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Production of cold antihydrogen atoms in large quantities

Production of cold antihydrogen atoms in large quantities. C. Regenfus. University of Zürich. On behalf of the ATHENA collaboration. Sept. 02: > 50k cold antiatoms produced. Introduction The ATHENA experiment + New results Summary Outlook. H detector.

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Production of cold antihydrogen atoms in large quantities

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  1. Production of cold antihydrogen atoms in large quantities C. Regenfus University of Zürich On behalf of the ATHENA collaboration Sept. 02: > 50k cold antiatoms produced • Introduction • The ATHENA experiment + • New results • Summary • Outlook H detector Antihydrogen candidate (real data, 4-prong event) ATHENA - Cold antihydrogen production

  2. Motivation Antihydrogen: The simplest antimatter counterpart to matter for testing fundamental physic principles • CPT symmetry (Theoretical underpinning of field theories) • Gravitational acceleration (Equivalence principle) A very high precision can be achieved by comparing antihydrogen to hydrogen ATHENA - Cold antihydrogen production

  3. Future: high resolution laser spectroscopy Atomic 1S - 2S transition by two-photon excitation (first order Doppler-free) Lyman a : D E = 10.2 eV = 2.5 x 1015 Hz = 122 nm UV 2 x 243 nm photons (mW) Lifetime of 2S state: 122 ms => precision ~10-16 H spectroscopy Need: Cold antihydrogen ( T < mK ) Capture in neutral trap Hydrogen reference cell Cesar et al. (1996) (Laser 3kHz, 150µK) Gravitation: atomic fountain / interferometry ATHENA - Cold antihydrogen production

  4. Present physics menu Plasma studies: new kind of plasma imaging • Particle losses in trap • (Re)combination mechanism • Production of cold antihydrogen in larger quantities Investigations • Antihydrogen energy distribution (+ inner states) • Laser spectroscopy on non trapped atoms • Trapping H and/or creation of a H beam ATHENA - Cold antihydrogen production

  5. The ATHENA collaboration Particle traps + control: INFN, Sez. di Genova, and Dipartimento di Fisica, Università di Genova, Italy EP Division, CERN, Geneva, Switzerland Department of Physics, University of Tokyo, Japan Precision lasers: Department of Physics and Astronomy, University of Aarhus, Denmark Instituto de Fisica, Rio de Janeiro, Centro de Educação Tecnologica do Ceara, Brazil Positron plasma: Department of Physics, University of Wales Swansea, UK Detector + Analysis: Physik-Institut, Zürich University, Switzerland INFN, Sez. di Pavia, and Dipartimento di Fisica Nucleare e Teorica, Università di Pavia, Italy Dipartimento di Chimica e Fisica per l'Ingegneria e per iMateriali, Università di Brescia, Italy ATHENA - Cold antihydrogen production

  6. Experimental overview Scint. Scint. Scint. 15 K , 10-11 mbar Main ATHENA features: Open access system (no sealed vacuum) Powerful e+ accumulation Plasma diagnosis and control High granularity imaging detector ATHENA - Cold antihydrogen production

  7. ATHENA Photo ATHENA - Cold antihydrogen production

  8. Penning traps ATHENA: Multi-ring Penning trap (choose Vzas you like ) • Trapped electron at B = 3 T, E = 1 eV, U ~ 10 V • Cyclotron motion (perpendicular to B) • f = 84 GHz, r ~ 1 µm • Emission of synchrotron radiation (cooling) • t cool ~ 0.3 s • Axial motion (along B) • f ~ 7 MHz, d ~µm … cm • E x B drift (‘magnetron’) (cooling over coupling) • f ~ kHz, r ~ mm • Single particle <=> Plasma • Coulomb coupling parameter: Ecoul/Etherm • Electrical screening distance: Debye length ATHENA - Cold antihydrogen production

  9. Antiproton decelerator (CERN) ATHENA - Cold antihydrogen production

  10. Antiproton capture and cooling with electrons • Capture dynamics • Capture trap (50 cm) 10 000 p / AD shot ATHENA - Cold antihydrogen production

  11. Positron accumulation Accumulation rate: 106 e+/s 150 million e+ / 5 min After transfer: 75 x 106 in mixing trap Positronplasma : r~2mm, l~32mm, n~2.5 x 108 / cm3 Lifetime: ~hours ATHENA - Cold antihydrogen production

  12. Non destructive positron plasma diagnostics Complete model of plasma mode excitation (based on ‘Cold Fluid Theory’ * ) PLASMA SHAPE, LENGTH, DENSITY Plasma temperature change drive read * D. Dubin, PRL 66, 2076 (1991) ~ 30 MHz heat ATHENA - Cold antihydrogen production

  13. Detection principle of antihydrogen annihilations • H atom dissociates to p and e+ • by contact with the trap wall or • rest gas atoms • • pN -> charged and neutral pions • • e+ e- -> 511keV photons (back to back) Measure 1MeV on background of 2GeV Monte Carlo 511 keV opening angle Good spatial resolution (< 1 cm ) of charged vertex ( at least 2 prong events) Time coincidence (~ 1 µs) High rate capability (self triggering) ATHENA - Cold antihydrogen production

  14. Detector development Silicon micro strip layer • Compact design (radial thickness 3 cm) • High granularity (8K strips, 192 crystals) • Large solid angle (>75 %) Full detector installed: August 2001 All photodiodes replaced with APDs: Spring 2002 Mechanics for 77K • Much effort into R&D • Low temperature (~ 140 K) • High magnetic field (3 T) • Low power consumption • Light yield of pure-CsI crystals ? • CTE matching (Kapton, silicon, ceramics) • Electronic components Workshop Zürich , J. Rochet ATHENA - Cold antihydrogen production

  15. Pure-CsI crystals + Avalanche Photo Diodes • Read out close up • Crystal APD unit • Crystal detector performance Pure-CsI ~16 times higher light yield @ 80K C. Amsler, et al. :Temperature dependence of pure-CsI, scintillation light yield and decay time. NIM A 480, 494–500 (2002). ATHENA - Cold antihydrogen production

  16. Full GEANT Monte Carlo simulations Electrode (r = 1.25 cm) E&M cascades, Hadronic Showers (GEISHA) (> 10 keV) Geometry from AutoCAD Module-by-module (in)efficiency taken into account Same analysis routine for MC and data Radial vertex position ATHENA - Cold antihydrogen production

  17. Antiproton annihilations Electrode position (r = 1.25 cm) • Antiproton annihilation on the trap wall (real data, 3-prong event) • strip hits (inner + outer layer) => p vertex • crystals hit (matched to charged tracks) • vertex resolution, ~ 4 mm (curvature not resolved) ATHENA - Cold antihydrogen production

  18. Plasma imaging (antiprotons only) p vertex evolution in time Powerful plasma and loss diagnostics ! ATHENA - Cold antihydrogen production

  19. Mixing trap (nested penning trap*) In one mixing cycle (5 min) we mix ~104 antiprotons with ~108 positrons * G. Gabrielse et al., Phys. Lett. A129, 38 (1988) ATHENA - Cold antihydrogen production

  20. Cooling of antiprotons by 75 million positrons • Rapid cooling (< 20 ms) • Decreasing energy of antiprotons • Increasing separation of plasmas ATHENA - Cold antihydrogen production

  21. Antiprotons in the positron plasma Energy loss by dE/dx and thermalization Incoming antiproton e+ cloud (108/cm3) T = 10K ….. 10000K (by RF heating) ATHENA - Cold antihydrogen production

  22. Antihydrogen production 1. Fill positron well in mixing region with 75·106 positrons; allow them to cool to ambient temperature (~15 K) 2. Launch 104 antiprotons into mixing region 3. Mixing time 190 s - continuous monitoring by detector (charged trigger) 4. Repeat cycle every 5 minutes (data for 165 cycles) For comparison: “hot” mixing = continuous RF heating of positron cloud (suppression of antihydrogen production) ATHENA - Cold antihydrogen production

  23. Antiproton annihilation rate (charged trigger rate) High initial rate ~ 100 Hz Background trigger rate ~ 0.5 Hz ATHENA - Cold antihydrogen production

  24. Analysis Procedure Antihydrogen candidate (real data, 4-prong event) Event reconstruction (165 mixing cycles ~ 2 days) • Reconstruct annihilation vertex (103 k) • Search for ‘clean’ 511 keV-photons: exclude crystals hit by charged particles + its 8 nearest neighbours • ‘511 keV’ candidate = 400… 620 keV no hits in any adjacent crystals • Select events with two ‘511 keV’ photons • Reconstruction efficiency ~ 0.25 % = “golden” events ! ATHENA - Cold antihydrogen production

  25. Antihydrogen Signal (“golden” events) Opening angle between two 511 keV photons (seen from charged particle vertex) Comparison with Monte Carlo M. Amoretti et al., Nature419, 456 (2002) > 50,000 produced antiatoms (conservative estimate) Background: mixing with hot positrons ATHENA - Cold antihydrogen production

  26. Background measurements Opening angle between two 511 keV photons (seen from charged particle vertex) Can antiproton annihilations on electrode fake back-to-back signal? No ! 1) Secondary e+ within 10 mm ~ 0.1 % 2) Monte Carlo - no peak 3) Measurement - no peak Histogram: Antiproton-only data (99,610 vertices, 5,658 clean 2-photon events plotted). Dots: Antiproton + cold positrons, but analyzed using an energy window displaced upward so as not to include the 511 keV photo-peak M. Amoretti et al., Nature419, 456 (2002) ATHENA - Cold antihydrogen production

  27. Antihydrogen = main source of annihilations Cold Hot X-Y vertex distribution Time distribution of golden events and all annihilations ATHENA - Cold antihydrogen production

  28. Physics of antihydrogen production ANTIHYDROGEN VERSUS BACKGROUND ABSOLUTE PRODUCTION RATES DEPENDENCE ON TEMPERATURE ANGULAR DISTRIBUTION PRELIMINARY ATHENA - Cold antihydrogen production

  29. Opening angle fit Fit Input MC Hbar Data Fit Background Background cos(qgg) cos(qgg) Fit Result PRELIMINARY Fit result: ~ 2/3 of the events are antihydrogen ATHENA - Cold antihydrogen production

  30. Vertex spatial distribution fit PRELIMINARY Antihydrogen on trap electrode Antihydrogen on trapped ions or rest gas Compare to cold mix data Average fraction of antihydrogen 65 ± 10 % during mixing ! In 2002, ATHENA produced 0.7 ± 0.3 Million antihydrogen atoms => ATHENA - Cold antihydrogen production

  31. Rate of antihydrogen production Analysis: • 65 ± 10 % antihydrogen • ~ 50 % vertex / annihilation PRELIMINARY High Initial Rate (> 100 Hz) High S/B (~ 10:1) in first seconds ATHENA - Cold antihydrogen production

  32. Pulsed antihydrogen production Vertex Counts Heat On Mixing time -> Vertex Z position sec sec Switch positron heating Off/On resp. On / Off We observe: Annihilation rate Heat On Rise time ~ 0.4 s (Positron cooling time) Mixing time PRELIMINARY Vertex distribution along z ATHENA - Cold antihydrogen production

  33. Antihydrogen Production - T dependence Radiative Three-body s(T) dependence T-0.5 T-4.5 Final state n < 10 n >> 100 Stability (re-ionization) high low Expected rates ~ Hz ? ATHENA - Cold antihydrogen production

  34. Summary First production and detection of cold antihydrogen - high positron accumulation rate = fast duty cycle - sensitive detector = observe clear signals High rate production - initial rate > 100 Hz, average rate ~ 10 Hz Antihydrogen dominates annihilation signal (~ 2/3) Pulsed antihydrogen production Temperature dependence measured Antihydrogen production at room temperature ATHENA - Cold antihydrogen production

  35. Outlook Next steps - physics Next steps - technology Study … Formation process Spectroscopy High precision comparison 1S-2S Hyperfine structure More … Increase formation rate More antiprotons Laser induced recombination Gravitational effects E ~ 0.000 1 meV Atom interferometry Trapping and cooling ... Anti-Hydrogen at E < 0.05 meV ? Dense plasmas in magnetic multipole fields ? Laser cooling? Collisions with ultra-cold hydrogen atoms? ATHENA - Cold antihydrogen production

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