I urval från Stockholms universitets publikationsdatabas

• Proton and Neutron Induced Single Event Upsets in FPGAs for the PANDA Experiment

  Markus Preston (et al.). IEEE Transactions on Nuclear Science

  Artikel

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• Feasibility studies for the measurement of time-like proton electromagnetic form factors from ̄pp→μ+μ−at PANDA at FAIR

  2021. G. Barucca (et al.). European Physical Journal A 57 (1)

  Artikel

  This paper reports on Monte Carlo simulation results for future measurements of the moduli of time-like proton electromagnetic form factors, vertical bar G(E)vertical bar and vertical bar G(M)vertical bar, using the (p) over barp -> mu(+)mu(-) reaction at PANDA (FAIR). The electromagnetic form factors are fundamental quantities parameterizing the electric and magnetic structure of hadrons. This work estimates the statistical and total accuracy with which the form factors can be measured at PANDA, using an analysis of simulated data within the PandaRoot software framework. The most crucial background channel is (p) over barp -> pi(+)pi(-), due to the very similar behavior of muons and pions in the detector. The suppression factors are evaluated for this and all other relevant background channels at different values of antiproton beam momentum. The signal/background separation is based on a multivariate analysis, using the Boosted Decision Trees method. An expected background subtraction is included in this study, based on realistic angular distributions of the background contribution. Systematic uncertainties are considered and the relative total uncertainties of the form factor measurements are presented.

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• FPGA-based algorithms for feature extraction in the PANDA shashlyk calorimeter

  2020. Markus Preston, Pawel Marciniewski, Per-Erik Tegnér. Journal of Instrumentation 15 (8)

  Artikel

  PANDA is one of the four experimental pillars of the upcoming FAIR facility in Darmstadt, Germany. In PANDA, an antiproton beam with an energy between 1.5 and 15 GeV/c will interact in a hydrogen or nuclear target, allowing for studies of various aspects of non-perturbative QCD . Motivated by the high interaction rates and the diverse physics goals of the experiment, a triggerless readout approach will be employed. In this approach, each detector subsystem will be equipped with intelligent front-end electronics that independently identify signals of interest in real time. In order to detect the most forward-directed photons, electrons and positrons in PANDA, a shashlyk-type calorimeter is being constructed. This detector consists of 1512 individual cells of interleaved plastic scintillators and lead plates, and the output signals will be digitised by sampling ADCs and processed in real time by FPGAs. As part of the triggerless approach, these FPGAs will perform so-called feature extraction on the digitised signals, where the pulse-height and time of incoming pulses are extracted in real time. A substantial pile-up rate is expected, and it is foreseen that the chosen algorithm should enable reconstruction of such events. In this work we present the development of a real-time algorithm based on the well known Optimal Filter, which both improves the overall time resolution of the shashlyk detector and allows reconstruction of pile-up events with good time and energy resolution.

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• Proton- and Neutron-Induced Single-Event Upsets in FPGAs for the PANDA Experiment

  2020. Markus Preston (et al.). IEEE Transactions on Nuclear Science 67 (6), 1093-1106

  Artikel

  Single-event upsets (SEUs) affecting the configuration memory of a 28-nm field-programmable gate array (FPGA) have been studied through experiments and Monte Carlo modeling. This FPGA will be used in the front-end electronics of the electromagnetic calorimeter in PANDA (Antiproton Annihilation at Darmstadt), an upcoming hadron-physics experiment. Results from proton and neutron irradiations of the FPGA are presented and shown to be in agreement with previous experimental results. To estimate the mean time between SEUs during operation of PANDA, a Geant4-based Monte Carlo model of the phenomenon has been used. This model describes the energy deposition by particles in a silicon volume, the subsequent drift and diffusion of charges in the FPGA memory cell, and the eventual collection of charges in the sensitive regions of the cell. The values of the two free parameters of the model, the sensitive volume side $d = 87$ nm and the critical charge $Q_{\text {crit}} = 0.23$ fC, were determined by fitting the model to the experimental data. The results of the model agree well with both the proton and neutron data and are also shown to correctly predict the cross sections for upsets induced by other particles. The model-predicted energy dependence of the cross section for neutron-induced upsets has been used to estimate the rate of SEUs during initial operation of PANDA. At a luminosity of $1\cdot 10<^>{31}$ cm$<^>{-2}\,\,\text{s}<^>{-1}$ , the predicted mean time between upsets (MTBU) is between 120 and 170 h per FPGA, depending on the beam momentum.

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• Precision resonance energy scans with the PANDA experiment at FAIR

  2019. Karolyn Makonyi (et al.). European Physical Journal A 55 (3)

  Artikel

  This paper summarises a comprehensive Monte Carlo simulation study for precision resonance energy scan measurements. Apart from the proof of principle for natural width and line shape measurements of very narrow resonances with PANDA, the achievable sensitivities are quantified for the concrete example of the charmonium-like X(3872) state discussed to be exotic, and for a larger parameter space of various assumed signal cross-sections, input widths and luminosity combinations. PANDA is the only experiment that will be able to perform precision resonance energy scans of such narrow states with quantum numbers of spin and parities that differ from JPC=1--.

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• Technical design report for the (P)over-barANDA Barrel DIRC detector

  2019. Karoly Makonyi (et al.). Journal of Physics G 46 (4)

  Artikel

  The (P) over bar ANDA (anti-Proton ANnihiliation at DArmstadt) experiment will be one of the four flagship experiments at the new international accelerator complex FAIR (Facility for Antiproton and Ion Research) in Darmstadt, Germany. (P) over bar ANDA will address fundamental questions of hadron physics and quantum chromodynamics using high-intensity cooled antiproton beams with momenta between 1.5 and 15 GeV/c and a design luminosity of up to 2 x 10(32) cm(-2) S-1. Excellent particle identification (PID) is crucial to the success of the (P) over bar ANDA physics program. Hadronic PID in the barrel region of the target spectrometer will be performed by a fast and compact Cherenkov counter using the detection of internally reflected Cherenkov light (DIRC) technology. It is designed to cover the polar angle range from 22 degrees to 140 degrees and will provide at least 3 standard deviations (s.d.) pi/K separation up to 3.5 GeV/c, matching the expected upper limit of the final state kaon momentum distribution from simulation. This documents describes the technical design and the expected performance of the (P) over bar ANDA Barrel DIRC detector. The design is based on the successful BaBar DIRC with several key improvements. The performance and system cost were optimized in detailed detector simulations and validated with full system prototypes using particle beams at GSI and CERN. The final design meets or exceeds the PID goal of clean pi/K separation with at least 3 s.d. over the entire phase space of charged kaons in the Barrel DIRC.

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• Feasibility study for the measurement of pi N transition distribution amplitudes at (P)over-barANDA in (P)over-barp -> J/psi pi(0)

  2017. Karoly Makonyi (et al.). Physical Review D 95 (3)

  Artikel

  The exclusive charmonium production process in (P) over barp annihilation with an associated pi 0 meson (p) over barp -> J/psi pi(0) is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J/psi -> e(+) e(-) decay channel with the AntiProton ANnihilation at DArmstadt ((P) over bar ANDA) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the (P) over barp -> pi(+)pi(-)pi(0) and (p) over barp -> J/psi pi(0)pi(0) reactions are performed with PANDAROOT, the simulation and analysis software framework of the (P) over bar ANDA experiment. It is shown that the measurement can be done at (P) over bar ANDA with significant constraining power under the assumption of an integrated luminosity attainable in four to five months of data taking at the maximum design luminosity.

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• Measurements and Simulations of Single-Event Upsets in a 28-nm FPGA

  2017. Markus Preston (et al.). PoS - Proceedings of Science 313

  Artikel

  Single-event upsets in the configuration memory of the 28-nm Xilinx Kintex-7 FPGA, used in the PANDA electromagnetic calorimeter, have been studied. Results from neutron and proton irradiations at energies up to 184 MeV are presented and compared with previous experimental results. In order to gain information about the energy-dependence of the single-event upset cross section, a GEANT4-based Monte Carlo simulation of upset mechanisms in nanometric silicon volumes has been developed. The results from this model are shown to agree with the experimental data for both neutrons and protons. Knowledge about the energy dependence of the cross section and of the particle flux at the location of the front-end modules in PANDA enables better estimates of the mean time between failures in the electromagnetic calorimeter. At PANDA, a total neutron flux of 1·10² cm⁻² s⁻¹ at the location of the front-end modules is expected at the lowest antiproton beam momentum and a luminosity of 1·10³¹ cm⁻² s⁻¹, leading to a predicted Mean Time Between Failures of 47 ± 10 hours per FPGA in the electromagnetic calorimeter.

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• Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR

  2016. Karoly Makonyi (et al.). European Physical Journal A 52 (10)

  Artikel

  Simulation results for future measurements of electromagnetic proton form factors at PANDA (FAIR) within the PandaRoot software framework are reported. The statistical precision with which the proton form factors can be determined is estimated. The signal channel (p) over barp -> e(+)e(-) is studied on the basis of two different but consistent procedures. The suppression of the main background channel, i.e. (p) over barp -> pi(+)pi(-), is studied. Furthermore, the background versus signal efficiency, statistical and systematical uncertainties on the extracted proton form factors are evaluated using two different procedures. The results are consistent with those of a previous simulation study using an older, simplified framework. However, a slightly better precision is achieved in the PandaRoot study in a large range of momentum transfer, assuming the nominal beam conditions and detector performance.

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• Study of doubly strange systems using stored antiprotons

  2016. Karoly Makonyi (et al.). Nuclear Physics A 954, 323-340

  Artikel

  Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the PANDA experiment at FAIR. For the first time, high resolution gamma-spectroscopy of doubly strange Lambda Lambda-hypernuclei will be performed, thus complementing measurements of ground state decays of Lambda Lambda-hypernuclei at J-PARC or possible decays of particle unstable hypernuclei in heavy ion reactions. High resolution spectroscopy of multistrange Xi(-) -atoms will be feasible and even the production of Omega(-) -atoms will be within reach. The latter might open the door to the vertical bar S vertical bar = 3 world in strangeness nuclear physics, by the study of the hadronic Omega(-) -nucleus interaction. For the first time it will be possible to study the behavior of Xi(+) in nuclear systems under well controlled conditions.

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• Experimental access to Transition Distribution Amplitudes with the PANDA experiment at FAIR

  2015. Karoly Makonyi, Per Erik Tegnér, Klas Marcks von Würtemberg. European Physical Journal A 51 (8)

  Artikel

  Baryon-to-meson Transition Distribution Amplitudes (TDAs) encoding valuable new information on hadron structure appear as building blocks in the collinear factorized description for several types of hard exclusive reactions. In this paper, we address the possibility of accessing nucleon-to-pion (pi N) TDAs from (p) over barp -> e(+)e(-)pi(0) reaction with the future PANDA detector at the FAIR facility. At high center-of-mass energy and high invariant mass squared of the lepton pair q(2), the amplitude of the signal channel (p) over barp -> e(+)e(-)pi(0) admits a QCD factorized description in terms of pi N TDAs and nucleon Distribution Amplitudes (DAs) in the forward aid backward kinematic regimes. Assuming the validity of this factorized description, we perform feasibility studies for measuring (p) over barp -> e(+)e(-)pi(0) with the PANDA detector. Detailed simulations on signal reconstruction efficiency as well as on rejection of the most severe background channel, i.e. (p) over barp -> pi(+)pi(-)pi(0) were performed for the center-of-mass energy squared s = 5 GeV2 and s = 10 GeV2, in the kinematic regions 3.0 < q(2) < 4.3 GeV2 and 5 < q(2) < 9 GeV2, respectively, with a neutral pion scattered in the forward or backward cone vertical bar cos theta(pi 0)vertical bar > 0.5 in the proton-antiproton center-of-mass frame. Results of the simulation show that the particle identification capabilities of the PANDA detector will allow to achieve a background rejection factor of 5 . 10(7) (1 . 10(7)) at low (high) q(2) for s = 5 GeV2, and of 1 . 10(8) (6 . 10(6)) at low (high) q(2) for s = 10 GeV2, while keeping the signal reconstruction efficiency at around 40%. At both energies, a clean lepton signal can be reconstructed with the expected statistics corresponding to 2 of integrated luminosity. The cross sections obtained from the simulations are used to show that a test of QCD collinear factorization can be done at the lowest order by measuring scaling laws and angular distributions. The future measurement of the signal channel cross section with PANDA will provide a new test of the perturbative QCD description of a novel class of hard exclusive reactions and will open the possibility of experimentally accessing pi N TDAs.

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• Evaluating vacuum phototriodes designed for the PANDA electromagnetic calorimeter

  2014. Karoly Makonyi (et al.). Nuclear Instruments and Methods in Physics Research Section A 763, 36-43

  Artikel

  In this work properties of a vacuum phototriode (VPT) and preamplifier unit designed for the electromagnetic calorimeter of the PANDA experiment being built at FAIR are investigated. With the use of lead tungstate and lanthanium bromide scintillators the VPT properties are studied at low photon energies, from tens of key in the lanthanium bromide measurements and between 10 MeV and 60 MeV in the lead tungstate measurements. At these energies the noise of the VPT unit can be expected to influence its performance significantly. It is shown that the noise contribution to the measured energy resolution, under optimal conditions, is consistent with a fluctuation of (one standard deviation) approximately 200 electrons at the VPT anode. For a lead tungstate crystal this is equivalent to a noise of 1.2 MeV. For lanthanium bromide this makes it possible to use VPTs for gamma ray spectroscopy above a few hundreds of keV without noticeable effects on the energy resolution compared to measurements with a standard photomultiplier.

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• Technical design report for the PANDA (AntiProton Annihilations at Darmstadt) Straw Tube Tracker

  2013. Karoly Makonyi, Per-Erik Tegnér, K. M. von Wurtemberg. European Physical Journal A 49 (2), 25

  Artikel

  This document describes the technical layout and the expected performance of the Straw Tube Tracker (STT), the main tracking detector of the PANDA target spectrometer. The STT encloses a Micro-Vertex-Detector (MVD) for the inner tracking and is followed in beam direction by a set of GEM stations. The tasks of the STT are the measurement of the particle momentum from the reconstructed trajectory and the measurement of the specific energy loss for a particle identification. Dedicated simulations with full analysis studies of certain proton-antiproton reactions, identified as being benchmark tests for the whole PANDA scientific program, have been performed to test the STT layout and performance. The results are presented, and the time lines to construct the STT are described.

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• The response of lead-tungstate scintillators (PWO) to photons with energies in the range 13 MeV-64 MeV

  2012. Klas Marcks von Wurtemberg (et al.). Nuclear Instruments and Methods in Physics Research Section A 679, 36-43

  Artikel

  The response of a matrix of 25 lead tungstate (PWO) scintillator detectors, operated at -25 degrees C, to photons in the range 13 MeV-64 MeV has been measured at the tagged-photon facility at MAX-lab, Lund. The tapered PWO crystals, each with a length of 200 mm and a cross-section of 24.4 x 24.4 mm(2) in the front end, read out by 19 mm photomultiplier tubes, were arranged in a 5 x 5 matrix. The response was measured for photons directed towards the centre of the central crystal as well as for photons directed towards the corner of the central crystal, where four crystals meet. The obtained energy resolution surpasses what has been published so far and is close to the limit given by Poisson statistics and escaped energy. For photons directed towards the centre(corner) of the central crystal the relative energy resolution, defined as (FWHM/2.35)/E-gamma, decreases from 7.3%(11.0%) at E-gamma = 13 MeV to 3.3%(3.6%) at E-gamma = 64 MeV. The reconstructed point of impact of a photon in this energy range is determined with an uncertainty (one standard deviation) of 7.3 +/- 0.1 mm.

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• Production of eta and 3 pi mesons in the pd -> (HeX)-He-3 reaction at 1360 and 1450 MeV

  2010. K. Schonning (et al.). European Physical Journal A 45 (1), 11-21

  Artikel

  The cross-sections of the pd -> He-3 eta, pd -> He-3 pi(0)pi(0)pi(0) and pd -> He-3 pi(+)pi(-)pi(0) reactions have been measured at the beam kinetic energies T-p = 1360 MeV and T-p = 1450 MeV using the CELSIUS/WASA detector setup. At both energies, the differential cross-section d sigma/d Omega of the eta meson in the pd -> He-3 eta reaction shows a strong forward-backward asymmetry in the CMS. The ratio between the pd -> He-3 pi(+)pi(-)pi(0) and pd -> He-3 pi(0)pi(0)pi(0) cross-sections has been analysed in terms of isospin amplitudes. The reconstructed invariant-mass distributions of the pi pi, He-3 pi and (3)He2 pi systems provide hints on the role of nucleon resonances in the 3 pi production process.

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• The pd -> He-3 eta pi(0) reaction at T-p=1450 MeV CELSIUS/WASA Collaboration

  2010. K. Schonning (et al.). Physics Letters B 685 (1), 33-37

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  The cross section for the pd -> He-3 eta pi(0) reaction has been measured at a beam energy of 1450 MeV using the WASA detector at the CELSIUS storage ring. The He-3 was detected in coincidence with four photons from the decays of the two mesons. The data indicate that the production mechanism involves the formation of the Delta(1232) isobar. Although the beam energy does not allow the full peak of this resonance to be seen, the invariant mass distributions Of all three pairs of final particles are well reproduced by a phase space Monte Carlo simulation weighted with the p-wave factor of the square of the pi(0) momentum in the He-3 pi(0) system.

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• eta-meson production in proton-proton collisions at excess energies of 40 and 72 MeV

  2010. H. Petren (et al.). Physical Review C. Nuclear Physics 82 (5), 55206

  Artikel

  The production of eta mesons in proton-proton collisions has been studied using the WASA detector at the CELSIUS storage ring at excess energies of Q = 40 MeV and Q = 72 MeV. The eta was detected through its 2 gamma decay in a near-4 pi electromagnetic calorimeter, whereas the protons were measured by a combination of straw chambers and plastic scintillator planes in the forward hemisphere. About 6.9 x 10(4) and 9.3 x 10(4) events were found at Q = 40 MeV and Q = 72 MeV, respectively, with background contributions of less than 5%. A simple parametrization of the production cross section in terms of low partial waves was used to evaluate the acceptance corrections. Strong evidence was found for the influence of higher partial waves. The Dalitz plots show the presence of p waves in both the pp and the eta {pp} systems and the angular distributions of the eta in the center-of-mass frame suggest the influence of d-wave eta mesons.

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•  Exclusive measurtement of two-pion production in the _dd->⁴Heππ reaction

  2009. Christoph Bargholtz (et al.). Nuclear Physics A 825 (1-2), 71-90

  Artikel

  The results from the first kinematically complete measurement of the reaction are reported. The aim was to investigate a long standing puzzle regarding the origin of the peculiar ππ-invariant mass distributions appearing in double pion production in light ion collisions, the so-called ABC effect. The measurements were performed at the incident deuteron energies of 712 MeV and 1029 MeV, with the WASA detector assembly at CELSIUS in Uppsala, Sweden. We report the observation of a characteristic enhancement at low ππ-invariant mass at 712 MeV, the lowest energy yet. At the higher energy, in addition to confirming previous experimental observations, our results reveal a strong angular dependence of the pions in the overall centre of mass system. The results are qualitatively reproduced by a theoretical model, according to which the ABC effect is described as resulting from a kinematical enhancement in the production of the pion pairs from two parallel and independent NN→dπ sub-processes.

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•  Production of the ω meson in the pd -> 3He ω reaction at 1450 MeV and 1360 MeV

  2009. Christoph Bargholtz (et al.). Physical Review C. Nuclear Physics 79 (4), 044002

  Artikel

  The production of ω mesons in the pd→³Heω reaction has been studied at two energies near the kinematic threshold, T_p=1450 MeV and T_p=1360 MeV. The differential cross section was measured as a function of the ω c.m. angle at both energies over the whole angular range. Whereas the results at 1360 MeV are consistent with isotropy, strong rises are observed near both the forward and backward directions at 1450 MeV. Calculations made using a two-step model with an intermediate pion fail to reproduce the shapes of the measured angular distributions and also underestimate the total cross sections

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•  The pp -> d pi(+)pi(0) reaction – a case of Delta Delta excitation without ABC effect

  2009. Per-Erik Tegnér, Pia Thörngren-Engblom. International Journal of Modern Physics A 24 (2-3), 561-563

  Artikel

  The ABC effect, a low-mass enhancement in the invariant ππ mass, is observed in double-pionic fusion reactions leading to a bound nuclear system in the final state. From previous measurements there have been indications that this phenomenon is resctricted to the σ channel of the ππ system. With exclusive measurements of the pp → dπ⁺π⁰ reaction at T_p = 1.1 GeV we demonstrate that, indeed, the ABC effect does not occur in the vector-isovector ππ channel (ρ channel) despite the fact that the ΔΔ excitation is oberved to be the dominant reaction process. We also show that this reaction is well described by a t-channel ΔΔ excitation with the subsequent decay into the vector-isovector ππ channel given by the ρ channel operator

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• Measurement of h meson decays into lepton-antilepton pairs

  2008. Christoph Bargholtz (et al.). Physical Review D. Particles and fields 77 (3), 32004-32008

  Artikel

  A search for rare lepton decays of the η meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay η→e⁺e^-e⁺e^- events are reported with a background of 1.3±0.2 events. This allows to set an upper limit to the branching ratio of 9.7×10^-5 (90% CL). The branching ratio for the decay η→e⁺e^-γ is determined to (7.8±0.5_stat±0.8_syst)×10^-3 in agreement with world average value. An upper limit (90% CL) for the branching ratio for the η→e⁺e^- decay is 2.7×10^-5 and a limit for the sum of the η→μ⁺μ^-μ⁺μ^- and η→π⁺π^-μ⁺μ^- decays is 3.6×10^-4.

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• Properties of the WASA pellet target and a stored intermediate-energy beam

  2008. Christoph Bargholtz (et al.). Nuclear Instruments and Methods in Physics Research Section A 587 (2-3), 178-187

  Artikel

  Experimental data from the reaction close to threshold have been used to investigate time-dependent properties of the WASA pellet target and the stored beam of 892.8 MeV protons in the CELSIUS accelerator. The detection of ³He ions in solid-state detectors provides an excellent almost background free trigger for η production. Pellet interactions with the surrounding material and with the beam lead to evaporation of deuterium gas into the beam pipe. Approximately 30% of the registered η decay events are due to interactions in deuterium gas outside the pellets. Due to beam–target interaction the beam is transversely heated and appears to acquire a component of a slightly lower energy.

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• Measurement of the η -> π⁺π^-e⁺e^- branching ratio

  2007. Christoph Bargholtz (et al.). Physics Letters B 644 (5-6), 299-303

  Artikel

  The reaction at threshold was used to provide a clean source of η mesons for decay studies with the WASA detector at CELSIUS. The branching ratio of the decay η→π⁺π⁻e⁺e⁻ is measured to be (4.3±1.3±0.4)×10⁻⁴.

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• Performance of HPGe detectors in high magnetic fields

  2007. A. Sanchez Lorente (et al.). Nuclear Instruments and Methods in Physics Research Section A 573 (3), 410-417

  Artikel

  A new generation of high-resolution hypernuclear gamma-spectroscopy experiments with high-purity germanium detectors (HPGe) are presently designed at the FINUDA spectrometer at DA Phi NE, the Frascati phi-factory, and at (P) over bar ANDA, the (p) over barp hadron spectrometer at the future FAIR facility. Both, the FINUDA and (P) over bar ANDA spectrometers are built around the target region covering a large solid angle. To maximise the detection efficiency the HPGe detectors have to be located near the target, and therefore they have to be operated in strong magnetic fields (B approximate to I T). The performance of HPGe detectors in such an environment has not been well investigated so far. In the present work VEGA and EUROBALL Cluster HPGe detectors were tested in the field provided by the ALADiN magnet at GSI. No significant degradation of the energy resolution was found, and a change in the rise time distribution of the pulses from preamplifiers was observed. A correlation between rise time and pulse height was observed and is used to correct the measured energy, recovering the energy resolution almost completely. Moreover, no problems in the electronics due to the magnetic field were observed.

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• Tagging of η mesons using the pd → ³Heη reaction near threshold

  2006. Chr Bargholtz (et al.). Instruments and experimental techniques (New York) 49 (4), 461-467

  Artikel

  A zero-degree spectrometer for tagging η mesons on the CELSIUS/WASA facility is described, and its characteristics are presented. Tagging of η mesons is performed by detecting ³He ions produced by reaction pd → ³Heη close to the production threshold. The low background level (<2%) is in good agreement with the data obtained earlier on the SATURNE accelerator.

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