[en] This paper reviews the search for light dark matter in beam dump experiments with a special emphasis on the necessity of beam purity for precise background rejection at the sensitivities aimed at these experiments. As a case study we cite the P348 experiment which has test beam time in Fall 2015 at the SPS H4 beam line at CERN and aims to search for the U"′(1) gauge boson, A"′, which as per one model of dark matter mediates a weak interaction between ordinary matter and dark matter via mixing of these “dark photons” with ordinary photon. The experiment aims to probe the still unexplored area of mixing strength 10"-"5≤ϵ≤10"-"3 and masses M_A_"′≤100 MeV by using 10–300 GeV electron beam from the CERN SPS. This paper presents the simulation results for rejection of background due to beam impurity, by tracking the incoming particles with Micromegas detectors at a level <10"-"1"0

[en] We present a new experiment, Mu-MASS, aiming for a 1000-fold improvement in the determination of the 1S-2S transition frequency of Muonium (M), the positive-muon/electron bound state. This substantial improvement beyond the current state-of-the-art relies on the novel cryogenic M converters and confinement techniques we developed, on the new excitation and detection schemes which we implemented for positronium spectroscopy and the tremendous advances in generation of UV radiation. This experiment is planned to be performed at the Paul Scherrer Institute (PSI). Interesting anomalies in the muon sector have accumulated: notably the famous anomalous muon magnetic moment (g-2) and the muonic hydrogen Lamb shift measurement which prompted the so-called proton charge radius puzzle. These tantalizing results triggered vibrant activity on both experimental and theoretical sides. Different explanations have been put forward including exciting solutions invoking New Physics beyond the Standard Model. Mu-MASS could contribute to clarifying the origin of these anomalies by providing robust and reliable values of fundamental constants such as the muon mass and a value of the Rydberg constant independent of finite size effects.

[en] The unprecedented flux of low energy antiprotons delivered by the Extra Low ENergy Antiprotons (ELENA) ring, being under commissioning at CERN, will open a new era for precision tests with antimatter including laser and microwave spectroscopy and tests ofits gravitational behaviour. Here we present an alternative to magnetic trapping to perform ultra-high precision laser spectroscopy of antihydrogen. The proposed scheme is to load the ultra cold anti-hydrogen atoms produced by the GBAR experiment in an optical trap tuned at the magicwavelength of the 1S–2S transition in order to measure this interval at a level comparable or even better than its matter counter part. This will provide a very accurate test of Lorentz/CPT violating effects which can be parametrised in the framework of the Standard Model Extension.

[en] In this paper, a new experiment is presented to measure the 1S-2S transition of positronium, the bound state of an electron and a positron. The goal is to improve the current accuracy by a factor of 5 to reach a precision of the order of 0.6 ppb, to check recent QED calculations. This accuracy is challenging, but it seems well within reach in view of the technological advances that have occurred during the last two decades. We will present the details of the experimental setup, the advances in the production of positronium, the developments of the laser system, and as well our new experimental technique for the detection of Ps in the 2S state. (author)

[en] Full text: Muonium (Mu=μ⁺e^-) is used in Mu spectroscopy for extracting fundamental constants (m_μ, α, R_∞), and for testing bound-state QED theories. However, the precision is limited by the lack of a high quality Mu source, in terms of vacuum yield, low energy and reliability. Here, we propose a new way to improve Mu production in vacuum by using SiO₂ porous materials. The vacuum yield of Mu is expected to be around 40 %, which is a factor of 4 improvement compared to existing methods. Moreover, the production will be tested down to cryogenic temperatures, corresponding to Mu energies of a few eV. The measurement will be performed at PSI using the μE4 beamline in summer 2011. Mu vacuum yields will be measured by observing time distributions of decay positrons in our apparatus and by means of muon spin resonance techniques (μSR). At the same time, information about diffusion (both in classical and quantum mechanical regime, depending on the temperature) of Mu in porous material can possibly be extracted. The motivation and principle of the experiment, together with results from GEANT4 simulations will be presented. (author)

[en] The results of a new search for positronium decays into invisible final states are reported. Convincing detection of this decay mode would be a strong evidence for new physics beyond the standard model (SM): for example, the existence of extra-dimensions, of milli-charged particles, of new light gauge bosons or of mirror particles. Mirror matter could be a relevant dark matter candidate. In this paper the setup and the results of a new experiment are presented. In a collected sample of about (6.31±0.28)x10⁶ orthopositronium decays, no evidence for invisible decays in an energy [0,80] keV was found and an upper limit on the branching ratio of orthopositronium o-Ps→invisible could be set: Br(o-Ps→invisible)<4.2x10^-7(90%C.L.) Our results provide a limit on the photon mirror-photon mixing strength ε≤1.55x10^-7(90%C.L.) and rule out particles lighter than the electron mass with a fraction Q_x≤3.4x10^-5 of the electron charge. Furthermore, upper limits on the branching ratios for the decay of parapositronium Br(p-Ps→invisible)≤4.3x10^-7(90%C.L.) and the direct annihilation Br(e⁺e^-→invisible)≤2.1x10^-8(90%C.L.) could be set

[en] We report the foremost phase of a fourth generation positron source, being constructed at the Federal University of Rio de Janeiro. Positron yields are reported by making use of the ¹⁹F(p,αe⁺e⁻)¹⁶O reaction, where the fluorine target is in the form of a CaF₂ pellet. Positron production has been observed by detecting 511 keV annihilation gamma rays emerging from the irradiated CaF₂ target.

[en] The PSI low-energy μSR spectrometer is an instrument dedicated to muon spin rotation and relaxation measurements. Knowledge of the muon beam parameters such as spatial, kinetic energy and arrival-time distributions at the sample position are important ingredients to analyze the μSR spectra. We present here the measured energy losses in the thin carbon foil of the muon start detector deduced from time-of-flight measurements. Muonium formation in the thin carbon foil (10 nm thickness) of the muon start detector also affect the measurable decay asymmetry and therefore need to be accounted for. Muonium formation and energy losses in the start detector, whose relevance increase with decreasing muon implantation energy (<10 keV), have been implemented in Geant4 Monte Carlo simulation to reproduce the measured time-of-flight spectra. Simulated and measured time-of-flight and beam spot agrees only if a small fraction of so called ''unmoderated'' muons which contaminate the mono-energetic muon beam of the μSR spectrometer is introduced. Moreover the sensitivity of the beam size and related upstream-downstream asymmetry for a specially shaped ''nose'' sample plate has been studied for various beam line settings, which is of relevance for the study of thermal muonium emission into vacuum from mesoporous silica at cryogenic temperatures

[en] We consider the feasibility of observing the gravitational quantum states of positronium. The proposed scheme employs the flow-throw technique used for the first observation of this effect with neutrons. Collimation and Stark deceleration of Rydberg positronium atoms allow selecting the required velocity class. If this experiment could be realized with positronium, it would lead to a determination of g for this matter-antimatter system at the few % level. As discussed in this contribution, most of the required techniques are currently available but important milestones have to be demonstrated experimentally before such an experiment could become reality. Those are the efficient focusing of a bunched positron beam, Stark deceleration of Rydberg positronium, and its subsequent excitation into states with large angular momentum. We provide an estimate of the efficiencies we expect for these steps and assuming those could be confirmed we calculate the signal rate

[en] The understanding of the origin of dark matter has great importance for cosmology and particle physics. Several interesting extensions of the standard model dealing with solution of this problem motivate the concept of hidden sectors consisting of SU(3)_C x SU(2)_L x U(1)_Y singlet fields. Among these models, the mirror matter model is certainly one of the most interesting. The model explains the origin of parity violation in weak interactions, it could also explain the baryon asymmetry of the Universe and provide a natural ground for the explanation of dark matter. The mirror matter could have a portal to our world through photon-mirror photon mixing (ε). This mixing would lead to orthopositronium (o-Ps) to mirror orthopositronium oscillations, the experimental signature of which is the apparently invisible decay of o-Ps. In this paper, we describe an experiment to search for the decay o-Ps→invisible in vacuum by using a pulsed slow positron beam and a massive 4π BGO crystal calorimeter. The developed high efficiency positron tagging system, the low calorimeter energy threshold and high hermiticity allow the expected sensitivity in mixing strength to be ε ≅ 10^-9, which is more than one order of magnitude below the current Big Bang Nucleosynthesis limit and in a region of parameter space of great theoretical and phenomenological interest. The vacuum experiment with such sensitivity is particularly timely in light of the recent DAMA/LIBRA observations of the annual modulation signal consistent with a mirror type dark matter interpretation.