Dear Mirjam, Thank you very much for the referee report. We understand that PLB, categorically, does not publish serial publications and we agree with this policy. However, we assure you that our paper is not a serial publication. We believe the text of the introduction section was insufficiently explicit as to our primary goals so it had the erroneous appearance of a serial publication. There is significant and new content in our paper and we quickly summarize the issues before addressing the individual referee comments. It is true indeed that we have a published one paper on the co-annihilation region involving tau signals at the LHC. However, that paper was about doing a measurement of Delta M [mass difference between the stau and the neutralino] as a powerful way of establishing that we are in the co-annihilation region. In that paper we made a significant assumption about the availability of a high quality gluino mass measurement. We have since realized that there are no applicable studies that show a gluino mass measurement is possible at the level required (5% at 10 fb-1). The only study that is potentially applicable [Ref[13] in our new paper by Paige and Hinchliffe] studies a large tan\beta scenario (as we use) but does not use a small Delta M and uses a much smaller gluino mass. There are good reasons to believe that methods would either not achieve a ~ 10\% precision, or if it did it would require significantly more than 10 fb-1 of luminosity. Thus, a new, high quality and early method of measuring the gluino mass remains crucial, not only in its own right, but as a vital component of the establishment of the co- annihilation region. Our paper addresses this issue directly. In particular, we present new methodology to measure the gluino mass and do so in a way that is likely to be the most sensitive. In re-reading the text we see now that this primary motivation for our analysis, in the introduction of the original draft, was unclear. We are glad the referee pointed this out so we could fix it and make it more explicit. We next walk through the referees comments and respond to them individually, including where we have changed the text. "This paper studies the prospects for measurement of the mass difference between the neutralino LSP and the stau, assuming that the LSP is the cold dark matter, and that agreement with the relic density measured by WMAP is attained via LSP co-annihilation with the stau lepton which coincidently is close in mass with the LSP. While there is really no explanation of this mass coincidence, there is a region of the commonly used mSUGRA model (also adopted in this paper) where the stau and the lightest neutralino can be close in mass." We are pleased to find that the referee is familiar with our scenario. The proximity of the stau and the neutralino mass in the mSUGRA model occurs due to the factors arising from the RGEs as shown in [Nucl.Phys.B606:59,2001]. We have made this more explicit in the introduction and added this reference. "The scenario studied in this paper has already been studied by a subset of these authors in a paper already published in Physics Letters (Ref. 13 of the present paper), where the detectability of the tau signal as well as the prospects for the determination of the mass difference between the scalar tau and the neutralino in LHC experiments have been examined." We agree with the referee's comments up to this point in the paragraph. "The present study is clearly a follow-up of the previous paper where all the essential ideas were laid out." In our previous paper we assumed that the gluino mass can be measured at the level of 5% in order to establish the co-annihilation region. As we mentioned above, there exists no study/method in the literature which shows that it is possible with the amount of luminosity that would be needed to establish the stau-neutralino co-annihilation region. In this paper, we showed how to measure the gluino mass in the context of mSUGRA and the mass difference between the stau and the neutralino at the same time with high accuracy. The study presented in the present paper is not a simply a "follow-up" since the major idea of measuring gluino mass with this accuracy as presented in this paper is totally absent in our previous paper. We have made changes in the introduction (5th paragraph) and conclusion to make this more clear. Further, there are many new ideas laid that are essential to our new results. In particular, a new observable N_OS-LS is used as a measurement value (as opposed to just a way to discover SUSY in the co-annihilation region) and that it has excellent and inversely proportionally relationships to both DeltaM and MGluino. This is explicitly shown in Figure 4. Again, as we mentioned earlier that we studied the measurement of Delta M in our previous paper but not the gluino mass measurement which is the primary goal of this paper. "The authors motivate the present paper by arguing that in their earlier study (Ref. 13) they had assumed that the gluino mass would be independently known (presumably from a study of multijet plus missing transverse momentum events), whereas they do not assume the same for the present analysis. While they did indeed assume that an independent data sample would lead to a determination of the gluino mass, I think this was an extremely reasonable assumption, and not a shortcoming of their analysis." We fundamentally disagree with this assessment of how reasonable the assumption is. After a full review of the literature we find that there are NO gluino mass measurements studies for the co-annihilation region. Since the existing study [Ref[13] in our new draft, Paige and Hinchliffe] for a large tan\beta scenario (as we use) does not use a small Delta M and uses a much smaller gluino mass a significantly larger luminosity must be collected in order for that measurement to achieve its stated \sim 10\% precision. Further, the observable $M_{\rm eff}$ constructed out of the 4 jets plus missing energy final state (as is used in the discovery of SUSY signal and gluino mass) also may not work in our scenario, since the squark and the gluino masses are close in this co- annihilation region and two out of the four jets can easily be tau jets. Once the taus counted as jets, the neutrinos arising from their decay would create further problems in the analysis. That being said, this rationale was not laid out in the original text clearly. We have fixed the introduction and the conclusion, as mentioned earlier, to make it more explicit. The text should now make it more clear that this is not simply a minor expansion of our previous work, but rather a major new step forward in studying the prospects for measuring the SUSY parameters in the co-annihilation region. "The new item in this paper, I think, is the claim that they can simultaneously determine the gluino mass and the LSP-stau mass difference from the tau data sample alone. Fig. 4 is their demonstration of this. " This is correct. "However, if I understand correctly, this must be a model-dependent result. The count rate (for OS-LS events) is governed by the gluino mass, while the TWO independent neutralino masses and the stau mass naively govern the di-tau mass distribution. Of course, the latter is also affected by the gluino mass via the boost that the second neutralino gets when it is produced in gluino decay. What I then do not understand is how, without further assumptions, the two bands in fig. 2 can determine the gluino mass and the LSP-stau mass difference. It seems to me that for given values of these two quantities, the bands would change if the second neutralino mass were changed. If this is correct, the analysis presented in this paper must be MODEL-DEPENDENT (in this case dependent on the gaugino mass unification condition together with the fact that the two lightest neutralinos are gaugino-like)." Again, our text must have been unclear because within an mSUGRA context the count rate is governed by both the gluino mass and by Delta M. This is shown explicitly in Figures 2a and 2b. However, we have made this more explicit by adding an equation in Section 3. Similarly, the mtt mass is also governed by both Deltam (directly) and the gluino mass (indirectly through the mSUGRA relations). This is shown in Figure 3, and equation 1. In particular the neutralino2 and neutralino1 masses are directly related via the mSUGRA relations. We have this relationship, and how mtt is a function of MGluino, more explicit by adding a new equation in Section 3. This is not an issue of boost of the objects. The referee is correct that these relations are model-dependent. It is also true that the cross over point of the bands in Figure 4 would be changed if the second neutralino mass were changed. However, the second neutralino mass is directly related to the other masses via the mSUGRA relations as described above. We don't see this as a substantive problem because we have explicitly used an mSUGRA model. We have added more text to indicate more explicitly how these parameters would change if the mSUGRA relations were released (in particular gaugino universality), however we have not attempted to study the breakdown of universality or its impact on our measurements as this is outside the scope of this paper. However, we have indicated that if an independent measurement of a gluino mass were made, we could study this directly at the LHC. " It seems to me to be really stretching it when (in Sec. 4) the authors suggest that their analysis may yield the only determination of the gluino mass. Won't the multi-jet sample at the LHC provide this information (except if gluinos are way too heavy -- which is not the case for the paprameters they choose in their illustration)?" We agree that this was overstated and have softened the wording. "While the analysis is probably technically correct, I think it is fair to regard it as a follow-up of their previous study, extended to other regions of the parameter space. The one novel feature, for reasons I detailed in the previous paragraph, does not seem to me to be a real gluino mass determination. While this is a matter of opinion, I do not think it is appropriate to publish a series of follow-up papers in a letter journal (even though it is not difficult to find examples of such serial publications even in Physics Letters B). This is, however, a matter that the journal editors should decide on. Independent of the publication venue, I think that the reader would be better served if the authors would clarify just what the meaning of Fig. 4 is in view of the remarks of the previous paragraph; if they indeed agree (I think that they will, since they do say on p. 9 that agreement of the gluino mass with that extracted directly will serve as a test of their scenario) that this is model-dependent it would be best to be explicit about it. In this case, I do not think though that it is reasonable to claim that the tau events are a measurement of the gluino mass -- as they do both in the title and abstract." We are pleased to see that the referee believes that our result is technically correct. However, for the reasons given above we strongly believe that our paper is not a "follow up," and it is simply untrue that just extended our results to "other regions of parameter space." We are not only making a measurement of DeltaM more robust, but we are showing that a measurement of MGluino is possible, and with good precision. This high quality measurement is crucial to establishing that we are indeed in the co- annihilation region. For the reasons given above, we believe the previous version of our text made it unclear why this measurement technique is indeed a real gluino mass determination. The text has been fixed both in the introduction and in section 3 for this problem. This includes a better lead up to the understanding of Figure 4. We also have modified the title. To conclude, we believe that we have produced an important and novel work on the prospects of measuring SUSY parameters in the important co-annihilation region of SUSY. This work not only describes novel techniques to robustly measure DeltaM, it provides the first study to determine the gluino mass in the co-annihilation region, and appears to be the best measurement technique at large tanBeta. We can see why our previous version of the text might have been erroneously interpreted as a serial publication and are indebted to the referee for pointing out that both the motivation for our work and the description of the relationships between the measurement values on the SUSY parameters were unclear. We hope that the new, fixed version of the text makes it more explicit why this is an independent result and worthy of publication in its own right. We hope our responses, and the new text, make this case, and look forward to a positive response.