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Progress with Cold Antihydrogen

Progress with Cold Antihydrogen. Work presented mostly that of the ATHENA collaboration. ATHENA – circa 2004. Athena/AD-1 Collaboration. Overview of Talk. Introduction and Motivations Apparatus and Techniques antiproton capture and cooling positron accumulation and plasma diagnostics

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Progress with Cold Antihydrogen

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  1. Progress with Cold Antihydrogen Work presented mostly that of the ATHENA collaboration Michael Charlton

  2. ATHENA – circa 2004 Athena/AD-1 Collaboration Michael Charlton

  3. Overview of Talk Introduction and Motivations Apparatus and Techniques antiproton capture and cooling positron accumulation and plasma diagnostics antihydrogen formation and detection Results first formation antiproton cooling temperature dependence spatial distributions Summary and Outlook Michael Charlton

  4. PHYSICS GOALS |Antihydrogen | = | Hydrogen | ? Gravity CPT Michael Charlton

  5. Overview of the ATHENA Apparatus Michael Charlton

  6. Early Photograph- ATHENA Michael Charlton

  7. Antiproton Decelerator - AD Michael Charlton

  8. Antiprotons - Capture and Cooling ATHENA Antiproton Capture Trap Scheme first demonstrated by the TRAP collaboration. See: Gabrielse et al, PRL 57 2504 (1986) and Gabrielse et al, PRL 63 1360 (1989) Michael Charlton

  9. Positron Accumulation - ATHENA Buffer Gas Positron Accumulator – developed by Surko group. See e.g. Murphy and Surko, PRA 46 5696 (1992) Surko and Greaves, Phys. Plasmas 11 2333 (2004) Surko, Greaves and Charlton, Hyp. Int. 109 181 (1997) Michael Charlton

  10. ATHENA Accumulator Electrodes Michael Charlton

  11. Positron Accumulation - ATHENA Open circles: no rotating electric field Closed circles: rotating field applied see e.g. Jorgensen et al, Non-neutral Plasma Physics, AIP Vol. 606 35 (2002) and van der Werf et al, Appl. Surf. Sci. 194 312 (2002) Michael Charlton

  12. Positron Transfer - ATHENA • Transfer efficiency ~ 50 % • Cold positrons for antihydrogen : 75 million / 5 min. • Positron plasma : r ~ 2 mm, l ~ 32 mm, n ~ 2.5x108 cm-3 • Lifetime ~ hours. Michael Charlton

  13. Plasma Diagnostics/Control - ATHENA Non-destructive Simultaneous determination pbar injection into positrons Monitoring of plasma  no change due to pbars Amoretti et al, PRL 91 55001 (2003) and Phys. Plasmas, 10 3056 (2003) Equivalent Circuit Model RF Plasma Heating Plasma Shape, Density, Particle Number, Temperature Michael Charlton

  14. ATHENA Antiproton Traps Early Photograph Michael Charlton

  15. Antihydrogen Production- ATHENA 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 sec - continuous monitoring by detector 4. Repeat cycle every 5 minutes (data for 165 cycles) For comparison: “hot” mixing = continuous RF heating of positron cloud (suppression of formation) Nested Penning trap approach suggested by Gabrielse et al, Phys. Lett. A 129 38 (1988) Michael Charlton

  16. Antiproton cooling by e+ - ATHENA Michael Charlton

  17. Antiproton Cooling by e+ - ATHENA Main results: [104 antiprotons launched at 30 eV into a 15 K positron plasma of density around 108 cm-3] Those antiprotons which overlap physically with the positron cloud cool quickly and antihydrogen formation begins after about 10-20 ms. Instantaneous antihydrogen rates over 400 s-1 have been recorded. Antihydrogen formation continues for many tens of seconds as the positron plasma slowly expands. Antiprotons appear in the side wells. This is attributed to field ionization of weakly-bound antihydrogen atoms. [See Amoretti et al, Phys. Letts. B 590 133 (2004)] Michael Charlton

  18. Antihydrogen Detection - ATHENA • Charged tracks to reconstruct antiproton annihilation vertex. • Identify 511 keV photons from e+-e- annihilations. • Identify space and time coincidence of the two. • Compact (3 cm thick) • Solid angle > 70% • High granularity • Operation at 140K, 3 T Michael Charlton

  19. Antihydrogen Detection - ATHENA • R & D (selected) : • Low temperature • Low power consumption First installation : August 2001 Photodiode replacement, APD : Spring 2002 Michael Charlton

  20. Analysis Procedure - ATHENA • Reconstruct annihilation vertex• 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 % Michael Charlton

  21. Cold Antihydrogen - ATHENA Monte Carlo Hbars Si strips qgg Hbar 104 pbars 108 e+ 2.5 cm qgg 3T CsI crystals • 104 pbars & 108 e+ mixed in Penning trap 104 pbars • Hbar forms, annihilates on electrode • pbar annihilates into charged pions • e+ annihilates into back-to-back gs 108 e+ • cos(qgg), opening angle of two 511keV gs, seen from the vertex, is plotted • Neutral pions give uncorrelated background Hbar Annihilation Hbar Formation Michael Charlton

  22. ATHENA Observations - Signal Cold Mixing : 103270 vertices, 7125 2x511keV events 131± 22 events Hot Mixing : Scaled (x1.6) to 165 mixing cycles. Amoretti et al., Nature 419 456 (2002) Michael Charlton

  23. ATHENA Observations - Background Antiprotons only : [in harmonic well] 99,610 vertices, 5,658 2x511keV events. Amoretti et al., Nature 419 456 (2002) Michael Charlton

  24. ATHENA Annihilation Distribution Hot Mixing Cold Mixing Amoretti et al., Nature 419 456 (2002) Michael Charlton

  25. Antihydrogen Emission Angles ATHENA Vertex Z Distribution Madsen et al, PRL 94 033403 (2005) Michael Charlton

  26. ATHENA Golden Events Golden Event Selection Hbar approx. cut efficiency ~50% 131± 22 GoldenEvents Charged Vertex ~10% Opening Angle (2×511 keV g) ~5% Golden Events Total: ~0.25% • Very restrictive cuts: threw away >99.7% of events • Can connection be made between Hbars and Vertices? Michael Charlton

  27. Pbar Annihilation Vertices - ATHENA Substantial Fraction of Vertices: Hbars Michael Charlton

  28. Vertex Spatial Distribution Fits - ATHENA Cold Mix Data Hbar (MC) BG (Hot Mix) Fit Result Pbar Vertex XY Projection (cm) Fit Result Pbar vertex R distribution (cm) Michael Charlton

  29. ATHENA Fit Results Hbar fraction in during mixing (ave. over 180 sec) ~65 ±10 % g g opening angle Vertex XY distribution Vertex R distribution Two g eventsyield Charged trigger yield ~700k reconstructed vertices  ~400k Hbars In 2002/3, we produced ~ Two Million Hbars Michael Charlton

  30. Antihydrogen production and trigger rate - ATHENA Trigger rate vs time during cold mixing • 85% of initial (<1s) trigger rate is due to antihydrogen • Peak rate >300 Hz • 2002 cold mixing : 0.5 106 antiatoms • 17% of the injected antiprotons recombine • Trigger rate is a good proxy for the antihydrogen signal Trigger rate Events with vertex corrected for efficiency From Amoretti et al. Phys. Letts B 578 (2004) 23 zoom of the first sec of mixing time Michael Charlton

  31. Modulation of Hbar Production - ATHENA Mixing time (sec) Mixing time Mixing time (sec) Vertex Counts Heat On Heat On Vertex Z position sec sec RF heating of e+ to switch off formation A Pulsed Source of Cold Antihydrogen Michael Charlton

  32. Modulation of Hbar Production - ATHENA Heat OFF Heat On/Off every 3 sec • Rise time contains Physics • Positron Plasma Cooling time • Hbar formation temperature dependence • Study ongoing (MC Fujiwara – priv. communication, June 2005) Michael Charlton

  33. Formation Processes + Radiative Three-body Radiative Three-body Rate T dependenceT-0.6 T-4.5 Final staten < 10 n >> 100 Stability (re-ionization) high low Expected rates~10sHzfast ??? Michael Charlton

  34. Antihydrogen production temperature dependence (1) ATHENA Opening angle Trigger rate vs time 306+-30 meV (3500 K) (Hot mixing) DT=43+-17 meV (500K) DT=15+-15 meV (175K) Cold mixing Michael Charlton

  35. Antihydrogen production temperature dependence (2) ATHENA data From Amoretti et al. Phys. Letts B 583 (2004) 59 Opening angle excess Proportional to the total number of detected antihydrogen in a mixing cycle No simple interpretation –pbars not in thermal equilibrium with positrons ... Tot. number of triggers in 180 sec T scaling 3body 300-400 Hz initial rate : 10 times the expected rate for radiative recombination Scaling law Peak trigger rate Michael Charlton

  36. Summary – results from ATHENA ATHENA Antihydrogen Apparatus High rate, High duty cycle (5 min-1), Versatile [Amoretti et al NIM A 518 679 (2004)] First production and detection of cold antihydrogen [Amoretti et al, Nature 456 419 (2002)] Main results since then In 2002/3 we produced ~2 Million Hbars High initial rate production > 400 Hz [ Amoretti et al, Phys Lett B 578 23 (2004)] Modulation of Hbar formation: A Pulsed Hbar Source Temperature dependence ~ T – (0.7 +/- 0.2) [Amoretti et al.,Phys Lett B 583 59 (2004)] [Needs extra work for interpretation – see e.g. Robicheaux, PRA 70 022510 (2004); arrested nature of 3-body process in finite positron plasmas] Michael Charlton

  37. Summary – results from ATHENA Main results since then … continued Many measurements of antiproton cooling upon mixing with a positron plasma – shed light on dynamics of antihydrogen formation [Amoretti et al, Phys. Lett. B 590 133 (2004)] Hbar emission angles; points to epithermal antihydrogen emission [Madsen et al, PRL 94 033403 (2005)] More to come … Michael Charlton

  38. Conclusions and outlook • What is the quantum state of the antihydrogen atoms? • Laser stimulated recombination to n = 11 manifold – tried in 2004 … analysis ongoing, but no obvious enhancement of antihydrogen rate • In beam experiments, early spectroscopy? Seem to be ruled out. • Capture (and cooling?) of antihydrogen in a magnetic gradient trap • Dense plasmas in multipole B-fields …see below • Precision spectroscopy • 1S-2S • Hyperfine splitting • Gravity measurements Michael Charlton

  39. Project ALPHA Antihydrogen Laser PHysics Apparatus University of Aarhus:P.D. Bowe,N. Madsen, J.S. Hangst Auburn University:F. Robicheaux University of California, Berkeley:W. Bertsche, E. Sarid, J. Fajans University of Liverpool:A. Boston, P. Nolan, M. Chartier, R.D. Page Riken:Y. Yamazaki Federal University of Rio de Janeiro:D. Miranda, C.L. Cesar University of Tokyo:R. Funakoshi, L.G.C. Posada, R.S. Hayano TRIUMF:K. Ochanski, M.C. Fujiwara, J. Dilling University of Wales, Swansea:L. V. Jørgensen, D.P. van der Werf, D.R.J. Mitchard, H.H. Telle, M. Jenkins, A. Variola*, M. Charlton University of Manitoba:G. Gwinner University of Calgary: R.I. Thompson * current address: Laboratoire de L’Accelerateur Lineaire; Orsay New collaboration recently approved by CERN Michael Charlton

  40. Trapping Neutral Anti-atoms Ioffe-Pritchard Geometry quadrupole winding mirror coils Well depth ~ 0.7 K/T Solenoid field is the minimum in B Based on Berkeley/Swansea results: not a good idea… Michael Charlton

  41. Acknowledgements Members of the ATHENA collaboration Members of the ALPHA collaboration Colleagues at Swansea UK financial support from EPSRC AD staff and all support from CERN Particular thanks; Bernie Deutch*, Rod Greaves, Jeffrey Hangst, Michael Holzscheiter, Finn Jacobsen, Michael Nieto, Cliff Surko *deceased Michael Charlton

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