ASACUSA Status and Outlook: antihydrogen Towards the production of an antihydrogen beam N. Kuroda, S. Ulmer, D.J. Murtagh, Simon Van Gorp, M. Corradini, M. Diermaier, M. Leali, C. Malbrunot, V. Mascagna, O. Massiczek, K. Michishio, A. Mohri, H. Nagahama, Y. Nagashima, Y. Nagata, M. Otsuka, B. Radics, C. Sauerzopf, K. Suzuki, M. Tajima, H. A. Torii, L. Venturelli, B. Wünschek, N. Zurlo, H. Higaki, Y. Kanai, E. Lodi-Rizzini, Y. Matsuda, E. Widmann, and Y. Yamazaki

Overview Introduction to the ASACUSA-Cusp experiment Antiproton trap (MUSASHI) Positron trap Cusp Trap Results from 2012 Towards a beam of antihydrogen

Acronyms Pt1 ASACUSA : Atomic Spectroscopy And Collisions Using Slow Antiprotons

Motivation Antihydrogen is the simplest antiatom consisting of an antiproton ( H ) and a positron ( e + ) A sample of antihydrogen amenable to spectroscopic investigation would allow comparisons to be made with hydrogen atoms. Resulting in a high precision test of CPT symmetry. The ASUACUSA-Cusp experiment aims to perform high precision spectroscopy of the ground state hyperfine structure of antihydrogen.

Spectroscopy Method Rabi-like beam spectroscopy1,2 Rabi, I. I., Kellogg, J. M. B. & Zacharias, J. R. Phys. Rev. 46, 157–163 (1934). A. Mohri and Y. Yamazaki, Europhys. Lett. 63 (2003) 207 [2] Y. Enomoto et al., Phys.Rev.Lett. 105 (2010) 243401

The ASACUSA Cusp experiment Positron Trap Cusp Trap Antiproton Trap Hbar detector RFQD

The ASACUSA Cusp Experiment Antiproton trap For storage of antiprotons from the AD ring Positron accumulator Production and storage of positrons Cusp trap Antihydrogen production and focusing p Positron accumulator Cusp trap Antiproton trap Kuroda, N., S. Ulmer, D. J. Murtagh, S. Van Gorp, Y. Nagata, M. Diermaier, S. Federmann, et al. Nature Communications 5 (2014).

AD & RFQD The AD cycles every 100s 3.5GeV/c antiprotons are cooled to 100MeV/c (5.3MeV) and extracted to experimental zones Of the order 10 million antiprotons per cycle The RFQD further reduced the antiproton energy from 5.3MeV to 115keV

Acronyms Pt2 MUSASHI : Monoenergetic Ultra-Slow Antiproton Source for High-precision Investigation

Antiproton Trap - MUSASHI MRE antiprotons Extraction Electrodes Electrodes are cooled to ~10K via contact with cold-bore (4-6K) Vacuum < 10 −12 Torr Superconducting solenoid provides 2.5T B field

Antiproton Trap - MUSASHI Degrader foil reduces incoming antiproton energy to ~10keV Catching bias ~-13kV Antiprotons are cooled with ~3× 10 8 electrons A rotating wall electric field is superimposed on the trap ring electrodes to control the antiproton density 1-2 million antiprotons are trapped per AD cycle Antiprotons can be extracted with eV energies. Cyclotron cooling T~1s for electrons.

Positron Accumulation Before the 2012 antiproton beam was delivered, significant improvements were made to the ASACUSA-Cusp positron accumulator. The compact gas cell reported previously1 was extended and the tungsten mesh moderators replaced. 1. Imao, H., K. Michishio, Y. Kanai, N. Kuroda, Y. Enomoto, H. Higaki, K. Kira, et al. J. Phy: Conf. Ser. 225, no. 1 (2010)

Positron Beam Producion Positrons are produced by the decay of a 22Na source in conjunction with a moderator The W foil moderators used in previous experimental runs were replaced with a solid Ne ice grown onto a conical aperture in front of the source window. This was expected to increase the beam intensity by an order of magnitude.

Positron Trap

Positron Trap M1 M14 G4 G3 G2 G1 This new gas cell was expected to improve the trapping efficiency by a factor of 2-3

Positron Trap Approximately 1e6 positrons were accumulated in 15s Lifetime ~ 13s Predicted lifetime >100s Problem with : Electronic Noise Ground Loops

Transfer to the Cusp Positrons must be transferred into the Cusp trap, this process is repeated multiple times to accumulate ~30 million positrons in the cusp trap Whilst positrons are stored in the Cusp trap a rotating wall electric field is applied to compress the cloud e+ Positron trap Cusp trap

Positron Storage in the Cusp Trap The maximum number transferred to the cusp in 2012 was 60 million Antihydrogen experiments typically used 30 million positrons compressed to 1mm in the mixing potential 𝜌~1× 10 14

The Cusp Trap MCP MRE antiprotons Thermal Shield Thermal Shield SC Magnet in anti-Helmholtz configuration i.e. a cusped field (Bmax ~2.7T) Cold-bore T~10K MRE T~15K

The Cusp Trap To observe a high polarization fraction (and focusing of the beam) cold antihydrogen is required For 3K antihydrogen the number exiting the Cusp trap should be enhanced by a factor of 50 above a solid angle consideration.

Antihydrogen Production 3e5 antiprotons injected from MUSASHI 3e7 positrons stored in the cusp trap 420kHz RF is injected onto one of the Cusp trap MRE electrodes to prolong antihydrogen formation

Field Ionization detection method No RF 420KHz

Detection Field free region Cusp Trap Production region Detector 2.7m Field free region BGO Crystal inside vacuum tube (OD=10cm t=5mm) 5 plastic scintillators surrounding BGO (t=10mm, SA~2pi) Coincidence between 2 plastic scintillators for background discrimination Background reduced by factor of ~1000 Signal reduced by a factor of 2 -400V (94 V/cm)  n>43 are ionized -2000V (452 V/cm) n>29 are ionized

Results Field ionisation filter -400V (n<43) Background measured by replacing positrons with electrons Energy deposited in the BGO crystal for events with double coincidences from the 5 plastic scintillators detectors. Kuroda, N., S. Ulmer, D. J. Murtagh, S. Van Gorp, Y. Nagata, M. Diermaier, S. Federmann, et al. Nature Communications 5 (2014).

Results Top plot shows number of counts with background subtracted Bottom plot shows the number of counts corrected for the energy dependant detection efficiency predicted by GEANT 4 simulation. 25h-1 n<43 16h-1 n<29 Kuroda, N., S. Ulmer, D. J. Murtagh, S. Van Gorp, Y. Nagata, M. Diermaier, S. Federmann, et al. Nature Communications 5 (2014).

Outlook After the 2012 antiproton run CERN shutdown the accelerator chain to upgrade the LHC Work began to improve parts of the ASACUSA-Cusp experiment. Further improvements to the positron accumulator Adiabatic transport of pbar from MUSASHI to the Cusp trap New Cusp trap magnet

Positron Accumulation 2014 B field increase to 1T from 0.3T Filters installed into the vacuum system Lifetime ~100s

Adiabatic transport 153.7±0.3 eV 145±2 eV 3.2±0.5 eV 24±2 eV before transport after transport Mean 153.7±0.3 eV 145±2 eV Sigma 3.2±0.5 eV 24±2 eV before transport after transport Mean 16.2±0.4 eV 11.4±0.8 eV Sigma 2.3±0.5 eV 3.7±0.7 eV By decreasing the injection energy of protons and adding pulse coils, the energy spread of the protons was improved by a factor of ～6.

Double Cusp Magnet Improved focusing at higher T  enhancement of beam over solid angle.

Outlook Radics, B., D. J. Murtagh, Y. Yamazaki, and F. Robicheaux. Physical Review A 90, no. 3 (2014)

Conclusion During 2012 antihydrogen was observed 2.7m away from the production region. No evidence for focusing of antihydrogen with the Cusp trap  too energetic? Improvements during LS1 may increase the ‘beam’ intensity

ASACUSA Cusp team in 2012