High precision experiments on antiprotonic helium at CERN, ASACUSA
Anna Sótér [email protected]
Eötvös Loránd University, Budapest, Hungary and MaxPlanckInstitut für Quantenoptik, Garching, Germany
Zimányi 2008 Winter School on Heavy Ion Physics, Budapest Outline (And the big questions of Life...)
brief history of antiprotonic helium (what?)
motivations in investigating matterantimatter systems (why?)
CERN Antiproton Decelerator (AD) (where?)
ASACUSA @ CERN AD (who?)
instrumentation and experiments of ASACUSA (how?)
results up to 2007 (was it worthy?)
outlook (what will we do tomorrow?)
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Discovery of antiprotonic helium
In matter the lifetime of antiprotons ∼ 1 ps Delayed annihilation in liquid helium:
E < 25 eV
Discovered in 1991 at KEK (Japan)
Iwasaki et al., Phys. Rev. Lett. 67 (1991) 1246
The antiprotonic helium – after collisions – reaches thermal equilibrium in 1 ns. The electron is on 1s ground state, while the antiproton occupies a large n~38 state (same bounding energy than the other electron had before!)
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Reasons for investigating antiprotonic helium I.
Curiosity...
Antiprotonic helium is a metastable system which contains matter and antimatter. It might give an answer about a few basic question. Why can't we see antimatter in the Universe? No antimatter signatures have been observed in diffuse cosmic gamma rays, charged cosmic rays, or cosmic microwave background. No trace of “antigalaxies” within 3 billion light years...
● the word is “barionically asymmetric” ● CP violation is not enough strong to explain it:
we have to find an other explanation.... For example, CPTviolation?
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Reasons for investigating antiprotonic helium II.
But before that, a bit more innocent curiosity...
antiprotonic helium is unique three body system, due to the microsecond scale lifetime.
(The remaining electron removes the ldegeneracy for the same n > it suppresses the collisional Stark effect and Stark decay. The Auger decay is suppressed as well: n > n1 level spacings ~ 2 eV, ionization energy ~25 eV, Auger process from (l ~ n1) states means large momentum jump > highly hindered)
This lifetime allows us to apply laserspectroscopy on this strange exotic atom, which is almost a moleculelike object due to the large mass of the antiproton... – so why don't we look at it?
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Reasons for investigating antiprotonic helium III.
Back to the CPT violation The antiprotonic helium is a unique interface between matter and antimatter. This allows us to probe properties of the orbiting antiproton: mass, charge, magnetic moment Observing any difference in this values from the proton would mean the violation of CPT. (Of course this violation in the baryonic sector is not the only way)
But why do we “want” to violate CPT? It works very well! (Feynman diagrams...) And to develop it, we have to reject fundamental axioms: Lorentz invariance, locality of interactions, or unitarity is it really worthy?
The Standard Model cannot explain fully the neutrino oscillations (LSND, MiniBooNE results – cannot be explained within the SM with 3 neutrinos) > SMEs with CPT (Lorentz) violating terms. The SM is not complete yet – quantum gravity, Planckscale physics YES.
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest How to check CPT invariance?
Theories: Kostelecky – tandem model, SM extension, explaines all observed neutrino osc. Barenboim et al. : SM extension, CPTviolating terms with quantum gravity effect
A few experimental methods:
Bmeson factories (BaBar, Belle) B0 antiB0 oscillations (orientation in spacetime). Effect:
TRAP collaboration: cyclotron frequency of pbar and p, (q/m ratio) Relative difference:
K meson and its antiparticle – comparison of masses in kaon oscillations – rel. difference: < ASACUSA collaboriation: a more indirect way due to the highprecision spectroscopy of antiprotonic helium: there exists a QED calculation (Korobov, Kino) about the spectrum lines of pbarheli, which contains in parameters the proton/antiproton/electron masses > assumptions, CODATA, fits:
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest The experimental realization: laser spectroscopy
The antiproton is captured into a metastable state, and casdades down slowly (34 microseconds). The idea is to enforce promt annihilation, by exciting the antiprotonic helium into an Augerstate (when the electron is emitted, the antiproton annihilates promt in the nucleus) ... to achieve this, at first we need a high luminosity, low energy antioproton beam...
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Antiproton Decelerator (AD) @ CERN
Antiprotons are created in 26GeV collisions between protons, with low efficiency: 1 pbar / 1 million p collisions.
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Cooling and decelerating at AD
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Experiments at AD
Atomic Spectroscopy And Collisions Using Slow Antiprotons spokesman: prof. Ryugo S. Hayano Tokyo, Munich, Budapest, Debrecen, Vienna, Brescia
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Instrumentation I. The RFQD
We constructed an RFQD to decelerate the antiprotons to keVenergies needed for atomic physics experiments.
Radio Frequency Quadrupole 6m long device, synthesizes 50000 atoms per minute in a cryogenic Decelerator target at T=5 K. (> 50 keV) Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Instrumentation II. Microwire detectors
Microwire secondary electron emission detector:
Nondestructively measures the spatial XY profile of the antiproton beam at low energies (10100 keV), using d = 510 µm wires arranged in XY grid structure and charge sensitive preamplifiers.
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Instrumentation III.: lasers
We need lasers with very small fluctuation in wavelength. 10 W cw pump lasers (Nd:YVO4) Ti:S+dye lasers locked to a frequency comb pulse amplification with Ti:S resonators chirp compensation with EOM
Ti:S and its pump Nd:YVO4 Menlo Sys. frequency comb Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Determination of charge and mass of the antiproton I.
With developing the laser system, we were able to measure transitions with high precision (10 MHz)
we have high precision QED calculations (Korobov, Kino) relativistic corr, Lambshift... these calculations contains the electron, antiproton and He nucleus masses as parameters to test CPT, we look at the difference between m(p) and m(pbar), q(p) and q(pbar) (we let them to vary relatively to each other, and use CODATA for proton) pbarheli binding energies are roughly proportional to correlation between the fractional mass and charge change!
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Determination of charge and mass of the antiproton II.
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest The spin magnetic moment of the antiproton I.
Splitting of spectral lines in antiprotonic helium: HF – interaction between the antiproton angular momentum and the electron spin SHF – antiproton spin
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest The spin magnetic moment of the antiproton II.
One needs numerical solutions of the optical Blochequations to describe the populations.
The precision is not reaches yet the PDG value.
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Dopplerfree spectroscopy methods
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Summary and outlook
Future plans: increasing precision with applying new laser spectroscopy techniques, new cryostat, etc. .... and producing antihelium, of course.
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest Thank you for your attention!
The talk was mostly based on our latest detailed report:
R. S. Hayano, M. Hori, D. Horváth, E. Widmann: Reports on Progress in Physics, 70 (2007) 19952065
(I used figures from M. Hori, D. Horváth and T. Pask)
This, and the other related papers you can find on our website:
http://asacusa.web.cern.ch/ASACUSA/
Anna Sótér: High precision experiments on antiprotonic helium, Zimányi 2008 Winter School, Budapest