Search

Although they have not yet been detected, axions and axion-like particles (ALPs) continue to maintain the interest (even increasingly so) of the rare-event searches community as viable candidates for the Dark Matter of the Universe but also as a solution for several other puzzles of astrophysics. Their property of coupling to photons has inspired different experimental methods for their detection, one of which is the helioscope technique. The CERN Axion Solar Telescope (CAST) is the most sensitive helioscope built up to date and has recently published part of the latest data taken with the magnet bores gradually filled with 3He, probing the mass range up to 1.17 eV. The International AXion Observatory (IAXO) is being proposed as a facility where different axion studies can be performed, with the primary goal to study axions coming from the Sun. Designed to maximize sensitivity, it will improve the levels reached by CAST by almost 5 orders of magnitude in signal detection, that is more than one order of magnitude in terms of gaγ. Here we will summarize the most important aspects of the helioscopes, and focus mainly on IAXO, based on the recent papers [1, 2].

The inclusive η-momentum spectrum from annihilations at rest in liquid hydrogen was measured at LEAR. Branching ratios were obtained for $$\begin{gathered} p\bar p \to \eta \omega \left( {1.04_{ - 0.10}^{ + 0.09} } \right)\% ,\eta \rho ^0 \left( {0.53_{ - 0.08}^{ + 0.20} } \right)\% , \hfill \\ \pi a_2 \left( {8.49_{ - 1.10}^{ + 1.05} } \right)\% ,\eta \pi ^0 \left( {1.33 \pm 0.27} \right) \times 10^{ - 4} , \hfill \\ \end{gathered} $$ , and ηη(8.1±3.1)×10−5. An upper limit for of 1.8×10−4 at 95% CL was found. The ratio of the branching ratios is BR(ηϱ)/BR(ηω)=0.51−0.06+0.20. For the ratio of branching ratios into two pseudoscalar mesons, we have BR(ηπ0)/BR(π0π0)=0.65±0.14, BR(ηη)/BR(π0π0), BR(ηη′)/BR(π0π0) at 95% CL, and BR(ηη)/BR(ηπ0).

The low-energy part of thep0 spectrum associated with annihilation at rest was measured in order to search for bound baryonium-like states. The upper limit for reaching such states via the emission of monochromaticp0's was found to be 8% per annihilation in the mass region of 1650 MeV. The low-energy part of the ? spectrum from annihilations at rest was also observed.

New experimental results on electron emission from PLZT ceramics of composition 2/95/5, subjected to rectangular high-voltage pulses are reported. The dependence of the emitted electron charge on the electric field strength and temperature was investigated. The energy of the emitted electrons was estimated by applying a decelerating potential to an auxiliary grid electrode. Emitted current densities of several A/cm2 and emitted charges up to ∼ 1 μC/cm2 (∼1013 electrons/cm2) were observed.

The X-ray spectrum emerging from a liquid-hydrogen target when stopping antiprotons was measured with high resolution in order to determine the strong interaction shift and width of the atomic 1s level. Owing to strong Stark quenching only weak structures could be observed. The upper limit of the yield of any one of theK-series transitions is 3.5×10-4 (95% C.L.) per stopped antiproton, assuming no broadening of the 1s level. Possible identifications of the weak lines with theK-series transitions are discussed.

The X-ray spectrum associated withK- stopping in liquid hydrogen was measured with high resolution Si(Li) detectors. The totalK X-ray yield is not larger than 8×10-4 per stoppedK- assuming no line broadening. A weak line pattern was found, which was tentatively ascribed to theK- HK-series X-rays. The shift and width of the 1s level, deduced from this pattern, are e1s=+270±80 eV andG=560±260 eV, respectively.

Energies and widths of pionic 3d-2p transitions of30Zn,32Ge, and33As have been measured with a Ge detector. The values of the 2p shifts obtained from the measuremente2p(Zn)=7.0±1.4keV,e2p(Ge)=5.5±0.9keV, ande2p(As)=4.6±0.9keV show a decreasing behaviour for largeZ, which is caused by an increasings-wave contribution as predicted by theory.

The polarization reversal in thick ferroelectric crystals has been performed with pulsed HV. A time-dependent dielectric constant e has been observed in the (ms-μs) range. The time variable e can also be used for making visible the polarization reversal of the crystal.

The light emitted during polarization reversal of different ferroelectric single crystals (FEs) has been studied quantitatively by using a technique from nuclear spectroscopy. The time spectra contain characteristic features and indicate strong correlation between the switching process and the light emission. The duration of each light pulse is 10-7-10-8 s. These signals can be used for defining each particular polarization reversal.

Experiments on fast spontaneous polarization changes in PZT ceramics are described. The interactions between spontaneous polarization Ps and space-charge polarization Psp.ch. are discussed. The fast polarization changes are made with the aim of producing electron beam emission and acceleration from ferroelectric surfaces.

The absorption of stoppedp- in181Ta and209Bi has been investigated by studying prompt and delayed?-ray spectra. Absolute cross-sections for the yield of isotopes per capturedp- in (p-, xn) reactions, as well as the relative probability of populating nuclear states of different spins have been measured for the hafnium and lead isotopes, respectively. A spin as high as 20 has been observed in the production of204Pb. The ground-state rotational bands of the hafnium isotopes are excited to spin values up to 16. Neutron multiplicities as large as 15 have been observed for both targets. A neutron multiplicity of ?8 is most probable for both tantalum and bismuth targets.

The branching ratios of annihilations into the neutral final states 2p0, p0?, and 2? are measured by stopping antiprotons in liquid hydrogen. They are , , andB??<1.7×10-6 (95% c.l.).

We describe the experimental method and report the results of electron emission from PLZT-2/95/5 ceramics subjected to rectangular HV pulses. The influence of HV amplitude, of gas pressure, and of temperature on electron beam current-density and charge was investigated. The kinetic energy was estimated by applying a decelerating field. Emitted current-density pulses of several A/cm2 and charges of 1 μC/cm2 are measured. A tentative interpretation is given.

By Mössbauer absorption experiments the magnetic hyperfine splitting has been observed for the 2+ states of180W and182W in a tungsten iron alloy (3.6 at%W). Since theg-factor of the 2+ state of182W is known the measured splitting of the182W line could be used for the calibration of the magnetic hyperfine field and the measurement with180W gave then for the unknowng2+-factor of180W: $$g_{2 + } (^{180} W) = 0.260 \pm 0.017.$$ By use of a WO3 absorber the electric quadrupole splittings in the same states were measured. The ratio of the quadrupole moments was derived $$\frac{{Q_{2 + } (^{180} W)}}{{Q_{2 + } (^{182} W)}} = 0.983 \pm 0.022.$$ This ratio is somewhat smaller, but more accurate than the weighted means of previous results and in disagreement with the theoretical prediction.

The Mößbauer effect of the 129 keV transition in 195Pt has been observed. By use of a Ge(Li) detector any contribution from the strong 99 keV Mößbauer line could be eliminated. The width of the resonance absorption line corresponds to the natural line width. We derived from the magnitude of the observed Mößbauer effect the branching ratio in the decay of the 129 keV level as I (129)/I (31) = ( 5.7 ± 1.6)% .