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4th Concept Detector

IDAG meeting, 14 April, 2009

P. Grannis, R. Godbole, E. Elsen, T. Kobayashi, S-K Kim

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General comments

Two 4th authors or 4th also ILD; two also SiD; one is both ILD and SiD

Compared with ILD and SiD, there is very little discussion of optimization (B field, radial, axial boundaries, etc.) Also little focus on potential alternate technologies. The 4th concept starts from quite definite technology choices at the outset and then designs around them.

Point is made that there is benefit from subdetectors that do not require information from other subdetectors (e.g. PFA calorimeters require tracking info). Also that 4th “does not require auxiliary detectors” (tail catchers, intermediate silicon tracking, etc.) Is this really a benefit? If a combination of subdetectors does the job, is that OK?

Point made to beware of “engineering creep” – degradation of performance when engineering details are filled in (supports, cooling, cabling etc.). This is a valid concern, but is 4th better off in this regard than other concepts?

There appear to be many inconsistencies in the LoI (#BGO Xtals, numbers in plots ≠ text, calorimeter depth, etc.)

A table of the main detector parameters (radii, z, B fields, typical resolutions etc.) would be very welcome.

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Vertex detector

No explicit 4th Concept effort on vertex detector; they claim to use the SiD design (but apparently without the SiD added pixel disks designed to bridge the gap between vertex and outer tracking). Some version of a vertex detector is employed in their simulations.

Occupancy plot Fig. 39 is not clear enough to evaluate

4th claims to integrate over 10 bunches, but SiD claims to resolve a single bunch.

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Propose open cell (0.6cm) drift chamber with ~240 cells in depth. 19<R<150 cm. Stereo angles of 55 – 213 mrad. There are 66K wires. Use a slow gas, as in the KLOE chamber, with 90% He/10% iButane (flammable). Drift occurs within 1 bunch crossing.

Performance is based on MC simulation (with 2cm cells?). (1/p) = 4 x 10-5 (sagitta error) with MCS term of 8 x 10-3 (ILD claims (1/p)=2x10-5 ).

Why is 4th Higgs recoil mass resolution (Z() H) so much worse (295 MeV) relative to ILD (77 MeV)?

Central feature is use of cluster counting. (No previous collider detector of this sort to my knowledge)

Scope traces of pulses are shown, but there is no prototype available. An algorithm, not well described in LoI, takes hit time of successive clusters and a probabilistic model of cluster formation to get a best estimator for the impact parameter b of track wrt wire.

How does this algorithm work in strong magnetic field when clusters drift on curves? In multiply hit cells?

Simulation shows (b) ≈ 40 m

Tracking

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Occupancy in inner layer for ttbar 6 jet events approaches 1!

Tracking continued

No forward tracking is discussed (‘may possibly need’). Resolution plots from central chamber show serious resolution degradation for < 20O, so I agree that forward tracking looks needed. The proposed end plates of the central chamber are domed to carry the load (and increase the length of inner wires, hence occupancy on inner wires), so impinge on the space wanted for Fwd tracking.

They do mention the possibility of inserting Si disks either within the chamber volume (accessibility, cooling?), or outside the end plate (MCS problems).

At end of LoI, mention adding a forward toroid magnet to improve p/p !

Alignment, calibration was not discussed.

Electronics design is not well specified:. Is power cycling planned?

Black: signal tracks

Red: one background evt

Claim (dE/dx) = 2.5% on paper, 3.7% realized, based on truncated mean cluster count.

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Tracking questions:

1. The CluCou concept still relies on simulation, not prototypes.

2. We would like to see more detailed description of the algorithm for impact parameter, and the specific details of the MC simulation. In particular,

3. What is the plan for forward tracking options

4. What efforts have been made to optimize the geometrical parameters of the chamber (e.g. # cells, outer radius).

5. What is power consumption, power cycling plan, effect on temperature in VTX cavity?

6. Give more detailed description of the domed end plates.

Do optimization of tracking: cell size, drift distance, incorporation of forward tracking, chamber radii, etc.

What is the effect of multiple track occupancy in the cells? What is the performance after simulation of the front end cluster formation electronics? How sensitive are algorithms to Lorentz force on drift electrons and change in B field strength? On diffusion along the drift distance?

Verify the simulations with actual prototype chambers in beams

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Calorimetry

4th Concept relies on dual readout (DR) calorimetry as a central feature of the detector. The LoI realization has a DR BGO crystal front section aimed largely at EM showers (high and low wavelength filters to pick up Cerenkov and scintillation light). Crystal size is 1x1 cm2 x 25 X0. with crystals oriented radially. (May perhaps go to 2x2 cm2 crystals??)

BGO is followed by a brass matrix fiber spaghetti calorimeter. Clear quartz fibers are sensitive mainly to Cerenkov signal, hence dominantly EM portion of shower; scintillating fibers are more sensitive to the hadronic component. Delayed time scintillation light is sensitive to neutrons released in nuclear breakup, so in this sense it is a Triple Readout calorimeter.

384K projective crystals (1x1cm2)

24K projective fiber cal towers

Outer radius of Cal ~ 280 cm?

1.3 (BGO), 7.3 (fiber) = 8.6

(not 10 as sometimes indicated)

BGO

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C = E(c1 x fEM + c2 x (1-fEM))

S = E(s1 x fEM + s2 x (1-fEM))

Nucl = n1 x Sdelayed

Measure C, S, (Sdelayed) jet by jet; know cj, sj (beam calibrations). Solve for E (and fEM)

Simulated jet E resolution = 29%/√E + 1.2% (including Nucl term) and 34%/√E (without Nucl term) 200 GeV response is

narrow, Gaussian

Calorimetry continued

Energy resolution claimed is very good: Measure both EM and hadronic components of shower and weight them appropriately separately. Further, measure nuclear breakup energy through delayed scint pulse due to neutrons.

pion linearity

Puzzle: Fig. 44 shows (E)/E=30%/√E for dijets

Fig. 45 shows (E)/E=40%/√E for single jets

Why are these sampling terms so different? In absence of angular errors, they should be the same.

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Calorimetry continued

Extensive beam tests were made with (the laterally challenged) DREAM prototype, some with borrowed BGO in front. Performance in DREAM test was achieved by ‘cheating’, using known EBM to get fEM of a shower. LoI says 64%/√E without cheating! (Earlier presentations for combined C+S claimed better??)

4th argues that a single calibration with known energy e’s and ’s gives the response of the calorimeter to its component EM and hadronic components. This calibration has been performed at 40 – 50 GeV and gives the good resolution/linearity for E > ~20 GeV. (But jets contain many low energy particles!)

Light transducers are not discussed for either calorimeter.

Signal pathways for inner BGO calorimeter not discussed. Light collection uniformity across BGO face not discussed.

Calibration is not discussed in much detail. If all 400K towers were to be calibrated in beam, this is a large job! In situ calibrations claimed to be based on Z’s (Giga Z is suggested, but this would come late in ILC running, and would take ~1 yr).

There is no separate forward calorimeter; the BGO/fiber cal extends to 4O (cos = 0.9975). Occupancy in forward towers is not discussed.

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Cerenkov signal for 300 GeV pi

Scintillation signal for 300 GeV piDREAM MC

DREAM MC

The addition of the BGO calorimeter is a new feature from previous presentations. The LoI reports a simulation of the combined calorimeters and comparison to the DREAM test. The details of the combination are not documented, though the LoI and DREAM fiber calorimeters are different in depth. My reading is that simulation and test are not in agreement in all cases:

Calorimetry continued

?

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Calorimetry questions

1. Is a single calibration at 45 GeV sufficient to obtain accurate EM/ hadronic response factors at low energy, for different particle species?

2. Provide support for claim that the ~30%/√E claimed for 4th fiber cal is consistent with measured DREAM 64%/√E (no cheat) with lateral leakage.

3. Provide detail on the method & assumptions to demonstrate that combining BGO & fiber cal works. Justify BGO for crystals. Compare fiber cal only, and BGO+fiber combined, to justify the cost of the BGO.

4. Discuss the calibration in situ. If using Z’s, is the time for collecting sufficient statistics commensurate with potential calibration drift times?

5. Specify the light transducers and cabling paths

6. Discuss the electronics design for the time history measurements in the fiber calorimeter

7. Justify the choice of projective towers (pointing cracks) vs. non-projective (showers cross tower boundaries)

8. Justify the overall geometric choices (Rcal, depth, segmentation) with some performance/cost optimizations

9. Performance of the calorimeter at small angles?

TEST A PROTOTYPE BGO/FIBER CAL!

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Particle ID

13 different handles on particle ID are discussed. Some (dE/dx resolution, e/had in calorimeter, TOF from Cherenkov calorimeter signal) seem more performant than in other concepts.

The simulated and measured (DREAM) e/p profiles for S/C measurements do not seem to agree (size of electron clump).

Simulated 45 GeV e and Data 40 GeV e and 50 GeV

Question: Provide (perhaps process specific) e/pi/K/p efficiency/ purity information?

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Dual Solenoid 3.5T solenoid at R~300cm and 1.5T solenoid at R~550cm to return the flux. Wall of circular coils at z~620cm to contain flux.

Bending by solenoid compensated in separate solenoid at z=7m.

Conductor/coils based on CMS.

Muon chambers between solenoidsOpen geometry requires radiation shielding (1 (1.5) m concrete + B4C liner to allow work on other detector while on IP); about 40g field at 15m.

Suggested advantages of open solenoids: Much lower mechanical forces than with iron return Better field orientation for forward muons Both FF elements (QD0 & QF1) on detector, so unified ground motions (n.b. The other detectors incorporate QD0 but not QF1, so break-point between machine and detector is different.) Allows future upgrades without major refitting Provide laser paths for option Reduced crane requirements

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Dual Solenoid questions

1. Impact of incorporating QF1 on detector (effect on hall length)? Is there real advantage for ground motion control? Can this capture of the QF1 by the 4th detector be made compatible with the ILC MDI requirement, and with the other detector that operates in push-pull?

2. Develop a comparison of physics, MDI complexity and cost for dual solenoid vs. conventional iron return.

3. Does the dual solenoid, end wall coil configuration satisfy the B-field constraints of machine optics at the IR? What tolerances need to be set on the coil alignment, field shaping etc.?

4. What happens when one or the other (or both) solenoids quench?

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Muon system

Muon chambers made of Al straw tubes of R=2.3cm fill the annulus between solenoids. The same cluster counting technique is proposed as for the central tracker. The muon tubes integrate 6 bunch crossings.

31K barrel tubes of length 12 m (3 separate wires in length, ganged together). No stereo layers, but current division for z coordinate.

End wall muon chambers with 18 tube planes (9K); stereo of ±60O

Claim alignment is easier than Atlas due to redundancy on tracks, so no need for complex laser system.

Muon system questions:

1. What benefit from the second muon momentum measurement over just ID?

2. Is cluster counting really needed for muons?

3. What are muon system stand-alone resolutions in r and z vs. ?

4. What is error ellipse at muon system from projection of inner muon track?

5. Justify that a more complex laser alignment system is not needed.