Introduction

First (and second) paragraph:

A reference should also be made to the ”fast simulations” developed by CMS and ATLAS, which are two to three orders of magnitude faster than the GEANT-based simulations, while minimizing the loss of accuracy, and allowing the ”complex reconstruction algorithms” to be used.

(Andrea's temporary comment) I don't think it's very relevant, but just for the sake of compromise, we can do. For ATLAS, I know this reference: ​http://inspirehep.net/record/1196761

but it is only for tracking; a more generic one, although it is just a conference proceeding, is ​http://inspirehep.net/record/1211010

(I suggest to cite both, for completeness.) For CMS, the most recent and appropriate is: ​http://inspirehep.net/record/1214935

but there is the delicate point that there is not his name on it ;)

So in addition one could also cite ​http://inspirehep.net/record/1117120 (but not this one alone, because some details are now obsolete, like the pileup treatment). Both are conference proceedings, but it is standard practice in CMS to cite them. And, still for CMS, one could argue that also this one should be cited, because it contains comparison to data: ​http://inspirehep.net/record/1230052 Please let me know if you think that these are too many citations.

Third paragraph:

L4: It’s not enough to say that the magnetic field is uniform (as this adjective qualifies only the absolute value in Tesla). The word ”axial” and the expression ”along the beam direction” could be used to the sake of clarity.

L5: The energy smearing applies also to all other particles, not only to photons and electrons. Why are these two particles singled out here ?

L6-7: ”Jets and missing energy can be computed with the particle-flow al- gorithm.” is an incorrect sentence. First ”the particle-flow algorithm” would probably need to be somehow defined, or at least given a reference. Sec- ond, ”the particle-flow algorithm” does not deliver jets and missing energy, it delivers a list of reconstructed and identified particle candidates. Jets and missing (transverse) energy can then be obtained from either calorimeter de- posits, or from these particle candidates. Both approaches are conceptually and technically identical for jets and missing energy. This misconception of the PF reconstruction appears in several places in the article, and most likely in several aspects of the simulation implementation too. A number of the comments that follow are related to this aspect.

The suggestion regarding the last two comments is to explain that all particle energies are smeared according to parameterized detector resolutions, and that physics objects used in physics analyses (isolated leptons, isolated photons, jets, missing transverse energy, taus) are derived from these smeared energies. The concept of calorimeter and particle flow algorithm is to be kept for the next paragraph.

Paragraph 4:

L1: Add ”which was only simulating energy deposits in the calorimeters” or anything closer to the truth, after ”predecessor”.

L3: Add ”to deliver a list of reconstructed and identified particles as close as possible to the true (generated) list.” after ”sub-detectors”

L6: ”fully modular” would need some more explanation for the reader to understand it. But is it so important for a JHEP article ?

Paragraph 5:

L2/L3: Propose to drop. The software implementation is out of context.

PAGE 3

Par 2:

L5/6/7: This sentence starts with ”As for the tracking efficiency”, but nothing was said about the tracking efficiency settings prior to this sentence. A mention of the fact that this efficiency can be user-defined should appear at the beginning of the paragraph, and replace ”(good)”.