A.Variola

1
(No Transcript)
2
ATHENA / AD-1
First cold antihydrogen atoms production and
detection. The ATHENA Experiment ATHENA
Collaboration Alessandro Variola IRES
Strasbourg, 7th March 2003
3
LONG TERM PHYSICS GOALS
Antihydrogen Hydrogen ?
Gravity
CPT
4
FIRST GOAL
PRODUCTION AND DETECTION OF COLD ANTIHYDROGEN
Na-22 e Production (MeV) Moderation Accumulation
(eV) Transfer cooling (meV)
AD p- Production (GeV) Deceleration (MeV)
Hbar
109
108 e
1012
104 p-
Trapping (keV) Cooling ( meV)
p- and e in mixing trap interacting cooling
Antihydrogen formation
Detection of annihilation
5
Steps for Hbar Production

• Pbars / Positrons
• Production
• Deceleration
• Trapping
• Cooling
• Transfer
• Mixing

6
A multi-disciplinary team
7
Overview - ATHENA / AD-1
8
Antiproton Decelerator (1)
9
Antiproton Decelerator (2)
2 107 antiprotons / cycle P 100 MeV/c (E 5
MeV)
10
Trapping and cooling the trap
Catching electrodes
Armonic region trapping and cooling
Transfer electrodes
11
Cooling

• Electron cooling (pbars)

ATHENA 20 / 30 sec

• Radiative cooling (positrons)

ATHENA 0.3 sec
12
Antiprotons - Capture and Cooling
5.0 MeV antiproton bunch (2107) from AD
Segmented Si (67 µ) beam counter
Antiproton Capture Trap
5. Transfer to mixing trap 10,000 cold
antiprotons / AD shot
13
Positron Accumulation (1)
Solid Ne moderator (T6 K)
Na-22 1.4 GBq
14
Positron Accumulation (2)
Accumulation rate 106 e/sec 150 million
positrons / 5 min
15
Positron Transfer
Transfer positrons from accumulator into
mixing trap (e 50 ) Positrons cool by
synchrotron radiation at B3T 75 million cold
positrons Non-destructive diagnostics gives
plasma parameters R 2.0 mm L 32 mm n
2.5 108 cm-3 Life time many hours
16
Positron non-destructive diagnostics
Under equilibrium condition, at T0, the positron
plasma shape is an ellipsoid (Cold Fluid Theory)
As far as interaction with electromagnetic waves
is concerned the plasma behaves like an e.m
cavity. Matching ellipsoidal with cylindrical
boundary conditions Dubin PRL 22 April 1991 it
is possible to obtain the dispersion relation and
so the frequencies of the electromagnetic modes
of the plasma. These depend on plasma density,
radius, length and temperature. So the
frequencies determination is an efficient
diagnostics technique. In Athena we developed a
method based on the determination of the
equivalent circuit parameters
17
Hbar signature
Hbar Annihilation
Hbar Formation
18
511 keV background
511 keV background from antiproton
annihilation - Antiproton annihilation produces
neutral pions - Decay gammas (5-500 MeV) convert
in magnet - Secondary positrons stop and
annihilate - Homogeneous 511 keV photon
background - Can produce (fake) 2 x 511 keV
photon events - BUT No angular correlation!
19
Antihydrogen Detector
GOAL DESIGN Vertex from tracking of charged
particles Compact (radial thickness 3
cm) Identification of 511 keV gammas Large
solid angle (gt 70 ) Time- and space coincidence
of tracks gammas High granularity (8 K strips,
192 crystals) Operation at T 140 K, B 3
Tesla
20
Antihydrogen Detector - RD, Installation
Much effort into RD, because low
temperature ( 140 K) high magnetic field (3
T) low power consumption - Light yield of
pure CsI crystals ? - expansion coefficients
(kapton, silicon, ceramics) - electronic
components (capacitors, amplifiers)
Full detector installed August 2001 All
photodiodes replaced with APDs Spring 2002
21
Antihydrogen Detector - Antiprotons only
Antiproton Annihilation (example) - into three
charged particles - hits on strips (r-phi) and
pads (z) , inner/outer layer - 3 crystals hit by
tracks - vertex reconstruction s 3-4 mm
(curvature _at_ 3 T)
22
Z Position Calibration
23
Evolution of Antiproton Annihilation
Capture antiprotons electrons Tracking of
antiproton annihilations -gt Real-time imaging of
plasma dynamics Pbar Tomography
3D Image of pbar annihilation
24
CsI - Photon Energy Resolution
25
Principal achievements before Summer 2002
Ingredients for cold antihydrogen production
ready 104 antiprotons captured, cooled and
transferred to mixing trap 150 million positrons
accumulated per 5 minute cycle 75 million
positrons transferred to mixing trap and stored
for several hours Antihydrogen detector fully
commissioned and working Antiproton vertex
resolution s 3-4 mm (antiproton
tomography) 511 keV peak from positrons observed
in situ Plasma mode diagnostics implemented in
mixing and catching traps
26
Mixing procedure
positrons
Nested trap configuration
27
Antiproton cooling by 75 million positrons
28
Cooling Measurements
interaction time
interaction time
29
Recombination rate
Grad1.55 10-10 T -0.63 ne sec-1 pbar e ?
Hbar hn Gstim(1G) Grad G 7.3 10-5 n5
I T-1K n quantum number, I intensityW
cm-2 pbar e hn ? Hbar 2hn Gcoll3.8
10-9 T-4.5 ne2 sec-1 pbar e e (e-) ?
Hbar e (e-) pbar Ps ? Hbar e- Gtot
Grad Gcoll 6 10-9 T-2.18 ne1.37 sec-1
necm-3 positron
density, TK temperature
30
Comparison
Radiative Three-body Recombination rate Per
pbar s-1 0.0036 (10 K ne 108)
1201.7 (10 K ne 108) T dependence T-0.63
T-4.5 Final state n lt 10 n gtgt 10 Stability
(re-ionization) high low Expected rates
Hz ???
31
Antihydrogen Annihilation
Antihydrogen signal - within time resolution
few µsec - charged vertex, determine position -
identify two converted 511 keV gammas - plot
cos Q between 2 photons as seen from vertex -
identify peak at cos Q -1
32
Production of Antihydrogen
1. Fill positron well in mixing region with
75106 positrons allow them to cool to ambient
temperature (10 K) 2. Launch 104 antiprotons
into mixing region 3. Mixing time 190 sec -
continuous monitoring by detector 4. Repeat cycle
every 5 minutes - take data for 165 cycles
For comparison hot mixing continuous RF
heating of positron cloud (suppression of
recombination)
33
Hbar measurements and background
? gt50000 Cold Antihydrogen
Background Measurements
1. Hot-Mix mixing with RF heated e
(3000K) ?turning off Hbar formation
2. Pbar-Only annihilation in interaction
region 3. Displaced Eg window
34
Distribution of annihilation points
35
Preliminary
Preliminary results from data analysis (to be
published)
36
Data MC fit
Fit Result

• Good agreement between Data and MC fit

37
XY fit
38
Fits results
Two g opening angle Vertex XY distribution
Vertex R distribution
Based on 560K reconstructed vertices
In total, ATHENA produced 1.0 0.3 Million
hbars!
39
Rates

Exploiting spatial distribution, signal and
background de-convoluted in time-dependent manner
Antihydrogen produced with
Log scale
Hbar signal
High Initial Rate (gt100 s)
Background
High Signal-to-Background (up to 101)
40
Hbar pulsed source
RF heating of e to switch off formation
A Pulsed Source on Cold Antihydrogen !
41
Heat on/off analysis
Heat OFF (Hbar ON)
(dN/dR)/R
Heat ON (Hbar OFF)
Gamma opening angle cos(qgg)
Vertex radial distribution (cm)
42
Angular distribution
Vertex Z Distribution

• Detected Antihydrogen isotropic
• Some radial component possible
• Focused beam excluded

43
T dependence
effects of heating on the trigger rates
High statistics for 1) no heating COLD
MIXING 2) DT 15 15 meV 175 K 3) DT 43
17 meV 500 K 4) DT 306 30 meV
3500 K HOT MIXING
44
Summary

• 104 antiprotons mixed with 7107 cold positrons
• First production and detection of cold
  antihydrogen
• Powerful e accumulator, position sensitive
  detector
• Preliminary New Results
• In 2002 we produced 1 Million Hbars!
• High initial rate production gt 100 Hz
• Modulation of Hbar formation A Pulsed Hbar
  Source
• Temperature dependence
• Plasma modes, Mixing processes, Hbar emission
  angles, etc etc
• ATHENA Antihydrogen Apparatus
• High rate, High duty cycle (5 min-1), Versatile

45
Outlook
Antihydrogen

Study Formation process
Spectroscopy High precision comparison
1S-2S Hyperfine structure
More Increase formation rate (more
antiprotons)
Gravitational effects E 0.000 1 meV
Trapping and cooling ... Anti-Hydrogen at E lt
0.05 meV ? Dense plasmas in magnetic multipole
fields ? Laser cooling? Collisions with
ultra-cold hydrogen atoms?
A new precision tool for science
46
Outlook
Atomic and plasma physics Understand
formation process Increase formation rate

Access to inner states Ionization method Laser
spectroscopy
Trapping / Antihydrogen beam ... Antihydrogen
energy distribution Isotropic emission of
Antihydrogen ?
47
Outlook
Formation Large program to understand H
formation process dependence on density of
positron plasma number of antiprotons (linear
with increasing number ? Up to which limit ?)
method of interaction (initial energy of
antiprotons) e temperature (in more detail)
dE/dx of p in e (vs. density, e temperature,
) Positronium Can positronium be formed in a
manner similar to Antihydrogen ? Understand
formation process Test Antihydrogen formation via
positronium in simultaneous injection of e- and
p into e (Deutch et al., 1986)
48
Outlook
Laser spectroscopy laser stimulated
recombination 2-step process continuum ? nd
followed by nd ? 2p (pulsed CW laser) 3d
820 nm 3d ? 2p 656 nm 4d 1459 nm 4d ? 2p
486 nm 5d 2279 nm 5d ? 2p 434 nm via 3d
ASACUSA excimer pumped dye laser Aarhus CW dye
laser via 4d Swansea YAG pumped OPO Aarhus 1s
? 2s laser (CW 500 mW) BUT low rep. rate
(100 Hz), short pulses ( 10 ns) for pulsed
lasers ? low duty cycle depends on 3-body
recombination process
49
END
Thanks to the CERN AD Staff Cristoforo Benvenuti
and Paolo Chiggiato Sergio Bricola, Giuliano
Sobrero Claire Massip, Claude Fischer the
SL/BI/PM Section And many others
50
Time evolution of antihydrogen production
51
X-Y Distribution of antihydrogen candidates
52
Annihilation of antiprotons on electrodes
Tomography of trapped antiproton plasmas
XY projection
YZ projection
53
Annihilation of antiprotons on rest gas
Annihilation on residual gas (p 10-9 mbar)
XY projection
54
Comparison of positron accumulation schemes
ATHENA ATRAP Accumulation
parameters Scheme Buffer gas Magnetized
ee- Final pressure 10-10 Æ 10-14 mbar 5 10-17
mbar Transfer eff. 50 80 Rate
min-1 50 Mio 0.03 Mio Plasma parameters No.
of e 75 Mio 0.25 Mio Radius
cm 0.2 0.2 Length cm 3.2 0.2 Density
cm-3 2.5108 0.07 108
from G. Gabrielse et al. - Phys.Lett. B507,1
(2001)
55
Si strips
56
ATRAP Apparatus
57
Combination processes (1)
58
Combination processes (2)
Small energy transfer ( meV) Æ E(final states)
- kT Æ n gtgt 100 (s n46) Æ long lifetime
(gt 0.1 s) Æ unstable (re-ionization for n gt 50)
59
511 keV Multiplicity Distribution
Plot angle
60
Locally produced secondary positrons?
1. Rough estimate - Probability for ee-
conversion 0.15 cm / 8.9 cm 1.7 -
Probability for e stopping and annihilating lt 5
- TOTAL PROBABILITY for local creation
annihilation of e lt 0.001
2. Measurement
61
Z Position of antiproton annihilations
62
(No Transcript)
63
ATHENA - Photo
64
Interlude Trapped Particles
A penning trap is a quantum system
Trapped electron at B 3 T, E 1 eV, U 10
V 1) Cyclotron motion (perpendicular to B) f
n 10 GHz, r µm Emission of synchrotron
radiation cooling t cool 0.3 s 2) Axial
motion (along B) Mode (1,0), stable f MHz, d
µm cm 3) E x B drift (magnetron) Unstable
f kHz, r mm
65
How a trap works Plasma stability
Axial gtpotential well Radial

• Quality parameter lifetime

66
Z Position Calibration Method
67
Antiproton-Positron Interaction - dE/dx
68
Analysis Procedure
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
69
Antihydrogen Signal
70
Comparison of width with MC
71
Background measurements
Histogram Antiproton-only data (99,610
vertices, 5,658 clean 2-photon events plotted).
Dots Antiproton cold positrons, but
analyzed using an energy window displaced upward
so as not to include the 511 keV photo-peak