CMS Bulletin

MUON DETECTORS: RPC

In the second part of 2013 the two main activities of the RPC project are the reparation and maintenance of the present system and the construction and installation of the RE4 system. Since the opening of the barrel, repair activities on the gas, high-voltage and electronic systems are being done in parallel, in agreement with the CMS schedule.

In YB0, the maintenance of the RPC detector was in the shadow of other interventions, nevertheless the scaffolding turned out to be a good solution for our gas leaks searches. Here we found eight leaking channels for about 100 l/h in total.

10 RPC/DT modules were partially extracted –– 90 cm –– in YB0, YB–1 and YB–2 to allow for the replacement of FE and LV distribution boards. Intervention was conducted on an additional two chambers on the positive endcap to solve LV and threshold control problems. Until now we were able to recover 0.67% of the total number of RPC electronic channels (1.5% of the channels were dead at the end of 2013 run).

In YB–1, where a total leak rate of about 260 l/h was measured, we found 13 leaking chambers. The problem was found to be a failure of one or two of the T connectors in the gas-distribution lines. In seven chambers, the broken T connectors were accessible without extracting the chamber and were repaired, reducing the total leak rate to 135 l/h.

The HV problems (disconnected or single-gap-operation-mode chambers) were mostly due to a broken tripolar connector on the chamber. Until now we were able to fix most of the problems by replacing the connectors or disconnecting only one gap out of the four/six gaps. This will allow an increase of the efficiency of about 1.9% of the RPC η partitions (rolls) and recovery of 0.5% of the total electronic channels.

Since June 2013, 72 chambers have been successfully built, tested (at Belgium, India and CERN) and assembled (at CERN) in 36 Super Modules (SM) for the RE4 positive endcap.

On 11 and 12 November, a trial installation was performed, and three Super Modules were successfully mounted and dismounted by a Pakistani/Italian/Mexican/Belgian/CERN team, confirming that the installation of six SMs per day is possible with a six-person team. Important protocols on SM orientation, storage space allocation at Point 5, SM lifting, workforce, logistics and teamwork were established during this exercise. The most important result was the reassessment of the RE4 positioning in Z. The RE4 plane was approved to be moved 20 mm closer to IP to avoid conflict with YE4 plane. The installation of the RE4 positive endcap is scheduled for December 2013 and the tools, procedure and workforce needs are set.

Integration of the services on the negative endcap have already started. 36 double gas patch panels were installed on the YE–3 periphery last week. Cooling mini-manifolds, gas piping between the gas-distribution rack and the patch panels, RPC trigger fibers, high-voltage, low-voltage and signal cables should be installed by end January 2014.  The gas and cooling connections of the installed Super Modules on the positive end (RE+4) should be completed by Christmas.

We still have 36 SMs to go for the RE4 negative endcap. The gap production of the 216 gaps needed to build the 72 chambers is ongoing in South Korea, as well as the chamber production and testing at India/Belgium/CERN. Several gap shipments are foreseen for November, December and January. The first batch of SMs is expected at the end of February by a Belgian/Bulgarian/Georgian/Mexican team. The installation of the negative side is foreseen in April 2014.

During and after the installation of the RE4 chambers, the most relevant issue for the DPG will be the development of the appropriate code needed for the commissioning of these chambers. Most of the code needed is already written and has been extensively used and tested during 2011 and 2012 Runs, however the inclusion of the new chambers to all our routines is an important task that is getting started and needs to be done as soon as possible.

RE4 inclusion in the software is moving forward in parallel with studies done on the previous data (Run 2012). Studies concerning the detector ageing and the RPC background have been of special interest.