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ASACUSA Experiment at CERN’s Antiproton Decelerator

ASACUSA Experiment at CERN’s Antiproton Decelerator. Atomic Spectroscopy And Collisions Using Slow Antiprotons. M. Hori CERN. LEAP 2000 Conference Venezia, Italy August 2000. Institute of Applied Physics, Tsukuba University, Azuma, T

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ASACUSA Experiment at CERN’s Antiproton Decelerator

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  1. ASACUSA Experiment at CERN’sAntiproton Decelerator Atomic Spectroscopy AndCollisions Using SlowAntiprotons M. Hori CERN LEAP 2000 ConferenceVenezia, ItalyAugust 2000

  2. Institute of Applied Physics, Tsukuba University, Azuma, T Institute of Physics, University of Tokyo, Franzén K Y Higaki, H Hyodo, T Ichioka, T Komaki, K, Kuga, T Kuroda, N Kuroki, K Torii, H, A. Yamazaki, Y Research Institute for Particle and Nuclear Physics, Bakos, J, S. Horváth, D Juhasz, B Ujvari, B Institute of Physics and Astronomy, University of Aarhus, Bluhme, H Knudsen, H Merrison, J Uggerhöj, U Thompson, R Department of Physics, University of Wales Swansea, Charlton, M Institut fur Kernphysik, Dörner, R Schmidt-Böcking, H CERN, Eades, J Ketzer, B Hori, M Department of Physics, University of Tokyo, Fujiwara, M Funakoshi, R Hayano, R, S. Ishikawa, T Sakaguchi, J Suzuki, K Yamaguchi, H Widmann, E KVI, Hoekstra, R Department of Physics, Tokyo Institute of Technology, Iwasaki, M RIKEN, Kambara, T Kojima, T Nakai, Y Oshima, N Mohri, A Wada, M Yamazaki, T Institute for Molecular Science, Kumakura, M Morita,M Institute for Storage Ring Facilities, University of Aarhus, Möller, S P Uggerhöj, E Ciril -Lab. Mixte CEA-CNRS, Rothard, H. GSI, Scheidenberger, C Universität Freiburg, Ullrich, J Department of Experimental Physics, St. Patrick's College, Slevin, J. A. Department of Physics, Tokyo Metropolitan University, Tanuma, H.

  3. Physics Goals • High precision spectroscopy of metastable antiprotonic atoms. • Bound-state QED • CPT theorem • high-precision 3-body theories • Atomic cascade • Chemical-physics • Atomic collisions at very low energies • Stopping power • Ionization • Channeling • Antiprotonic atom formation

  4. Metastable antiprotonic helium atoms T < 25 eV e- He2+ • 3% metastable fraction • Large (n, l) states (=40) are metastable in even densehelium, 1 ms lifetimes. • Auger decay suppressed • Stark mixing suppressed e- e- He2+ e-

  5. Metastable atoms Cerenkov counter AD Antiproton pulse 2X107 particles T=5.3 MeV 300-600 ns long 4-5 mm diameter Laser pulse Prompt annihilation Metastable atoms 3% with τ=3～4μｓ Gating Laser spike

  6. 1993-1994Laser -induced annihilationexperimentsat LEAR N. Morita et.al. Theory and experiment agree at the 1000 ppm level....

  7. Systematic studies of transition energies T.Yamazaki, R.S.Hayano, N.Morita, E.Widmann, J.Eades et.al. Relativistic(Korobov 1996) non-relativistic(Korobov 1995) Theory and experiment agree at the ppm level....

  8. Experimental accuracy forlaser spectroscopy 0.5 ppm After Lamb shift corrections,experiment-theory agreement at 2 ppm Cyclotron frequency <10-9 precisionTRAP / ATRAP Rydberg constant5X10-7 precisionAntiprotonic helium H.A. Torii et.al.

  9. improved laser system • better absolute calibration Proton mass in eV/c2 • pulse-amplified CW laser • collision-free environment R.S.Hayano et.al.

  10. Experiments continued at the AD….

  11. 597-nm resonance reacquired at AD(Dec 2, 1999)

  12. High-precision measurement of the resonance lines Factor 2-3 improvement over LEAR experimentsHigh precision achieved using pulsed antiproton beams

  13. Measurement of deeply-bound UV (372-nm) resonance • (35,33)->(34,32) at 372-nm detected.Shows atoms formed in narrow band between n=37-40…. (n,l)=(37,34) (n,l)=(35,33) Annihilation time

  14. (n,l)=(37,35)->(38,33) at 726 nm. Hyperfine structure of metastable antiprotonic helium atom resolved. • Improved pulse-to-pulse intensity and position stability. • Improved laser bandwidth and stability. and at AD….. Fast extraction at LEAR...

  15. Hyperfine structure (4-levels) Antiproton orbital angular momentum Electron spin Antiproton spin High precision using laser/microwave triple resonance Determine antiproton magnetic moment Measurement of hyperfine structure Bakalov, V.I. Korobov, E. Widmann

  16. Microwave resonator system f=13 GHz transition frequency. Field strength 10 gauss Input power 100 W. E.Widmann, J.Sakaguchi, T.Ishikawa et.al.

  17. How to go to higher precision with transition energy? Various factors that limit experimental accuracy to 0.5 ppm • Bandwidth of the pulsed laser 1.2 GHz (0.6 GHz at AD, better diagnostics) • Collision-induced shift ～1 GHz • Collision-induced broadening <0.5 GHz • Doppler broadening 0.5 GHz Additional factors that will limit future high-precision experiments: • AC Stark effect <50 MHz • Natural width 0.1～50 MHz • Laser phase-modulation <50 MHz • Systematics of antiproton beam large! -> but understood at AD (higher intensity) The goal is to measure the transitions with an accuracy better than50 ppb.

  18. Ultimate-precision experiment 392.42 nm 392.42 nm e- He2+ (n,l)=(36,35)→(34,33) (34,33)→(35,32) • Cancellation of first-order Doppler width with 392.42-nm laser • Natural linewidth of transition 0.3 MHz • Depletion of (n,l)=(34,33) and signal detection, using 457.65-nm dye-laser. • Ultimate measurement precision <10 MHz 392.42 nm Intermediatevirtual state Auger decay 392.42 nm

  19. Radio-frequency Post-deceleratorDeveloped by CERN PS division • Decelerate antiprotons from 5.3 MeV to~ 20 keV • Buncher + HEBT + Energy corrector + 200 MHz RFQ + LEBT • Beam emittances essentially preserved • Transmission (deceleration efficiency) 50% • Output energy variable W.Pirkl et.al.

  20. 5 MeV protons from Tandem • RF power tests completed at CERN • Tests using protons at Aarhus tandem • Installation at AD in October, first physics in November

  21. ~ 50 keV antiproton non-destructive detector • 2-dimmensional readout • Ultra-high vacuum compatible (no outgasing) • Tested with 20-50 keV protons

  22. Antiprotonic helium atoms at ultra-low densities • Direct coupling to RFQ decelerator • Differential pumping + ultra-thin beam window • Very high efficiency of stopping antiprotons, in helium/hydrogen at ultra-low densities (P<1 mb, T=5 K) • Non-destructive measurement of beam profile.

  23. Ultra-narrow banded CW pulse-amplified laser • <50 MHz bandwidth • Very high output power (50-80 mJ at 392 nm) • Random trigger capability (synchronization with AD beam)

  24. Primordial states of antiprotonic helium • First direct measurement of primary population (n,l) of exotic atom. • Some diabatic-state type theories predict initial metastable population of 30%, due to higher-lying states n>40. • Other theories predict populations only in n=38 vicinity (3% metastable fraction) at ANY density. • Laser spectroscopy of n=50 states using Optical Parametric Oscillator laser. G.Ya.Korenman

  25. Experimental values for initial capture

  26. Energy-loss • Antiproton dE/dX at T=0.1 ~ 50 keV • Solid (100 Å) and gas(~ 10 mbar) • ESA ready at Aarhus, precision proton data! S.P.Moller et.al. U.Mikkelsen et.al.

  27. Protonium atoms in large (n,l) states have 1-10 ms lifetimes. Antiprotonic helium in dense helium have 3 ms lifetimes Auger decay is suppressed. n=35-41 states are populated. Extended to t=10 ms in vacuum? higher n (up to 100?) are populated Antiprotonic lithium in vacuum may also be metastable Auger process highly suppressed? Metastable antiprotonic atoms in vacuum K. Ohtsuki

  28. What do you need? Ultra-low energy antiprotons at T<10 eV Collision-less environment High-density atomic hydrogen target at P=10-3 mb. Protonium production in single collisions J.Cohen

  29. Primary population (n,l) tuned by varying antiproton energy T. Angular distribution of emitted Auger electron. Primary populations of antiprotonic atoms J.Cohen

  30. Extension of LEAR data to lower energies (T<10 keV) Double ionization measurements may help us understand theory-experiment discrepancy in double-ionization of helium. Ionization of simple atoms by antiprotons H. Knudsen et.al.

  31. Production of eV beam Y.Yamazaki et.al.

  32. Beamline developed at UT-Komaba B=5 Tesla superconducting solenoid, with high-speed ramp of magnetic field. Negative hydrogen ion source (to simulate antiprotons) Y.Yamazaki, N.Oshima, H.Higaki, T.Ichioka et.al.

  33. 100-mm long harmonic region (to trap >1e7 antiprotons, and radially compress to < 1mm) Segmented electrodes for applying rotating wall V=15 kV catching electrode Mechanical precision 10mm, to suppress diocotron instabilities and prolong trapping lifetime. Antiproton trap T.Ichioka, H.Higaki, A.Mohri, M. Hori, Y.Yamazaki et.al.

  34. Radial compression of electron cloud via “rotating wall” method T.Ichioka, H.Higaki et.al.

  35. Electron-cooling of H- ionsInjection energy of H- at 100 eVElectron energy 0.1 eVB=1 TeslaDemonstrated cooling of 106 H- ions to T<1 eV in 10 seconds T.Ichioka, H.Higaki, A. Mohri et.al.

  36. High-efficiency extraction of antiprotons from trap using Einzel lenses in “acceleration mode” Differential pumping from 10-5 mb to 10-11 mb via adjustable slits Extraction of antiprotons from trap K.Y.Franzen, N.Kuroda et.al.

  37. Conclusion Using new experimental techniques…. • Very low energy beams (10 eV) • Very high-precision spectroscopy systems (<10-8) We will measure antiprotonic atoms and interactions between antiprotons and atoms in a completely new regime. • Bound-state QED • CPT theorem • high-precision 3-body theories • Atomic cascade • Chemical-physics • Stopping power • Ionization • Channeling • Antiprotonic atom formation

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