ASACUSA collaboration Meeting : Proposal for Run 4 and beyond

2 Apr 2025, 10:45 → 4 Apr 2025, 17:00 GMT

5th floor (Blackett Laboratory, Imperial College London )

Masaki Hori (Imperial College London)

Wednesday 2 April

1 Welcome

Speaker: Masaki Hori (Imperial College London)

2 Spectroscopy of excited states of Hbar & wild ideas in Antimatter chemistry

Experiments on excited states of antihydrogen already present in the beam will be proposed and presented including Lamb shift measurements (sensitive to antiproton radius) and spectroscopy of Ry states (sensitive to anti-Rydberg constant). Far future prospects for making different low energy antimatter species may be presented if I have time.

Speaker: Dr Daniel James Murtagh (Austrian Academy of Sciences (AT))

ExcitedStates.pdf

ExcitedStates.pptx

3 Plasma and trap development to improve the properties of the antihydrogen beam

Antiprotons:
The Double Cusp Magnet is optimized to focus ground state low-field-seeking (GS-LFS) atoms with kinetic energy equivalent to a temperature T in the range 5 < T < 20 K. If we can reduce the Hbar energy to this range, then at least x10 more GS-LFS atoms will escape the trap as a beam compared to 2024 (or more than x10, since lower T increases the time Hbar spends in the positron plasma → deexcitation).
With ALPHA-like mixing, we reduce Hbar T mainly by reducing pbar T, which is increasingly difficult as we increase the number of pbar in the plasma. Note: the ToF signal suggests that many Hbar are well below plasma T, which could be explained by collisional cooling in repeated passes through the positrons.
With the beam scheme, the pbar energy is set by the potentials and the scoop T, which is lower than for a large pbar plasma (~100 K in 2024) because e-kick is done per-scoop, so that fewer e- are kicked at one time. This is further motivation to pursue the beam scheme, in spite of its technical challenges.

Positrons:
Reducing the temperature of the positrons reduces the average principal quantum number of the Hbar and increases the chances that a stable atom is formed at low radius. Thus, both the low-n fraction and the absolute number of beam-like atoms are greater with colder positrons. Increasing the number of positrons also means more chances to deexcite on the way out of the plasma.
In 2024 we used 120 Me+ at 44 K. Our trap should be able to fit at least x2 more positrons. We know of no fundamental reason why we should not be able to reach 25 K. With modifications to the trap, 10 K or lower may be possible.

Speaker: Eric Hunter (CERN)

Hardware Upgrades

15:50 Coffee break

4 Pulsed antihydrogen beams: Rydberg manipulation and charge exchange

Charge exchange between an antiproton and a positronium atom can produce antihydrogen. If Rydberg positronium is used a resonant mechanism can produce Rydberg antihydrogen in well defined states. The feasibility of using this mechanism to produce a pulsed antihydrogen beam will be explored.

Speaker: Ross Edward Sheldon (Austrian Academy of Sciences (AT))

AntihydrogenViaChargeExchange.pdf

AntihydrogenViaChargeExchange.pptx

RydbergAntihydrogenMethods.pdf

RydbergAntihydrogenMethods.pptx

5 Non-destructive diagnostics and manipulation techniques - overview and perspectives

An array of diagnostic and manipulation methods share the use of trap-wall electrostatic perturbations and/or induced-charge signals. Possibilities include measurement of basic sample properties (number, density, temperature) as well as their control (e.g., feedback- or autoresonant positioning, collective mode cooling). Some of these possibilities have been tossed around and partially tested in the last runs, highlighting critical aspects of their exploitation. Indeed, as these techniques are based on the detection of single-particle and collective-mode signals, their effective implementation may become harder (or at least different) as the particle number and temperature is reduced, and thus require hardware development and setup modifications. A discussion about the collaboration's long-term scientific plan seems the right time and place to evaluate pros and cons of endeavours in this direction.

Speaker: Giancarlo Maero (Università degli Studi e INFN Milano (IT))

Maero_Run4life.pdf

Maero_Run4life.pptx

6 A buffer gas free positron trap

In this presentation, a new idea for producing a buffer gas free higher efficiency positron trap will be presented

Speaker: Dr Martin Singer (MPIPP)

Thursday 3 April

7 Logistics

Speaker: Masaki Hori (Imperial College London)

8 Ramsey Spectroscopy

A grant application (FWF) is planned for this year. We will propose to develop the required techniques for Ramsey spectroscopy with hydrogen in a short (Rabi) setup in Vienna.
To achieve static magnetic fields of sufficient homogeneity over the increased volume of the Ramsey spectrometer a Type I superconducting tube shall be used. Providing the 1.42 GHz microwaves inside this tube without compromising the static field quality needs to be developed. The timeline would fit to finish developments and tests before the end of the next long shutdown in order to propose an built the Hbar Ramsey spectrometer based on the results.
(NB: the UHV requirements will benefit from such a cryogenic spectrometer beamline)

Speaker: Martin Simon (Austrian Academy of Sciences (AT))

9 Road to highest precision CPT tests

I will discuss the accuracy of current CPT tests and argue that the highest resolution for spectroscopy will require a fountain.

Speaker: Eberhard Widmann (Austrian Academy of Sciences (AT))

Widmann ASACUSA London 2025.pdf

10:45 Coffee break

10 Antiprotonic atom x-ray spectroscopy at ASACUSA

The PAX project seeks to perform highest precision x-ray spectroscopy of Rydberg states in antiprotonic atoms in order to study strong-field QED effects in a region heretofore unexplored [1]. The project is based on the confluence of low-energy antiproton beams at ELENA, and newly available Transition Edge Sensor (TES) microcalorimeter detectors that allow for 10E-4 intrinsic energy resolution in the ~100 keV regime, while maintaining high quantum efficiency [2].

I will present an overview of the PAX project, current status, and prospects for integrating the final experimental setup that includes a few mbar gas cell and large solid angle TES detector into the ASACUSA1 beamline.

[1] N. Paul et al, PRL 126, 173001 (2021)
[2] G. Baptista et al, arXiv:2501.08893 (2025)

Speaker: Dr Nancy Paul (Laboratoire Kastler Brossel (FR))

11 Mainboard closed session

12 Antiproton Impact Ionisation and Antiprotonic Atom Formation

MUSASHI can provide 1-1000 eV pbar beams that enable the study of elementary atomic processes of ionisation by antiproton impact and antiprotonic atom (pbarA) formation under single collision conditions. ASACUSA had measured ionisation cross sections of atomic or molecular targets such as D2, He, Ar, etc., down to 2.4 keV. However, atomic collisions at lower energies, especially below 1 keV, remain experimentally unexplored.
The theories of atomic collisions do not agree with each other. Atomic/Molecular collision experiment with MUSASHI beam will provide a unique opportunity to study at further low collision energies and to reveal atomic collision dynamics down to eV region with pbar impact. Possible targets are H, H2, He, Ar, etc., to measure ionisation cross sections and
pbar capture cross sections of H and He.

Speaker: Naofumi Kuroda (University of Tokyo (JP))

ASACUSA_atomiccollision_nk_2504.pdf

13 Pontecorvo reaction

We propose to study annihilation on three nucleons, p3He→ pn, for which no data exist. The annihilation mechanism is not well known with two competing models on the market, rescattering which involves hadrons, and fireball which involves quarks. The branching fraction is predicted to be around 10(−6) for the latter, compared to 10(-7)–10(-8) for rescattering. The experiment requires a continuous (DC) antiproton beam of 100 – 200 keV which is not available at this time, but is part of a possible consolidation programme of the AD/ELENA complex. The anticollinear 1 GeV nucleons will be detected by a detector made of scintillation counters. The detection efficiency forp 3He→ pn is 11% and the background rejection 108. The counting time for the fireball model is roughly estimated to be around 10 minutes for 1 Pontecorvo event.

Speaker: Claude AMSLER (SMI)

Pontecorvo_London.pdf

15:30 Coffee break

14 Measurements of Antiproton-Nucleus Cross-Sections

This proposal outlines a two-part experimental campaign aimed at improving our understanding of antiproton-nucleus interactions. In the first part, we propose the measurement of annihilation cross-sections of antiprotons at 100 keV using the ELENA decelerator in mini-bunch mode, using a time-of-flight technique. In the second part, we extend the study to energies of 5.3 MeV and above using antiprotons from the Antiproton Decelerator. The higher energy phase will target both annihilation cross-sections and elastic scattering cross-sections, providing complementary data on nuclear structure and interactions. These experiments will fill gaps in current datasets, offering insights into nuclear physics, particle physics, and cosmology.

Speaker: Luca Venturelli (Universita di Brescia (IT) and INFN)

Measurement_Antiproton-Nucleus_Cross-Sections_London_2025.pdf

15 MCP counting efficiency vs. antiproton reflections

Antiprotons can reflect from MCP surfaces. We aim to characterize this effect to inprove our diagnostics. By extracting particles from a pure antiproton plasma from the Cusp trap to the Cusp MCP in short bunches, we are able to measure their arrival times. If we make a histogram of arrival times, we expect a main peak upon first arrival, as well as multiple smaller peaks from reflections between the MCP and the trap. Biasing the MCP front would allow us to investigate this effect in different energy regimes.

Speaker: Marcus Bumbar (University of Vienna (AT))

Pbar reflection.pdf

16 Antiproton Interferometry and the Aharonov-Bohm Effect (AIABE)

We propose a three-step program to address the issue of antiproton interferometry and the Aharonov-Bohm effect with the antiproton. In the first part of the development we will make use of the (100 keV) TELMAX beam to characterize the geometrical reconstruction by pions of the antiprotons impact point. The following step will be the first direct demonstration of antiproton interferometry, realized by means of dedicated gratings and a high resolution emulsion detector. Finally, once produced the interferometric pattern, we will study the Aharonov-Bohm effect, which has never been observed for any particles other than the electron. The second and third steps will require the very low energy (250 eV) ASACUSA antiproton beam from the MUSASHI system.

Speaker: Marco Giammarchi (Università degli Studi e INFN Milano (IT))

GiammarchiInterferometry.pdf

Friday 4 April

17 Future ideas for Hbar Detection

In this talk I will discuss options for upgrading the antihydrogen detector.

Speaker: Viktoria Kraxberger (Austrian Academy of Sciences (AT))

Antihydrogen Detection

18 Antiprotonic helium atoms, PAX incorporation into ASACUSA-1 beamline, status of antideuteron R&D at AD, and other ideas

Speaker: Masaki Hori (Imperial College London)

10:20 Coffee break

19 ASACUSA proposal discussion

20 ASACUSA proposal discussion and any other business (ends earlier if possible)