SPSC meeting (feb. 3th, 2004): Progress Report on the ATHENA experiment

1. SPSC meeting (feb. 3th, 2004): Progress Report on the ATHENA experiment Gemma Testera (INFN- Genova) on behalf of the ATHENA collaboration J. S. Hangst, N. Madsen G. Bonomi, A. Bouchta, M.Doser, M.H.Holzscheiter,A. Kellerbauer,R. Landua Institute for Phys. and Astron. (Aarhus) Denmark CERN, Geneva (Switzerland) P.D. Bowe, M. Charlton, L.V. Jorgensen, D.J.R. Mitchard, D.P. van der Werf M.C. Fujiwara, Y. Yamazaki Atomic Phys. Lab, RIKEN (Japan) Dep. of Phys., Univ of Wales Swansea (UK) C. Amsler, I. Johnson,H. Pruys,C. Regenfus, J. Rochet R. Funakoshi,R.S. Hayano Dep. of Phys. and Inst. of Phys. (Tokyo) (Japan) Inst. of Phys. Zurich Univer. (Switzerland) C. Lenz Cesar M. Amoretti, C. Canali, C. Carraro, V. Filippini, A. Fontana, P. Genova, V. Lagomarsino, E. Lodi Rizzini, M. Macri, G. Manuzio, P.Montagna, A. Rotondi, G. Testera, A. Variola, L. Venturelli, N. Zurlo Fed. Univ. Of Rio de Janeiro (Brazil) Ist. Naz. Fisica Nucl. and Univ. of Brescia, Genova, Pavia (Italy)

2. M. Amoretti et al. (ATHENA COLL.) “Production and detection of cold antihydrogen atoms” Nature 419 2002 456 M. Amoretti et al. (ATHENA COLL.) “Positron plasma diagnostic and temperature control for antihydrogen production” Phy. Rev. Lett. 91 2003 05501 M. Amoretti et al. (ATHENA COLL.) “Complete non destructive diagnostic of non neutral plasmas based on the detection of the electrostatic modes” Phys. Plasmas 10 2003 3056 M. Amoretti et al. (ATHENA COLL.) “ The ATHENA antihydrogen apparatus” NIM A 518 (2004) 679 M. Amoretti et al. (ATHENA COLL.) “High rate production of antihydrogen” Phys. Lett. B 578 (2004) 23 M. Amoretti et al (ATHENA COLL.) “Antihydrogen production temperature dependence” Phys. Lett. B in press M. Fujiwara et. al (ATHENA COLL. ) “Three dimensional annihilation imaging of trapped antiprotons” Phys. Rev. Lett. in press event in ATHENA • Offline analysis of the data collected during the 2002 run • New developments and preliminary results from 2003 run • Plans for next year

3. 2002 run: Antihydrogen production cyle 2) e+ handling 1) antiproton handling • Catch antiprotons (5KV), cool (30 sec) • stack 3AD shots in the catching trap • transfer antiprotons in the recombination region • dump all the electrons • about 104 antiprotons ready for recombination • Positron accumulation ~ 106 e+/sec • 300-600 kHz rotating wall in the accumulator • Compression factor in the accumulator: about 4 • 150 million positrons / 300 sec • 50% transfer efficiency in 3T • 7 107 positrons ready for recombination • Mixing for 180 secs in a nested trap • Detection of the annihilations by the antihydrogen detector • Positron detection by the non destructive plasma mode diagnostic • Positrons: density 1.7 108/cm3, L=3.2 cm, r=2.5 mm in the mixing trap • Storage time : thousands of seconds • Expected positron temperature: 15 Kelvin • No positron heating: cold mixing (Hbar production) • Controlled positron heating: hot mixing (background)

4. z Rp Zp Non destructive plasma mode diagnostic Dipole mode f1 Quadrupole mode f2 • a= Zplasma/Rplasma (aspect ratio) detection drive 1)f1,f2a, density 2)Line shape fit (dipole mode)N heating on 3)Controlled heating by RF drive around the dipole frequency (about 20-21 MHz) Shift of the quadrupole frequency DT (NOT T) About 15 meV resolution in 2002 (better in 2003) heating off M. Amoretti et al (ATHENA COLLABORATION) PRL91 (2003) 05501, Phys. Plasmas 10 (2003) 3056

5. qgg 104 pbars 108 e+ Antihydrogen detector Vertex rec. eff.: 50% Position resolution (s): 4 mm Silicon trigger efficiency: (85 +-10)% Photon energy resolution: 24% (FWHM) @ 511KeV Photon detection efficiency: 20% Full simulation by Montecarlo based on GEANT 3.21 CsI crystals Opening angle distribution Si strips 131± 22 GoldenEvents (>50000 Hbars) in sept 2002 3T Amoretti et al.,(ATHENA coll.)Nature419 (2002) 456

6. Beyond the golden events M. Amoretti et al. (ATHENA collaboration) Phys. Lett. B 578 (2004) 23 • Further analysis using all the informations present in the data and the Montecarlo code • Vertex radial distribution2. Full shape of the opening angle distribution 1) Vertex radial distribution fit xy xy Hot mix xy Cold mix MC dn/dr hot mixing: annihilation around the trap center dn/dr Cold mixing dn/dr:annihilations on trap walls (MC or “pbar only”)

7. 2)Full shape of the opening angle distribution Antihydrogen annihilations : of cold mixing vertices (2002 run)

8. 2002 run: time evolution of the antihydrogen production Reconstructed vertices (Hz) during cold mixing vs time: Separation of the signal from background by the radial vertex fit data antihydrogen background

9. 2002 run: antihydrogen production and trigger rate 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 zoom of the first sec of mixing time

10. Future experiments...........fundamental physics with cold Hbar........ ............we need to understand and control the antihydrogen production • Recombination mechanism (radiative vs 3body) • plasma temperature dependence • plasma density dependence n or n2 • internal states distribution • interplay between recombination and ionization (field ionization, collisional..) • energy of the antihydrogen • direction of the escaping antihydrogen • dynamics of the antiprotons cooling by positrons, recombination, cloud separation in the nested trap • dependence on the antiproton number and positron number • optimization of the Hbar production cycle • insertion of laser light to influence the inner states • We investigated some of these questions during the 2002 run • We devoted the most part of the 2003 run to continue these studies • We implemented technical and methodological developments

11. 2002 run: Antihydrogen production temperature dependence Opening angle excess Proportional to the total number of detected antihydrogen in a mixing cycle 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 Room temperature

12. 2003 run : improvements on plasma detection mode • From frequency domain to time domain: realization of a custom board • better signal to noise ratio (low excitation amplitude) • better frequeny resolution (from 5 kHz to 1KHz) (Typ. freq. 20-30 MHz) • Good monitor of plasma with high (>50 ) aspect ratio positron compression in the mixing trap • DT resolution from 15 meV to 1 meV • fastest scan time to locate the freq. (50 MHz scan took minutes in 2002 and a few sec now ) • use of a single electrode • higher repetition rate Quadrupole mode frequency shift vs heating voltage Positron plasma temperature (eV) increase vs heating voltage Previous sensitivity

13. 2003 run: More positrons and higher plasma density • Upgrading during 2003 • Phosphor screen + CCD in place of the Faraday cup in the accumulator • Stacking of several positron shots in the mixing trap • Rotating wall in the mixing trap: control of the plasma density before mixing using the improved diagnostic Positrons stacking in the mixing trap: 4.7 107 e+/stack(200 sec/stack) Images of positrons in the accumulator: without RW and with RW 1.2 109 e+

14. 2003 run: positron density dependence of the antihydrogen production Extensive studies to optimize the conditions to perform rotating wall in the mixing trap (frequency sweep 6.7-MHz,time duration 26 sec,amplitude 12V) 10 sec cooling time before mixing: syncrotron radiation Density up to 1×1010 reached in these tests • Compression α = 80 n=7×109 cm-3 rp=0.2 mm • No RW α = 20n = 8×108 cm-3 rp=0.9 mm • Expansion α = 7n = 1.5×108 cm-3rp=2.2 mm Example of trigger rate vs time :PRELIMINARY DATA All the structures disappear heating the plasma (about 3500 K)

15. 2003 run: Optimization of the antihydrogen production procedure 2002 run: stack 3 AD shots transfer, 180 sec mixing time antiprotons and e+ dump 5 shots (450 sec)/cycle 2 shots lost 2003 run: stack 2 AD shots transfer, 70 sec mixing time antiprotons and e+ dump 3 shots (180 sec)/cycle 1 shot lost 2003 run: continuos mixing and e+ stacking mix e+ and antiprotons and cool new antiprotons at the same time stack 10 e+ shots in the mixing trap No pbar shots lost e- gun primary current 10 mA 500ms e+ e+ - Pbar+e- e+ e+ e+

16. 108 /cm3 Continuos mixing and e+ stacking Example of e+ density vs time (sec) during the continuos mixing and e+ stacking • Initial reduction of density • Almost stable density after a few e+ shots • Increase of the radius: better overlap with antiprotons • Linear increase of the positron number: 5 107/shot New e+ shot followed by electron current (10 times) Non destructive monitor 200 sec sec

17. 2003 run: Antihydrogen production Radial vertex ( dn/dr 1/r) distributions MC Hbar only Cold mixing 2002 Cold mixing 2003 Continuos mixing and e+ stacking

18. e+ Antiprotons dynamics during antihydrogen formation (2002+2003 data) 15-17% of the injected antiprotons recombine. Axial and or radial separation between the two clouds ??? Cooling and antihydrogen formation ? “Axial separation” Study of the antiproton energy distribution vs time by slowly lowering the potential well “Radial separation”

19. Correlation between antiproton cooling and Hbar formation (2002+2003data) The energy distribution shows that in 20 ms about 40% of pbars reaches thermal equilibrium with positrons (30 eV injection energy) The trigger rate shows an onset at 20-30 ms Standard 2002 cold mixing Trigger vs time (ms) 0 20 40 60 80 Lower energy= faster cooling = prompt Hbar production Onset of the trigger rate as a function of the injection energy (2003 data standard cold mixing) Higher energy=delayed Hbar production 20 ms Total Hbar production almost independent on the injection energy Trig. Rate vs time (sec) On longer time scales (seconds) cooling of the remaining (poorly overlapping with positrons???) pbars is observed consistent with the Hbar production

20. Evidence of axial separation between antiprotons and e+ and antihydrogen formation (2002+2003 data) The energy distribution shows that after a few tenths of ms the lateral pbar wells (region III) begin to be populated 2003 run Opening angle distribution 40-70 sec with pbar re-injection and without ms Re-injection of the antiprotons after 40 sec from the mixing

21. e+ 2003 run: toward antiproton cloud radial compression • Optimize the radial overlap between pbars and e+ • Future experiments (neutral and charged particles confinement and instabilities) • (E.P.Gilson,J. Fajans PRL 90 1 (2003) • ... cooling by electrons reduces the axial and radial energy but do not realize compression Fast small (tens of mm) cyclotron motion y • Coupling the two pbar radial motions • Use e- to remove the radial energy • Cooling+compression x Slow (mm) magnetron motion Results: • Sideband coupling of the radial motion by a quadrupole excitation at the true cyclotron freq. works in presence of electrons • Electron cooling of the radial energy following a coupling p pulse has been observed • Additional work is needed to study the compression efficiency

22. Conclusions and plans for 2004 • We routinely produce antihydrogen by the Athena apparatus • 2002+2003 data: more than 2 millions antiatoms • The role of various physical parameters has been studied • Additional work is needed, many open questions still remain • Insertion of laser light is our main goal for 2004 : modifications of the apparatus and tests have been performed near the end of the 2003 run • Beam time requests: as last year Many people and Institutes of the collaboration are working to prepare letters of intent or proposals for future experiments at AD with cold antihydrogen

23. ATHENA apparatus Mixing in the nested trap T=15 Kelvin M. Amoretti et al (ATHENA COLLABORATION) NIM A 518 (2004) 679

24. 2002 run: spatial distribution of antihydrogen formation z Distribution of the z coordinate of antihydrogen vertices Cold mixing almost isotropic distribution (small radial excess)

25. Cold mixing 2002 and 2003

26. 2002 run: antihydrogen production temperature dependence 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 M. Amoretti et al. (ATHENA collaboration) accepted by Phys. Lett. B...