A.Variola

1
ATHENA / AD-1
Lantimatière va-t-elle briller? Collaboration
ATHENA Alessandro Variola , I.N.F.N Genova -
Italy LPHNE Jussieu PARIS 15 Janvier 2004
2
Antiparticles
1927 Dirac Relativistic Quantum Mechanics 1932
Anderson positrons from cosmic rays 1955
Discovery of the antiproton at the Bevatron
Anderson
Relativistic (hot) Antihydrogen

• 1992 Suggestion by Munger et al pbar Z ? hbar
  
• 1996 Production of 9 antihydrogen atoms
  reported at LEAR

LEAR 1986-1996
Emilio Segre, Clyde Wiegand, Edward Lofgren Owen
Chamberlain, Tom Ypsilantis
Paul Dirac
3
Motivations
Gravity
CPT Symmetry
Cosmology
Cold Antihydrogen
Particle
Atomic
Plasma
Trap
Lasers
MC/Software
Cryo/UHV
Detectors
4
LONG TERM PHYSICS GOALS
Antihydrogen Hydrogen ? And why cold ?
Gravity
CPT
Neutral kaon analysis model dependent
Alternative Hyperfine structure
Fundamental Symmetries
5
CPT invariance

• P and CP are violated
• CPT theorem
• Assumptions
• Local Quantum Field Theory, Lorenz Invariance,
  Unitary
• ( c.f. Barenboim et al. PLB 02 versus
  Greenberg PRL 02)
• Consequences for particles and antiparticles
• Equal mass, (total) lifetime
• Equal and opposite charge and magnetic moment
• Identical energy levels

6
Long-term goal precision spectroscopy

• Two photon spectroscopy

7
FIRST GOAL
-
PRODUCTION AND DETECTION OF COLD ANTIHYDROGEN

e
P
Hbar
Na-22 e Production (MeV) Moderation Accumulation
(eV) Transfer cooling (meV)
AD p Production (GeV) Deceleration (MeV)
-
108 e
104 p
-
1012
109
p- and e in mixing trap interacting cooling
Antihydrogen formation
Trapping (keV) Cooling ( meV)
Detection of annihilation

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

8
Antiproton Decelerator Complex at CERN
P 26 GeV/c

• Pulsed beam
• 4107 /pulse, every 100 sec
• 3 experiments at AD
• Asacusa --- pbar-He, collisions
• Athena --- antihydrogen
• Atrap --- antihydrogen

• Economical successor of LEAR

9
(No Transcript)
10
Overview - ATHENA / AD-1
Antiproton Capture Trap
11
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
12
Trapping and cooling the trapSingle Particle
A penning trap is a quantum system
Catching electrodes
Transfer electrodes
Armonic region trapping and cooling
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
13
How a trap works Plasma stability /
CoolingMulti-particle regime
Axial gtpotential well Radial Quality parameter
lifetime
ATHENA 0.3 sec

• Radiative cooling (positrons)

• Electron cooling (pbars)

ATHENA 20 / 30 sec
14
Positron Accumulation
Solid Ne moderator (T6 K)
Accumulation rate 106 e/sec 150 million
positrons / 5 min (record !!!!)
Na-22 1.4 GBq
15
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
New Technique !!!!
16
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
17
Detector What is the Hbar Signature? How to
Find It...
Spatio-temporal coincidence of the annihilation
products
511 keV background from antiproton annihilation -
Antiproton annihilation can produce 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!
Si strips
Hbar Annihilation
Hbar Formation
2.5 cm
3T
CsI crystals
18
(No Transcript)
19
Antihydrogen Annihilation
Antihydrogen signal - within time resolution
few µsec - charged vertex, determine position -
identify two converted 511 keV gammas - plot
cos qgg between 2 photons as seen from vertex -
identify peak at cos qgg -1
GOLDEN EVENTS 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
20
ATHENA - Photos
21
Expected SignalRecombination Rate

• Grad1.55 10-10 T -0.63 ne sec-1
• pbar e ? Hbar hn
• Gcoll3.8 10-9 T-4.5 ne2 sec-1
• pbar e e (e-) ? Hbar e (e-)
• pbar Ps ? Hbar e-
• Gstim(1 G) Grad
  sec-1
• G 7.3 10-5 n5 I T-1K

• Radiative
  Three-body (coll)
• G per pbar s-1 (10 K ne 108)
• 0.0036
  1201.7
• T dependence T-0.63 T-4.5
• Final state n lt 10 n gtgt 10
• Stability high
  low
• (re-ionization)
• Expected rates Hz ???

22
Main Achievements before Summer 2002
So we mixed
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
23
Antiproton Cooling by 75 Million Positrons
24
Cooling Dynamics Measurements
interaction time
interaction time
25
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)
26
Hbar Measurements and Background
Amoretti et al., Nature 419 (2002) 456 .1st
production detection of cold Antihydrogen
131 22 Golden Events
? gt50000 Cold Antihydrogen
2. Pbar-Only annihilation in interaction
region 3. Displaced Eg window
1. Hot-Mix mixing with RF heated e
(3000K) ?turning off Hbar formation
Background Measurements
27
Distribution of Annihilation Points
28
But.Data MC fit
Opening Angle
BG (Hot Mix)
Hbar (MC)
Data
Fit
Background
X Y distribution
Cold Mix data
Fit Result
cos(qgg)
Radial distribution
29
Fits Results
Two g opening angle Vertex XY distribution
Vertex R distribution
In total, ATHENA produced 1.0 0.3 Million
Hbars!
30
High Rate Production
A.Amoretti et al Phys. Lett. B

Exploiting spatial distribution, signal and
background de-convoluted in time-dependent manner
Antihydrogen produced with
High Initial Rate (gt100 Hz)
High Signal-to-Background (up to 101)
31
New resultsTemperature 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
32
Hbar production vs Temperature
Accepted for pubblication - Phys. Lett. B
room temperature
room temperature
Rates higher than naive 2-body model Temperature
scaling non-trivial ? Many theoretical works in
progress
33
New Results 3D Imaging of Trapped Pbars
34
Hbar (neutral) versus Pbars (charged)
New way to select signal from backgound
Hot spots at the edges
35
Preliminary Results (to be published)
Z distribution
RF on
RF off
RF off
Vertex Counts
Vertex Z position
Mixing time (sec)
A Pulsed Source on Cold Antihydrogen !
36
SpectroscopyWhy we want to do it?

• Qualitatively different from any other
  measurements performed or proposed
• Revealing the true colors of antimatter
• Painting the antimatter
• Looking into the (anti)world without sun glasses
• We have emotional needs to see anti-atoms!
• Want to Shed Light on Anti-Matter
• And..not too loud.beat ATRAP (our competitor)
  again

37
Towards First Spectroscopy

• Original roadmap
• I Making Hbars
• II Trap Hbars for 1s-2s spectroscopy
• Difficulties
• Need a new magnet
• ( 2 years ?)
• Neutral and charged trap may not be compatible
• GilsonFajans
• StowellDavidson

• Other laser exp possible with current setup?
• Resonant ionization
• disappearance exp
• Stimulated recombination
• Proposed early 1990s by Wolf
• (Complex scheme with high laser powers)
• ATHENA Phase 1.5
• Single step pulsed
• Single step CW

38
Idea Laser Stimulated Recombination
Inspired by A. Wolf 1993
hn
e

• Tunable 13C18O2 laser (45W)
• Measure increase in annih. rate vs frequency
• Realistic estimate 60 Hz peak rate

377 nm
n2
39
(No Transcript)
40
Laser Stimulated Recombination

• Technical challenges
• Simultaneous overlap of pbars, e, laser
• Need to rebuild the trap with the optical windows
  into a cryostat
• Re-operate the whole system
• Effect of 50 W laser on
• Cryostat, Vacuum, Hbar production

41
A First Test (Preliminary)

• 18W CO2 laser shot
• 5 sec On-Off modulation
• Non-optimal wavelength
• Non-optimal focusing
• Vacuum problem
• No damage to apparatus!
• Trigger increase with laser on ? vacuum effects?
• Next Year
• Complete system
• Modulate with 10-100 Hz
• hbar versus bkgd via Vertex

No Laser
Number of triggers
Laser On/Off
Mixing time (ms)
42
Summary Outlook

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

• Outlook
• 2004
• Atomic and plasma physics AntiHydrogen
  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) Cyclotron
  cooling dE/dx of p in e (vs. density, e
  temperature, )
• Trapping / Antihydrogen beam ...Antihydrogen
  energy distribution. Isotropic emission of
  Antihydrogen ?
• Access to inner states Laser spectroscopy
  laser stimulated recombination / Ionisation
• Far future
• 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?
• Spectroscopy High precision comparison 1S-2S,
  Hyperfine structure
• Gravitational effects E 0.000 1 meV

43
THE END
Thanks to the CERN AD Staff Jacky Rochet
, Cristoforo Benvenuti and Paolo Chiggiato Sergio
Bricola, Giuliano Sobrero Claire Massip, Jacky
Rochet..again Claude Fischer the SL/BI/PM
Section And many others
STAY TUNED
44
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)
45
Recombination Processes (1)
46
Recombination 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)
47
(No Transcript)
48
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