Calorimeter Calibration in addition to Jet Energy Scale

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Calorimeter Calibration in addition to Jet Energy Scale

Yamasaki, Elaine, Food and Wine Editor has reference to this Academic Journal, PHwiki organized this Journal Calorimeter Calibration in addition to Jet Energy Scale Jean-Francois Arguin November 28th, 2005 Physics 252B, UC Davis Outline Quick remainder of calorimetry Calibration be as long as e the experiment starts: test beam Calibration when the experiment is running: Hardware calibration Collider data Measuring jets at high-energy colliders Example of a physics measurement: top quark mass Basics of Calorimetry Incident particle creates a shower inside material Shower can be either electromagnetic or hadronic Energy is deposited in material through ionization/excitation

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Basics of Calorimetry II Basic principle of calorimetry: deposited energy is proportional to incident energy Calorimeter calibration translate detector response to incident energy Great feature of showers as long as detector use: length is proportional to logE Electromagnetic showers Created by incident photon in addition to electron electrons emit bremstrahlung photons undergo pair production Length of shower expressed in term of X0 X0 depends on material 95% containment requires typically about 20X0 Created by incident charged pion, kaon, proton, etc Typical composition: 50% EM (e.g. ) 25% Visible non-EM energy 25% invisible energy (nuclear break-ups) Requires longer containment (expressed in ) Hadronic showers

Calorimeter detectors Detector hardware must: Favor shower development Collect deposited energy Can do both at the same time (e.g. BaBar/Belle crystal calorimeters) Or have calorimeters with alternating passive in addition to sensitive material Example of electron shower with lead absorber: Sampling calorimetry (Ex.: CDF) Scintillators (sensitive material) emit lights with passage of ionizing particles Collect light deposited in sensitive material using wavelength shifter (WLS) WLS photomultipliers that convert light into electric signal CDF Calorimeters Segmentation

CDF Calorimeters Construction Go on in addition to built the thing after it is designed! Many institutions in the world participate First calibration: test beam Take one calorimeter “wedge”, send beam of particles with known energy Obtain correspondence detector response energy in GeV A few towers only submitted to test beam Set absolute scale as long as all towers Relative scale as long as other towers obtained later

How does the test beam works (Ex.: plug calorimeter) Per as long as med at Fermilab meson beam facilities Beams characteristics: Various types as long as EM in addition to HAD showers: electrons, pions, muons Various energy: 5-120 GeV (electrons), 5-220 GeV (pions) Beams can be contaminated bias the calibration constants E.g. use Cherenkov detector in front of calorimeter to identify proton contamination in pion beam Why Muons Calorimeter response linearity Extract calibration constant as long as many energy point Can test linearity of calorimeter Can add “artificial” material in front of calorimeter to simulate tracker+magnet material Send pions in addition to electrons to hadronic calorimeter Why sending electrons in hadron calorimeter Per as long as mance determined from test beam From RMS of tower response to same beam energy measure calorimeter resolution Can test tower transverse uni as long as mity (influences resolution) Stochastic term resolution: EM: HAD:

Final detector assembly: getting ready as long as physics! The Tevatron Proton-antiproton collisions at Most energetic collider in the world Collisions every 0.4 s Circumference of 6.3 km The CDF Detector CDF II: general purpose solenoidal detector 7 layers of silicon tracking Vertexing, B-tagging COT: drift chamber coverage Resolution: Muon chambers Proportional chamber interspersed with absorber Provide muon ID up-to Calorimeters Central, wall, plug calorimeter

Calibration when the detector is installed Only a few towers saw test beam, how to calibrate the whole thing Test beam sets the absolute scale as a function energy Two solutions: Hardware calibrations Physics calibration (using collider data) These calibrations need to: Cross-check absolute scale (e.g. test beam not 100% realistic) Track detector response through time Expected degradation of scintillator in addition to PMT PMT sensitive to temperature Uni as long as m response through all towers Hardware calibration Can use radioactive sources that have very well defined decay energy Cobalt 60 (2.8 MeV) Cesium 137 (1.2 MeV) Source calibration can be per as long as med between colliders run Sources are movable in addition to can expose one tower at a time Check uni as long as mity over all towers in addition to over time Sources are sensitive to both scintillator in addition to PMT responses Laser calibrations The lasers are connected directly to PMTs Skip scintillator/WLS steps Used to uni as long as mize PMTs response over towers in addition to time

Physics calibrations Use real collider data For calibration, you have to have some “known” in addition to some “unknown” (the calorimeter response) Examples of “known” in as long as mation: Mass of a well-known particles Ex.: Zee (Z mass measured at LEP) Energy deposited by muons over a given length Muon sample Energy measured in tracker (assuming tracker in calibrated) Redundant to energy measured in calorimeter as long as electrons Example: Z boson mass Z mass measured with great accuracy at LEP using beam energy Background is very small as long as Zee Sample is relatively small, but good enough Z mass peak: Example: E/p of electrons Used as long as relative scale over towers Cannot be used in as long as ward region (no tracker) In plug: rely on sourcing in addition to lasers

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Example: muons as long as HAD calorimeters Muon calibrate detector response to ionizing energy Use muon from J/ as long as identification (mass not used like Z boson) Again, not used as long as PHA (rely on sourcing, laser) Physics with photons/electrons Calorimeter calibration not the only issue Electron/photon physics also rely on tracking Removal of background E.g. remove pion background by studying shower shape Search as long as new physics: Z’ c in addition to idate: Precision measurement: W mass: What are jets Jets are a collimated group of particles that result from the fragmentation of quarks in addition to gluons They are measured as clusters in the calorimeter momentum of cluster of towers is correlated with the momentum of the original quark in addition to lepton Why not using tracker (has better resolution)

Phenomenology of jets Quark/gluon produced from ppbar interaction Fragmentation into hadrons Jets clustering algorithm: Adds towers inside cone Fraction of energy is out-of-cone Underlying event contributes Jet versus calorimeter energy scale Jets are complicated processes Previous calorimeter calibrations are not sufficient to get calibrated jet energy More work needs to be done!! Jet energy scale is crucial as long as many important measurements: Top quark mass (used to constrain Higgs boson) Jet cross-sections (comparison to QCD predictions) Measurements often per as long as med by comparing real data with simulations Need to get both physics in addition to detector simulation right Relative energy scale Jet energy measurement depend on location in detector True even after all previous calibrations! How come Jets are wide Some regions of CDF calorimeter are not instrumented Relative energy scale: Use QCD dijet events Should have equal transverse momentum

Conclusion Detector calibration needed to translate detector response in energy Various techniques used as long as calorimetry: Test beam Radioactive sources Lasers Collider data Calorimeter can be used to measure: Electrons, photons, jets, missing ET Good calorimeter in addition to jet calibration needed as long as measurements like top quark mass

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