Transcript Test Page for SPSC talk

Progress with Cold
Antihydrogen
Work presented mostly that
of the ATHENA
collaboration
Michael Charlton
ATHENA – circa 2004
Athena/AD-1 Collaboration
Aarhus
Rio de Janeiro (URFJ)
P.Bowe, J.S. Hangst, N. Madsen
C. Lenz Cesar
Brescia
E. Lodi-Rizzini, L. Venturelli, N. Zurlo
Swansea
CERN
M. Charlton, L. Jørgensen,
D. Mitchard, H.H. Telle, D.P. van der Werf
G. Bonomi, M. Doser,
A. Kellerbauer, R. Landua
Tokyo/Riken
Genoa
M. Amoretti, C. Canali C. Carraro, V. Lagomarsino,
M. Macri, G. Manuzio, G. Testera, A. Variola
M. Fujiwara, R. Funakoshi,
R. Hayano, Y. Yamazaki
Pavia
Zurich
A. Fontana, P. Genova
P. Montagna, A. Rotondi
C. Amsler, H. Pruys,
C. Regenfus, J Rochet
Michael Charlton
Overview of Talk
Introduction 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 | ?
Gravity
CPT
Michael Charlton
Overview of the ATHENA Apparatus
Michael Charlton
Early Photograph- ATHENA
Michael Charlton
Antiproton Decelerator - AD
From PS:
1.5x1013 protons/bunch, 26 GeV/c
2 Injection at 3.5 GeV/c
1 Antiproton
Production
4 Extraction
( 2x107 in 200 ns)
Co
olin
g
ATRAP
3 Deceleration and
ASACUSA
Sto
cha
stic
Cooling
(3.5 - 0.1 GeV/c)
0
10
Electron Cooling
20 m
Michael Charlton
ATHENA
Antiprotons - Capture and Cooling
a) Degrading
Solenoid - B = 3 Tesla
e-
ATHENA
t=0s
Antiprotons
Degrader
Cold electron cloud
[cooled by Synchtrotron Radiation, ~ 0.4s]
99.9% lost
b) Reflecting
0.1%
E<5kV
Potential
t = 200 ns
Antiproton Capture Trap
c) Trapping
Potential
t = 500 ns
c) Cooling
Potential
[through Coulomb interaction]
t ~ 20 s
Scheme first demonstrated by the
TRAP collaboration. See:
Gabrielse et al, PRL 57 2504 (1986)
and
Gabrielse et al, PRL 63 1360 (1989)
Michael Charlton
Positron Accumulation - ATHENA
Segmented electrode
for Rotating Wall
300 Gauss guiding fields
Coldhead
Beam strength:
6 million e+ per second
T=6K
50 mCi 22Na
Solid neon moderator
Energy loss through collisions
e+
e+
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)
Michael Charlton
ATHENA Accumulator Electrodes
Michael Charlton
Positron Accumulation - ATHENA
Accumulated positrons / millions
200
Open circles:
no rotating electric field
150
Closed circles:
rotating field applied
100
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)
50
0
0
200
400
600
Accumulation time / sec.
Michael Charlton
Positron Transfer - ATHENA
CsI
1.2 T puls ed m agnet
Faraday Cup
CsI
Detector
Cold-nos e ~ 15 K
Faraday Cup
• 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.
Michael Charlton
Plasma Diagnostics/Control - ATHENA
Amoretti et al, PRL 91 55001 (2003) and Phys.
Plasmas, 10 3056 (2003)
Equivalent Circuit Model
RF Plasma Heating
Non-destructive
Simultaneous
determination
pbar injection into positrons
Plasma Shape, Density,
Particle Number,
Temperature
Monitoring of plasma  no change due to pbars
Michael Charlton
ATHENA Antiproton Traps
Early Photograph
Michael Charlton
Antihydrogen Production- ATHENA
Fill positron well in mixing region with 75·106 positrons;
1.
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:
-125
“hot” mixing = continuous RF
heating of positron cloud
antiprotons
-100
(suppression of formation)
-75
-50
0
2
4
6
8
Length (cm)
10
12
Nested Penning trap approach suggested by
Gabrielse et al, Phys. Lett. A 129 38 (1988)
Michael Charlton
Antiproton cooling by e+ - ATHENA
with electrons
antiprotons w ith electrons
-60
-40
-20
0
190s mixing
2
4
6
8
10
12
antiproton cooling by positrons
-60
-40
-20
0
2
No Positrons
4
6
8
10
12
antiprotons at injection
-60
-40
-20
0
High
Potential
l
Low
Michael Charlton
2
4
6
Length (cm)
8
10
12
Antiproton Cooling by e+ - ATHENA
Main results:
[104 antiprotons launched at 30 eV into a 15 K positron plasma of density around 10 8 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.
511 keV 

Silicon micro
strips

• Compact (3 cm thick)
• Solid angle > 70%
• High granularity
• Operation at 140K, 3 T
CsI
crystals

511 keV

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 keV
no hits in any adjacent crystals
• Select events with two ‘511 keV’ photons
• Reconstruction efficiency ≤ 0.25 %
Michael Charlton
Cold Antihydrogen - ATHENA
104 pbars & 108 e+ mixed in Penning trap
Hbar forms, annihilates on electrode
pbar annihilates into charged pions
e+ annihilates into back-to-back s
cos(q), opening angle of two 511keV s,
seen from the vertex, is plotted
 Neutral pions give uncorrelated background
•




104 pbars
108 e+
Monte Carlo
2.5 cm
Si strips
4Hbar
 Annihilation
10q
pbars
108 e+
Hbar Formation
Hbars
q
CsI crystals
Hbar
3T
Michael Charlton
ATHENA Observations - Signal
Cold Mixing :
200
180
160
Cold mixing
Hot mixing
103270 vertices,
7125 2x511keV events
131± 22 events
140
120
100
80
Hot Mixing :
60
40
Scaled (x1.6) to 165 mixing
cycles.
20
0
-1
-0.5
0
cos(q)
0.5
1
Amoretti et al., Nature 419 456 (2002)
Michael Charlton
ATHENA Observations - Background
200
Antiprotons only :
[in harmonic well]
Antiprotons only
180
Cold mixing (displaced E window)

160
99,610 vertices,
5,658 2x511keV events.
140
120
100
80
60
Amoretti et al., Nature
419 456 (2002)
40
20
0
-1
-0.5
0
0.5
cos()
Michael Charlton
1
ATHENA Annihilation Distribution
Hot Mixing
Cold Mixing
3
3
200
180
2
2
1
1
160
140
120
0
100
0
80
-1
-1
-2
-2
60
40
20
-3
-3
-3
-2
-1
0
1
Horizontal position (cm)
2
3
0
-3
-2
-1
0
1
2
Horizontal position (cm)
Amoretti et al., Nature 419 456 (2002)
Michael Charlton
3
Antihydrogen Emission Angles
ATHENA Vertex Z Distribution
Michael Charlton
Madsen et al, PRL 94 033403 (2005)
ATHENA Golden Events
Golden Event Selection
200
180
160
140
Hbar
Cold mixing
Hot mixing
~50%
131± 22 Golden Events
Charged
Vertex
120
100
~10%
80
Opening Angle
(2×511 keV )
60
40
20
0
-1
approx. cut
efficiency
~5%
-0.5
0
0.5
1
cos(q)
Golden Events
Total: ~0.25%
 Very restrictive cuts: threw away >99.7% of events
 Can connection be made between Hbars and Vertices?
Michael Charlton
Pbar Annihilation Vertices - ATHENA
Substantial Fraction of Vertices: Hbars
200
180
160
Cold mixing
Hot mixing
140
120
100
80
60
40
20
0
-1
-0.5
0
cos(q)
Michael Charlton
0.5
1
Vertex Spatial Distribution Fits - ATHENA
Hbar (MC)
Cold Mix Data
BG (Hot Mix)
Pbar Vertex XY Projection (cm)
Fit Result
Pbar vertex R distribution (cm)
Michael Charlton
Fit Result
ATHENA Fit Results
  opening angle
Vertex XY distribution
Vertex R distribution
Two  events yield
Charged trigger yield
Hbar fraction in during mixing
(ave. over 180 sec)
~65 ±10 %
~700k reconstructed vertices  ~400k Hbars
In 2002/3, we produced ~ Two Million Hbars
Michael Charlton
Antihydrogen production and trigger rate - ATHENA
Trigger rate vs time during cold mixing
•85% of initial (<1s) trigger rate
is due to antihydrogen
Trigger
rate
• Peak rate >300 Hz
Events with
vertex
corrected for
efficiency
• 2002 cold mixing : 0.5 106
antiatoms
• 17% of the injected antiprotons
recombine
• Trigger rate is a good proxy for
the antihydrogen signal
zoom of the first sec of
mixing time
Michael Charlton
From Amoretti et al.
Phys. Letts B 578
(2004) 23
Modulation of Hbar Production - ATHENA
Vertex Counts
RF heating of e+ to switch off formation
Heat On
Heat On
Vertex Z position
Mixing time
Mixing time (sec)
Mixing time (sec)
sec
sec
A Pulsed Source of Cold Antihydrogen
Michael Charlton
Modulation of Hbar Production - ATHENA
Heat OFF
Rise time contains Physics
Heat On/Off every 3 sec
• Positron Plasma Cooling time
• Hbar formation temperature
dependence
•Study ongoing (MC Fujiwara – priv.
communication, June 2005)
Michael Charlton
Formation Processes
+
Radiative
Three-body
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 Hz
fast ???
Michael Charlton
Antihydrogen production temperature dependence (1)
ATHENA
Trigger rate vs time
306+-30 meV (3500 K)
(Hot mixing)
DT=43+-17 meV (500K)
DT=15+-15 meV (175K)
Cold mixing
Michael Charlton
Opening angle
Antihydrogen production temperature dependence (2)
ATHENA data
From Amoretti et al.
Phys. Letts B 583
(2004) 59
Opening angle excess
Proportional to the total
number of detected
antihydrogen in a mixing
cycle
No simple interpretation –
pbars not in thermal
equilibrium with positrons ...
Tot. number of triggers in
180 sec
T scaling
3body
300-400 Hz initial rate : 10 times
the expected rate for radiative
Peak trigger rate
recombination
Scaling law
Michael Charlton
T
0.7  0.2
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
Project ALPHA
Antihydrogen Laser PHysics Apparatus
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
New collaboration
recently approved by
CERN
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
Michael Charlton
Trapping Neutral Anti-atoms
Ioffe-Pritchard Geometry
quadrupole winding
mirror coils
U    B
Well depth ~ 0.7 K/T
BQ  grsin2qrˆ  grcos2qqˆ  gyxˆ  gxyˆ
Solenoid field is the minimum in B

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
Michael Charlton