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Symposium on Prospects in the Physics of Discrete Symmetries (DISCRETE)

Pulsed Production of Antihydrogen in AEgIS

Nicola Zurlo, C. Amsler, M. Antonello, Alexander S. Belov, G. Bonomi, Roberto Sennen Brusa, M. Caccia, A. Camper, R. Caravita, F. Castelli, Patrick Cheinet, D. Comparat, Giovanni Consolati, Andrea Demetrio, L. Di Noto, M. Doser, Mattia Fanì, R. Ferragut, J. Fesel, S. Gerber, Marco G. Giammarchi, A. Gligorova, L. T. Glöggler, F. Guatieri, Stefan Haider, Alexander Hinterberger, A. Kellerbauer, Olga Khalidova, D. Krasnický, Vittorio Lagomarsino, C. Malbrunot, S. Mariazzi, V. Matveev, Simon Müller, Giancarlo Nebbia, P. Nédélec, L. Nowak, Markus K. Oberthaler, Emmanuel Oswald, Davide Pagano, Luca Penasa, V. Petráček, Luca Povolo, F. Prelz, M. Prevedelli, B. Rienäcker, Ole Myren Rohne, Alberto Rotondi, H. Sandaker, R. Santoro, G. Testera, Ingmari C. Tietje, V. Toso, T. Wolz, P. Yzombard, Christian Zimmer

Published Jun 13, 2022• 0 citations
Publisher

Abstract

Cold antihydrogen atoms are a powerful tool to probe the validity of fundamental physics laws, and it's clear that colder atoms, generally speaking, allow an increased level of precision. After the first production of cold antihydrogen ($\bar{H}$) in 2002, experimental efforts have progressed continuously (trapping, beam formation, spectroscopy), with competitive results already achieved by adapting to cold antiatoms techniques previously well developed for ordinary atoms. Unfortunately, the number of $\bar{H}$ atoms that can be produced in dedicated experiments is many orders of magnitude smaller than available hydrogen atoms, which are at hand in large amount, so the development of novel techniques that allow the production of $\bar{H}$ with well defined conditions (and possibly control its formation time and energy levels) is essential to improve the sensitivity of the methods applied by the different experiments. We present here the first experimental results concerning the production of $\bar{H}$ in a pulsed mode where the time when 90\% of the atoms are produced is known with an uncertainty of around 250~ns. The pulsed $\bar{H}$ source is generated by the charge-exchange reaction between Rydberg positronium atoms ($Ps$) and trapped antiprotons ($\bar{p}$), cooled and manipulated in an electromagnetic trap: $$ \bar{ p}+Ps^* \rightarrow \bar{H}^* + e^- $$ where Rydberg positronium atoms, in turn, are produced through the implantation of a pulsed positron beam into a mesoporous silica target, and are excited by two subsequent laser pulses, the first to $n=3$, the second to the needed Rydberg level ($n \simeq 17$). The pulsed production allows the control of the antihydrogen temperature, and facilitates the tunability of the Rydberg states, their de-excitation by pulsed lasers and the manipulation through electric field gradients. In fact, the production of pulsed antihydrogen is a major milestone in the AEgIS experiment to perform direct measurements of the validity of the Weak Equivalence Principle for antimatter.

DOI
10.22323/1.405.0079

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Pulsed production of antihydrogen

C. Amsler, M. Antonello, Alexander Belov +53 more

Abstract Antihydrogen atoms with K or sub-K temperature are a powerful tool to precisely probe the validity of fundamental physics laws and the design of highly sensitive experiments needs antihydrogen with controllable and well defined conditions. We present here experimental results on the production of antihydrogen in a pulsed mode in which the time when 90% of the atoms are produced is known with an uncertainty of ~250 ns. The pulsed source is generated by the charge-exchange reaction between Rydberg positronium atoms—produced via the injection of a pulsed positron beam into a nanochanneled Si target, and excited by laser pulses—and antiprotons, trapped, cooled and manipulated in electromagnetic traps. The pulsed production enables the control of the antihydrogen temperature, the tunability of the Rydberg states, their de-excitation by pulsed lasers and the manipulation through electric field gradients. The production of pulsed antihydrogen is a major landmark in the AE $$\bar{g}$$ ḡ IS experiment to perform direct measurements of the validity of the Weak Equivalence Principle for antimatter.

Communications Physics•Feb 8, 2021•76 citations

The Production and Investigation of Cold Antihydrogen Atoms

H. Pittner

This work reports on experiments in which antihydrogen atoms have been produced in cryogenic Penning traps from antiproton and positron plasmas by two different methods and on experiments that have been carried out subsequently in order to investigate the antihydrogen atoms. By the first method antihydrogen atoms have been formed during the process of positron cooling of antiprotons in so called nested Penning traps and detected via a field ionization method. A linear dependence of the number of detected antihydrogen atoms on the number of positrons has been found. A measurement of the state distribution has revealed that the antihydrogen atoms are formed in highly excited states. This suggests along with the high production rate that the antihydrogen atoms are formed by three-body recombination processes and subsequent collisional deexcitations. However current theory cannot yet account for the measured state distribution. Typical radii of the detected antihydrogen atoms lie in the range between 0.4 µm and 0.15 µm. The deepest bound antihydrogen atoms have radii below 0.1 µm. Antihydrogen atoms with that size have chaotic positron orbits so that for the first time antihydrogen atoms have been detected that cannot be described by the GCA-model. The kinetic energy of the weakest bound antihydrogen atoms has been measured to about 200 meV, which corresponds to an antihydrogen velocity of approximately 6200 m/s. A simple model suggests that these atoms are formed from only one deexcitation collision and methods that might lead to a decrease of the antihydrogen velocity are presented. By the second method antihydrogen atoms have been synthesized in charge-exchange processes. Lasers are used to produce a Rydberg cesium beam within the cryogenic Penning trap that collides with trapped positrons so that Rydberg positronium atoms are formed via charge-exchange reactions. Due to their charge neutrality the Rydberg positronium atoms are free to leave the positron trapping region. The Rydberg positronium atoms that collide with nearby stored antiprotons form antihydrogen atoms in charge-exchange reactions. So far, 14 +/- 4 antihydrogen atoms have been detected background-free via a field-ionization method. The antihydrogen atoms produced via the two-step charge-exchange mechanism are expected to have a temperature of 4.2 K, the temperature of the antiprotons from which they are formed. A method is proposed by which the antihydrogen temperature can be determined with an accuracy of better than 1 K from a measurement of the time delay between antihydrogen annihilation events and the laser pulse that initiates the antihydrogen production via the production of Rydberg cesium atoms. First experiments have been carried out during the last days of the 2004 beam time, but the number of detected antihydrogen annihilations has been too low for a determination of the antihydrogen temperature. Trapped antiprotons have been directly exposed to laser light delivered by a Titanium:Sapphire laser in order to investigate if the laser light causes any loss on the trapped antiprotons. Experiments have shown that no extra loss occurs for laser powers of less than 590 mW. This is an important result against the background of the future plan to confine antihydrogen atoms in a combined Penning-Ioffe trap and then to carry out laser spectroscopy on these atoms, since it reveals that laser light does not cause an increase of the pressure in the trapping region to the extend that annihilations with the background gas become noticeable. The ATRAP Collaboration plans to precisely investigate antihydrogen atoms. The ultimate goal is to test the CPT-theorem by a high precision measurement of the 1S-2S transition of antihydrogen and a comparison with the precisely known value of the corresponding transition in hydrogen. This thesis presents the achievement of the first step towards this challenging goal: the production of cold antihydrogen itself.

•Jan 1, 2005•0 citations

Positron Manipulation and Positronium Laser Excitation in AEgIS

S. Mariazzi, R. Caravita, Stefano Aghion +80 more

Production of antihydrogen by using the charge exchange reaction, as proposed by AEgIS (Antimatter Experiment: gravity, Interferometry, Spectroscopy), requires the formation of a dense cloud of positronium atoms excited to Rydberg states. In this work, the recent advances in AEgIS towards this result are described. Namely, the manipulation of positrons to produce bunches containing more than 108 particles and the laser excitation of positronium to Rydberg states, using n=3 as intermediate level, are presented.

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Two-stage Rydberg charge exchange: An efficient method for production of antihydrogen

Eric A. Hessels, Dean M. Homan, M. J. Cavagnero

An efficient method for production of cold antihydrogen $(\mathrm{H}\ifmmode\bar\else\textasciimacron\fi{})$ is proposed. Alkali-metal atoms laser excited to a Rydberg state are charge exchanged with cold trapped positrons, producing Rydberg states of positronium. In a second Rydberg-state charge exchange, the positronium atoms give up their Rydberg positrons to cold trapped antiprotons, producing Rydberg states of $\mathrm{H}\ifmmode\bar\else\textasciimacron\fi{}$. These $\mathrm{H}\ifmmode\bar\else\textasciimacron\fi{}$ atoms soon decay down to the ground state, and, because they are cold, could be trapped in a magnetic trap. The efficiency of the process results from the extremely large cross sections for Rydberg charge exchange. Classical trajectory Monte Carlo calculations indicate an $\mathrm{H}\ifmmode\bar\else\textasciimacron\fi{}$ instantaneous production rate of 10${}^{6}/$s.

Physical Review A•Mar 1, 1998•87 citations

ATRAP antihydrogen experiments

C. H. Storry, M. M. Aggarwal, A. Akbari +37 more

Abstract Antihydrogen (Hbar) was first produced at CERN in 1996. Over the past decade our ATRAP collaboration has made massive progress toward our goal of producing large numbers of cold Hbar atoms that will be captured in a magnetic gradient trap for precise comparison between the atomic spectra of matter and antimatter. The AD at CERN provides bunches of 3 × 107 low energy Pbars every 100 seconds. We capture and cool to 4 K, 0.1% of these in a cryogenic Penning trap. By stacking many bunches we are able to do experiments with 3 × 105 Pbars. ∼100 e+/sec from a 22Na radioactive source are captured and cooled in the trap, with 5 × 106 available experiments.We have developed 2 ways to make Hbar from these cold ingredients, namely 3‐body collisions, and 2‐stage Rydberg charge exchange. In the first case, Pbars are injected into a nested trap containing e+. Hbar is formed when 2 e+ and 1 Pbar collide. In 2‐stage Rydberg charge exchange, laser‐excited caesium (Cs) enters the trap through a small hole. Rydberg positronium is formed when a e+ captures an e‐from a Cs. These atoms exit the trap, some passing through a nearby cloud of cold Pbars. A 2nd charge‐exchange results when a Pbar captures the e+, forming Hbar. We have also developed techniques to measure the excited‐state distribution of the Hbar and measure their velocity. I will present results from these experiments and discuss the next generation of apparatus to be commissioned this year. This new apparatus includes a e+ accumulator built at York University providing many more e+. The new Pbar annihilation detector provides spatial information of annihilations. Windows allow lasers to enter the trap for spectroscopic measurements and for laser cooling of the Hbar. Possibly the most exciting inclusion in this new apparatus is the inclusion of a neutral particle trap which may, for the first time, capture the Hbar and lead to the first atomic spectrum from antimatter. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Physica status solidi. C, Conferences and critical reviews/Physica status solidi. C, Current topics in solid state physics•Jul 11, 2007•3 citations

Laser-Controlled Antihydrogen Production by Two-Stage Charge Exchange

C. H. Storry

Our ATRAP collaboration has now demonstrated a second technique for antihydrogen (H̄) production. Lasers are used for the first time to control the production of H̄ atoms in our cryogenic apparatus at CERN. As suggested in ref. [2] and first reported in ref. [1], lasers excite a thermal beam of cesium (Cs) atoms to a Rydberg state. In a first charge exchange collision one of these laser‐excited Cs atoms (Cs*) and a cold e+ produces positronium (Ps). Our measurements at Harvard([3]) and at CERN([1]) confirm CTMC simulations([2]) that the laser‐selected binding energy in the Cs atom is preserved by the collision and results in Ps with the selected binding energy. A second charge exchange is between one of these Ps atoms and a trapped p̄ . H̄ is produced by this second collision and is expected to again have the same binding energy. One advantage of this technique as discussed in ref. [2] is that the H̄ produced is expected to be extremely cold, at the temperature of the trapped p̄ , allowing for possible confinement of the H̄ atoms in a magnetic trap.

AIP conference proceedings•Jan 1, 2005•0 citations
Cold antihydrogen atoms are a powerful tool to probe the validity of fundamental physics laws, and it's clear that colder atoms, generally speaking, allow an increased level of precision. After the first production of cold antihydrogen (Hˉ\bar{H}Hˉ) in 2002, experimental efforts have progressed continuously (trapping, beam formation, spectroscopy), with competitive results already achieved by adapting to cold antiatoms techniques previously well developed for ordinary atoms. Unfortunately, the number of Hˉ\bar{H}Hˉ atoms that can be produced in dedicated experiments is many orders of magnitude smaller than available hydrogen atoms, which are at hand in large amount, so the development of novel techniques that allow the production of Hˉ\bar{H}Hˉ with well defined conditions (and possibly control its formation time and energy levels) is essential to improve the sensitivity of the methods applied by the different experiments. We present here the first experimental results concerning the production of Hˉ\bar{H}Hˉ in a pulsed mode where the time when 90% of the atoms are produced is known with an uncertainty of around 250~ns. The pulsed Hˉ\bar{H}Hˉ source is generated by the charge-exchange reaction between Rydberg positronium atoms (PsPsPs) and trapped antiprotons (pˉ\bar{p}pˉ​), cooled and manipulated in an electromagnetic trap: pˉ+Ps∗→Hˉ∗+e−\bar{ p}+Ps^* \rightarrow \bar{H}^* + e^-pˉ​+Ps∗→Hˉ∗+e− where Rydberg positronium atoms, in turn, are produced through the implantation of a pulsed positron beam into a mesoporous silica target, and are excited by two subsequent laser pulses, the first to n=3n=3n=3, the second to the needed Rydberg level (n≃17n \simeq 17n≃17). The pulsed production allows the control of the antihydrogen temperature, and facilitates the tunability of the Rydberg states, their de-excitation by pulsed lasers and the manipulation through electric field gradients. In fact, the production of pulsed antihydrogen is a major milestone in the AEgIS experiment to perform direct measurements of the validity of the Weak Equivalence Principle for antimatter.
Abstract Antihydrogen atoms with K or sub-K temperature are a powerful tool to precisely probe the validity of fundamental physics laws and the design of highly sensitive experiments needs antihydrogen with controllable and well defined conditions. We present here experimental results on the production of antihydrogen in a pulsed mode in which the time when 90% of the atoms are produced is known with an uncertainty of ~250 ns. The pulsed source is generated by the charge-exchange reaction between Rydberg positronium atoms—produced via the injection of a pulsed positron beam into a nanochanneled Si target, and excited by laser pulses—and antiprotons, trapped, cooled and manipulated in electromagnetic traps. The pulsed production enables the control of the antihydrogen temperature, the tunability of the Rydberg states, their de-excitation by pulsed lasers and the manipulation through electric field gradients. The production of pulsed antihydrogen is a major landmark in the AE gˉ\bar{g}gˉ​ ḡ IS experiment to perform direct measurements of the validity of the Weak Equivalence Principle for antimatter.
This work reports on experiments in which antihydrogen atoms have been produced in cryogenic Penning traps from antiproton and positron plasmas by two different methods and on experiments that have been carried out subsequently in order to investigate the antihydrogen atoms. By the first method antihydrogen atoms have been formed during the process of positron cooling of antiprotons in so called nested Penning traps and detected via a field ionization method. A linear dependence of the number of detected antihydrogen atoms on the number of positrons has been found. A measurement of the state distribution has revealed that the antihydrogen atoms are formed in highly excited states. This suggests along with the high production rate that the antihydrogen atoms are formed by three-body recombination processes and subsequent collisional deexcitations. However current theory cannot yet account for the measured state distribution. Typical radii of the detected antihydrogen atoms lie in the range between 0.4 µm and 0.15 µm. The deepest bound antihydrogen atoms have radii below 0.1 µm. Antihydrogen atoms with that size have chaotic positron orbits so that for the first time antihydrogen atoms have been detected that cannot be described by the GCA-model. The kinetic energy of the weakest bound antihydrogen atoms has been measured to about 200 meV, which corresponds to an antihydrogen velocity of approximately 6200 m/s. A simple model suggests that these atoms are formed from only one deexcitation collision and methods that might lead to a decrease of the antihydrogen velocity are presented. By the second method antihydrogen atoms have been synthesized in charge-exchange processes. Lasers are used to produce a Rydberg cesium beam within the cryogenic Penning trap that collides with trapped positrons so that Rydberg positronium atoms are formed via charge-exchange reactions. Due to their charge neutrality the Rydberg positronium atoms are free to leave the positron trapping region. The Rydberg positronium atoms that collide with nearby stored antiprotons form antihydrogen atoms in charge-exchange reactions. So far, 14 +/- 4 antihydrogen atoms have been detected background-free via a field-ionization method. The antihydrogen atoms produced via the two-step charge-exchange mechanism are expected to have a temperature of 4.2 K, the temperature of the antiprotons from which they are formed. A method is proposed by which the antihydrogen temperature can be determined with an accuracy of better than 1 K from a measurement of the time delay between antihydrogen annihilation events and the laser pulse that initiates the antihydrogen production via the production of Rydberg cesium atoms. First experiments have been carried out during the last days of the 2004 beam time, but the number of detected antihydrogen annihilations has been too low for a determination of the antihydrogen temperature. Trapped antiprotons have been directly exposed to laser light delivered by a Titanium:Sapphire laser in order to investigate if the laser light causes any loss on the trapped antiprotons. Experiments have shown that no extra loss occurs for laser powers of less than 590 mW. This is an important result against the background of the future plan to confine antihydrogen atoms in a combined Penning-Ioffe trap and then to carry out laser spectroscopy on these atoms, since it reveals that laser light does not cause an increase of the pressure in the trapping region to the extend that annihilations with the background gas become noticeable. The ATRAP Collaboration plans to precisely investigate antihydrogen atoms. The ultimate goal is to test the CPT-theorem by a high precision measurement of the 1S-2S transition of antihydrogen and a comparison with the precisely known value of the corresponding transition in hydrogen. This thesis presents the achievement of the first step towards this challenging goal: the production of cold antihydrogen itself.
Production of antihydrogen by using the charge exchange reaction, as proposed by AEgIS (Antimatter Experiment: gravity, Interferometry, Spectroscopy), requires the formation of a dense cloud of positronium atoms excited to Rydberg states. In this work, the recent advances in AEgIS towards this result are described. Namely, the manipulation of positrons to produce bunches containing more than 108 particles and the laser excitation of positronium to Rydberg states, using n=3 as intermediate level, are presented.
An efficient method for production of cold antihydrogen $(\mathrm{H}\ifmmode\bar\else\textasciimacron\fi{})$ is proposed. Alkali-metal atoms laser excited to a Rydberg state are charge exchanged with cold trapped positrons, producing Rydberg states of positronium. In a second Rydberg-state charge exchange, the positronium atoms give up their Rydberg positrons to cold trapped antiprotons, producing Rydberg states of $\mathrm{H}\ifmmode\bar\else\textasciimacron\fi{}$. These $\mathrm{H}\ifmmode\bar\else\textasciimacron\fi{}$ atoms soon decay down to the ground state, and, because they are cold, could be trapped in a magnetic trap. The efficiency of the process results from the extremely large cross sections for Rydberg charge exchange. Classical trajectory Monte Carlo calculations indicate an $\mathrm{H}\ifmmode\bar\else\textasciimacron\fi{}$ instantaneous production rate of 106/{}^{6}/6/s.
Abstract Antihydrogen (Hbar) was first produced at CERN in 1996. Over the past decade our ATRAP collaboration has made massive progress toward our goal of producing large numbers of cold Hbar atoms that will be captured in a magnetic gradient trap for precise comparison between the atomic spectra of matter and antimatter. The AD at CERN provides bunches of 3 × 107 low energy Pbars every 100 seconds. We capture and cool to 4 K, 0.1% of these in a cryogenic Penning trap. By stacking many bunches we are able to do experiments with 3 × 105 Pbars. ∼100 e+/sec from a 22Na radioactive source are captured and cooled in the trap, with 5 × 106 available experiments.We have developed 2 ways to make Hbar from these cold ingredients, namely 3‐body collisions, and 2‐stage Rydberg charge exchange. In the first case, Pbars are injected into a nested trap containing e+. Hbar is formed when 2 e+ and 1 Pbar collide. In 2‐stage Rydberg charge exchange, laser‐excited caesium (Cs) enters the trap through a small hole. Rydberg positronium is formed when a e+ captures an e‐from a Cs. These atoms exit the trap, some passing through a nearby cloud of cold Pbars. A 2nd charge‐exchange results when a Pbar captures the e+, forming Hbar. We have also developed techniques to measure the excited‐state distribution of the Hbar and measure their velocity. I will present results from these experiments and discuss the next generation of apparatus to be commissioned this year. This new apparatus includes a e+ accumulator built at York University providing many more e+. The new Pbar annihilation detector provides spatial information of annihilations. Windows allow lasers to enter the trap for spectroscopic measurements and for laser cooling of the Hbar. Possibly the most exciting inclusion in this new apparatus is the inclusion of a neutral particle trap which may, for the first time, capture the Hbar and lead to the first atomic spectrum from antimatter. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Our ATRAP collaboration has now demonstrated a second technique for antihydrogen (H̄) production. Lasers are used for the first time to control the production of H̄ atoms in our cryogenic apparatus at CERN. As suggested in ref. [2] and first reported in ref. [1], lasers excite a thermal beam of cesium (Cs) atoms to a Rydberg state. In a first charge exchange collision one of these laser‐excited Cs atoms (Cs*) and a cold e+ produces positronium (Ps). Our measurements at Harvard([3]) and at CERN([1]) confirm CTMC simulations([2]) that the laser‐selected binding energy in the Cs atom is preserved by the collision and results in Ps with the selected binding energy. A second charge exchange is between one of these Ps atoms and a trapped p̄ . H̄ is produced by this second collision and is expected to again have the same binding energy. One advantage of this technique as discussed in ref. [2] is that the H̄ produced is expected to be extremely cold, at the temperature of the trapped p̄ , allowing for possible confinement of the H̄ atoms in a magnetic trap.