Antimatter Jan Meier Seminar: Experimental Methods in Atomic Physics May, 8th 27
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 PS21, 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
Prediction of antimatter 1928 - Paul Dirac (Nobel prize 1933) Dirac equation of a free electron r r r ˆ ˆ 2 r ih + ih c α β m e c Ψ = t solution delivers two energy eigenvalues: E ± = ± c 2 r p 2 + m 2 e c 4 r ( r, t ) Does negative enery eigenvalue have physical meaning? (P.A.M. Dirac, Proc. R. Soc. A 117 (1928) 61)
= z y x α α α α ˆ ˆ ˆ ˆ r = 1 1 1 1 ˆ x α = ˆ i i i i α y = 1 1 1 1 ˆ z α = 1 1 1 1 ˆβ
Dirac interpretation e - Dirac sea e - e + is a hole
1949 Feynman-Stückelberg interpretation Positron is a particle (not a hole ) Positron is a (positively charged) electron, travelling backwards in time electron positron some other electron
CPT-Theory Transformations C, P and T: C (charge conjugation) P (parity inversion) T (time inversion) q q r r x x t t B B ; f CPT transformation: r r ( q, x, t) f ( q, x, t)
CPT Symmetry A CPT transformation transforms a particle into its corresponding anti-particle particle e - e + Anti-particle q, x r, t CPT r q, x, t Standard Model: For every particle type there is a corresponding antiparticle type (some electrically neutral bosons, like Z, γ and η c = antiparticles) cc are their own
Ħ CPT invariance under certain conditions, relativistic quantum field theories say: Physics (i.g. all physical laws, equations, processes) is invariant under CPT transformations + Hˆ Ψ = ih t Ψ CPT transformation ˆ CPT( H Ψ ) = CPT( ih Ψ t ) p e - e + + + H
Prospect of Ħ spectroscopy
Violation of CPT invariance Historical: P (theory:lee,yang; Exp.:Wu), CP violations (J.H. Christenson) (C.S. Wu et al., Phys. Rev. 15 (1957) 1413) (J.H. Christenson et al., Phys. Rev. Lett. 13 (1964) 138) String theory Kostelecky (standard model extension) (R. Bluhm et al., Phys. Rev. Lett. 82 (1999) 2254)
Matter-antimatter asymmetry matter??? Big Bang energy energy + matter antimatter t t= now possible explanations: CPT violation, breaking of Baryon number conservation CP violation, breaking of Baryon number conservation, out of equilibrium situation (H.R. Quinn, SLAC-PUB-8784 (21))
First observations of antimatter
First detection of antimatter 1932 - Carl Anderson (Nobel prize 1936) secondary cosmic rays cloud chamber From particle track: q Positron < + 2e mpositron < 2m e Positron (e + ) (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. 1, 947 (1955)) (B. Cork, Phys. Rev. 14, 1193 (1956))
Natural sources of antimatter Beta(plus)-decay 22 11 Na 22 1 Ne + e + + ν e secondary cosmic rays + e, + μ,π
Is there antimatter in (primary) cosmic rays? 1998 - AMS-1 ten day flight on Discovery prototype m ~ 3 tons No evidence for primary antimatter! 29 212 AMS-2 three years on ISS m ~ 7 tons Goal: detection of He, He and heavier nuclea
Artificial sources of antimatter and experiments with Ħ
antiproton production principle (since 1954): proton beam traget (e.g. Be, Cu) particle-antiparticle pairs like,p p p 1 13 intensity 1 7 = 26 GeV c (J. Eades, Rev. of modern phys. Vol.71, No.1 (1999)) p γ p target nucleus
PS21 Experiment (1995 first Ħ detection) PS (Proton Synchrotron) at CERN
Ħ PS21 at LEAR (Low Energy Antiproton Ring) p = 1.94GeV/c 11 Ħ detected! Xe cluster e -,e+ pair creation is a rare process only if, Z get close two photon collision production only if rel. energy, e+ < 13.7 ev probability =. 1 %
E862 at Fermilab (1996) beam p = 3..9 GeV/c detection of 99 Ħ γ Ħ e + e - p H 2 beam
AD (Antiproton Decelerator) (since July 2) AD deceleration and cooling p : 3.5 ->.1 GeV/c ATHENA (22) (Ħ detection by detector) ATRAP (22) (Ħ detection by reionization)
The ATHENA experiment T 1K from AD
positron production Solid Neon is best known positron moderator Neon gas 22 Na T=6K solid Neon layer low energy positrons
Antiproton capturing E = 5 MeV t p = 2 ns n 1 7 loss rate: 1 3 n 1 4 5kV
Antiproton positron mixing Mixing trap : nested potential with both positive and negative ions production of several million Ħ between 22 and 24
Ħ detection CsI crystal calorimeter Si strips to follow the path
ATHENA measurements Measurement of the spatial distribution of Ħ in dependence of e + plasma temperature model: 2.5mm e + plasma and isotropical emission of Ħ 32mm spatial distribution is independent of e + plasma temperature Ħ is not emitted isotropically
Model: temperature measurement -Recombining rotate with e + plasma; isotropically produced Ħ propagates with momentum of -using two temperatures to describe nonequilibrium conditions -spatial distribution measurement provides temperature ratio from measurement: T = (1 ± 2) T para p perp p With perp T p 15K surrounding temperature para T p 15K and e + are not in thermal equilibrium i.g. cooling rate is much lower than recombination rate! (N. Madsen, Phys. Rev. Lett. 94 (25) 3343)
Temperature measurement at ATRAP Measurement 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 : corresponds to E kin T H = 2meV = 24K (G. Gabrielse, Phys. Rev. Lett. 93 (24) 7341)
The ALPHA Project (since 26, successor to ATHENA) 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? Summary: ATRAP: T Ħ 24 K ATHENA: T Ħ 15 K
Ħ trapping with magn. quadrupole trap depth high field seekers low field seekers E ΔE = μ ΔB r = μ r B B r sol in Kelvin For B r = 1T, B sol=6t T ΔB.1T T =.7K ΔE k B K T =.7 ΔB T
B r r B r sol B = + 2 2 B sol B r ΔB = B 2 sol + B 2 r B sol
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) e + e - Cooled in Penning trap T 1mK Stark accelerator Ħ * v 1m/s In AEGIS: With two gratings and position dependent detector Precision: 1%
conclusion Low temperatures needed for trapping Ħ and to do spectroscopy experiments (CPT test; precision 1 13!!!) 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!