Status Report: A Detector for Measuring the Ground State Hyperfine Splitting of Antihydrogen

The ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration at the Antiproton Decelerator at CERN aims to measure the ground state hyperfine structure of antihydrogen. A Rabi-like spectrometer line has been built for this purpose. A detector for counting antihydrogen is located at the end of the beam line. This contribution will focus on the tracking detector, whose challenging task it is to discriminate between background events and antiproton annihilations originating from antihydrogen atoms which are produced only in small amounts.Comment: Presented at the Seventh Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, June 20-24, 201

An atomic hydrogen beam to test ASACUSA's apparatus for antihydrogen spectroscopy

The ASACUSA collaboration aims to measure the ground state hyperfine splitting (GS-HFS) of antihydrogen, the antimatter pendant to atomic hydrogen. Comparisons of the corresponding transitions in those two systems will provide sensitive tests of the CPT symmetry, the combination of the three discrete symmetries charge conjugation, parity, and time reversal. For offline tests of the GS-HFS spectroscopy apparatus we constructed a source of cold polarised atomic hydrogen. In these proceedings we report the successful observation of the hyperfine structure transitions of atomic hydrogen with our apparatus in the earth's magnetic field.Comment: 8 pages, 4 figures, proceedings for conference EXA 2014 (Exotic Atoms - Vienna

Machine Learning for Antihydrogen Detection in ASACUSA

Alle fundamentalen Wechselwirkungen des Standard Modells der Teilchenphysik sind invariant unter der kombinierten Transformation von Ladungskonjugation, Parität und Zeitumkehr (CPT). Es folgt, dass die fundamentalen Eigenschaften von Teilchen und Antiteilchen betragsmäßig gleich sind. Infolgedessen sollten auch die Spektren von Atomen und deren Antiatomen gleich sein. Das einfachste stabile Atom, das gänzlich aus Antimaterie besteht, ist Antiwasserstoff. Sein Materiegegenstück, Wasserstoff, ist eines des meist untersuchten atomaren Systeme. Ein Vergleich der Spektren von Wasserstoff und Antiwasserstoff liefert daher einen der sensitivsten Tests der CPT Symmetrie. Die ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) Kollaboration hat das Ziel die Übergangsfrequenz der Hyperfeinstruktur von Antiwasserstoff im Grundzustand in einem Rabi-ähnlichen Strahlexperiment zu messen und somit die CPT Symmetry mit höchster Präzision zu testen. Antiprotonen und Positronen werden in einer Teilchenfalle zu Antiwasserstoff kombiniert. Die neutralen Antiatome verlassen die Falle als polarisierter Strahl and treten in den Spektroskopieapparat ein, der aus einer Mikrowellenkavität und einem Sextupolmagneten besteht. Am Ende des Aufbaus annihilieren die Antiatome in einem Detektor, der im Fokus dieser Arbeit steht. Die Aufgabe des Detektors ist, die ankommenden Antiwasserstoffatome zu zählen und somit Signal von Hintergrund zu unterscheiden. Letzterer ist von Höhenstrahlung dominiert. Der Detektor besteht aus einem positionsempfindlichen Kalorimeter im Zentrum eines zweilagigen Hodoskops zum Nachweis der Sekundärteilchen der Annihilation. Im Zuge dieser Arbeit sind mehrere Hardware- und Softwareverbesserungen der Diskriminierung von Signal und Hintergrund durchgeführt worden. Insbesondere ist eine effiziente, auf experimentellen Daten basierende Machine Learning Analyse zur Identifizierung von seltenen Antiwasserstoffannihilationen und Hintergrundereignissen entwickelt worden. Der Algorithmus wurde mit Antiprotonannihilationen, die während dedizierten Extraktionen zum Detektor aufgenommen wurden, und Hintergrundereignissen, die während Perioden ohne Antiprotonen in den Fallen gemessen wurden, trainiert. Das wichtigste Resultat ist die erste Messung der Hauptquantenzahlverteilung der produzierten Antiwasserstoffatome im feldfreien Raum. Das Ergebnis deutet darauf hin, dass ein Teil der Antiwasserstoffatome in niedrigen Energiezuständen produziert wird. Jedoch ist die Rate noch nicht ausreichend genug, um Spektroskopie zu betreiben, und das Ziel einer Messung des Hyperfeinübergangs mit ppm Genauigkeit noch nicht zum Greifen nah. Des Weiteren wurde die Positionsauflösung des Hodoskops kürzlich durch ein Upgrade bestehend aus szintillierenden Fasern verbessert. Ein drei-dimensionaler Trackingalgorithmus wurde im Zuge dieser Arbeit entwickelt, mit dem Ziel, die Vertices von Annihilationen zu bestimmen. Information über die Position der Annihilationen ist hilfreich um Antiwasserstoffereignisse, die auf dem zentralen Detektor annihilieren, von jeden zu unterschieden, die upstream vom Detektor am Strahlrohr auftreffen.All fundamental interactions described within the Standard Model of particle physics are invariant under the combined transformation of charge conjugation, parity and time reversal (CPT). As a consequence, the fundamental properties of particles and their antiparticles are identical (mass, lifetime) or sign-opposite (charge, magnetic moment). Thus, atoms and antiatoms should also have the same characteristic spectra. The simplest stable atom composed solely of antimatter is antihydrogen and its matter counterpart hydrogen is one of the most precisely studied atomic systems. Therefore a comparison of the spectra of hydrogen and antihydrogen allows one of the most stringent tests of CPT. In order to test CPT symmetry with high precision, the \acs{ASACUSA} (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration aims to measure the ground state hyperfine splitting of antihydrogen in a Rabi-type beam experiment. Antiprotons and positrons form antihydrogen in a mixing trap. The antiatoms leave the trap as a polarised beam and reach the spectroscopy beamline consisting of a microwave cavity for inducing hyperfine transitions and a state-analysing sextupole magnet. At the end of the apparatus, the antiatoms annihilate in a detector which is the focus of this thesis. Its purpose is to count the arriving antihydrogen atoms and to distinguish these signal events from the cosmic-ray dominated background. The detector is composed of a position sensitive central calorimeter which records the annihilation and a surrounding two-layered hodoscope for tracking annihilation products (pions). In the course of this thesis, improvements of the signal and background discrimination on the hardware and the software level have been carried out. Most notably, a data-driven machine learning analysis has been developed to distinguish rare antihydrogen annihilations from background events with high efficiency. The algorithm is trained and evaluated with antiproton events recorded during dedicated direct antiproton extractions to the detector and background events gathered during periods without antiprotons in the traps. The most important result is the first measurement of the distribution of principle quantum numbers of the produced antihydrogen atoms in a magnetic field-free region. The outcome indicates that a small fraction of antihydrogen atoms in low-lying states are produced. The rate however is not yet sufficient for spectroscopy, and the goal of a relative precision for the hyperfine frequency at the ppm level is not yet within reach. Recently, the hodoscope's position resolution has been improved by an upgrade consisting of scintillating fibres. During this thesis, a three-dimensional tracking algorithm has been developed in order to determine the vertices of annihilation events. Information on the position of the annihilation helps to distinguish antihydrogen events annihilating on the central detector from possible annihilations upstream

Machine learning for antihydrogen detection in ASACUSA

Alle fundamentalen Wechselwirkungen des Standard Modells der Teilchenphysik sind invariant unter der kombinierten Transformation von Ladungskonjugation, Parität und Zeitumkehr (CPT). Es folgt, dass die fundamentalen Eigenschaften von Teilchen und Antiteilchen betragsmäßig gleich sind. Infolgedessen sollten auch die Spektren von Atomen und deren Antiatomen gleich sein. Das einfachste stabile Atom, das gänzlich aus Antimaterie besteht, ist Antiwasserstoff. Sein Materiegegenstück, Wasserstoff, ist eines des meist untersuchten atomaren Systeme. Ein Vergleich der Spektren von Wasserstoff und Antiwasserstoff liefert daher einen der sensitivsten Tests der CPT Symmetrie. Die ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) Kollaboration hat das Ziel die Übergangsfrequenz der Hyperfeinstruktur von Antiwasserstoff im Grundzustand in einem Rabi-ähnlichen Strahlexperiment zu messen und somit die CPT Symmetry mit höchster Präzision zu testen. Antiprotonen und Positronen werden in einer Teilchenfalle zu Antiwasserstoff kombiniert. Die neutralen Antiatome verlassen die Falle als polarisierter Strahl and treten in den Spektroskopieapparat ein, der aus einer Mikrowellenkavität und einem Sextupolmagneten besteht. Am Ende des Aufbaus annihilieren die Antiatome in einem Detektor, der im Fokus dieser Arbeit steht. Die Aufgabe des Detektors ist, die ankommenden Antiwasserstoffatome zu zählen und somit Signal von Hintergrund zu unterscheiden. Letzterer ist von Höhenstrahlung dominiert. Der Detektor besteht aus einem positionsempfindlichen Kalorimeter im Zentrum eines zweilagigen Hodoskops zum Nachweis der Sekundärteilchen der Annihilation. Im Zuge dieser Arbeit sind mehrere Hardware- und Softwareverbesserungen der Diskriminierung von Signal und Hintergrund durchgeführt worden. Insbesondere ist eine effiziente, auf experimentellen Daten basierende Machine Learning Analyse zur Identifizierung von seltenen Antiwasserstoffannihilationen und Hintergrundereignissen entwickelt worden. Der Algorithmus wurde mit Antiprotonannihilationen, die während dedizierten Extraktionen zum Detektor aufgenommen wurden, und Hintergrundereignissen, die während Perioden ohne Antiprotonen in den Fallen gemessen wurden, trainiert. Das wichtigste Resultat ist die erste Messung der Hauptquantenzahlverteilung der produzierten Antiwasserstoffatome im feldfreien Raum. Das Ergebnis deutet darauf hin, dass ein Teil der Antiwasserstoffatome in niedrigen Energiezuständen produziert wird. Jedoch ist die Rate noch nicht ausreichend genug, um Spektroskopie zu betreiben, und das Ziel einer Messung des Hyperfeinübergangs mit ppm Genauigkeit noch nicht zum Greifen nah. Des Weiteren wurde die Positionsauflösung des Hodoskops kürzlich durch ein Upgrade bestehend aus szintillierenden Fasern verbessert. Ein drei-dimensionaler Trackingalgorithmus wurde im Zuge dieser Arbeit entwickelt, mit dem Ziel, die Vertices von Annihilationen zu bestimmen. Information über die Position der Annihilationen ist hilfreich um Antiwasserstoffereignisse, die auf dem zentralen Detektor annihilieren, von jeden zu unterschieden, die upstream vom Detektor am Strahlrohr auftreffen.All fundamental interactions described within the Standard Model of particle physics are invariant under the combined transformation of charge conjugation, parity and time reversal (CPT). As a consequence, the fundamental properties of particles and their antiparticles are identical (mass, lifetime) or sign-opposite (charge, magnetic moment). Thus, atoms and antiatoms should also have the same characteristic spectra. The simplest stable atom composed solely of antimatter is antihydrogen and its matter counterpart hydrogen is one of the most precisely studied atomic systems. Therefore a comparison of the spectra of hydrogen and antihydrogen allows one of the most stringent tests of CPT. In order to test CPT symmetry with high precision, the \acs{ASACUSA} (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration aims to measure the ground state hyperfine splitting of antihydrogen in a Rabi-type beam experiment. Antiprotons and positrons form antihydrogen in a mixing trap. The antiatoms leave the trap as a polarised beam and reach the spectroscopy beamline consisting of a microwave cavity for inducing hyperfine transitions and a state-analysing sextupole magnet. At the end of the apparatus, the antiatoms annihilate in a detector which is the focus of this thesis. Its purpose is to count the arriving antihydrogen atoms and to distinguish these signal events from the cosmic-ray dominated background. The detector is composed of a position sensitive central calorimeter which records the annihilation and a surrounding two-layered hodoscope for tracking annihilation products (pions). In the course of this thesis, improvements of the signal and background discrimination on the hardware and the software level have been carried out. Most notably, a data-driven machine learning analysis has been developed to distinguish rare antihydrogen annihilations from background events with high efficiency. The algorithm is trained and evaluated with antiproton events recorded during dedicated direct antiproton extractions to the detector and background events gathered during periods without antiprotons in the traps. The most important result is the first measurement of the distribution of principle quantum numbers of the produced antihydrogen atoms in a magnetic field-free region. The outcome indicates that a small fraction of antihydrogen atoms in low-lying states are produced. The rate however is not yet sufficient for spectroscopy, and the goal of a relative precision for the hyperfine frequency at the ppm level is not yet within reach. Recently, the hodoscope's position resolution has been improved by an upgrade consisting of scintillating fibres. During this thesis, a three-dimensional tracking algorithm has been developed in order to determine the vertices of annihilation events. Information on the position of the annihilation helps to distinguish antihydrogen events annihilating on the central detector from possible annihilations upstream

Measurement of the principal quantum number distribution in a beam of antihydrogen atoms

The ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration plans to measure the ground-state hyperfine splitting of antihydrogen in a beam at the CERN Antiproton Decelerator with initial relative precision of 10−6 or better, to test the fundamental CPT (combination of charge conjugation, parity transformation and time reversal) symmetry between matter and antimatter. This challenging goal requires a polarised antihydrogen beam with a sufficient number of antihydrogen atoms in the ground state. The first measurement of the quantum state distribution of antihydrogen atoms in a low magnetic field environment of a few mT is described. Furthermore, the data-driven machine learning analysis to identify antihydrogen events is discussed.ISSN:1434-6060ISSN:1434-607

The HL-LHC Beam Gas Vertex Monitor - Simulations for Design Optimisation and Performance Study

The Beam Gas Vertex (BGV) instrument is a non-invasive transverse beam profile monitor being designed as part of the High Luminosity Upgrade of the LHC (HL-LHC) at CERN. Its aim is to continuously measure bunch-by-bunch beam profiles, independent of beam intensity, throughout the LHC cycle. The primary components of the BGV monitor are a gas target and a forward tracking detector. Secondary particles emerging from inelastic beam-gas interactions are detected by the tracker. The beam profile is then inferred from the spatial distribution of reconstructed vertices of said interactions. Based on insights and conclusions acquired by a demonstrator device that was operated in the LHC during Run 2, a new design is being developed to fulfill the HL-LHC specifications. This contribution describes the status of the simulation studies being performed to evaluate the impact of design parameters on the instrument’s performance and identify gas target and tracker requirements

New Gas Target Design for the HL-LHC Beam Gas Vertex Profile Monitor

The Beam Gas Vertex (BGV) instrument is a novel non-invasive transverse beam profile monitor under development for the High Luminosity Upgrade of the Large Hadron Collider (HL-LHC). Its principle is based on the reconstruction of the tracks and vertices issued from beam-gas inelastic hadronic interactions. The instrument is currently in the design phase, and will consist of a gas target, a forward tracking detector installed outside the beam vacuum chamber and computing resources dedicated to event reconstruction. The transverse beam profile image will then be inferred from the spatial distribution of the reconstructed vertices. With this method, the BGV should be able to provide bunch-by-bunch measurement of the beam size, together with a beam profile image throughout the whole LHC energy cycle, and independently of the beam intensity. This contribution describes the design of the gas target system and of the gas tank of the future instrument

The HL-LHC Beam Gas Vertex Monitor - Performance and Design Optimisation Using Simulations

The Beam Gas Vertex (BGV) instrument is a novel non-invasive beam profile monitor and part of the High Luminosity Upgrade of the Large Hadron Collider (LHC) at CERN. Its aim is to continuously measure emittance and transverse beam profile throughout the whole LHC cycle, which has not yet been achieved by any other single device in the machine. The BGV consists of a gas target and a forward tracking detector to reconstruct tracks and vertices resulting from beam-gas interactions. The beam profile is inferred from the spatial distribution of the vertices, making it essential to achieve a very good vertex resolution. Extensive simulation studies are being performed to provide a basis for the design of the future BGV. The goal of the study is to ascertain the requirements for the tracking detector and the gas target within the boundary conditions provided by the feasibility of integrating it into the LHC, budget and timescale. This contribution will focus on the simulations of the forward tracking detector. Based on cutting-edge track and vertex reconstruction methods, key parameter scans and their influence on the vertex resolution will be discussed

Annihilation detector for an in-beam spectroscopy apparatus to measure the ground state hyperfine splitting of antihydrogen

The matter-antimatter asymmetry observed in the universe today still lacks a quantitative explanation. One possible mechanism that could contribute to the observed imbalance is a violation of the combined Charge-, Parity- and Time symmetries (CPT). A test of CPT symmetry using anti-atoms is being carried out by the ASACUSA-CUSP collaboration at the CERN Antiproton Decelerator using a low temperature beam of antihydrogen—the most simple atomic system built only of antiparticles. While hydrogen is the most abundant element in the universe, antihydrogen is produced in very small quantities in a laboratory framework. A detector for in-beam measurements of the ground state hyperfine structure of antihydrogen has to be able to detect very low signal rates within high background. To fulfil this challenging task, a two layer barrel hodoscope detector was developed. It is built of plastic scintillators with double sided readout via Silicon Photomultipliers (SiPMs). The SiPM readout is done using novel, compact and cost efficient electronics that incorporate power supply, amplifier and discriminator on a single board. This contribution will evaluate the performance of the new hodoscope detector