A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 1 ATHENA - Cold antihydrogen production Production of cold antihydrogen atoms in large quantities.

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1 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 1 ATHENA - Cold antihydrogen production Production of cold antihydrogen atoms in large quantities Introduction The ATHENA experiment + New results Summary Outlook On behalf of the ATHENA collaboration C. Regenfus University of Zürich H detector Antihydrogen candidate (real data, 4-prong event) Sept. 02: > 50k cold antiatoms produced

2 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 2 ATHENA - Cold antihydrogen production 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

3 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 3 ATHENA - Cold antihydrogen production Future: high resolution laser spectroscopy Atomic 1S - 2S transition by two-photon excitation (first order Doppler-free) Lyman   E = 10.2 eV = 2.5 x 10 15 Hz = 122 nm UV 2 x 243 nm photons (mW) Lifetime of 2S state: 122 ms => precision ~10 -16 Cesar et al. (1996) (Laser 3kHz, 150µK) Need: Cold antihydrogen ( T < mK ) Capture in neutral trap Hydrogen reference cell H spectroscopy Gravitation: atomic fountain / interferometry

4 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 4 ATHENA - Cold antihydrogen production 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

5 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 5 ATHENA - Cold antihydrogen production 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

6 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 6 ATHENA - Cold antihydrogen production Experimental overview 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 Scint.

7 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 7 ATHENA - Cold antihydrogen production ATHENA Photo

8 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 8 ATHENA - Cold antihydrogen production Penning traps 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: E coul /E therm Electrical screening distance: Debye length ATHENA: Multi-ring Penning trap (choose V z as you like )

9 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 9 ATHENA - Cold antihydrogen production Antiproton decelerator (CERN)

10 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 10 ATHENA - Cold antihydrogen production Antiproton capture and cooling with electrons Capture dynamics Capture trap (50 cm) 10 000 p / AD shot

11 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 11 ATHENA - Cold antihydrogen production Positron accumulation Accumulation rate: 10 6 e + /s 150 million e + / 5 min After transfer: 75 x 10 6 in mixing trap Positron plasma : r~2mm, l~32mm, n~2.5 x 10 8 / cm 3 Lifetime: ~hours

12 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 12 ATHENA - Cold antihydrogen production Non destructive positron plasma diagnostics read heat drive Complete model of plasma mode excitation (based on ‘Cold Fluid Theory’ * ) PLASMA SHAPE, LENGTH, DENSITY Plasma temperature change * D. Dubin, PRL 66, 2076 (1991) ~ 30 MHz

13 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 13 ATHENA - Cold antihydrogen production 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) Good spatial resolution (< 1 cm ) of charged vertex ( at least 2 prong events) Time coincidence (~ 1 µs) High rate capability (self triggering) 511 keV opening angle Monte Carlo Measure 1MeV on background of 2GeV

14 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 14 ATHENA - Cold antihydrogen production Detector development 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 Full detector installed: August 2001 All photodiodes replaced with APDs: Spring 2002 Compact design (radial thickness 3 cm) High granularity (8K strips, 192 crystals) Large solid angle (>75 %) Workshop Zürich, J. Rochet Silicon micro strip layer Mechanics for 77K

15 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 15 ATHENA - Cold antihydrogen production Pure-CsI crystals + Avalanche Photo Diodes Read out close up Crystal APD unit Crystal detector performance ~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). Pure-CsI

16 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 16 ATHENA - Cold antihydrogen production Full GEANT Monte Carlo simulations 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 Electrode (r = 1.25 cm) Radial vertex position

17 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 17 ATHENA - Cold antihydrogen production Antiproton annihilations 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) Electrode position (r = 1.25 cm)

18 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 18 ATHENA - Cold antihydrogen production Plasma imaging (antiprotons only) Powerful plasma and loss diagnostics ! p vertex evolution in time

19 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 19 ATHENA - Cold antihydrogen production Mixing trap (nested penning trap*) In one mixing cycle (5 min) we mix ~10 4 antiprotons with ~10 8 positrons * G. Gabrielse et al., Phys. Lett. A129, 38 (1988)

20 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 20 ATHENA - Cold antihydrogen production Cooling of antiprotons by 75 million positrons Rapid cooling (< 20 ms) Decreasing energy of antiprotons Increasing separation of plasmas

21 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 21 ATHENA - Cold antihydrogen production Antiprotons in the positron plasma Energy loss by dE/dx and thermalization e + cloud (10 8 /cm 3 ) T = 10K ….. 10000K (by RF heating) Incoming antiproton

22 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 22 ATHENA - Cold antihydrogen production Antihydrogen production 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 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)

23 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 23 ATHENA - Cold antihydrogen production Antiproton annihilation rate (charged trigger rate) Background trigger rate ~ 0.5 Hz High initial rate ~ 100 Hz

24 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 24 ATHENA - Cold antihydrogen production Analysis Procedure 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 ! Antihydrogen candidate (real data, 4-prong event) Event reconstruction (165 mixing cycles ~ 2 days)

25 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 25 ATHENA - Cold antihydrogen production Antihydrogen Signal (“golden” events) Opening angle between two 511 keV photons (seen from charged particle vertex) > 50,000 produced antiatoms (conservative estimate) Background: mixing with hot positrons Comparison with Monte Carlo M. Amoretti et al., Nature 419, 456 (2002)

26 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 26 ATHENA - Cold antihydrogen production Background measurements 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 Opening angle between two 511 keV photons (seen from charged particle vertex) M. Amoretti et al., Nature 419, 456 (2002) 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

27 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 27 ATHENA - Cold antihydrogen production Antihydrogen = main source of annihilations Hot Time distribution of golden events and all annihilations Cold X-Y vertex distribution

28 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 28 ATHENA - Cold antihydrogen production Physics of antihydrogen production ANTIHYDROGEN VERSUS BACKGROUND ABSOLUTE PRODUCTION RATES DEPENDENCE ON TEMPERATURE ANGULAR DISTRIBUTION PRELIMINARY

29 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 29 ATHENA - Cold antihydrogen production Opening angle fit Fit result: ~ 2/3 of the events are antihydrogen Fit Result Fit Input MC Hbar Background cos(   ) Data Fit Background PRELIMINARY

30 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 30 ATHENA - Cold antihydrogen production Vertex spatial distribution fit => Antihydrogen on trap electrodeAntihydrogen 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 PRELIMINARY

31 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 31 ATHENA - Cold antihydrogen production Rate of antihydrogen production High Initial Rate (> 100 Hz) High S/B (~ 10:1) in first seconds Analysis: 65 ± 10 % antihydrogen ~ 50 % vertex / annihilation PRELIMINARY

32 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 32 ATHENA - Cold antihydrogen production Pulsed antihydrogen production Mixing time sec Vertex Z position Heat On Vertex Counts Mixing time -> Heat On Switch positron heating Off/On resp. On / Off We observe: Annihilation rate Vertex distribution along z Rise time ~ 0.4 s (Positron cooling time) PRELIMINARY

33 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 33 ATHENA - Cold antihydrogen production Antihydrogen Production - T dependence RadiativeThree-body  (T) dependenceT -0.5 T -4.5 Final staten > 100 Stability ( re-ionization )highlow Expected rates~ Hz?

34 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 34 ATHENA - Cold antihydrogen production 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

35 A DPG Frühjahrstagung Aachen 13.03.03 C. Regenfus Uni-Zürich 35 ATHENA - Cold antihydrogen production Outlook More … Increase formation rate More antiprotons Laser induced recombination Trapping and cooling... Anti-Hydrogen at E < 0.05 meV ? Dense plasmas in magnetic multipole fields ? Laser cooling? Collisions with ultra-cold hydrogen atoms? Spectroscopy High precision comparison 1S-2S Hyperfine structure Gravitational effects E ~ 0.000 1 meV Atom interferometry Study … Formation process Next steps - technology Next steps - physics