Maintaining a high reconstruction efficiency and low misidentification rate of muon reconstruction at High Luminosity is a high priority for CMS.

The TDR presented by the GEM group is extremely exhaustive in documenting the implementation of GE1/1, a set of chambers located close to the ME1/1 region capable of improving CMS triggering and reconstruction capabilities in the 1.6 < |η| < 2.2 region. The proposed GE1/1 system shows a clear recovery of reconstruction efficiency across the board, especially for higher eta.

The authors should be congratulated for the high maturity level of this TDR, probably higher than “The Muon Project TDR” ( CERN/LHCC 97-32) in this reviewer opinion. Especially notable are the discussions on execution of the Project - including QA/QC elements and subdivision of work among collaborating Institutions – and on elements of Detector Control System during operations.

Authors have also addressed the comments and recommendations provided to them in the early stages of the definition of the GE1/1 proposal through the “Review of the GEM Proposal (Feb ’13)” and the “GEM Follow-up Trigger Review (May ’13)”.

Below are few “High Level Comments/Recommendations”. I also included some “Lower Level Issues/Questions” and a set of small grammar/spelling corrections I noticed here and there (by no mean exhaustive).

High Level Comments/Recommendations

1) The TDR describes a system designed for leveled luminosity of L=5x1034 and a total Integrated Luminosity of 3000 fb-1. Since Fall 2014 there has been an ongoing discussion among the proponents of the HL-LHC effort on the machine side for an “ultimate” leveled Luminosity of 7.5 x 1034 and an Integrated Luminosity of 4000 fb-1 for the HL-LHC run(s) in the 2025-2035 decade. Since any system designed for the HL-LHC runs will have to cope with the questions of “standard” and “ultimate” Luminosity, we suggest the authors to include a discussion of the system operability at 7.5 x 1034.

Recommendation #1: Evaluate performance of the GE1/1 system at Ultimate Luminosity (7.5 x 1034) as well as the default HL-LHC Luminosity (5 x 1034).

Anna & Archana: need to synchronize with operating conditions shown in Technical Proposal and so we need to have feedback on that from Upgrade Managers; they have been informed of this comment.

2) The TDR describes a world-wide collaboration that will be involved in the assembly of the GE1/1 system. All the institutions involved are solid and reliable members of the CMS Collaborations, and the proponents are envisioning a “training process” at CERN to “uniformize” the quality of the assembly process. Nevertheless, there is no discussion of a process to control “localized improvements” and either distribute them widely or understand their effect on the final system. While the TDR is not the place to have a fully developed “Process/Production Control Plan”, we encourage the adoption of a system to control activities at various location. This Reviewer is biased toward the usage of Travelers and Procedures for each assembly step, but alternative forms of control can be envisaged.

Archana:This will be done by means of "Travellers" coordinated, steered and executed by means of a database quality management system. This is already being implemented and is included in the Chapter 5 (Fig. 5.2) and database section of Chapter 8.

Recommendation #2: While not formally part of the TDR, we recommend the proponents to institute and adopt a formal “Process/Production Control Plan” to manage the inevitable differences that might develop across multiple Collaborating Institutions on aspects of Production.

Lower Level Issue/Questions

1. Line 1235 mentions “Some Data Losses” in High Occupancy events for the SPZS VFAT3 data type. The “losses” should be quantified, at least in average.
TDR change: The sentence has been removed to avoid confusion. Comment to Reader: Table 4.3 shows the probability of losses occurring due to saturation of the link for data rates exceeding those expected for GE11 and ME0. The probability of losses is very low; less than 1 for 10^7 events in GE11.

2. Line 1574 mentions a Production process in which components are all delivered and inspected at CERN before being shipped to assembly sites. Connected to recommendation #2 above, a proper system for Parts Control and/or Kits Preparation should be envisaged.
OB: we added a sentence about that

3. (Minor) Line 1970 is missing the minimum threshold below which GEANT stop tracking particles.
AM: Added

4. Line 2635 is missing the technical solution to implement the thermal contact between the cooling pipes and the thermal screen. Such solution should be developed quickly.

5. Line 3223 mentions 3 spare chambers and 2% additional spare material and components. In this reviewer opinion, the quantity of material and components spares is utterly insufficient and may hinder smooth production lines. Spare levels of ~5-10% (depending on the component) are more adequate for a detector system of this complexity.
Anna : the percentage of spare material was agreed with Upgrade Financial committee. We have re-discussed it

Corrections/Spelling Issues

Line 2441: “aflter” to “after”
MT: done

Line 1753: Loose one “turned on”
MT: done

Line 2049: “Comparies” to “compares”
RH: Done

Line 2685: “aidss” to “aids”
RH: Done

Line 2786: “on powering on the system” to “on powering of the system” %
MM: ... changed in "when the system is powered on"