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AntimatterAntimatter
Jan MeierSeminar: Experimental Methods in Atomic Physics
May, 8th 2007
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Overview• Antimatter and CPT theorie
– what is antimatter?– what physics does it follow to?
• First observations of antimatter• Natural sources of antimatter• Artificial sources of antimatter and experiments with
antihydrogen– PS210, E862 (first detections of Ħ )– ATHENA, ATRAP (spatial and velocity distribution and
temperature measurements)– ALPHA (trapping of Ħ )– AEGIS (gravity measurement)
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Antimatter and CPT theorie
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( ) 0,ˆˆ 2rrrrr
hh =Ψ⎟⎠⎞
⎜⎝⎛ −∇⋅+
∂∂ trcmcit
i eβα
Dirac equation of a free electron
Prediction of antimatter
solution delivers two energy eigenvalues:
4222 cmpcE e+±=±r
Does negative enery eigenvalue have physical meaning?
1928 - Paul Dirac(Nobel prize 1933)
(P.A.M. Dirac, Proc. R. Soc. A 117 (1928) 610)
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⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛=
z
y
x
ααα
αˆˆˆ
ˆr
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛
=
0001001001001000
ˆ xα
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛
−
−
=
000000000
000
ˆ
iii
i
yα
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛
−
−=
001000011000
0100
ˆ zα
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛
−−
=
1000010000100001
β̂
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Dirac interpretation
e+ is a “hole“
e-
“Dirac sea“ e-
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1949 Feynman-Stückelberg interpretation
• Positron is a particle (not a “hole“)• Positron is a (positively charged) electron,
travelling backwards in time
positron
electron
some other electron
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CPT-TheoryTransformations C, P and T:
xx rr−→P (parity inversion)
C (charge conjugation)
T (time inversion) tt −→
qq −→
CPT transformation:
),,(),,( txqftxqf −−−→rr
BB −→; …
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A CPT transformation transforms a particle into its corresponding anti-particle
particle Anti-particle
e- e+
CPTtxq ,, r txq −−− ,, r
⇒ Standard Model:For every particle type there is a corresponding antiparticle type
(some electrically neutral bosons, like Z0, γ and ηc= are their own antiparticles)
cc
CPT Symmetry
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CPT invariance
Physics (i.g. all physical laws, equations, processes) is invariant under CPT transformations
Ψ∂∂
=Ψt
iH hˆ
−+
CPT transformation
)()ˆ( Ψ∂∂
=Ψt
iCPTHCPT h
+ −+−
ĦpH
e- e+
under certain conditions, relativistic quantum field theories say:
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Prospect of Ħ spectroscopy
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Violation of CPT invariance
• String theory• Kostelecky (standard model extension)• …
Historical: P (theory:Lee,Yang; Exp.:Wu), CP violations (J.H. Christenson)
(R. Bluhm et al., Phys. Rev. Lett. 82 (1999) 2254)
(C.S. Wu et al., Phys. Rev. 105 (1957) 1413)(J.H. Christenson et al., Phys. Rev. Lett. 13 (1964) 138)
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Matter-antimatter asymmetry
Big Bangenergy
???
tt=0 now
matter
antimatter
matter+
possible explanations: • CPT violation, breaking of Baryon number conservation• CP violation, breaking of Baryon number conservation, out of equilibrium situation
energy
(H.R. Quinn, SLAC-PUB-8784 (2001))
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First observations of antimatter
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First detection of antimatter
1932 - Carl Anderson
From particle track:
eqPositron 2+<
ePositron mm 20<
“Positron“ (e+)
cloud chambersecondary cosmic rays
(Nobel prize 1936)
(C.D. Anderson, Phys. Rev. 43 (1933) 491)
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Further detections of antiparticles
• 1955 - antiproton at Lawrence Berkeley National Laboratory (Chamberlain, Sergé,
Wiegand, Ypsilantis)• 1956 - antineutron (B. Cork)
(S.L. Chamberlain, Phys. Rev. 100, 947 (1955))
(B. Cork, Phys. Rev. 104, 1193 (1956))
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Natural sources of antimatter
• Beta(plus)-decay
• secondary cosmic rays
eeNeNa ν++→ +2210
2211
πμ ,, ++e
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Is there antimatter in (primary) cosmic rays?
1998 - AMS-01 ten day flight on Discovery
2009 – 2012AMS-02
No evidence for primaryantimatter!
“prototype“ m ~ 3 tons
three years on ISS
m ~ 7 tons
Goal:detection of He,and heavier nuclea
eH
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Artificial sources of antimatter and experiments with Ħ
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antiproton productionprinciple (since 1954):
traget (e.g. Be, Cu)proton beam particle-antiparticle pairs like ,p
p
target nucleus
γp
cGeV26=pp
1013
intensity 107(J. Eades, Rev. of modern phys. Vol.71, No.1 (1999))
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PS210 Experiment (1995 first Ħ detection)
PS (Proton Synchrotron) at CERN
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PS210 at LEAR (Low Energy Antiproton Ring) p = 1.94GeV/c
Xe cluster
e-,e+ pair creation is a rare process• only if , Z get close• two photon collision
probability = 0.000 000 000 000 000 01 %
Ħ production only ifrel. energy , e+ < 13.7 eV
11 Ħ detected!
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E862 at Fermilab (1996)
beamp = 3..9 GeV/c
H2 beam
detection of 99 Ħ
γ
e+
e-
p
Ħ
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AD (Antiproton Decelerator) (since July 2000)
AD
• ATHENA (2002)(Ħ detection by detector)• ATRAP (2002)(Ħ detection by reionization)
deceleration and coolingp : 3.5 -> 0.1 GeV/c
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The ATHENA experiment
from AD
T≈10K
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positron production
Solid Neon is best known positron moderatorNeon gas
solid Neon layer“low energy“ positrons
22NaT=6K
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Antiproton capturing
5kV
n ≈ 104
E = 5 MeVtp = 200 nsn ≈ 107
loss rate: 103
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Antiproton positron mixing
• production of several million Ħ between 2002 and 2004
“Mixing trap“: nested potential with both positive and negative ions
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Ħ detection
CsI crystal calorimeter
Si strips to “follow the path“
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ATHENA measurementsMeasurement of the spatial distribution of Ħin dependence of e+ plasma temperature
model:
e+ plasma
32mm
2.5mm andisotropicalemission of Ħ
• spatial distribution is independent of e+ plasma temperature• Ħ is not emitted isotropically
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temperature measurementModel: -Recombining rotate with e+ plasma; isotropically produced Ħpropagates with momentum of -using two temperatures to describe nonequilibrium conditions-spatial distribution measurement provides temperature ratio
K150≥⇒ parapT
K15≥perppT
(N. Madsen, Phys. Rev. Lett. 94 (2005) 033403)
perpp
parap TT 2)(10±=from measurement:
Withsurrounding temperature
and e+ are not in thermal equilibrium i.g. cooling rate is much lower than recombination rate!
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Temperature measurement at ATRAPMeasurement of velocity distribution:• Oscillating field (at radiofrequencies)• Ionization probability in oscillating field
is higher for slower Ħ• detection of ionized Ħ (antiprotons)
Best fit for : meV200=kinE
corresponds to K2400=HT
(G. Gabrielse, Phys. Rev. Lett. 93 (2004) 073401)
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The ALPHA Project (since 2006, successor to ATHENA)
Summary:• ATRAP:
– TĦ ≈ 2400 K• ATHENA:
– TĦ ≥150 K
•Goal: Trapping Ħ for spectroscopy!•Since Ħ is neutral it can not be trapped in a Penning trap!•Other method: using magn. momentum of Ħ•But: How deep is such a trap? How hot is Ħ allowed to be?
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Ħ trapping with magn. quadrupole
BErr
⋅−= μ
BkET Δ
∝
trap depth
“low field seekers“
“high field seekers“
T1.0≈Δ⇒ B
BE Δ⋅=Δ μ BT Δ⋅=TK7.0
solBr For Br = 1T, Bsol=6T
K07.0=T
in Kelvin
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solBrrB
r
22rsol BBB +=
solrsol BBBB −+=Δ⇒ 22
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Helmholz configuration for axial trappig
Anti-Helmholz configuration for radial trapping
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AEGIS project (planned to be in AD)Goal: direct measurement of g for Ħ
Rydberg positronium Beam (laser exited)
Stark accelerator
Cooled in Penning trapT≈100mK
Ħ *
In AEGIS: With two gratings and position dependent detectorPrecision: ∼1%
v∼100m/s
e+e-
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conclusion
• Low temperatures needed for trapping Ħ and to– do spectroscopy experiments (CPT test; precision
1013!!!)– test gravity for antimatter
• Temperatures still to high for trapping!• Challange: Cooling of negative ions ( ) to build Ħ at
very low temperatures (∼mK)• Futher cooling of Ħ with lasercooling (if convenient
lasersystems are developed)
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Thank You for Your attention!