here my comments on version 300 of the GEM TDR draft (Nov. 24, 2014):

- Overall a well written document with many (too many) details, but not presented in a very good order

- General remarks/questions:

o GEM detector / physics:

- I am not convinced about the gas flow reaching all the corners, independent of chamber orientation and gas density (section 2.3.5) why cant you include the foils in the simulation what is the minimum gas flow you require ?

- how can you control the flatness of the inner two foils ? If you reach

1. 1. u at the surface, what flatness do you claim for the inner ones?

- long term reliabilty of spring loaded contacts ? more than one per voltage (redundancy) ?

o the order of the different sub-sections is not always clear me: why do we first discuss the diffusion coefficients, and only afterwards the general suitability of the GEM technology ? why does the detailed motivation for high rate detectors come only in chapter 6 ? why do we discuss the peculiarities of the different prototypes if we dont know yet how the detector finally looks like (baseline layout) ? it is very difficult to understand the voltage dependent plots like fig.2.8 if we dont know the baseline voltage value(s) to be used (why not indicated in these figures ?)

o it would be very helpful to have a concise "executive summary" of how the GE1/1 looks like at the beginning. Some information I have not found at all in the draft: what are the baseline voltages ? where in the introduction do you point out that only one space coordinate is measured ?

o references: you should be more "generous": GEM should get a reference early, GBT, VFAT3 etc should have a reference, figure 2.6 from LHCb needs a reference in the caption....

o many figures need to be improved

o all institutes are listed, but in the text in general the individual tasks are not assigned to an institute - fine. but the production sites receive particular emphasis: discussion, picture - is that justified (maybe it is...)

- detailed comments following line numbering: (note: a question mark signals that I am not sure about my proposed change)

156 redundancy => measurement

167 greatest => "highest" or "most important"

170 of the CMS... 1.2 (article and no closing parenthesis)

183 particular utility => main strength

185 greatest => strongest

191 H2Tau is jargon, please avoid

193-200: shouldnt one say that the muon system is needed also for muon identification - the tracker can't contribute here!

fig 1.1: why are figures out of order ? is there a special reason ?

fig.1.1, caption: Level-1 Trigger rates

fig.1.1.: the drop of the rate alone doesnt mean too much if we dont know if the signal efficiency is kept high! please add a sentence in the text.

217-219: please add figure with drawing of GE1/1 geometry! a must!

217-219: you need to give a motivation for this geometry. To say that it is implemented in the simulation does not mean much.

fig. 1.2: show also GE2/1 etc (different color)!

233 links => link

235 250um resolution with respect to what (layer, chamber, superchamber)

256 that is => which are

275 seen => illustrated

280 this => the

290 you refer to the "physics performancees outlined in Ch.1" to derive detailed parameters for the chambers. But in chapter 1 I find near to nothing, only qualitative statements like "improve the reconstruction efficiency". I suggest you are much more quantitative in chapter 1.

293 "Hit rate capability"

fig.2.1 caption: "Scanning Electron Microscope"

fig.2.2 can be improved. geometrical data (2mm, 1mm) and voltages would be very helpful

305-306: do you want to say that the resolution is limited anyway be ME1/1 ? please give the ME1/1 phi resolution.

320 response

342 of about 3 T in the endcap region

fig.2.3. right: what for ? remove

fig. 2.4: remove double! improve figure resolution

376 "long term" => over many years

441 please give size in addition to simply saying "1 m class"

443 in total

447 remove "but"

fig. 2.7: what are the structures shown in these pictures ?

461 I have not understood the "pull out pieces"

fig. 2.8: define effective gas gain

494-501: give 3 digits for percentages everywhere (not 98% and later 97.8%) same for fig. 2.10 bottom

fig. 2.9 middle: rescale pulse charge axis

504e MeasurementS

fig. 2.10 top: CF2 ??? this is efficiency per chamber (3-layers ?) what are the other voltage values (except v_drift) ?

fig. 2.10 caption bottom: "sigmoid functions are fitted to the experimental data to obtain the efficiency curves"

fig. 2.11: clean-up

505: above

508: which 10 chambers ?

fig. 2.12: where does resolution dependence on eta come from ? inclincation angle ? strip pitch variation ?

fig. 2.12 caption: difficult to understand geometry without drawing or a reference to a drawing.

554: in the presence of a (?)

fig. 2.16: font too small. scale of z- and r-axes ?

569-575: do you simulate also B field ?

fig. 2.17: please compare to B=0

fig. 2.18 why not up to 3 T ? left: such large angles are irrelevant right: which angle between B,E ?

fig. 2.19 caption: as a function

592 need up to

fig. 2.22: bigger, please! explain what is shown

fig. 2.23: please indicate the starting points of the seven (?) electrons

614 helpful for comparison: what is GWP of CO2 ?

615 remove "most importantly"

620 keeping a

621 ensure a

623 remove "Results... 2015" (appears again in line 631)

627 candidate => replacement

section 2.3 table with basic paramters (geometry, HV, gain etc) would be helpful close to the beginning.

647 an => one

647 destroy only that

fig. 2.2.8 add eta sector numbers

654: where is white end in fig. 2.29 ?

fig. 2.30: relation between left and right side ???

690 and of the assembly

formula 2.3: reference ?

709 drop "best" data, yielding D_GEM = ...

fig 2.3.2 caption: Behavior -> Relation between tension and....

fig 2.33 bigger!

749 and fig 2.34: I am confused: which are the two (?) shielded sectors ?

fig. 2.34: why not split into two figures?

fig. 2.35: explain "corrected and normalized" (corrected for what?)

842 modified easily

fig. 2.42: better picture please

fig. 2.44, 2.46 captions: I would add a few "a", "the".

fig 2.46 caption: remove "one of the editors..."

886 result

926 off of ?

960 system

xxxxxxxxxxxxxx

chapters 4-5: NOT YET READ XXXXXXXXX

1657 experiment's

1662 in this environment

1665 and describe

1673 which background ?

1674 a gas of neutrons and of secondary photons, electrons and positrons...

1676 particles can propagate for seconds without interacting: which ? photons ? no!! neutrons ? I dont believe that!

1677 interact

1679 long-lived neutrons

1681 background is a significant

1683 radiation increases

1684 degraded resolutions

1689 From now on: !!! I will not comment on fragments like "(end C.R.)" nor on missing text and figures !!!

1692 dont need parentheses

table 6.2 explain parameters and discuss their relevance for CMS why last column partially empty ? where are 300/fb year ? when will these scenarios become reality ? is background rate proportional to lumi ?

1701 and following: long-living -> long-lived (?)

1706 produce an ionization

1722 drop "of interest"

1724 the percentages (99%..) should come out of the Fluka simulation

1722-1730 to some extent repeats section 6.1

1783 CSCs and RPCs

1734 From now on: !!! no correction of typos etc any more - to early !!!

1745 where does this number for the rate come from ? from figures 6.1/6.2 and the particle fluxes in table 6.3 ?

table 6.3: total flux uncertainty (upper part of table) too small compared to sum of individual contributions (lower part)

1752 "hydrogen and other, heavier, nuclei"

1768 FOCUS ???

1797-1808 and figure 6.3 please define "primary" and "prompt"

1809 !!! stop reading chapter 6 - it is clearly not ready for a review!

to be continued XXXXX

best, Thomas