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How to do Calorimetry at CLIC ?

How to do Calorimetry at CLIC ?. Graham W. Wilson 8th May 2001. Introduction. CLIC environment : Bunch spacing of 0.67 ns (LHC 25 ns, TESLA 330 ns) 154 bunches in 100 ns. Bunch length 30 m m (LHC 30 cm, TESLA 300 m m) 3.4 gg ->hadrons events with pT>3.2 GeV per BX

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How to do Calorimetry at CLIC ?

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  1. How to do Calorimetry at CLIC ? Graham W. Wilson 8th May 2001

  2. Introduction • CLIC environment : • Bunch spacing of 0.67 ns (LHC 25 ns, TESLA 330 ns) • 154 bunches in 100 ns. • Bunch length 30 mm (LHC 30 cm, TESLA 300mm) • 3.4 gg->hadrons events with pT>3.2 GeV per BX • 500 gg->hadrons per 100 ns train ! • Need more detailed understanding of energy flow in the gg->hadrons events to understand impact on wide-angle physics.

  3. Guesses at gg characteristics • TESLA at 500 GeV has 0.02 gg/BX with each event carrying 100 GeV of energy. • For CLIC at 3 TeV, 3.4 gg/BX. Assume 300 GeV per event. • Assume 30 GeV of scalar ET per event measured with 10% precision. • Assume 150 GeV of energy lost in BP at mean angle of 20 mrad (ET = 3 GeV) • So, ET smearing of about 5 GeV per event. • And vector ET smearing of 100 GeV per train. (ie. 0.07 of Eb) • Compare this with typical pT_min of 0.07 Eb for SUSY studies with a veto angle of 35 mrad. • So for 5sigma at 0.1 Eb, need a factor of 10 lower smearing from gg, ie accept 1-2 BXs and not 154 ! • If the bunch-length can also be used -> can improve a bit too. • Conclusion : gg looks like a big problem

  4. Calorimetry Philosophy ? • Energy flow ? • Using tracker and high granularity ECAL, HCAL to reconstruct particles and energy without double counting. • Depending on the physics channel (eg.qqbar) the boost and collimation of the jets may prohibit efficient separation of tracks from photons. • However the multi-fermion final states (6,8,10 etc) should be quite suited to the approach adopted for TESLA • Jet Calorimetry ? • accept that calorimetry wins over tracking for energy measurement at high E and adopt a calorimeter focussed detector design ? • Since “compensation” relies on collecting slow neutrons - this approach has little potential for reducing bunch pileup.

  5. Bunch structure • 0.67 ns is way beyond existing large scale calorimeter capabilities • TESLA Si-W concept may be pushed to of order 50 ns but little use if the train is 100 ns long. • Looks like at least part of the calorimeter should be designed to be fast. (-> hybrid solution) • Eg. Si-W high transverse granularity (1cm*1cm) augmented with scintillator tiles (10cm*10cm) with many longitudinal samplings for better E-resolution and time stamping. • Shower-max too.

  6. Alternative Faster Technologies ? • Liquid Kr, Xe • potentially few ns resolution, high granularity • cryostats …. • Scintillating crystals • granularity a problem. Some of the more promising (eg. BaF2) emit in UV -so not so clear • Scintillator • granularity not obvious, channel count, calibration

  7. Summary • CLIC poses many challenges to the detector. • Physics program. Pretty clear that di-lepton recoil mass and charm reconstruction is probably not THE detector design issue - so maybe the relative weight on vertex/tracker vs calorimeter should be reconsidered. (-> lower B, larger R) • If we want and can separate particles from different BX’s we need to do it at least in the calorimeter for photons and neutrals.

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