A novel type of resistive Micromegas combining a Bulk mesh and a resistive pad board is presented. Readout pads are covered by a thin insulating layer with a top resistive coating segmented into resistive pads. Readout and resistive pads are electrically connected by means of planar resistors embedded in the insulator, enabling fast clearance of the avalanche charge from the resistive surface. The maximum gas gain achieved by these resistive detectors is similar to that of non-resistive Micromegas. A possible saturation of the gain for large energy deposits in the gas was investigated by means of Fe-55 quanta and electromagnetic showers in the 30-200 GeV energy range, but no significant deviation from a proportional response was found. With a suitable choice of the resistance, these detectors demonstrate negligible gain drop and no sparking up to X-ray fluxes of similar to 1 MHz/mm(2) which constitutes a major improvement over non-resistive Micromegas. Spark suppression was also verified in a hadron beam for prototypes with a pad resistance as low as 40 k Omega or above. Passive protections of the front-end electronics against sparks (diodes on a printed circuit board) are therefore not required for these resistive detectors.

Resistive micromegas is proposed as an active element for sampling calorimetry. Future linear collider experiments or the HL-LHC experiments can profit from those developments for Particle Flow Calorimetry. Micromegas possesses remarkable properties concerning gain stability, reduced ion feedback, response linearity, adaptable sensitive element granularity, fast response and high rate capability. Recent developments on Micromegas with a protective resistive layer present excellent results, resolving the problem of discharges caused by local high charge deposition, thanks to its RC-slowed charge evacuation. Higher resistivity though, may cause loss of the response linearity at high rates. We have scanned a wide range of resistivities and performed laboratory tests with X-rays that demonstrate excellent response linearity up to rates of (a few) times 10 MHz / cm 2 , with simultaneous mitigation of discharges. Beam test studies at SPS/CERN with hadrons have also shown a remarkable stability of the resistive Micromegas and low currents for rates up to 15 MHz / cm 2 . We present results from the aforementioned studies confronted with MC simulation

The 8.4 T, 10 m long transverse magnetic field of a twin aperture LHC bending magnet can be utilized as a macroscopic coherent solar axion-to-photon converter. Numerical calculations show that the integrated time of alignment with the Sun would be 33 days/yr with the magnet on a tracking table capable of ±5° in the vertical direction and ±40° in the horizontal direction. The existing lower bound on the axion-to-photon coupling constant can be improved by a factor between 30 and 100 in 3 yr, i.e., gaγγ≲9×10−11GeV−1 for axion masses ≲ 1 eV. This value falls within the existing open axion mass window. The same set-up can simultaneously search for low- and high-energy celestial axions, or axion-like particles, scanning the sky as the Earth rotates and orbits the Sun.

The 8.4 T and 10 m long magnetic field of a twin aperture LHC bending magnet can be utilized as a macroscopic coherent (solar) axion-to-photon converter. A computer simulation shows that such a magnet is in an optimum (horizontal) position and aligned with the Sun's core in June and December. The integrated time of alignment is similar to 1 to 33 days per year, assuming +/- 1.5 degrees to +/- 5 degrees tracking along the vertical and +/- 1.5 degrees to +/- 40 degrees along the horizontal, respectively. The existing experimental lower limit on the axion-to-photon coupling constant can be improved in similar to 3x2 months exposure (within 3 years), by a factor up to similar to 50-100, i.e., g(alpha gamma gamma) < (4 - 9) . 10(-11) GeV-1 for m(alpha) < 0.01 - 1 eV, which pervades the presently open axion mass window. The same set-up can simultaneously search for low- and high-energy celestial axions or axion-like particles, whatever their origin, scanning the sky as the Earth rotates and evolves.