DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
1A
ATHENA - Cold antihydrogen production
Production of cold antihydrogen atoms in large quantities
• Introduction
• The ATHENA experiment +
• New results
• Summary
• Outlook
On behalf of the ATHENA collaboration
C. Regenfus
University of Zürich
H detector
Antihydrogen candidate (real data, 4-prong event)
Sept. 02: > 50k cold antiatoms produced
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
2A
ATHENA - Cold antihydrogen production
Motivation
Antihydrogen: The simplest antimatter counterpart to matter
for testing fundamental physic principles
• CPT symmetry (Theoretical underpinning of field theories)
• Gravitational acceleration (Equivalence principle)
A very high precision can be achieved by comparing antihydrogen to hydrogen
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
3A
ATHENA - Cold antihydrogen production
Future: high resolution laser spectroscopy
Atomic 1S - 2S transition by two-photon excitation (first order Doppler-free)
Lyman E = 10.2 eV = 2.5 x 1015 Hz = 122 nm UV 2 x 243 nm photons (mW)Lifetime of 2S state: 122 ms => precision ~10-16
Cesar et al. (1996)(Laser 3kHz, 150µK)
Need: Cold antihydrogen ( T < mK )
Capture in neutral trap
Hydrogen reference cell
243 nm LASER
Mirror
H
H spectroscopy
Gravitation: atomic fountain / interferometry
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
4A
ATHENA - Cold antihydrogen production
Present physics menu
Plasma studies: new kind of plasma imaging
• Particle losses in trap
• (Re)combination mechanism
• Production of cold antihydrogen in larger quantities
Investigations
• Antihydrogen energy distribution (+ inner states)
• Laser spectroscopy on non trapped atoms
• Trapping H and/or creation of a H beam
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
5A
ATHENA - Cold antihydrogen production
The ATHENA collaboration
Particle traps + control:INFN, Sez. di Genova, and Dipartimento di Fisica, Università di Genova, Italy
EP Division, CERN, Geneva, SwitzerlandDepartment of Physics, University of Tokyo, Japan
Precision lasers:Department of Physics and Astronomy, University of Aarhus, Denmark
Instituto de Fisica, Rio de Janeiro, Centro de Educação Tecnologica do Ceara, Brazil
Positron plasma:Department of Physics, University of Wales Swansea, UK
Detector + Analysis:Physik-Institut, Zürich University, Switzerland
INFN, Sez. di Pavia, and Dipartimento di Fisica Nucleare e Teorica, Università di Pavia, ItalyDipartimento di Chimica e Fisica per l'Ingegneria e per iMateriali, Università di Brescia, Italy
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
6A
ATHENA - Cold antihydrogen production
Experimental overview
Positron Accumulator
AntihydrogenDetector(T= 140 K)
0 1 m
0 10 cm
Na-22Source
AntiprotonCapture Trap Mixing Trap
CsI crystals
Si stripdetectors
Cryostat
e+3 T superconducting solenoid
15 K , 10-11 mbar
Main ATHENA features: Open access system (no sealed vacuum)Powerful e+ accumulation Plasma diagnosis and control High granularity imaging detector
Scint. Scint.Scint.
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
7A
ATHENA - Cold antihydrogen production
ATHENA Photo
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
8A
ATHENA - Cold antihydrogen production
Penning traps
Trapped electron at B = 3 T, E = 1 eV, U ~ 10 V
• Cyclotron motion (perpendicular to B)
f = 84 GHz, r ~ 1 µm
Emission of synchrotron radiation (cooling)
t cool ~ 0.3 s
• Axial motion (along B)
f ~ 7 MHz, d ~µm … cm
• E x B drift (‘magnetron’) (cooling over coupling)
f ~ kHz, r ~ mm
Single particle <=> Plasma
Coulomb coupling parameter: Ecoul/Etherm
Electrical screening distance: Debye length
ATHENA:Multi-ring Penning trap (choose Vz as you like )
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
9A
ATHENA - Cold antihydrogen production
Antiproton decelerator (CERN)
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
10A
ATHENA - Cold antihydrogen production
Antiproton capture and cooling with electrons
p
5 MeV
50 cm
Antiproton Capture Trap
Solenoid (3 T)
Degrader
Degrading
Trapping
Cooling
Vacuume-
TrappingPotential
5 KV
Cold electron cloud(Cooled by Synchrotron Radiation,
τ=0.4 3 )s at T
. /Univ of Genova IT
(t=0)
(t=200 )ns
(t=20-30 )s
• Capture dynamics
• Capture trap (50 cm)
10 000 p / AD shot
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
11A
ATHENA - Cold antihydrogen production
Positron accumulation
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+
Accumulation rate: 106 e+/s
150 million e+ / 5 min
After transfer: 75 x 106 in mixing trap
Positron plasma : r~2mm, l~32mm, n~2.5 x 108 / cm3
Lifetime: ~hours
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
12A
ATHENA - Cold antihydrogen production
Non destructive positron plasma diagnostics
read
heat
drive
Complete model of plasma mode excitation
(based on ‘Cold Fluid Theory’ * )
PLASMA SHAPE, LENGTH, DENSITY
Plasma temperature change* D. Dubin, PRL 66, 2076 (1991)
kΔT =mzp
2
5ω2
h( )
2−ω2( )
2
[ ] 3−ωp
2α2
2ω22
d2 f(α)dα2
⎡
⎣ ⎢ ⎤
⎦ ⎥
−1
~ 30 MHz
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
13A
ATHENA - Cold antihydrogen production
Detection principle of antihydrogen annihilations
• H atom dissociates to p and e+
by contact with the trap wall or rest gas atoms
• pN -> charged and neutral pions
• e+ e- -> 511keV photons (back to back)
Good spatial resolution (< 1 cm ) of chargedvertex ( at least 2 prong events)
Time coincidence (~ 1 µs)
High rate capability (self triggering)
511 keV opening angle
Monte Carlo
Measure 1MeV on background of 2GeV
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
14A
ATHENA - Cold antihydrogen production
Detector development
Much effort into R&D
• Low temperature (~ 140 K)
• High magnetic field (3 T)
• Low power consumption
• Light yield of pure-CsI crystals ?
• CTE matching (Kapton, silicon, ceramics)
• Electronic components
Full detector installed: August 2001
All photodiodes replaced with APDs: Spring 2002
• Compact design (radial thickness 3 cm)
• High granularity (8K strips, 192 crystals)
• Large solid angle (>75 %)
Workshop Zürich , J. Rochet
Silicon micro strip layer
Mechanics for 77K
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
15A
ATHENA - Cold antihydrogen production
Pure-CsI crystals + Avalanche Photo Diodes
22Na
T = 150 K
0
2000
4000
6000
8000
511 keV
back scatter
1275 keV
10000
FWHM = 18%
12000
Pulse height [keV] cos()
4000
3000
2000
1000
-1.0 -0.5 00 60 500 1000 1500 0.5 1.0
e+e−
γ(511 )keV
γ(511 )keV
• Read out close up • Crystal APD unit
• Crystal detector performance
~16 times higher light yield @ 80K
C. Amsler, et al. :Temperature dependence of pure-CsI, scintillation light yield and decay time. NIM A 480, 494–500 (2002).
Pure-CsI
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
16A
ATHENA - Cold antihydrogen production
Full GEANT Monte Carlo simulations
E&M cascades, Hadronic Showers (GEISHA) (> 10 keV)
Geometry from AutoCAD
Module-by-module (in)efficiency taken into account
Same analysis routine for MC and data
Electrode (r = 1.25 cm)
Radial vertex position
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
17A
ATHENA - Cold antihydrogen production
Antiproton annihilations
Antiproton annihilation on the trap wall (real data, 3-prong event)
• strip hits (inner + outer layer) => p vertex
• crystals hit (matched to charged tracks)
• vertex resolution, ~ 4 mm (curvature not resolved)
Electrode position (r = 1.25 cm)
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
18A
ATHENA - Cold antihydrogen production
Plasma imaging (antiprotons only)
-10 -5 0 5 100
10
20
30
40
50
60
70
Longitudinal Position [cm]-10 -5 0 5 10
0
10
20
30
40
50
60
70
Longitudinal Position [cm]
Antiprotons and electrons
Early times
Late times
Potential
Potential
Powerful plasma and loss diagnostics !
p vertex evolution in time
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
19A
ATHENA - Cold antihydrogen production
Mixing trap (nested penning trap*)
In one mixing cycle (5 min) we mix ~104 antiprotons with ~108 positrons
* G. Gabrielse et al., Phys. Lett. A129, 38 (1988)
0 2 4 6 8 10 12
-50
-100
-75
-125
Length (cm)
antiprotons
108
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
20A
ATHENA - Cold antihydrogen production
Cooling of antiprotons by 75 million positrons
• Rapid cooling (< 20 ms)• Decreasing energy of antiprotons• Increasing separation of plasmas
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
21A
ATHENA - Cold antihydrogen production
Antiprotons in the positron plasma
Energy loss by dE/dx and thermalization
e+ cloud (108/cm3)
T = 10K ….. 10000K(by RF heating)
Incoming antiproton
1 2 3 4 5
5
10
15
20
25
30
Te=300 K
Te=30 K
Te=3000 K
ne = 2.5 108 cm
-3
Le = 3.2 cm
Antiproton kinetic energy [eV]
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
22A
ATHENA - Cold antihydrogen production
Antihydrogen production
1. 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 s - continuous monitoring by detector (charged trigger)
4. Repeat cycle every 5 minutes (data for 165 cycles)
For comparison:
“hot” mixing = continuous RF heating of positron cloud
(suppression of antihydrogen production)
0 2 4 6 8 10 12
-50
-100
-75
-125
Length (cm)
antiprotons
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
23A
ATHENA - Cold antihydrogen production
Antiproton annihilation rate (charged trigger rate)
Background trigger rate ~ 0.5 Hz
High initial rate ~ 100 Hz
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
24A
ATHENA - Cold antihydrogen production
Analysis Procedure
• Reconstruct annihilation vertex (103 k)
• 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 % = “golden” events !
Antihydrogen candidate (real data, 4-prong event)
Event reconstruction (165 mixing cycles ~ 2 days)
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
25A
ATHENA - Cold antihydrogen production
Antihydrogen Signal (“golden” events)
Opening angle between two 511 keV photons(seen from charged particle vertex)
-1 -0.5 0 0.5 10
20
40
60
80
100
120
140
160
180
200
Mixing with cold positrons
Mixing with hot positrons
131± 22 events
cos(Θγγ)
> 50,000 produced antiatoms (conservative estimate)
Background: mixing with hot positrons-1 -0.75 -0.5
0
20
40
60
80
100
120
140
160
180
200
cosΘγγ
Angular resolution from MC simulation( )normalised to peak height
- - 511 Back to back keV peak from antihydrogen annihilation
Comparison with Monte Carlo
M. Amoretti et al., Nature 419, 456 (2002)
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
26A
ATHENA - Cold antihydrogen production
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
-1 -0.5 0 0.5 10
20
40
60
80
100
120
140
160
180
200
Antiprotons only
Cold mixing (displaced E window)γ
(cos Θγγ)
Opening angle between two 511 keV photons (seen from charged particle vertex)
M. Amoretti et al., Nature 419, 456 (2002)
Can antiproton annihilations on electrode fake back-to-back signal?
No !
1) Secondary e+ within 10 mm ~ 0.1 %
2) Monte Carlo - no peak
3) Measurement - no peak
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
27A
ATHENA - Cold antihydrogen production
Antihydrogen = main source of annihilations
Hot
Time distribution of golden events and all annihilations Cold
X-Y vertex distribution
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
28A
ATHENA - Cold antihydrogen production
Physics of antihydrogen production
ANTIHYDROGEN VERSUS BACKGROUND
ABSOLUTE PRODUCTION RATES
DEPENDENCE ON TEMPERATURE
ANGULAR DISTRIBUTION
PRELIMINARY
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
29A
ATHENA - Cold antihydrogen production
Opening angle fit
Fit result: ~ 2/3 of the events are antihydrogen
Fit ResultFit Input MC
Hbar
Background
cos(γγ)
cos(γγ)
Data
Fit
Background
PRELIMINARY
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
30A
ATHENA - Cold antihydrogen production
Vertex spatial distribution fit
=>
Antihydrogen on trap electrode Antihydrogen on trapped ions or rest gas Compare to cold mix data
Average fraction of antihydrogen65 ± 10 % during mixing !
In 2002, ATHENA produced0.7 ±± 0.3 Million antihydrogen atomsPRELIMINARY
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
31A
ATHENA - Cold antihydrogen production
Rate of antihydrogen production
High Initial Rate (> 100 Hz)
High S/B (~ 10:1) in first seconds
Analysis:
• 65 ± 10 % antihydrogen
• ~ 50 % vertex / annihilation
PRELIMINARY
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
32A
ATHENA - Cold antihydrogen production
Pulsed antihydrogen production
Mixing time
secsec
Ver
tex
Z p
osi
tio
n
Heat OnHeat On
Ver
tex
Co
un
ts
Mixing time ->
Heat OnHeat On
Switch positron heating Off/On resp. On / Off We observe:
Annihilation rate
Vertex distribution along z
Rise time ~ 0.4 s(Positron cooling time)
PRELIMINARY
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
33A
ATHENA - Cold antihydrogen production
Antihydrogen Production - T dependence
Radiative Three-body
(T) dependence T-0.5 T-4.5
Final state n < 10 n >> 100
Stability (re-ionization) high low
Expected rates ~ Hz ?
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
34A
ATHENA - Cold antihydrogen production
Summary
First production and detection of cold antihydrogen
- high positron accumulation rate = fast duty cycle
- sensitive detector = observe clear signals
High rate production
- initial rate > 100 Hz, average rate ~ 10 Hz
Antihydrogen dominates annihilation signal (~ 2/3)
Pulsed antihydrogen production
Temperature dependence measured
Antihydrogen production at room temperature
DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich
35A
ATHENA - Cold antihydrogen production
Outlook
More …
Increase formation rate
More antiprotons
Laser induced recombination
Trapping and cooling ...Anti-Hydrogen at E < 0.05 meV ?
Dense plasmas in magnetic multipole fields ?
Laser cooling? Collisions with ultra-cold hydrogen atoms?
Spectroscopy
High precision comparison 1S-2S
Hyperfine structure
Gravitational effectsE ~ 0.000 1 meV
Atom interferometry
Study …
Formation process
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