Reply and Comments by GLD: IR task force

Q1(B) | Q2(geo) | Q3(lowQ) | Q4(max.bkg) | Q5(bkg.prms) | Q6(L*) | Q7(VTX_R) | Q8(2&20mr) | Q9(headon) | Q10(mini-veto) | Q11(bkg@2,20mr) | Q12(DID) | Q13(anti-solenoid) | Q14(up/downstream Pol) | Q15(Z-pole ) | Q16(e-e-) | Q17(detector assembly) | Q18(exp.hall)
  1. What factors determine the strength and shape of the magnetic field in your detector? Give a map of the field, at least on axis, covering the region up to +-20 m from the IP. What flexibility do you have to vary the features of this field map?
  2. Provide a GEANT (or equivalent) geometry description of the detector components within 10 meters in z of the IP and within a radial distance of 50 cm from the beamline.
  3. Would you mind if the baseline bunch-spacing goes to ~150 ns instead of ~300ns; with ~1/2 the standard luminosity per crossing and twice as many bunches?
  4. For each of your critical sub-detectors, what is the upper limit you can tolerate on the background hit rate per unit area per unit time (or per bunch)? Which kind of background is worst for each of these sub-detectors (SR, pairs, neutrons, muons, hadrons)?
    • VTX : 1x104/cm2/train for pair background and 1x1010/cm2/year for neutron. The former value is estimated from tracking capability, while the latter is estimated from the radiation damage.
    • CAL ; 1 (MIP) /cm2 /train, where 2820 - 5640 bunches/train, which is true for the digital readout.
    • TPC : The TPC pattern recognition can tolerate more than 20 times nominal random backgrounds ( warm machine of NLC), for example from synchrotron radiation. Backgrounds from compton scattering and neutrons can result in track segments, the choice of gas and high magnetic should mitigate these backgrounds. Muon backgrounds should not be a problem. Electrons and positrons from pairs and hadrons from two-photon interactions will be confused with genuine tracks; however, TPC particle identification will help in identifying some of these backgrounds. Background simulation studies need to be updated for ILC.
  5. Can the detector tolerate the background conditions for the ILC parameter sets described in the Feb. 28, 2005 document at www-project.slac.stanford.edu/ilc/acceldev/beamparameters.html ? Please answer for both 2-mrad and 20-mrad crossing angle geometries. If the high luminosity parameter set poses difficulties, can the detector design be modified so that the gain in luminosity offsets the reduction in detector precision?
  6. What is your preferred L*? Can you work with 3.5m < L* < 4.5m? Please explain your answer.
  7. What are your preferred values for the microvertex inner radius and length? If predicted backgrounds were to become lower, would you consider a lower radius, or a longer inner layer? If predicted backgrounds became higher, what would be lost by going to a larger radius, shorter length?
  8. Are you happy that only 20mr and 2mr crossing angles are being studied seriously at the moment? Are you willing to treat them equally as possibilities for your detector concept.
    • We prefer the smallest crossing angle even including headon with acceptable backgrounds, an extraction line including polarimeter and energy spectrometer, while as well known the 2mr and 20mr have been determined to be strawman's crossing angles by the ILC-WG4, November 2004. If the 2mr encounters a serious difficulty, we would like to suggest a further study on the minimum crossing angle in the range of 2 and 20mr.
  9. Is a 2mr crossing angle sufficiently small that it does not significantly degrade you ability to do physics analysis, when compared with head-on collisions?
    • Since the present BCAL can cover the angular region down to 5mr with the 2mr crossing angle, there is expected to be no difference between headon and 2mr crossing angle in term of the minimum veto angle measurement. However, we would like to reserve the headon scheme for physics studies on extremely precision measurements, e.g. Z-pole, SUSY, luminosity measurement, and there is active group (Kyoto university) for R&D on RF kicker which may realize the headon scheme.
  10. What minimum veto and/or electron-tagging angle do you expect to use for high energy electrons? How would that choice be affected by the crossing angle? How does the efficiency vary with polar angle in each case?
  11. What do you anticipate the difference will be in the background rates at your detector for 20mr and for 2 mr crossing angle? Give your estimated rates in each case.
    • Also, full simulation studies are necessary, which is under study.
  12. What is your preliminary evaluation of the impact of local solenoid compensation (see LCC note 143) inside the detector volume, as needed with 20mr crossing angle, on the performance of tracking detectors (silicon, and/or TPC, etc.)
  13. Similarly, what is you preliminary evaluation of the impact of compensation by anti-solenoids (LCC note 142) mounted close to the first quadrupole?
  14. Do you anticipate a need for both upstream and downstream polarimety and spectrometry? What should be their precision, and what will the effect of 2 or 20 mr crossing angle be upon their performance.
    • Generally, both polarimetry and spectrometry are desired for complementary measurements in order to estimate effects during collisions at IP. Detailed evaluation should be required at upstream and downstream cases for any depolarization in long beam line and experimental feasibility with huge background of disrupted/beamstrahlung beam, respectively.
  15. Is Z-pole calibration data needed? If so, how frequently and how much? What solenoid field would be used for Z-pole calibration? Are beam energy or polarization measurements needed for Z-pole calibration?
    • We are evaluating these issues for each detector. Also, we need how much luminosity is extected on Z-pole during the usual experimental run at ECM=500GeV. At present, we assume the luminosity(L) of 1033/cm2/s for VTX and CAL calibration runs, while L= 1032/cm2/s is assumed in the TPC calibration. Preliminary results are listed below;
      • VTX; If we have 1 fb-1 integrated luminosity, which can be achieved by 10 days run with 1033 luminosity, we can accumulate 3x106 muons (50M Z). Then we can get 1000hits/cm2 at the outermost layer of the VTX. This number would be enough to get precise position calibration of the VTX. So we would like to propose to have; 1 fb-1 Z-pole run : Once per run period (=one year?) and 100 pb-1 Z-pole run : Once per month.
      • CAL requires sufficient number, about 100, of MIP particles passing in every 1cm x 1cm segmentation for 100 m2 scintillator in the electromagnetic calorimeter. If muon pairs are only used (BR is 3.3%) on Z-pole, integrated luminosity of 10 fb-1 would be necessary, i.e. 100 days with L= 1033!. CAL group must study seriously if hadronic events can be used for the calibration, or some clever method.
      • TPC by R.Settles and M.Thomson: The answer needs a guess at how often problems with the detector will occur that require calibration data. To not just make a blind guess, we took the data from Lep2 running, where this procedure (Z pole running for calibration) was used several times when detector problems cropped up. The last year of Lep2 running (2000), where things were really being pushed by the machine, the track record was: Z Running needed at Lep2: =>per detector<= 3/pb at the beginning of the year, andone run of 0.5/pb during the year. So, we propose then to use the following working hypothesis: Z Running for ILC: =>per detector<= 10/pb at the beginning of a year, and one run of 1/pb during a year , since the detector(s) will be more complicated. If I remember correctly, the projected Z-pole luminosity for Tesla for "calibration" (i.e. no special beam gymnastics to push up the luminosity like would be needed for the "GigaZ") would be 1032/cm2sec so that calibration at the beginning of the year would take =>per detector<= 30hours of beam and during the year =>per detector<= 3hours of beam. To repeat, this is just a guess, but at least it is based on past experience. At the very beginning of the ILC operation, much more Z running would be needed for calibration of the detector(s). This will mainly be determined by the calorimeter; Calice has studied this but I don't remember what their number is, maybe somebody else does...
  16. Would you like the e-e- option to be included in the baseline, and if so what minimum integrated luminosity would you want?
    • Probably no, since there is no strong desire in GLD group at present. However, the e-e- option may be kept for the physics motivation may become relevant in future, in such way as SUSY or new physics would demand.
  17. What will be your detector assembly procedure.
  18. What size is required for the detector hall?