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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