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

Michael Charlton ATHENA – circa 2004 Aarhus P.Bowe, J.S. Hangst, N. Madsen Brescia E. Lodi-Rizzini, L. Venturelli, N. Zurlo CERN G. Bonomi, M. Doser, A. Kellerbauer, R. Landua Genoa M. Amoretti, C. Canali C. Carraro, V. Lagomarsino, M. Macri, G. Manuzio, G. Testera, A. Variola Pavia A. Fontana, P. Genova P. Montagna, A. Rotondi Rio de Janeiro (URFJ) C. Lenz Cesar Swansea M. Charlton, L. Jørgensen, D. Mitchard, H.H. Telle, D.P. van der Werf Tokyo/Riken M. Fujiwara, R. Funakoshi, R. Hayano, Y. Yamazaki Zurich C. Amsler, H. Pruys, C. Regenfus, J Rochet Athena/AD-1 Collaboration

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

Michael Charlton Overview of the ATHENA Apparatus

Michael Charlton Early Photograph- ATHENA

Michael Charlton Antiproton Decelerator - AD

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

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

Michael Charlton ATHENA Accumulator Electrodes

Michael Charlton 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 (2002) and van der Werf et al, Appl. Surf. Sci (2002)

Michael Charlton Positron Transfer - ATHENA Transfer efficiency ~ 50 % Cold positrons for antihydrogen : 75 million / 5 min. Positron plasma : r ~ 2 mm, l ~ 32 mm, n ~ 2.5x10 8 cm -3 Lifetime ~ hours.

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

Michael Charlton ATHENA Antiproton Traps Early Photograph

Michael Charlton Antihydrogen Production- ATHENA 1. Fill positron well in mixing region with 75·10 6 positrons; allow them to cool to ambient temperature (15 K) 2.Launch 10 4 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 (1988)

Michael Charlton Antiproton cooling by e + - ATHENA

Michael Charlton Antiproton Cooling by e + - ATHENA Main results: [10 4 antiprotons launched at 30 eV into a 15 K positron plasma of density around 10 8 cm -3 ] Those antiprotons which overlap physically with the positron cloud cool quickly and antihydrogen formation begins after about 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 (2004)]

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

Michael Charlton 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 Monte Carlo Hbars Hbar Cold Antihydrogen - ATHENA 10 4 pbars & 10 8 e + mixed in Penning trap 10 4 pbars 10 8 e + Si strips CsI crystals 2.5 cm 3T 10 8 e + Hbar forms, annihilates on electrode cos(   ), opening angle of two 511keV  s, seen from the vertex  is plotted 10 4 pbars   Hbar Annihilation pbar annihilates into charged pions e + annihilates into back-to-back  s Neutral pions give uncorrelated background Hbar Formation

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

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

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

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

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

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

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

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

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

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

Michael Charlton Modulation of Hbar Production - ATHENA 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) Heat OFF

Michael Charlton Formation Processes RadiativeThree-body Rate T dependenceT -0.6 T -4.5 Final staten > 100 Stability ( re-ionization )highlow Expected rates~10s Hzfast ??? Radiative Three-body +

Michael Charlton  T= meV (175K) Cold mixing  T= meV (500K) meV (3500 K) (Hot mixing) Opening angle Trigger rate vs time Antihydrogen production temperature dependence (1) ATHENA

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

Michael Charlton Summary – results from ATHENA ATHENA Antihydrogen Apparatus –High rate, High duty cycle (5 min -1 ), Versatile [Amoretti et al NIM A (2004)] First production and detection of cold antihydrogen [Amoretti et al, Nature (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 (2004)] –Modulation of Hbar formation: A Pulsed Hbar Source –Temperature dependence ~ T – (0.7 +/- 0.2) [Amoretti et al.,Phys Lett B (2004)] [Needs extra work for interpretation – see e.g. Robicheaux, PRA (2004); arrested nature of 3-body process in finite positron plasmas]

Michael Charlton 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 (2004)] –Hbar emission angles; points to epithermal antihydrogen emission [Madsen et al, PRL (2005)] –More to come …

Michael Charlton 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 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 Project ALPHA Antihydrogen Laser PHysics Apparatus New collaboration recently approved by CERN

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

Michael Charlton 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