The micro-RWELL detector for the phase-2 upgrade of the LHCb muon system

The micro-RWELL detector (mu-RWELL) is a single amplification stage resistive Micro Pattern Gaseous Detector (MPGD), based on a copper-clad polyimide foil patterned with a micro-well matrix coupled with the readout PCB through a DLC resistive film (10 divided by 100 M omega/). For the phase-2 upgrade of the LHCb experiment, proposed for the LHC Run-5, the excellent performance of the current muon detector will need to be maintained at 40 times the pile-up level experienced during Run-2. Requirements are challenging for the innermost regions of the muon stations: the detectors should exhibit a rate capability up to 1 MHz/cm2 and they are supposed to integrate a charge up to similar to 1 C/cm2. In this framework an intense optimization program of the micro-RWELL technology has been launched in the last year, together with a technology transfer to the industry operating in the PCB field. In order to fulfill the requirements, a new layout of the detector with a very dense current evacuation grid of the DLC has been designed. The detector, co-produced by the CERN-EP-DT-MPT Workshop, lead by one of the authors, and the ELTOS Company, has been characterized in terms of rate capability exploiting a high intensity X-ray Philips 2217/20 gun with a spot size (10 divided by 50 mm diameter) larger than the DLC grounding-pitch. A rate capability exceeding 10 MHz/cm2 has been achieved, in agreement with previous results obtained with m.i.p. at the Paul Scherrer Institute (PSI) in Villigen (CH). A long term stability test is in progress: a charge of about 5 mC/cm2 has been integrated over a period of about 16 days. The test will continue, in harder conditions (larger gain and X-ray flux), with the goal to integrate about 1 C/cm2 in one year, while a slice test of the detector is under preparation.