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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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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?,?)

  • 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


Energy distribution in jets

G.Bower - Chicago LCD Workshop


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


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


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


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


2 GeV Pbar on active hydrogen

Total Ionization Energy

Green: before fix Yellow: after fix

G.Bower - Chicago LCD Workshop


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


5 GeV Pi on active hydrogen.

Ionization energy

Before fix = red, After fix = blue

G.Bower - Chicago LCD Workshop


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


LD Description

G.Bower - Chicago LCD Workshop


SD Description

G.Bower - Chicago LCD Workshop


Old and new pi linearity

Old range: LD=15%,SD=20%

New range: LD=8%,SD=4%

G.Bower - Chicago LCD Workshop


Old and new pi resolutions

G.Bower - Chicago LCD Workshop


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


Gamma resolutions

G.Bower - Chicago LCD Workshop


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


Isolation of gammas

G.Bower - Chicago LCD Workshop


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


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


Cal Benchmark Tests

  • Accuracy of event selection.

  • Measurement of Higgs’ CP state.

G.Bower - Chicago LCD Workshop


Event Selection L Detector

% Efficiency

% Correct ID*

*assumes equal cross section for all 5 processes.

G.Bower - Chicago LCD Workshop


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


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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