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S. Ulmer

Publications and source records attributed to S. Ulmer.

At least 19 recordsLinked to original sources
arXiv2026

Full Single-Quantum Control of Particles in Penning Traps for Symmetry Tests at the Quantum Limit

The BASE collaboration aims to measure antimatter systems with the highest precision in order to perform a rigorous test of CPT symmetry and search for physics beyond the Standard Model. As part of the BASE collaboration, we pursue the development of quantum logic inspired cooling and detection techniques for g-factor measurements of (anti-)protons. Implementing these methods requires full quantum-level control of individual antimatter particles confined in cryogenic Penning traps. By mapping the (anti-)proton's internal state onto a co-trapped 9Be+ "logic" ion via free Coulomb coupling in a double-well potential, we can accelerate measurement cycles and push g-factor precision measurements on (anti-)protons toward the quantum limit. Here, we present an overview of the proposed method and the current status of the project, with special emphasis on the new cryogenic multi-Penning-trap stack and the proton detection system.

physics.atom-ph↗
arXiv2025

Measured Properties of an Antihydrogen Beam

We report a factor of $100$ increase in the antihydrogen beam intensity downstream of ASACUSA's Cusp trap: $320$ atoms detected per $15$-minute run. The beam contains many Rydberg atoms, which we selectively ionize to determine their velocity and binding energy. The time of flight signal is modeled using a $1\mathrm{D}$ Maxwellian velocity distribution with a temperature of $1500\,\mathrm{K}$, which is close to the measured antiproton plasma temperature. A numerical simulation reproduces the observed distribution of binding energies and suggests that about $16\%$ of the atoms may be in the ground state.

physics.ins-det↗
arXiv2025

Summary Report of the Physics Beyond Colliders Study at CERN

The Physics Beyond Collider (PBC) Study Group was initially mandated by the CERN Management to prepare the previous European Particle Physics Strategy Update for CERN projects other than the high-energy frontier colliders. The main findings were summarized in an PBC Summary Report submitted to the Strategy Update. Following the Update process, the PBC Study Group was confirmed on a permanent basis with an updated mandate taking into account the strategy recommendations. The Study Group is now in charge of supporting the proponents of new ideas to address the technical issues and physics motivation of the projects ahead of their review by the CERN Scientific Committees and decision by the Management. The present document updates the previous PBC summary report to inform the new ongoing European Particle Physics Strategy Update process, taking into account the evolution of the CERN and worldwide landscapes and the new projects under consideration within the Study Group.

hep-ex↗
arXiv2025

CERN AD/ELENA Antimatter Program

The CERN AD/ELENA Antimatter program studies the fundamental charge, parity, time (CPT) reversal invariance through high-precision studies of antiprotons, antihydrogen, and antiprotonic atoms. Utilizing the world-unique Antiproton Decelerator (AD) and the Extra Low Energy Antiproton (ELENA) decelerator, the program supports multiple groundbreaking experiments aimed at testing fundamental symmetries, probing gravity with antimatter, and investigating potential asymmetric antimatter/dark matter interactions. Some experiments focus on precision spectroscopy of antihydrogen, while others conduct the most precise tests of CPT invariance in the baryon sector by comparing proton and antiproton properties. Other efforts are dedicated to measure the ballistic properties of antihydrogen under gravity and performing antiproton-based studies of neutron skins in exotic nuclei. These efforts have led to major breakthroughs, including the first trapped antihydrogen, antihydrogen's first gravitational acceleration measurement, and record-breaking precision CPT-tests in the baryon sector. With continuous advancements in antimatter cooling, trapping, and transport, CERN's program is opening new frontiers in fundamental physics. Future goals, described in this document and reaching to timelines beyond 2040, include further improving the precision of antimatter studies, developing transportable antimatter traps, and advancing our understanding of quantum field theory, gravity, and dark matter interactions. Furthermore, new areas of hadron physics with antiprotons will be explored through studies of the Pontecorvo reaction, antineutron annihilation dynamics and hypernuclei decays. The CERN AD/ELENA Antimatter program remains at the forefront of experimental physics, pushing the limits of precision measurements to unravel the mysteries of the universe.

nucl-ex↗
arXiv2024

Orders of Magnitude Improved Cyclotron-Mode Cooling for Non-Destructive Spin Quantum Transition Spectroscopy with Single Trapped Antiprotons

We demonstrate efficient sub-thermal cooling of the modified cyclotron mode of a single trapped antiproton and reach particle temperatures $T_+=E_+/k_\text{B}$ below $200\,$mK in preparation times shorter than $500\,$s. This corresponds to the fastest resistive single-particle cyclotron cooling to sub-thermal temperatures ever demonstrated. By cooling trapped particles to such low energies, we demonstrate the detection of antiproton spin transitions with an error-rate $<0.000025$, more than three orders of magnitude better than in previous best experiments. This method will have enormous impact on multi-Penning-trap experiments that measure magnetic moments with single nuclear spins for tests of matter/antimatter symmetry, high-precision mass-spectrometry, and measurements of electron $g$-factors bound to highly-charged ions that test quantum electrodynamics.

physics.atom-ph↗
arXiv2024

Injection and capture of antiprotons in a Penning-Malmberg trap using a drift tube accelerator and degrader foil

The Antiproton Decelerator (AD) at CERN provides antiproton bunches with a kinetic energy of 5.3 MeV. The Extra-Low ENergy Antiproton ring at CERN, commissioned at the AD in 2018, now supplies a bunch of electron-cooled antiprotons at a fixed energy of 100 keV. The MUSASHI antiproton trap was upgraded by replacing the radio-frequency quadrupole decelerator with a pulsed drift tube to re-accelerate antiprotons and optimize the injection energy into the degrader foils. By increasing the beam energy to 119 keV, a cooled antiproton accumulation efficiency of (26 +- 6)% was achieved.

physics.acc-ph↗
arXiv2023

A 16 Parts per Trillion Comparison of the Antiproton-to-Proton q/m Ratios

The Standard Model (SM) of particle physics is both incredibly successful and glaringly incomplete. Among the questions left open is the striking imbalance of matter and antimatter in the observable universe which inspires experiments to compare the fundamental properties of matter/antimatter conjugates with high precision. Our experiments deal with direct investigations of the fundamental properties of protons and antiprotons, performing spectroscopy in advanced cryogenic Penning-trap systems. For instance, we compared the proton/antiproton magnetic moments with 1.5 ppb fractional precision, which improved upon previous best measurements by a factor of >3000. Here we report on a new comparison of the proton/antiproton charge-to-mass ratios with a fractional uncertainty of 16ppt. Our result is based on the combination of four independent long term studies, recorded in a total time span of 1.5 years. We use different measurement methods and experimental setups incorporating different systematic effects. The final result, $-(q/m)_{\mathrm{p}}/(q/m)_{\bar{\mathrm{p}}}$ = $1.000\,000\,000\,003 (16)$, is consistent with the fundamental charge-parity-time (CPT) reversal invariance, and improves the precision of our previous best measurement by a factor of 4.3. The measurement tests the SM at an energy scale of $1.96\cdot10^{-27}\,$GeV (C$.$L$.$ 0.68), and improves 10 coefficients of the Standard Model Extension (SME). Our cyclotron-clock-study also constrains hypothetical interactions mediating violations of the clock weak equivalence principle (WEP$_\text{cc}$) for antimatter to a level of $|\alpha_{g}-1| < 1.8 \cdot 10^{-7}$, and enables the first differential test of the WEP$_\text{cc}$ using antiprotons \cite{hughes1991constraints}. From this interpretation we constrain the differential WEP$_\text{cc}$-violating coefficient to $|\alpha_{g,D}-1|<0.030$.

physics.atom-ph↗
arXiv2023

Image-current mediated sympathetic laser cooling of a single proton in a Penning trap down to 170 mK axial temperature

We demonstrate a new temperature record for image-current mediated sympathetic cooling of a single proton in a cryogenic Penning trap by laser-cooled $^9$Be$^+$. An axial mode temperature of 170 mK is reached, which is a 15-fold improvement compared to the previous best value. Our cooling technique is applicable to any charged particle, so that the measurements presented here constitute a milestone towards the next generation of high-precision Penning-trap measurements with exotic particles.

physics.atom-ph↗
arXiv2023

Fast adiabatic transport of single laser-cooled $^9$Be$^+$ ions in a cryogenic Penning trap stack

High precision mass and $g$-factor measurements in Penning traps have enabled groundbreaking tests of fundamental physics. The most advanced setups use multi-trap methods, which employ transport of particles between specialized trap zones. Present developments focused on the implementation of sympathetic laser cooling will enable significantly shorter duty cycles and better accuracies in many of these scenarios. To take full advantage of these increased capabilities, we implement fast adiabatic transport concepts developed in the context of trapped-ion quantum information processing in a cryogenic Penning trap system. We show adiabatic transport of a single $^9\mathrm{Be}^+$ ion initially cooled to 2 mK over a 2.2 cm distance within 15 ms and with less than 10\,mK energy gain at a peak velocity of 3 m/s. These results represent an important step towards the implementation of quantum logic spectroscopy in the \ppbar system. Applying these developments to other multi-trap systems has the potential to considerably increase the data-sampling rate in these experiments.

physics.atom-ph↗
arXiv2023

Ultra thin polymer foil cryogenic window for antiproton deceleration and storage

We present the design and characterisation of a cryogenic window based on an ultra-thin aluminised PET foil at T < 10K, which can withstand a pressure difference larger than 1bar at a leak rate < $1\times 10^{-9}$ mbar$\cdot$ l/s. Its thickness of approximately 1.7 $\mu$m makes it transparent to various types of particles over a broad energy range. To optimise the transfer of 100keV antiprotons through the window, we tested the degrading properties of different aluminium coated PET foils of thicknesses between 900nm and 2160nm, concluding that 1760nm foil decelerates antiprotons to an average energy of 5 keV. We have also explicitly studied the permeation as a function of coating thickness and temperature, and have performed extensive thermal and mechanical endurance and stress tests. Our final design integrated into the experiment has an effective open surface consisting of 7 holes with 1 mm diameter and will transmit up to 2.5% of the injected 100keV antiproton beam delivered by the AD/ELENA-facility of CERN.

physics.ins-det↗
arXiv2023

Optical stimulated-Raman sideband spectroscopy of a single $^9$Be$^+$ ion in a Penning trap

We demonstrate optical sideband spectroscopy of a single $^9$Be$^+$ ion in a cryogenic 5 Tesla Penning trap using two-photon stimulated-Raman transitions between the two Zeeman sublevels of the $1s^{2}2s$ ground state manifold. By applying two complementary coupling schemes, we accurately measure Raman resonances with and without contributions from motional sidebands. From the latter we obtain an axial sideband spectrum with an effective mode temperature of (3.1 $\pm$ 0.4)~mK. This results are a key step for quantum logic operations in Pennings traps, applicable to high precision matter-antimatter comparisons tests in the baryonic sector of the standard model.

physics.atom-ph↗
arXiv2023

Upgrade of the positron system of the ASACUSA-Cusp experiment

The ASACUSA-Cusp collaboration has recently upgraded the positron system to improve the production of antihydrogen. Previously, the experiment suffered from contamination of the vacuum in the antihydrogen production trap due to the transfer of positrons from the high pressure region of a buffer gas trap. This contamination reduced the lifetime of antiprotons. By adding a new positron accumulator and therefore decreasing the number of transfer cycles, the contamination of the vacuum has been reduced. Further to this, a new rare gas moderator and buffer gas trap, previously used at the Aarhus University, were installed. Measurements from Aarhus suggested that the number of positrons could be increased by a factor of four in comparison to the old system used at CERN. This would mean a reduction of the time needed for accumulating a sufficient number of positrons (of the order of a few million) for an antihydrogen production cycle. Initial tests have shown that the new system yields a comparable number of positrons to the old system.

physics.atom-ph↗
arXiv2023

A proposal for a low-frequency axion search in the 1-2 $\mu$eV range and below with the BabyIAXO magnet

In the near future BabyIAXO will be the most powerful axion helioscope, relying on a custom-made magnet of two bores of 70 cm diameter and 10 m long, with a total available magnetic volume of more than 7 m$^3$. In this document, we propose and describe the implementation of low-frequency axion haloscope setups suitable for operation inside the BabyIAXO magnet. The RADES proposal has a potential sensitivity to the axion-photon coupling $g_{a\gamma}$ down to values corresponding to the KSVZ model, in the (currently unexplored) mass range between 1 and 2$~\mu$eV, after a total effective exposure of 440 days. This mass range is covered by the use of four differently dimensioned 5-meter-long cavities, equipped with a tuning mechanism based on inner turning plates. A setup like the one proposed would also allow an exploration of the same mass range for hidden photons coupled to photons. An additional complementary apparatus is proposed using LC circuits and exploring the low energy range ($\sim10^{-4}-10^{-1}~\mu$eV). The setup includes a cryostat and cooling system to cool down the BabyIAXO bore down to about 5 K, as well as appropriate low-noise signal amplification and detection chain.

physics.ins-det↗
arXiv2023

Slow positron production and storage for the ASACUSA-Cusp experiment

The ASACUSA Cusp experiment requires the production of dense positron plasmas with a high repetition rate to produce a beam of antihydrogen. In this work, details of the positron production apparatus used for the first observation of the antihydrogen beam, and subsequent measurements are described in detail. This apparatus replaced the previous compact trap design resulting in an improvement in positron accumulation by a factor of ($52\pm3)$

physics.plasm-ph↗
arXiv2023

SDR, EVC, and SDREVC: Limitations and Extensions

Methods for reducing the radius, temperature, and space charge of nonneutral plasma are usually reported for conditions which approximate an ideal Penning Malmberg trap. Here we show that (1) similar methods are still effective under surprisingly adverse circumstances: we perform SDR and SDREVC in a strong magnetic mirror field using only 3 out of 4 rotating wall petals. In addition, we demonstrate (2) an alternative to SDREVC, using e-kick instead of EVC and (3) an upper limit for how much plasma can be cooled to T < 20 K using EVC. This limit depends on the space charge, not on the number of particles or the plasma density.

physics.plasm-ph↗
arXiv2023

Feebly Interacting Particles: FIPs 2022 workshop report

Particle physics today faces the challenge of explaining the mystery of dark matter, the origin of matter over anti-matter in the Universe, the origin of the neutrino masses, the apparent fine-tuning of the electro-weak scale, and many other aspects of fundamental physics. Perhaps the most striking frontier to emerge in the search for answers involves new physics at mass scales comparable to familiar matter, below the GeV-scale, or even radically below, down to sub-eV scales, and with very feeble interaction strength. New theoretical ideas to address dark matter and other fundamental questions predict such feebly interacting particles (FIPs) at these scales, and indeed, existing data provide numerous hints for such possibility. A vibrant experimental program to discover such physics is under way, guided by a systematic theoretical approach firmly grounded on the underlying principles of the Standard Model. This document represents the report of the FIPs 2022 workshop, held at CERN between the 17 and 21 October 2022 and aims to give an overview of these efforts, their motivations, and the decadal goals that animate the community involved in the search for FIPs.

hep-ph↗
arXiv2023

BASE-STEP: A transportable antiproton reservoir for fundamental interaction studies

Currently, the only worldwide source of low-energy antiprotons is the AD/ELENA facility located at CERN. To date, all precision measurements on single antiprotons have been conducted at this facility and provide stringent tests of the fundamental interactions and their symmetries. However, the magnetic field fluctuations from the facility operation limit the precision of upcoming measurements. To overcome this limitation, we have designed the transportable antiproton trap system BASE-STEP to relocate antiprotons to laboratories with a calm magnetic environment. We anticipate that the transportable antiproton trap will facilitate enhanced tests of CPT invariance with antiprotons, and provide new experimental possibilities of using transported antiprotons and other accelerator-produced exotic ions. We present here the technical design of the transportable trap system. This includes the transportable superconducting magnet, the cryogenic inlay consisting of the trap stack and the detection systems, and the differential pumping section to suppress the residual gas flow into the cryogenic trap chamber.

physics.ins-det↗
arXiv2023

Testing CPT Invariance by High-Precision Comparisons of Fundamental Properties of Protons and Antiprotons at BASE

The BASE collaboration at the Antiproton Decelerator facility of CERN compares the fundamental properties of protons and antiprotons using advanced Penning-trap systems. In previous measurement campaigns, we measured the magnetic moments of the proton and the antiproton, reaching (sub-)parts-in-a-billion fractional uncertainty. In the latest campaign, we have compared the proton and antiproton charge-to-mass ratios with a fractional uncertainty of 16 parts in a trillion. In this contribution, we give an overview of the measurement campaign, and detail how its results are used to constrain nine spin-independent coefficients of the Standard-Model Extension in the proton and electron sector.

hep-ex↗