ILC-inspired TPC for Tlep ?

Philippe Schwemling

Machine relevant parameters

• Circumference : 80 km• Number of bunches : 4400 (@ Z peak)• Bunch spacing : 18.2 m (55 ns)

Most demanding : lowest energies (Z peak)Rates : 16.8 kHZ hadronic Z decays (1 every 60 μs avg, or 1 every 1091 BC) 33,6 kHz Bhabhas (1 every 120 μs avg, or 1 every 2182 BC)

ILC CLIC

Why consider a TPC at Tlep ?

• Large (continuous) tracking volume at reasonable price.• Strong past experience with TPCs (LEP)• Very low material budget (typically 0.05 X0 in r, up to

0.25 X0 including endplates)• Continuous tracking eases reconstruction of non-

pointing tracks :– Physics signatures– PFA

• dE/dx measurement (5% resolution)

ILD TPC parameters

• R internal : 229 mm• R out : 1808 mm• Z length : 2×2350 mm• Drift gas : Ar CF4(3%) isobutane (2%)• B=4 T• E = 350 V/cm (Arxiv 1006.3220v1)• Other data extracted from ILC TDR

Gas properties (Arxiv 1008.5068v2)

Dt=50 μm/cm ≈800 μm(Comparable to ILD announced2-hit r-ϕ resol : 2 mm) W=80 μm/ns drift time = 25μs

(B=4 T, E=350 V/cm)

Putting it all together

• Average time between hadronic events : 60 μs• Total drift time (electrons): 25 μs on

average, 0.4 hadronic event drifting in the TPC• Probability of events mixing in z negligible : 2-

hit r-z resolution is 8 mm, or 90 ns drift time, or 1.5 BC

• A ILD inspired TPC with Micromegas position measurement looks viable as a TLep detector.

Cooling and power pulsing considerations

• ILC TPC end-plate power dissipation : 100 W/m2 (with power pulsing, i.e. 1% of the dissipation at 100% duty cycle)

• TLep TPC endplate : 2700 W/m2 (not 10 KW/m2, power pulsing gains factor 27 only)

• Most of the power comes from the back-end, where progress can be expected R&D

• FE is 5 mW/channel for 10 mm2/channel (500 W/m2 without power pulsing)

• However, power pulsing is a source of complication, especially common mode noise.

Is power pulsing possible ?

• There will be a (not power pulsed) Si tracker inside the TPC

• There will also be a fast (compared to the TPC)calorimeter. If it has to be power pulsed, can alsocomplement it with a small non power-pulsed 4 π trigger layer (Si ? Scintillating fiber ?)• Si tracker and calorimeter can be used to trigger the TPC

readout electronics power.• There is a lot of latency to build the trigger decision (60

μs on average) !

Power pulsing in practice

HARDROC chip performance studies

2 μs would allow a significant power saving.

25 μs is relatively useless, but is the DAC is absolutely needed ?(used to program the internal trigger threshold)

Evaluation of the duty cycle

PictureTaken fromWenxing Wang’s thesis

Electronics live time : o (1 μs )+ 2 μs duty cycle can be about 5-10% (on average)

TPC endplate power consumption would immediately go down to 1000 W/m2

Distorsions due to ions

May be managed differently at Tlep than at ILC : gating secondary ions easier at Tlepbecause no need for continuous operation !

Ion drift time is about 1s ions from 16 800 successive collisions present at any time in drift volume

Ion back-flow (cont’d)• Primary ions will be a problem :• Primary ionization due to about 17 k events present at

the same time in the TPC• Calculations exist for ILC, to be transposed to Tlep.• Track distorsion can in principle be corrected since

charge distribution is known – How well can this work ? Simulations

• Note : ILC momentum resolution performance need dominated by hZ reconstruction.

• Is such performance needed for physics at the Z pole ?

Conclusions

• Effect of primary ions– To be quantified– If needed, performance of corrections to be studied

• Some R&D needed to minimize power consumption• Detector performance needed for Z-pole physics

may be revisited.• Strong existing detector expertise on TPCs at Saclay

(and elsewhere)• A TPC for TLep is an attractive option !