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Measuring Jets with High Resolution: Segmented Dual Readout Calorimeter

Measuring Jets with High Resolution: Segmented Dual Readout Calorimeter. Adam Para, Niki Saoulidou, Hans Wenzel, Shin-Shan Yu, Fermilab Tianchi Zhao, University of Washington. Jet Energy Measurement, what are the Problems?. Problem Set 1: If (Jet energy = energy of the fundamental parton)

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Measuring Jets with High Resolution: Segmented Dual Readout Calorimeter

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  1. Measuring Jets with High Resolution:Segmented Dual Readout Calorimeter • Adam Para, Niki Saoulidou, Hans Wenzel, Shin-Shan Yu, Fermilab • Tianchi Zhao, University of Washington

  2. Jet Energy Measurement, what are the Problems? • Problem Set 1: If (Jet energy = energy of the fundamental parton) • jet definition (cone size, kt cut-off, ..) • initial and final state radiation • underlying event(s) contribution • Problem Set 2: if(Jet energy = total energy of an ensamble of particles) • non-linear response of the calorimeter  dependence on the jet fragmentation • Different response (calibration) for the hadronic and electromagnetic showers  dependence on the p0 component of the jet Problem set 1 (detector independent) dominates at hadron colliders. At lepton colliders the detector response (problem set 2) dominates the jet energy resolution.

  3. An Ideal(??) Calorimeter • Imagine a large calorimeter (for example lead glass) with a perfect readout of all ionization energy deposited in it. The best possible detector?? Not quite, in fact.. • Electron/p0 response is measured very well, but pion energy measurement fluctuations are very large and the response is ~30% lower than that of an electron Q1: Why are electrons and charged pions so different? Q2: Where is the energy going?? Why missing energy fluctuates so much?

  4. The electron – hadron difference(understood since mid 80’s) • Electrons/photons interact with atomic electrons. Total energy of the incoming particle is converted into detectable kinetic energy of electrons • Hadrons interact with nuclei. They break nuclei and liberate nucleons/nuclear fragments. Even if the kinetic energy of the resulting nucleons is measured, the significant fraction of energy is lost to overcome the binding energy. Fluctuations of the number of broken nuclei dominates fluctuations of the observed energy • Large number of broken nuclei: • large number of slow neutrons • Small fraction of energy in a form of p0’s Very few broken nuclei: Small number of slow neutrons Large fraction of energy in a form of po’s

  5. The Path to High Precision Hadron Calorimetry: Compensation for the Nuclear Energy Losses • Compensation principle: E = Eobs + k*Nnucl • Two possible estimators of Nnucl: • Nnucl ~ Nslow neutrons • Nnucl ~ (1-Eem/Etot) • Cherenkov-assisted hadron calorimetry: Eem/Etot ~ ECherenkov/Eionization • ‘EM’ shower: relativistic electrons, relatively large amount of Cherenkov light • ‘hadronic’ shower – most of the particles below the Cherenkov threshold

  6. Cherenkov-assisted Calorimetry at Work: Single Particle Case • Use the ECherenkov/Eionization ratio to ‘correct’ the energy measurement Single particle energy resolution DE/E=0.25/√E Scales with energy like 1/VE (no ‘constant term’ Linear response Corrected pion shower energy = pion energy (“e/p”=1) Correction function independent of the actual shower energy

  7. Modelling Jets • Jet = (here) ensamble of particles • Jet models (to explore the dependence on the jet composition and fragmentation): • ‘basic’: • 50% of jet energy in 1 GeV particles • 20% of jet energy in 5 GeV particles • 10% of jet energy in 10 GeV particles • 10% of jet energy in 20 GeV particles • ‘high’: jets consist of 20 GeV particles • ‘low’: jets consist of 5 GeV particles • for all the above categories: e (= probability of particle being a po) = 0 or 0.2

  8. Measuring jets (== ensambles of particles) • Jet fragmentation (in)dependence • Resolution of Cherenkov-corrected energy measurement is nearly independent of the jet fragmentation • Resolution (and the response) of the uncorrected energy measurement dependent on the jet composition • Fluctuations of EM fraction of jets • do not contribute to the jet energy resolution for Cherenkov-corrected measurement • Dominate the jet energy resolution in the uncorrected case

  9. Practical Implementation of Cherenkov-assisted Hadron Calorimeter • Alternating layers of: • lead glass to read out Cherenkov light • scintillator to measure (sampled) ionization energy loss • Lead glass and scintillator light read out with WLS fiber/silicon photodetector • Longitudinal and transverse segmentation, as required by physics driven considerations, relatively easy • Thin layer of structural material (steel?) may be necessary for support • Ultimate hadron energy resolution likely dominated by sampling fluctuations (thickness of lead glass). Optimization in progress.

  10. Advantage in Comparison with DREAM (Fiber Based Dual Readout) • Very good energy resolution for electrons (using lead glass, nearly 100% sampling fraction), hence… • Uniform calorimeter (EM/Hadron) • Easy transverse and longitudinal segmentation • Relatively small number of photodetectors/readout channels • High yield/detection efficiency of the Cherenkov photons

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