October 27, 021D. Sillou Positronium CS du 15/02/2001

October 27, 022D. Sillou Measurement of the OrthoPositroniumLifetime Proposal

October 27, 023D. Sillou Positronium E= E H /2 = 6.8eV Radius = 2 r B = cm

October 27, 024D. Sillou Parapositronium S=0 C = (-1) L+S = (-1) n Ground state L=0 n = 2, 4, 6….  N(4)/N(2) ~ Lifetime ns

October 27, 025D. Sillou Orthopositronium S=1 C = (-1) L+S = (-1) n Ground state L=0 n = 3, 5….  N(5)/N(3) ~ Lifetime ~ 142 ns

October 27, 026D. Sillou QED and positronium  Most experimental results are in excellent agreement with QED:  At least 2 problems related to positronium have to be clarified:  Lifetime of o_Ps in vacuum (5.5  from th.)  Hyperfine splitting of Ps levels (3.5  from th.) And also: g-2 of muon 2.7  (E821 Brookhaven 8/02/2001)

October 27, 027D. Sillou History

October 27, 028D. Sillou Experimental situation Experiment in vacuum differs from theory by 5.5  Experiment in powder agrees with theory.But matter related corrections are ~ 10 times the discrepancy itself.

October 27, 029D. Sillou Theory Computation of B (2nd order corrections) = hard task Expected B ~ 40 but larger value was not excluded though about 10 times greater value was necessary to explain the discrepancy between vacuum measurements and o-Ps computed with B=0. Recently (2000) B = ==> 0-ps = ±  s -1 The computation was motivated by the existing discrepancy. This discrepancy persists.

October 27, 0210D. Sillou Why? The discrepancy at the level of with QED is unacceptable. Order  2 is now computed The positronium is the prototype model for bound states treatment in QCD [charmonium etc…]

October 27, 0211D. Sillou Experimental problems: In principle the experiment in vacuum is not very difficult: Orthopositronium should be: ** Formed. Beginning of history. You cut! **Confined, on walls pickoff seen as 511 keV . Should be measured and substracted as in Tokyo.  decay from vacuum seen as 3 . **Detection should not depend on positronium age. Cavity should be spherical. In summary: we take the best of previous experiments and add our improvements.

October 27, 0212D. Sillou Glossary: Pickoff: Annihilation of the e+ from the positronium with the wrong electron In 2 g. Contribution from this process Depends on the positronium kinetic Energy ant the number of collision (nombre collision ).

October 27, 0213D. Sillou Our experiment: Basic idea: 3  from o_Ps in vacuum 2  from the walls. Measure directly pickoff (as Tokyo) but 2  much smaller in vacuum. a 10% precision on the computed efficiency will be enough. >Ann Arbor was right and there is a discrepancy >Tokyo was right and there is no more any discrepancy >Both are right but matter in Tokyo experiment suppress coherent effects “ a la Glashow”

October 27, 0214D. Sillou Technical aspects: Vacuum < Torr Efficient e + moderator Well focused beam (1mm) Efficient e + tagging e + Intensity ≥ 10 3 /s Source 22 Na  + Continuous spectrum MeV Moderator Monochromatic ~1 eV Beamtransport Acceleration < 1keV Tagging Beam START

October 27, 0215D. Sillou cavity MgO Positronium formation Pickoff = 2  511 keV Setup STOP START  t ≤ 1ns Final state in vacuum: 3, 5 …  In walls only: 2, 4, …  5  /3  ~ 4  /2  ~ 10 -6

October 27, 0216D. Sillou What we will get Cut o-Ps formation History. B Pickoff line

October 27, 0217D. Sillou Summary Measurement in vacuum Direct pickoff measurement Small beam size ~mm. High beam rate 10 3 Hz Spherical cavity cavity surface

October 27, 0218D. Sillou

October 27, 0219D. Sillou

October 27, 0220D. Sillou Answer to Committee I ”Tokyo experiment takes place in a more HOMOGENEOUS medium”: The cavity includes SiO2 powder but also 22 Na source and scintillators!!! Also escape from target not excluded. Look at the setup (reference of their paper on previous transparency).

October 27, 0221D. Sillou Answer to Committee II ”Si la différence entre experiences et QED persiste, il est peu probable que cela mette en évidence l’effondrement de QED”: ( S. Glashow) A negative result would put aside many lingering doubts. A positive result (a vacuum lifetime disagreeing with qed) would be a truly momentous discovery. These days, spending so little for such a discovery (unlikely as it may seem) is a terrific bargain. I would approve the experiment immediately, and congratulate the collaboration in its willingness to engage is such a difficult task.

October 27, 0222D. Sillou Answer to Committee III The committee has joined to its report a mail from Tokyo group. We have some additional comments about it: Tokyo experiment takes place in a very inhomogeneous medium as stated before. Their claim about the precision of their pickoff correction seems to us very optimistic. In the annex to the committee’s report they announce new results: ±.03 ns :   th-exp) = (0.13 ± 2.9)  s -1 published 1995   th-exp) = (0.15 ± 1.5)  s -1 (referee report)

October 27, 0223D. Sillou 3 phases:  Phase I: Tuning and debugging  O_Ps formation in low density target  Study of Ge response and MC  Fitting procedures  First measurements of decay  Phase II: Slow Positrons beam  Detector construction  Vacuum  intensity, brightness, focusing…  Shutter, tagging  Phase III: Final setup  Technical runs  Start measurements

October 27, 0224D. Sillou What do we need ? 4 laboratories: ETHZ LAPP INFN INR Total budget 4370 kFF / 4 years (subj to approval) ETHZ 770 kFF IN2P32840 kFF INFN 260 kFF INR 500 kFF Technical support will be: 40% ETH Z+ INR

October 27, 0225D. Sillou What we need II ? Laboratory: ~30 m2 Phase I (2001) Installation of lab 30 days Mechanics 120 days [(30%)design)] Electronics 60 days Phase II (2002) Vacuum 150 days Mechanics 75 days Phase III (2003) Vacuum, Mechanics 150 days

October 27, 0226D. Sillou Who? After approval at LAPP: Precise with IN2P3 conditions for collaboration with INR (~Dubna IN2P3 in NOMAD). Refine needs at LAPP. Investigate more closely e + beam interest in the region. J-P Mendiburu, P. Nédélec, J-P Peigneux, D. Sillou

October 27, 0227D. Sillou Perpectives I: Fundamental physic with positronium. ortho or parapositronium properties (levels, hyperfine splitting…) interactions of positron/positronium with matter.

October 27, 0228D. Sillou Perpectives II: Applied Physics Positron beam takes more and more importance in materials studies due to: Positron sensitive to electronic density and positive vacancies positron studies offer a background free signal. Size of defects attainable Concentration of defects Doppler and collinearity technics which offer the possibility to measure the motion of electrons

October 27, 0229D. Sillou Figure 1. Positron annihilation spectroscopy fills a special niche in the group of techniques for general vacancy defect analysis. Shown are regions accessible to various standard techniques: optical microscopy (OM), neutron scattering (nS), transmission electron microscopy (TEM), scanning tunneling microscopy (STM), atomic force microscopy (AFM), and x-ray scattering (XRS). Positron techniques are both highly sensitive and can resolve the size of atomic vacancies at any depth in a sample. The solid green line outlines the range of interest for studies of fine lines used as electronic interconnects on semiconductor chips. Livermore

October 27, 0230D. Sillou Perpectives III: University, students, positions Experiments at this scale will allow to perform a lot of studies in collaboration with university with relatively short terms results. A positron beam would be one of the first in France (after the CERI in Orleans 06/2000) and would be appreciated by materials physicists and chimists in the region.

October 27, 0231D. Sillou Conclusions: The question of the orthopositronium lifetime is still open. Vacuum experiments is not in agreement with QED Powder experiment is in agreement with QEDbut to which extent can this result be interpreted as free space annihilation? The experiments presents a lot of interesting aspects: fundamental physic at LAPP, technical implications, and opportunities of developping collaborations with university and industry and definitely has discovery potential.

October 27, 0232D. Sillou