Michael Charlton

Progress with Cold Antihydrogen

Work presented mostly that of the ATHENA collaboration

Michael Charlton

ATHENA – circa 2004

AarhusP.Bowe, J.S. Hangst, N. Madsen

 

BresciaE. Lodi-Rizzini, L. Venturelli, N. Zurlo

 

CERNG. Bonomi, M. Doser,

A. Kellerbauer, R. Landua

 

GenoaM. Amoretti, C. Canali C. Carraro, V. Lagomarsino,

M. Macri, G. Manuzio, G. Testera, A. Variola

 

PaviaA. Fontana, P. Genova

P. Montagna, A. Rotondi

 

Rio de Janeiro (URFJ)C. Lenz Cesar

 

 

SwanseaM. Charlton, L. Jørgensen,

D. Mitchard, H.H. Telle, D.P. van der Werf

 

 

Tokyo/RikenM. Fujiwara, R. Funakoshi,

R. Hayano, Y. Yamazaki

 

 

ZurichC. Amsler, H. Pruys,

C. Regenfus, J Rochet

Athena/AD-1 Collaboration

Michael Charlton

Overview of TalkIntroduction and Motivations

Apparatus and Techniques

antiproton capture and cooling

positron accumulation and plasma diagnostics

antihydrogen formation and detection

Results

first formation

antiproton cooling

temperature dependence

spatial distributions

Summary and Outlook

Michael Charlton

PHYSICS GOALS

| Antihydrogen | = | Hydrogen | ?

CPTCPT GravityGravity

Michael Charlton

Overview of the ATHENA Apparatus

Michael Charlton

Early Photograph- ATHENA

Michael Charlton

Antiproton Decelerator - AD

ASACUSA

ATHENA

ATRAP

100S

toch

astic

Coo

ling

Electron Cooling

AntiprotonProduction

1

Injection at 3.5 GeV/c2

Deceleration andCooling(3.5 - 0.1 GeV/c)

3

Extraction( 2x107 in 200 ns)

4

From PS:1.5x1013 protons/bunch, 26 GeV/c

20 m

Michael Charlton

Antiprotons - Capture and Cooling

Antiproton Capture Trap

Degrader

Solenoid - B = 3 Tesla

e-Antiprotons

Cold electron cloud[cooled by Synchtrotron Radiation, ~ 0.4s]

t = 0 s

a) Degrading

b) Reflecting

Potential

99.9% lost

0.1%

t = 200 ns

Potentialt = 500 ns

E<5kV

c) Trapping

Potentialt ~ 20 s

c) Cooling

[through Coulomb interaction]

Scheme first demonstrated by the TRAP collaboration. See:

Gabrielse et al, PRL 57 2504 (1986) and

Gabrielse et al, PRL 63 1360 (1989)

ATHENA

Michael Charlton

Positron Accumulation - ATHENA

Buffer Gas Positron Accumulator – developed by Surko group.

See e.g. Murphy and Surko, PRA 46 5696 (1992)

Surko and Greaves, Phys. Plasmas 11 2333 (2004)

Surko, Greaves and Charlton, Hyp. Int. 109 181 (1997)

Coldhead

300 Gauss guiding fields

T = 6 K50 mCi 22Na

Solid neon moderator

Segmented electrodefor Rotating Wall

Beam strength:6 million e+ per second

e+

Energy loss through collisions

e+

Michael Charlton

ATHENA Accumulator Electrodes

Michael Charlton

Positron Accumulation - ATHENA

Accumulation time / sec.

0 200 400 600

Acc

um

ula

ted

po

sitr

on

s /

mill

ion

s

0

50

100

150

200

Open circles:no rotating electric field

Closed circles:rotating field applied

see e.g. Jorgensen et al, Non-neutral Plasma Physics, AIP Vol. 606 35 (2002) and van der Werf et al, Appl. Surf. Sci. 194 312 (2002)

Michael Charlton

Positron Transfer - ATHENA

• Transfer efficiency ~ 50 %• Cold positrons for antihydrogen : 75 million / 5 min.• Positron plasma : r ~ 2 mm, l ~ 32 mm, n ~ 2.5x108 cm-3

• Lifetime ~ hours.

1.2 T pulsed magnet

Detector Cold-nose ~ 15 KFaraday Cup

Faraday Cup

CsI

CsI

Michael Charlton

Plasma Diagnostics/Control - ATHENA

Equivalent Circuit Model

RF Plasma Heating

Plasma Shape, Density, Particle Number,

Temperature

Non-destructiveSimultaneous determination

Monitoring of plasma no change due to pbars

pbar injection into positrons

Amoretti et al, PRL 91 55001 (2003) and Phys. Plasmas, 10 3056 (2003)

Michael Charlton

ATHENA Antiproton Traps

Early Photograph

Michael Charlton

Antihydrogen Production- ATHENA1. Fill positron well in mixing region with 75·106 positrons;

allow them to cool to ambient temperature (15 K)

2. Launch 104 antiprotons into mixing region

3. Mixing time 190 sec - continuous monitoring by detector

4. Repeat cycle every 5 minutes (data for 165 cycles)

For comparison:

“hot” mixing = continuous RF heating of positron cloud

(suppression of formation)

0 2 4 6 8 10 12

-50

-100

-75

-125

Length (cm)

antiprotons

Nested Penning trap approach suggested by Gabrielse et al, Phys. Lett. A 129 38 (1988)

Michael Charlton

Antiproton cooling by e+ - ATHENAwith electrons

190s mixing

No Positrons

Potentiall

0 2 4 6 8 10 12

-40

-20

-60

Length (cm)

antiprotons at injection

-40

-20

-60

0 2 4 6 8 10 12

antiprotons with electrons

-40

-20

-60

0 2 4 6 8 10 12

antiproton cooling by positrons

High Low

Michael Charlton

Antiproton Cooling by e+ - ATHENA

Main results: [104 antiprotons launched at 30 eV into a 15 K positron plasma of density around 108 cm-3]

Those antiprotons which overlap physically with the positron cloud cool quickly and antihydrogen formation begins after about 10-20 ms.

Instantaneous antihydrogen rates over 400 s-1 have been recorded.

Antihydrogen formation continues for many tens of seconds as the positron plasma slowly expands.

Antiprotons appear in the side wells. This is attributed to field ionization of weakly-bound antihydrogen atoms.

[See Amoretti et al, Phys. Letts. B 590 133 (2004)]

Michael Charlton

Antihydrogen Detection - ATHENA

• Charged tracks to reconstruct antiproton annihilation vertex.• Identify 511 keV photons from e+-e- annihilations.• Identify space and time coincidence of the two.

Silicon microstrips

CsIcrystals

511 keV

511 keV

• Compact (3 cm thick)• Solid angle > 70%• High granularity• Operation at 140K, 3 T

Michael Charlton

Antihydrogen Detection - ATHENA

R & D (selected) :• Low temperature• Low power consumption

First installation : August 2001

Photodiode replacement, APD : Spring 2002

Michael Charlton

Analysis Procedure - ATHENA

• Reconstruct annihilation vertex

• Search for ‘clean’ 511 keV-photons:exclude crystals hit by charged particles+ its 8 nearest neighbours

• ‘511 keV’ candidate =400… 620 keVno hits in any adjacent crystals

• Select events with two ‘511 keV’ photons

• Reconstruction efficiency ≤ 0.25 %

Michael Charlton

Monte Carlo

Hbars

Hbar

Cold Antihydrogen - ATHENA• 104 pbars & 108 e+ mixed in Penning trap104 pbars

108 e+

Si strips

CsI crystals

2.5

cm

3T

108 e+

Hbar forms, annihilates on electrode

cos(), opening angle of two 511keV s, seen from the vertexis plotted

104 pbars

Hbar AnnihilationHbar Annihilation

pbar annihilates into charged pions e+ annihilates into back-to-back s

Neutral pions give uncorrelated background

Hbar FormationHbar Formation

Michael Charlton

ATHENA Observations - Signal

cos()

-1 -0.5 0 0.5 10

20

40

60

80

100

120

140

160

180

200

Cold mixing

Hot mixing

Cold Mixing :

103270 vertices,7125 2x511keV events

Hot Mixing :

Scaled (x1.6) to 165 mixingcycles.

131± 22 events

Amoretti et al., Nature 419 456 (2002)

Michael Charlton

ATHENA Observations - Background

-1 -0.5 0 0.5 10

20

40

60

80

100

120

140

160

180

200

Antiprotons only

Cold mixing (displaced E window)

cos()

Antiprotons only :[in harmonic well]

99,610 vertices, 5,658 2x511keV events.

Amoretti et al., Nature 419 456 (2002)

Michael Charlton

ATHENA Annihilation Distribution

-3 -2 -1 0 1 2 3-3

-2

-1

0

1

2

3

-3 -2 -1 0 1 2 3-3

-2

-1

0

1

2

3

0

20

40

60

80

100

120

140

160

180

200

Horizontal position (cm) Horizontal position (cm)

Cold Mixing Hot Mixing

Amoretti et al., Nature 419 456 (2002)

Michael Charlton

Antihydrogen Emission Angles

ATHENA Vertex Z Distribution Madsen et al, PRL 94 033403 (2005)

Michael Charlton

ATHENA Golden Events

Very restrictive cuts: threw away >99.7% of events Can connection be made between Hbars and Vertices?

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

Hbar

Charged Vertex

Opening Angle(2511 keV )

Golden Events

~50%

~10%

~5%

Total: ~0.25%

approx. cut efficiency

Golden Event Selection

Michael Charlton

Pbar Annihilation Vertices - ATHENA

Substantial Fraction of Vertices: Hbars

cos()

-1 -0.5 0 0.5 10

20

40

60

80

100

120

140

160

180

200

Cold mixing

Hot mixing

Michael Charlton

Vertex Spatial Distribution Fits - ATHENA

Cold Mix Data Fit ResultHbar (MC) BG (Hot Mix)

Pbar Vertex XY Projection (cm)

Pbar vertex R distribution (cm)

Fit Result

Michael Charlton

ATHENA Fit Results

opening angle Vertex XY distribution Vertex R distribution

Two eventsyieldCharged trigger yield

Hbar fraction in during mixing(ave. over 180 sec)

~65 ±10 %

In 2002/3, we produced ~ Two Million HbarsIn 2002/3, we produced ~ Two Million Hbars

~700k reconstructed vertices ~400k Hbars

Michael Charlton

zoom of the first sec of mixing time

Trigger rate

Events with vertex corrected for efficiency

•85% of initial (<1s) trigger rate is due to antihydrogen

• Peak rate >300 Hz

• 2002 cold mixing : 0.5 106 antiatoms

• 17% of the injected antiprotons recombine

• Trigger rate is a good proxy for the antihydrogen signal

Trigger rate vs time during cold mixing

Antihydrogen production and trigger rate - ATHENA

From Amoretti et al. Phys. Letts B 578 (2004) 23

Michael Charlton

Mixing time (sec)

Mixing time

Ver

tex

Cou

nts

Mixing time (sec)

Modulation of Hbar Production - ATHENA

Heat OnHeat On

secsec

Ver

tex

Z p

osit

ion

Heat OnHeat On

RF heating of e+ to switch off formation

A Pulsed Source of Cold AntihydrogenA Pulsed Source of Cold Antihydrogen A Pulsed Source of Cold AntihydrogenA Pulsed Source of Cold Antihydrogen

Michael Charlton

Modulation of Hbar Production - ATHENA

Heat On/Off every 3 sec

Rise time contains Physics• Positron Plasma Cooling time• Hbar formation temperature dependence•Study ongoing (MC Fujiwara – priv. communication, June 2005)

Heat OFF

Michael Charlton

Formation Processes

Radiative Three-body

Rate T dependence T-0.6 T-4.5

Final state n < 10 n >> 100

Stability (re-ionization) high low

Expected rates ~10s Hzfast ???

Radiative Three-body

+

Michael Charlton

T=15+-15 meV (175K)

Cold mixing

T=43+-17 meV (500K)

306+-30 meV (3500 K) (Hot mixing)

Opening angleTrigger rate vs time

Antihydrogen production temperature dependence (1)

ATHENA

Michael Charlton

Proportional to the total number of detected antihydrogen in a mixing cycle

T scaling 3body

300-400 Hz initial rate : 10 times

the expected rate for radiative

recombination

Scaling law2.07.0 T

Opening angle excess

Tot. number of triggers in 180 sec

Peak trigger rate

From Amoretti et al. Phys. Letts B 583 (2004) 59

Antihydrogen production temperature dependence (2)

No simple interpretation –pbars not in thermal equilibrium with positrons ...

ATHENA data

Michael Charlton

Summary – results from ATHENA • ATHENA Antihydrogen Apparatus

– High rate, High duty cycle (5 min-1), Versatile [Amoretti et al NIM A 518 679 (2004)]

• First production and detection of cold antihydrogen [Amoretti et al, Nature 456 419 (2002)]

• Main results since then– In 2002/3 we produced ~2 Million Hbars– High initial rate production > 400 Hz [ Amoretti et al, Phys Lett B 578

23 (2004)]

– Modulation of Hbar formation: A Pulsed Hbar Source– Temperature dependence ~ T – (0.7 +/- 0.2) [Amoretti et al.,Phys Lett B 583

59 (2004)] [Needs extra work for interpretation – see e.g. Robicheaux, PRA 70 022510 (2004); arrested nature of 3-body process in finite positron plasmas]

Michael Charlton

Summary – results from ATHENA

• Main results since then … continued

– Many measurements of antiproton cooling upon mixing with a positron plasma – shed light on dynamics of antihydrogen formation [Amoretti et al, Phys. Lett. B 590 133 (2004)]

– Hbar emission angles; points to epithermal antihydrogen emission [Madsen et al, PRL 94 033403 (2005)]

– More to come …

Michael Charlton

Conclusions and outlook

• What is the quantum state of the antihydrogen atoms?

• Laser stimulated recombination to n = 11 manifold – tried in 2004 … analysis ongoing, but no obvious enhancement of

antihydrogen rate

• In beam experiments, early spectroscopy? Seem to be ruled out.

• Capture (and cooling?) of antihydrogen in a magnetic gradient trap

• Dense plasmas in multipole B-fields …see below

• Precision spectroscopy

•1S-2S

•Hyperfine splitting

• Gravity measurements

Michael Charlton

University of Aarhus: P.D. Bowe, N. Madsen, J.S. Hangst

Auburn University: F. Robicheaux

University of California, Berkeley: W. Bertsche, E. Sarid, J. Fajans

University of Liverpool: A. Boston, P. Nolan, M. Chartier, R.D. Page

Riken: Y. Yamazaki

Federal University of Rio de Janeiro: D. Miranda, C.L. Cesar

University of Tokyo: R. Funakoshi, L.G.C. Posada, R.S. Hayano

TRIUMF: K. Ochanski, M.C. Fujiwara, J. Dilling

University of Wales, Swansea: L. V. Jørgensen, D.P. van der Werf, D.R.J. Mitchard,

H.H. Telle, M. Jenkins, A. Variola*, M. Charlton

University of Manitoba: G. Gwinner

University of Calgary: R.I. Thompson

* current address: Laboratoire de L’Accelerateur Lineaire; Orsay

Project ALPHA

Antihydrogen Laser PHysics Apparatus

New collaboration recently approved by CERN

Michael Charlton

Trapping Neutral Anti-atoms

quadrupole winding mirror coils

U B

B Q grsin 2 ˆ r grcos 2 ˆ gyˆ x gxˆ y

Solenoid field is the minimum in B

Well depth ~ 0.7 K/T

Ioffe-Pritchard Geometry

Based on Berkeley/Swansea results: not a good idea…

Michael Charlton

Acknowledgements

Members of the ATHENA collaboration

Members of the ALPHA collaboration

Colleagues at Swansea

UK financial support from EPSRC

AD staff and all support from CERN

Particular thanks;

Bernie Deutch*, Rod Greaves, Jeffrey Hangst, Michael Holzscheiter, Finn Jacobsen, Michael Nieto, Cliff Surko*deceased