AntimatterAntimatter

Jan MeierSeminar: Experimental Methods in Atomic Physics

May, 8th 2007

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)

Antimatter and CPT theorie

( ) 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)

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛=

z

y

x

ααα

αˆˆˆ

ˆr

⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜

⎝

⎛

=

0001001001001000

ˆ xα

⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜

⎝

⎛

−

−

=

000000000

000

ˆ

iii

i

yα

⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜

⎝

⎛

−

−=

001000011000

0100

ˆ zα

⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜

⎝

⎛

−−

=

1000010000100001

β̂

Dirac interpretation

e+ is a “hole“

e-

“Dirac sea“ e-

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

CPT-TheoryTransformations C, P and T:

xx rr−→P (parity inversion)

C (charge conjugation)

T (time inversion) tt −→

qq −→

CPT transformation:

),,(),,( txqftxqf −−−→rr

BB −→; …

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

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:

Prospect of Ħ spectroscopy

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)

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))

First observations of antimatter

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)

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))

Natural sources of antimatter

• Beta(plus)-decay

• secondary cosmic rays

eeNeNa ν++→ +2210

2211

πμ ,, ++e

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

Artificial sources of antimatter and experiments with Ħ

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))

PS210 Experiment (1995 first Ħ detection)

PS (Proton Synchrotron) at CERN

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!

E862 at Fermilab (1996)

beamp = 3..9 GeV/c

H2 beam

detection of 99 Ħ

γ

e+

e-

p

Ħ

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

The ATHENA experiment

from AD

T≈10K

positron production

Solid Neon is best known positron moderatorNeon gas

solid Neon layer“low energy“ positrons

22NaT=6K

Antiproton capturing

5kV

n ≈ 104

E = 5 MeVtp = 200 nsn ≈ 107

loss rate: 103

Antiproton positron mixing

• production of several million Ħ between 2002 and 2004

“Mixing trap“: nested potential with both positive and negative ions

Ħ detection

CsI crystal calorimeter

Si strips to “follow the path“

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

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!

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)

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?

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

solBrrB

r

22rsol BBB +=

solrsol BBBB −+=Δ⇒ 22

Helmholz configuration for axial trappig

Anti-Helmholz configuration for radial trapping

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-

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)

Thank You for Your attention!