1. 1 The ILD LoI IDAG Referees for ILD Benchmarking – J.A. Hewett, W.G. Li Tracking – R. Nickerson Calorimetry – D. Green MDI – T. Himmel

2. 2 Introduction The ILD Collaboration has done an excellent job in studying/optimizing the performance vs. a number of key detector parameters. ILD is keeping options open on specific detector technologies which seems prudent at this stage in the R&D process. The issues with relatively thin calorimetry have been mitigated by using the muon detectors as a calorimetric “tail catcher” behind the magnet coil. Nevertheless, some questions remain as set out in the following pages.

3. 3 ILD LoI – Vertex Detector I What is the headroom for the vertex detector due to machine backgrounds? If the pair background is higher than expected what is the mitigation plan? Is there a quantified uncertainty to the machine background – fig 2.3-5 ? How sensitive is the Higgs missing mass to the beam parameters, e.g. energy spread? – Gaussian 0.3 % ?, section 3.3.1.1

4. 4 ILD LoI – Vertex Detector II What is the plan to align several hundred million independent channels to ~ O (1 um)? How long does it take? What changes are there in flavor tagging if a mis-alignment or more noise is introduced? What kind of alignment accuracy is required to maintain the stated impact parameter resolution? What is the definition of the efficiency in the corresponding plots? What does it mean to have eff=100%? Flavor tagging is studied at Z mass. What will happen at higher energies?

5. 5 ILD LoI – TPC I What is the headroom for the TPC with respect to machine backgrounds? Is there a plan to mitigate if the backgrounds are higher than planned? For example how does one treat field distortions due to ions? Fake tracks are a problem for PFA. What is the tradeoff between tracking efficiency and fake tracks? The ILD, with many TPC hits, should be insensitive here. What is the alignment plan? How much time is needed for an in situ alignment using tracks themselves? Does this change the PFA strategy? Is the endplate included in the MC? Is a 15% Xo assumed? Is a 97% tile efficiency assumed?

6. 6 ILD LoI – TPC II How are E and B fields monitored for distortions? How big are the track distortions and charge loss due to ions? Will they change within the bunch train? Is the E field monitoring as fast as any ILC transient background bumps or must they be integrated over with loss of spatial resolution? How is the temp/pressure monitored and the information fed back into “alignment”? Have TPC misalignments been studied in full simulation w.r.t. physics goals/performance? The TPC needs to both establish and then maintain the alignment The TPC needs to “connect” to the Vertex detector. What is the effect of SIT/SET/FTD/EDT on the overall momentum resolution? On fakes?

7. 7 ILD LoI TPC III How big is the effect of the TPC membrane on track efficiency and momentum resolution due to multiple scattering? How is the double hit resolution implemented in the MC? It would be desirable to have a more quantitative description of the TPC and other tracker alignment procedures. 2 billion pixel pads is ~ 100 x the current state of the art. Can one extrapolate reliably? The MC should be performed with the expected or worse beam background and misalignments to evaluate if performance is robust.

8. 8 ILD LoI - Calorimetry If there are problems with particle flow, what is the penalty for the physics program? Is software compensation a possible approach? Does the 90% r.m.s. quote for resolution mask a problem with resolution tails and steeply falling spectra? – Table 3.2-2 Detector optimization is performed on the basis of PFA jet rms90%. This parameter however is not sensitive to the shifts of the mean energy due to particle loss at the acceptance boundaries, shower leakage, and loss of low momentum particles. How big are these effects? Can they influence the efficiency of jet reconstruction? Is the thickness sufficient with an instrumented tail catcher or is the thick coil an irreducible limitation? What is the relative importance of the tail catcher for higher energy jets?

9. 9 ILD LoI - ECAL The Si surface area is ~ 10 x larger than the current state of the art. Is the extrapolation reliable? Is there sufficient industrial capacity? There are 100 million channels. That is ~ 1000 x the current state of the art. How will gain uniformity (manufacturing) and cross calibration be insured, measured and then maintained? How long does calibration on the Z pole take? Is it short w.r.t. the calibration “drift” time? The test beam constant term – pg 72, pg 75 appears to be non-zero. What is the relation of non-uniformity of the active medium to the constant term? There will be a “constant term” in the energy resolution. Why is it zero in ILD? 10^12 pixels? This is 10000 x the LHC pixel detectors….. Is the extrapolation assured?

10. 10 ILD LoI - ECAL II Options: The crossed scintillator strip option appears to add to the complexity of PFA pattern recognition. Is there a loss of PFA performance of the scintillator option w.r.t. 1 cm^2 pixels? What is the Moliere radius in the 2 options? What is the cost comparison? What is the relative resolution of the digital and analogue calorimetry (ECAL and HCAL)? What is the relative PFA performance?

11. 11 ILD LoI - HCAL What about non-uniformity of the medium due to cracks, supports and the like. Does this not induce a constant term? How would that be corrected? How do you calibrate behind the ECAL? How long does it take to find enough hadrons of high momentum that do not interact in the ECAL? What is the scintillator option sensitivity to neutron backgrounds? Do the CALICE test beam results confirm the claims of the PFA proposed for ILD? What more needs to be done to be confident in the PFA technique? What is the MPPC “saturation” curve? How can it be corrected and what is the resolution loss? Can you use p.e. peaks to cross calibrate to a %? If not is there not a constant term?

12. 12 ILD LoI – General I When will there be a system test of power pulsing with ~ 1 % duty factor and a B field to assess Lorentz force issues – e.g. wire bonds? Does delayed readout preclude pulsing the power? If so what is done in this option? What time interval do the end effects in push-pull imply due to re-calibration and re-alignment? Could you provide a detailed discussion of the considerations which limited the ILD acceptance (in particular tracking) in the forward region? How much does this influence the physics reach? How does the acceptance in the forward region depend on B and L?

13. 13 ILD LoI – General II Why choose only barrels instead of barrels and disks? What cost is there to forward tracking and flavor tagging? Is there an ongoing plan to study ZHH with full and realistic simulation? What luminosity is then required? How long does the measurement take? The DAQ data volume is dominated by machine background. How much headroom is designed into the system? Table 5.1-1 Fig. 3.2.3 is mislabeled. The MC errors in Fig 3.2-4b should be reduced.