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)
- 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?
- The magnetic field together with the iron structure is shown in figures (pdf), and the field map data can be found here (htm or xls) ) .
- Factors which determine the strength and shape of the GLD magnetic field are;
(1) PFA performance. One of the figure of merits of PFA is proportional to BR2.
(2) TPC resolution. It is proportional to BL2. Strong magnetic field suppresses electron diffusion, which is preferable for getting better resolution. Field uniformity is necessary to get excellent momentum resolution.
(3) Beam background to VTX.
(4) Technical difficulty/cost problem of huge solenoid.
- Error estimation of the leakage field along the beam line; experiences of BELLE detector, KEK ( ppt, pdf ) and the brief explanation; which is to be compared with the tolerance of the field estimated by A.Seryi.
- 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.
- The GLD GEANT-4 geometry can be available in the homepage .
- The IR geometry, especially beam pipe and VTX innermost radius, depends on the machine parameters. Assuming that the accelerator will seamlessly operate in these parameter sets including the high luminosity one at one center-of-mass energy, the present baseline design should be optimized for the "worst" one which is the high luminosity at ECM=500GeV. Thus, we have the baseline design of beampipe and final quadrupoles in both cases of 2mr and 20mr crossing angles.
- 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
- CAL has no problem for the DAQ will be sufficiently fast.
- The TPC timing resolution is about 1.5 nsec. so that tracks from a
bunch 150 nsec. apart would not be confused. The integrated random
background over the TPC readout time of 50 µ sec. would be the same
for the two bunch spacing options.
Reference : This corresponds to LowQ option of the ILC parameter sets and estimation of incoherent pairs in VTX ( pdf) .
- 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.
- Can the detector tolerate the background conditions for the ILC
parameter sets described in the Feb. 28, 2005 document at
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?
- We would need to run background simulations for the different parameter sets, which is under study. Some of results are expected to be presented at SNOWMASS.
- What is your preferred L*? Can you work with 3.5m < L* < 4.5m?
Please explain your answer.
- We prefer L* of greater than 4.7m, assuming that the superconducting final quadrupole magnet (QD0) has a 20cm long transition length from cold to warm in front. Two major reasons are (1) to confine low-energy particles within the Be beam pipe, which are backscattered from the CH2 mask in front of BCAL with 2cm inner radius; i.e. maximum radii of 1.6, 1.92 and 1.99 cm at L*=4.5, 4.1 and 3.6m, respectively, and (2)for FCAL/mask to shield TPC active region against photons backscattered at BCAL in GLD, where FCAL and BCAL locate at 2.5 and 3.5m, respectively, from IP. Full simulation are necessary if the backscattered background can be tolerable at shorter L*, which are under studies. First results are expected to be presented at SNOWMASS.
References: pdf and ppt by Y.Sugimoto.
- 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?
- The preferable innermost radius of VTX might be less than 2cm and the polar angular coverage must be |cos &theta | < 0.95 , for good tagging efficiency of charm and bottom quarks as well as jet charge determination. However, the minimum radius must be limited by background consideration on synchrotron radiation profile and a core distribution of incoherent pairs. While the synchrotron radiation profile can be controlled by the collimation depth in BDS, the minimum radius depends on the machine parameters for different beamstrahlung and distruption effects during collisions. If the background is high, the inner radius of the VTX must increase by 10 to 20%. This increase affects the impact parameter resolution and the flavor tagging efficiency, while the effect would be at most 10 to 20% change.
References: recent study and reference therein.
- 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.
- 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.
- 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
- Minimum angular acceptance of the BCAL is 5mrad in both crossing angles, although the 20mr crossing angle scheme has less efficiency of tagging electron in small angles. Need full simulation to verify the experimental feasibility of detection efficiency in huge pair background as a function of crossing angle, which is under study; quick results .
- 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.
- 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.)
- We expect that TPC is the most sensitive detector for good momentum resolution. The DID effect in TPC is evaluating by Ron Settles who will write a LCC note on the effect.
Reference : DID (Detector Integrated Dipole) field has been calculated in GLD by A.Seryi et.al. . The field map is available here.
- Similarly, what is you preliminary evaluation of the impact of
compensation by anti-solenoids (LCC note 142) mounted close to the
- Also, full simulation studies are necessary, especially on background such as backscattered low-energy particles.
- 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.
- 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
- 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...
- 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.
- What will be your detector assembly procedure.
- Assembling procedure of the iron structure is shown in figures ( pdf ). Order of assembling detectors will be as follows; Iron structure-bottom -> Solenoid -> Iron structure-top -> CAL -> TPC-> Support tube for QC, BCAL, FCAL -> TPC slide out -> VTX, IT -> TPC slide back in -> Close endcap.
Before an installation of TPC, magnetic field of the solenoid has to be mapped in details together with the DID as well as the final quadrupole and the anti-solenoid if necessary.
- What size is required for the detector hall?
- Under following assumptions;
(1) Superconducting solenoid is constructed on the surface ground and put down through the vertical shaft of 15m diameter since no space is available for the construction in the cavern; (2) Detector assembly is done beside the beam line; (3) Machine study will be conducted without the detector / with the dedicated detector ; (4) Detector assembly can be conducted during the machine study; (5) The endcap can be opened sideway at the beam line for the maintenance; and (6) Space for the electronics hut is negligible; an area for the experimental hall is estimated to be 35m (width, along the beam line) x 80m (length) x 40m (height) as shown in figure ( pdf ) .
- During the SNOWMASS workshop, the size of the hall was optimized for the 2 IRs with 2mr and 20mr crossing angles; i.e. the above size is slightly large. The resultant size is 32m (width, along the beam line) x 72m (length) x 40m (height), where the beam line is 12m from the inner wall of the hall. Yamaoka's presentation is here ( ppt, pdf ).