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Methods of Experimental Particle Physics

Methods of Experimental Particle Physics. Alexei Safonov Lecture #16. Today Lecture. Presentations: CMS Calorimeter More on calorimeter energy reconstruction and Particle Flow (PF) Summary of Particle Identification Trigger Systems. Calorimeter Response.

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Methods of Experimental Particle Physics

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  1. Methods of Experimental Particle Physics Alexei Safonov Lecture #16

  2. Today Lecture • Presentations: • CMS Calorimeter • More on calorimeter energy reconstruction and Particle Flow (PF) • Summary of Particle Identification • Trigger Systems

  3. Calorimeter Response • A fairly typical examples of responses for non-compensating calorimeters • Note the broad shape in the response to hadrons • These are due to fluctuations in shower development • Note the offset • Non-compensation

  4. Calorimeter-Based Energy • Jet energy measurement using calorimeter: • Sum up the energy detected in each of the calorimeters: • Neutral pions will be recorded just fine (can set EM calorimeter scale to give EM energy right) • Charged pions (2/3 of the jet energy) have a spectrum of momenta, large fraction of energy for moderate energy jets sits in soft particles (that’s because QCD partons shower a lot, especially at softer scales where effective alpha_s is large plus you get those soft and collinear divergences) • High momentum ones will have some depositing most energy in HAD calorimeter, others will shower all over the place • Softer ones (most of the constituents of the jet) will likely not make it too far into the calorimeter and will have their energy significantly lower due to e/h not being equal to one • The result is an offset in the energy measurement

  5. Particle Flow • The key constraint to do well is you need well segmented calorimeter so that you can “see” the deposits and assign them to charged tracks, likely photons and likely neutral hadrons

  6. Calorimeter vs PF Reconstruction • Tau lepton decay products consist mainly of ±‘s and o‘s • Similar to a regular jet, but perhaps easier as taus don’t have many soft pions coming with it • Note the large offset in the calorimeter-based jet energy (blue) • Non-compensation and fluctuations in shower development are main causes for ti • Compare with Particle Flow • Note CDF is highly not optimal for PF: too large calorimeter towers (≈0.10.25) • Hard to separate overlapping particles Cf. typical tau size R~0.07 • Even with all the deficiencies, the difference is spectacular

  7. Case Study: The CMS Calorimeter System Alexx Perloff

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