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LCD Calorimeter Design Issues

LCD Calorimeter Design Issues. Gary R. Bower/Ron Cassell, SLAC Chicago LCD Workshop January 8, 2002. Calorimetry for jets. At NLC energies almost all physics events produce high mass particles (W, Z, t, H?,?)

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LCD Calorimeter Design Issues

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  1. LCD Calorimeter Design Issues Gary R. Bower/Ron Cassell, SLAC Chicago LCD Workshop January 8, 2002

  2. Calorimetry for jets • At NLC energies almost all physics events produce high mass particles (W, Z, t, H?,?) • Their most likely decay modes are into hadronic jets of charged and neutral final state particles. • Reconstructing the high mass particles accurately requires accurately measuring these final state particles. • Charged particles within tracker acceptance will be well measured. • The challenge is the neutrals and the forward charged particles. G.Bower - Chicago LCD Workshop

  3. Energy distribution in jets G.Bower - Chicago LCD Workshop

  4. Unprecedented opportunity • The parameter space of calorimeter design optimization is large. • Shower simulations are cpu intensive. • Recent advent of cheap computing power offers the opportunity to fully explore the design parameter space. G.Bower - Chicago LCD Workshop

  5. Tools required • One wants to be able to rapidly and easily ask and answer questions with simulations. • Need a flexible simulation tool (Gismo, Geant) and a large cpu batch farm. • Need many people who can commit enough time to do serious studies. • Shower simulation programs (EGS, Gheisha) verified with test beam data. G.Bower - Chicago LCD Workshop

  6. Gheisha problems • The Gheisha hadronic shower simulation has been very widely used in HEP for many years. • We discovered numerous coding errors in the program’s logic (not in physics models). • We have acquired quite a bit of anecdotal evidence that other users have found that Gheisha fails to correctly simulate real detector data. G.Bower - Chicago LCD Workshop

  7. Example Gheisha Problems • 2 GeV anti-proton on active dense hydrogen target deposits ~ 7GeV of ionization energy. • Large disparity between deposited ionization energy of pion and proton. • Non-conservation of energy in pi-nucleon interaction. • No charge exchange for pi-< 200MeV, too low for pi+<1GeV (no illustrative plot below). G.Bower - Chicago LCD Workshop

  8. 2 GeV Pbar on active hydrogen Total Ionization Energy Green: before fix Yellow: after fix G.Bower - Chicago LCD Workshop

  9. 5 GeV Pi- & P Ionization Energy Before fix: yellow = pi-, green = p, SD hadronic cal* After fix: blue = pi-, red = p, SD hadronic cal* *arbitrary sampling fraction. G.Bower - Chicago LCD Workshop

  10. 5 GeV Pi on active hydrogen. Ionization energy Before fix = red, After fix = blue G.Bower - Chicago LCD Workshop

  11. Result of fixing errors • Energy distributions are more gaussian. • LCD resolutions and linearity improved. • BUT this proves nothing until the old and fixed versions of Gheisha are tested against real detector data. G.Bower - Chicago LCD Workshop

  12. LD Description G.Bower - Chicago LCD Workshop

  13. SD Description G.Bower - Chicago LCD Workshop

  14. Old and new pi linearity Old range: LD=15%,SD=20% New range: LD=8%,SD=4% G.Bower - Chicago LCD Workshop

  15. Old and new pi resolutions G.Bower - Chicago LCD Workshop

  16. Caveat on pi improvements • The L detector improvements are entirely due to fixes in Gheisha. • The S detector improvements are partially due to a different technique for determining sampling fractions. • Old way: same sampling fraction used for both em and had showers • New way: different sampling fractions for em and had showers. G.Bower - Chicago LCD Workshop

  17. Gamma resolutions G.Bower - Chicago LCD Workshop

  18. Back to the design study program • Goal: build an EM Cal and reconstruction software that can isolate individual photons. • Goal: build EM and Had Cals and reconstruction software that can isolate individual hadronic showers and identify which showers are due to neutral hadrons. • Goal: minimize error in measuring shower energies. • Goal: minimize error in measuring location of showers. G.Bower - Chicago LCD Workshop

  19. Isolation of gammas G.Bower - Chicago LCD Workshop

  20. Refinement of gamma isolation • Further studies have shown increasing the cell energy threshold narrows the shower size and allows significant improvement in isolation rates (which are already very good). G.Bower - Chicago LCD Workshop

  21. Some Design Space Parameters • Sampling vs. fully active. • Cell size and shape. • Detector depth. • Digital or analog. • Radiator/Active material choices and layer sizes. • Readout technology. • Cost/benefit studies. G.Bower - Chicago LCD Workshop

  22. Cal Benchmark Tests • Accuracy of event selection. • Measurement of Higgs’ CP state. G.Bower - Chicago LCD Workshop

  23. Event Selection L Detector % Efficiency % Correct ID* *assumes equal cross section for all 5 processes. G.Bower - Chicago LCD Workshop

  24. CP=E Truth CP=E Truth CP=O Truth CP=O Truth CP=E Data CP=E Data 0.76 0.74 1.94 0.74 CP=O Data CP=O Data 1.41 0.86 0.76 0.47 Higgs’ CP state ChiSq pdf pi/pi case unsmeared ChiSq pdf pi/pi case 5% smearing of Z jet momentum G.Bower - Chicago LCD Workshop

  25. Summary • Establishing a validated accurate hadronic shower simulation program is absolutely essential for Had Cal studies. • Isolation of gammas is easy. • Isolation and measurement of neutral hadronic showers is main job of Had Cal and needs much work. • Optimization of design requires study of a very large parameter space. • Tests of optimization should be against specific important benchmark physics measurements. G.Bower - Chicago LCD Workshop

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