CMS Endcap Calorimeter for HL-LHC design. Trays Skirt for Backing HE Endcap Calorimeter accessibility. Technical proposal.

The existing Compact Muon Solenoid (CMS) Endcap Hadron Calorimeters (HE) have been in operation for several years and contributed substantially to the success of the CMS Physics Program. The High Luminosity Large Hadron Collider (HL-LHC) performance criteria, however, require a re-examination of the ability of the detector active material and electronics to meet the requirements of 3000 fb$^{-1}$ [1, 2]. Based on these studies, CMS proposes the replacement of the Endcap Calorimeters, which cover the region of pseudorapidity $1.5<\\mid \\eta \\mid<3.0$, with a new High-Granularity sampling Calorimeter (HGC). The current HE calorimeters are proposed to be converted to the Backing Hadron Calorimeter (BH). For the BH, the base line mechanical design, scintillator design and segmentation, and optical readout scheme must be defined by the end of 2016. Also upgraded Endcap design must provide the accessibility of BH and easy scintillators (megatiles) replacement [3]. This can be achieved by the adding of a new element "Trays Skirt". A possible design of this element is presented.