000 μm )Vacuum separationwindow (50 μm)

10-6 mbar

H annihilation produces ( in 2π ): 2 pions + 1 proton or 1 pion + 2 protons.

James Storey 74

10-11 mbar

H

10-6 mbar

Emulsion

( 50 μm )Emulsion

( 50 μm )Plastic/Glass base ( 200-1000 μm )Vacuum separationwindow (50 μm)

Emulsion based free-fall detector:How will it work?

Grain density → dE/dx → proton / pion separation.

James Storey 75

Measurements with antiprotons during the 2012 AD run:Experimental setup

emulsion films (yellow)

p

50 microns

5000 events / cm2

James Storey

p

Topographic readout of the emulsion by optical scan

77

200 microns

James Storey

Antiproton annihilation in a bare emulsion

78

150$µm$x$120$µm$x$50$µm$

James Storey 79

Prof. Gösta Ekspong (91)

1st observed annihilation star (Bevatron, 1955)

James Storey

Reconstructed tracks and annihilation vertices

80

emulsion films (yellow)

track perpendicular to emulsion surface = 0°

Angular distribution of reconstructed tracks

Reconstructed tracks

Reconstructed vertices

James Storey

p

stainless steel

Antiproton annihilation vertex resolution

81

μm)Impact parameter (0 1 2 3 4 5

a.u.

0.1

0.2 Bare emulsion sampleStainless steel sample

0

μm)z-coordinate of reconstructed vertex (-300 -260 -220 -180 -140 -100

Num

ber o

f ent

ries /

4μm

0

50

100

150

200

250

300

350

Emulsion layerBare emulsion sampleStainless steel sample

p

vertex resolutionvertex resolution perpendicular to

emulsion surface

r.m.s. resolution ≃ 1μmon the vertical position of

the annihilation vertex

James Storey

Hybrid detector concept: Nuclear Emulsion + Scintillating-fiber/Silicon Tracker (NEST)

82

π-

p

π+H

Scintillating fiber/Silicon TrackerNuclear Emulsion

Silicon strip detector (50 μm) + transparent

window

position~ position, TOF charged pion tracks, TOF

James Storey

Alignment between moiré gratings and emulsion detector

83

Absolute reference can be “stamped” directly on emulsion surface.

James Storey

Simulated performance

84

Annihilation position resolution = 1-2 μm

Efficiency (require 2 tracks traversing emulsion) = 50%

With a 2um position resolution how many antihydrogen atoms do we need for Δg/g = 1% ?

~600 fully reconstructed and time tagged Hbar annihilations

m)µResolution (0 2 4 6 8 10 12 14 16

Parti

cles

310

410

510

g/g=16

vertex resolution (microns)

# p

artic

les

Δg/g=1%

Implication: can afford to relax other (challenging) requirements e.g. Hbar temperature.

James Storey

Comparison: AEgIS vs. ALPHA

AEgIS: 500 x 100mK atoms → F=0.01

ALPHA: 500 x 10mK atoms → F=1

Systematics: F>110

Systematics: F=0.01

Timescale: 2-3 years.

Timescale: develop laser cooling of e+ & Hbar → 3-5 years (also required for spectroscopy). Solve systematic problems → ? years.

g

85

James Storey

AEgIS: Outlook

86

Antihydrogen production & beam creation.

First attempts at free-fall measurement.

2014

2015

James Storey

Summary

87

• No direct evidence against antigravity. Indirect limits are the subject of much debate.

+

-pe+

• Era of fundamental physics measurements with antihydrogen has begun. First, model independent, free-fall style measurement performed by ALPHA.

• Growing competition between experiments at the CERN AD to measure the free-fall of antihydrogen. AEgIS experiment is on schedule for a free-fall measurement in 2015.

Contact [email protected] if you would like to visit AEgIS!

9.8 ms-2

Matter Antimatter

???

Thanks for listening!

Documents

Measuring the gravitational acceleration of antimatter with