Viktor A. Matveev

Exploring the WEP with a pulsed cold beam of antihydrogen

The AEGIS experiment, currently being set up at the Antiproton Decelerator at CERN, has the objective of studying the free fall of antimatter in the Earth?s gravitational field by means of a pulsed cold atomic beam of antihydrogen atoms. Both duration of free fall and vertical displacement of the horizontally emitted atoms will be measured, allowing a first test of the WEP with antimatter.

The search for new physics at the Large Hadron Collider

We review the search for new physics to be performed at the Large Hadron Collider(LHC). Namely, we review the expectations for the Higgs boson, supersymmetry and exotica detection at LHC. We also describe the main parameters of the CMS and ATLAS detectors.

Surface acoustic wave propagation in graphene film

Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals.

Detection of low energy antiproton annihilations in a segmented silicon detector

The goal of the AEIS experiment at the Antiproton Decelerator (AD) at CERN, is to measure directly the Earths gravitational acceleration on antimatter by measuring the free fall of a pulsed, cold antihydrogen beam. The final position of the falling antihydrogen will be detected by a position sensitive detector. This detector will consist of an active silicon part, where the annihilations take place, followed by an emulsion part. Together, they allow to achieve 1% precision on the measurement of with about 600 reconstructed and time tagged annihilations. We present here the prospects for the development of the AEIS silicon position sentive detector and the results from the first beam tests on a monolithic silicon pixel sensor, along with a comparison to Monte Carlo simulations.

Computer and experimental modeling of target performance in particle beams and fusion or fission environments

Abstract Computer simulation of target performance in particle beams for fusion or fission irradiation is considered. Such simulation is realized by means of a set of Russian computer codes SHIELD, RADDAM, etc. The set can permit the full modeling of irradiation conditions of any possible installation in terms of such parameters as: • point defect generation by irradiation; • rate of accumulation of He atoms produced in nuclear reactions; • rate of accumulation of H atoms; • spectra of primary knock-on atoms in collision displacements and • temperature of the sample under irradiation. nThe evidence of possibilities for the modeling of different irradiation conditions (for example, fusion) at the RADEX facility of the INR RAS is presented. RADEX is the irradiation channel located inside the proton target of the beam stop of the INR RAS linear proton accelerator with energy up to 600xa0MeV. The proton target is situated in the bottom part of targets cylindrical container and is formed by tungsten plates, which are covered with a titanium coating and cooled by light water. The RADEX irradiation channel is located asymmetrically relatively to the vertical axis of the cylinder. The proton beam enters the irradiation channel through the aluminum alloy first wall, having passed through some of the tungsten plates, all of thickness ∼4xa0cm. Besides the proton flux, the irradiation channel is subjected to a neutron flux of a spallation spectrum. The location of the irradiation channel of the RADEX facility can be changed by rotation of the proton target about the vertical axis. There are six possible different positions of the irradiation channel, with angles of 0°, 60°, 120°, 180°, 240°, 300°, 360° relative to the proton beam direction. In the position 0, the proton and neutron fluxes are maximal in the irradiation channel, and the spectrum of primary knock-on atoms in the irradiated sample will be very hard due to the predominance of high-energy protons in the irradiation field. The spectrum can be significantly softened by means of rotation of the proton target around the vertical axis. Spectrum softening will also occur when the sample moves upwards in the irradiation channel away from the proton beam line. This gives us the possibility to change all five irradiation parameters pointed out above to model almost any possible irradiation installation. The example of computer modeling for the irradiation conditions of the ITER fusion device at the RADEX facility is presented.

Development of nuclear emulsions operating in vacuum for the AEgIS experiment

For the first time the AEgIS (Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy) experiment will measure the Earths local gravitational acceleration g on antimatter through the evaluation of the vertical displacement of an antihydrogen horizontal beam. This will be a model independent test of the Weak Equivalence Principle at the base of the general relativity. The initial goal of a g measurement with a relative uncertainty of 1% will be achieved with less than 1000 detected antihydrogens, provided that their vertical position could be determined with a precision of a few micrometers. An emulsion based detector is very suitable for this purpose featuring an intrinsic sub-micrometric spatial resolution. Nevertheless, the AEgIS experiment requires unprecedented operational conditions for this type of detector, namely vacuum environment and very low temperature. An intense R&D activity is presently going on to optimize the detector for the AEgIS experimental requirements with rather encouraging results.

Comparison of Planar and 3D Silicon Pixel Sensors Used for Detection of Low Energy Antiprotons

The principal aim of the AEgIS experiment at CERN is to measure the acceleration of antihydrogen due to Earths gravitational field. This would be a test of the Weak Equivalence Principle, which states that all bodies fall with the same acceleration independently of their mass and composition. The effect of Earths gravitational field on antimatter will be determined by measuring the deflection of the path of the antihydrogen from a straight line. The position of the antihydrogen will be found by detecting its annihilation on the surface of a silicon detector. The gravitational measurement in AEgIS will be performed with a gravity module, which includes the silicon detector, an emulsion detector and a scintillating fibre time-of-flight detector. As the experiment attempts to determine the gravitational acceleration with a precision of 1%, a position resolution better than 10 μm is required. Here we present the results of a study of antiproton annihilations in a 3D silicon pixel sensor and compare the results with a previous study using a monolithic active pixel sensor. This work is part of a larger study on different silicon sensor technologies needed for the development of a silicon position detector for the AEgIS experiment. The 3D detector together with its readout electronics have been originally designed for the ATLAS detector at the LHC. The direct annihilation of low energy antiprotons ( ~ 100 keV) takes place in the first few μm of the silicon sensor and we show that the charged products of the annihilation can be detected with the same sensor. The present study also aims to understand the signature of an antiproton annihilation event in segmented silicon detectors and compares it with a GEANT4 simulation model. These results will be used to determine the geometrical and process parameters to be adopted by the silicon annihilation detector to be installed in AEgIS.

AEgIS at ELENA: outlook for physics with a pulsed cold antihydrogen beam.

The efficient production of cold antihydrogen atoms in particle traps at CERN’s Antiproton Decelerator has opened up the possibility of performing direct measurements of the Earth’s gravitational acceleration on purely antimatter bodies. The goal of the AEgIS collaboration is to measure the value of g for antimatter using a pulsed source of cold antihydrogen and a Moiré deflectometer/Talbot–Lau interferometer. The same antihydrogen beam is also very well suited to measuring precisely the ground-state hyperfine splitting of the anti-atom. The antihydrogen formation mechanism chosen by AEgIS is resonant charge exchange between cold antiprotons and Rydberg positronium. A series of technical developments regarding positrons and positronium (Ps formation in a dedicated room-temperature target, spectroscopy of the n=1–3 and n=3–15 transitions in Ps, Ps formation in a target at 10u2009K inside the 1u2009T magnetic field of the experiment) as well as antiprotons (high-efficiency trapping of , radial compression to sub-millimetre radii of mixed plasmas in 1u2009T field, high-efficiency transfer of to the antihydrogen production trap using an in-flight launch and recapture procedure) were successfully implemented. Two further critical steps that are germane mainly to charge exchange formation of antihydrogen—cooling of antiprotons and formation of a beam of antihydrogen—are being addressed in parallel. The coming of ELENA will allow, in the very near future, the number of trappable antiprotons to be increased by more than a factor of 50. For the antihydrogen production scheme chosen by AEgIS, this will be reflected in a corresponding increase of produced antihydrogen atoms, leading to a significant reduction of measurement times and providing a path towards high-precision measurements. This article is part of the Theo Murphy meeting issue ‘Antiproton physics in the ELENA era’.

submitter : Positron Manipulation and Positronium Laser Excitation in AEgIS

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.

Testing the Weak Equivalence Principle with an antimatter beam at CERN

The goal of the AEgIS experiment is to measure the gravitational acceleration of antihydrogen – the simplest atom consisting entirely of antimatter – with the ultimate precision of 1%. We plan to verify the Weak Equivalence Principle (WEP), one of the fundamental laws of nature, with an antimatter beam. The experiment consists of a positron accumulator, an antiproton trap and a Stark accelerator in a solenoidal magnetic field to form and accelerate a pulsed beam of antihydrogen atoms towards a free-fall detector. The antihydrogen beam passes through a moir e deflectometer to measure the vertical displacement due to the gravitational force. A position and time sensitive hybrid detector registers the annihilation points of the antihydrogen atoms and their time-of-flight. The detection principle has been successfully tested with antiprotons and a miniature moir e deflectometer coupled to a nuclear emulsion detector.