Fourth Concept Calorimetry IDAG Dan Green Fermilab
DESY Review Previous calorimeter review was positive and supportive. Main issues are not technical but managerial.
Algebra for Dual Readout • Suppose both Q (quartz) and S (scint) are calibrated with an e beam, so Q and S are measured in “electron GeV”. • Suppose h/e is determined by mapping out pion/electron mean over a range of energy. • Where f = f(E) is the neutral energy fraction of the hadronic cascade. <f> evaluated a la Wigmans or Groom (PDG) – e.g. <f> = 0.11 log(E) • The aim of dual readout is to simultaneously measure E and f and thus avoid the resolution term due to neutral fluctuations event by event, dE = df(e-h) if the calorimeter is not compensating
Algebra - II • Measuring the Q and S response and knowing h/e for both Q and S, event by event E and f can be solved for: • The result for energy is linear in Q and S and therefore an ensemble of particles, a jet, can be measured and yield the correct energy, without df fluctuations, without the need to separate the energies of the individual hadrons in a jet as is needed in PF algorithms.
Algebra - III • On the other hand the result for f is non-linear, so that one gets a weighted mean for f. • For example 2 particle overlap in some cell:
Fourth @ Warsaw - Linearity Extracting E appears to be good to a few % w.r.t. the mean value.
Fourth UIC - Overall All fiber baseline. Depth is ~ 7.8 λ. Dual readout with time history (n)
Fourth- UIC, Energy Resolution Energy resolution achieved is within requirements
Fourth – UIC, n Detection The binding energy fluctuations are determined event by event using the delayed n recoils in the scint fibers. Note the anti-correlation of the n signal with the Q signal (e.m.)
Fourth – UIC, Particle ID Use S and C signals to separate mu (small energy deposit) and e (more C than S) and pions (mix of S and C)
Fourth – UIC, Crystals Baseline is fibers. Crystals have advantages. No longitudinal segmentation for redundant measurements.
Results from CMS Test Beams • For the LHC there have been extensive tests of the calorimetry • These data allow for the extraction of <fo>, the mean neutral fraction of a hadronic shower as a function of beam momentum for pion momenta between 2 and 300 GeV • There were TOF and Cerenkov available which made it possible to study responses to pi, K and p at low momenta.
Data on pion/electron Response This data was taken with a “mip” in the ECAL. The response is purely that of HCAL which is a brass/scintillator sandwich. Note that the data cannot be explained by a single logarithmic behavior for f.
Extraction of the Mean Neutral Fraction Assuming that for the HCAL, e/h = 1.4 independent of energy, one can extract the average neutral fraction as follows: Note that e/h=1.4 fits at high energy but fails, <fo> < 0 at low energies - < 10 GeV. If f>0 then pi/e > h/e=0.7
Particle Species Dependence The kaon and proton response is rather different from the pion response. In a single readout calorimeter this limits the resolution. In a dual readout it appears that a different f will be found at the same E for different species.
Depth of 7.8 Int Lengths Baseline is a fairly deep calorimeter with plastic (S) and quartz (Q) fibers. Depth is sufficient. Expect single particle resolution of: Where 35% -> 26% with slow n readout (binding energy losses) using time structure of S signal
Summary • The particle species dependence should be removed by solving for f event by event. For example f for pions will be larger than for p because the ‘leading particle’ can be a neutral pion in the former case, but a neutron in the latter. • Nevertheless, it would be useful to validate that assertion. • There appears to be energy dependence in the e/h ratios which appears at low energies. It would be useful for the Collaboration to log data below 20 GeV and then re-visit the calibration strategy. • In situ calibration of the HCAL if there is a crystal ECAL in front should be carefully examined.