Jets and Hadrons Calibration Strategy in ATLAS Ir e ne Vichou University of Athens - PowerPoint PPT Presentation

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Jets and Hadrons Calibration Strategy in ATLAS Ir e ne Vichou University of Athens

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  1. Jets and Hadrons Calibration Strategy in ATLAS Irene Vichou University of Athens Introduction Calibration Strategy (from testbeam to LHC data) Jet and hadron reconstruction In situ methods Z+jets and W  jj samples Conclusions

  2. The goal is to: reconstruct hadronic entities on the calorimeter but also muons to assist the Spectrometer and transfer the calibration csts be able to reproduce as precisely as possible their 4-momenta This implies: pass the knowledge of calorimeter response from the tests of modules to the assembled detector to physics events Physics cases mass reconstruction # jets and total E in SUSY searches jet veto down to 15 GeV QCD studies (… unexpected) Requirements Knowledge of E scale for jets should be ~1% Considerations Ringberg Calibration Workshop - Irene Vichou

  3. Physics systematics fragmentation ISR FSR underlying and MinBias Detector Systematics response different to charged and neutral hadrons non linearities B-field dead material longitudinal shower leakage lateral shower size granularity electronics noise ...Considerations Ringberg Calibration Workshop - Irene Vichou

  4. Layout of ATLAS calorimeters • Calorimeters in ATLAS cover up to |h|=5. • The electromagnetic calorimeter is a liquid argon accordion. • The hadronic calorimeter is an iron-scintillator device in the central region and Lar in the endcap and forward region • The EC cryostat houses EM, HAD and FCAL. Ringberg Calibration Workshop - Irene Vichou

  5. EM calorimeter segmentation • 3 longitudinal samplings • very fine strips in 1st • thick middle sampling • good for g/p0 separation • presampler in front for • energy recovery Ringberg Calibration Workshop - Irene Vichou

  6. Calibration Strategy Before LHC…. • Calibration with single particles at testbeam • transfer of calibration constants to all modules so that all calorimeters are set at the EM scale LHC start ! • intercalibration with single particles at LHC • in situ samples • W jet jet • Z(photon)+jet balance • for E regions not reached before? MC... Ringberg Calibration Workshop - Irene Vichou

  7. TileCal calibration with Cs AIM: Equalize cell responses and balance optical non-uniformities. All individual optical components are “seen” in a shadowgram. The precision in the cell response is 0.2% !!! There is a good correlation with muons ~ 3% Ringberg Calibration Workshop - Irene Vichou

  8. Calibration in test beam e/p response = f(e/h,p0 fraction) e/h (TileCal) = 1.3 ± 0.01 check resolution TileCal module p,e,m e,m • Muon response (90o) is due to ionisation • 1 in 8 modules will see particles • muon signals correlate with Cs, so... • Cs constants will be used to transfer the • responses to particles Ringberg Calibration Workshop - Irene Vichou

  9. Tuning the Monte-Carlo Combined Test of EM and HAD calorimeters in beams (only once for final ATLAS modules!) E Resolution 60% sampling term, 1.8% cst term 2 GeV noise term Linearity e/p ratio 1.35 to 1.37 • able to have a suitable hadronic shower Monte-Carlo • useful to establish energy reconstruction methods Ringberg Calibration Workshop - Irene Vichou

  10. Tuning the MC (G4) Pion Test beam results vs G4 for hadronic showers for Lar HEC Ringberg Calibration Workshop - Irene Vichou

  11. E/p for isolated hadrons p and k’s from W(Z) + jets tnt (t+t-) + jets, with t h nt at LHC • Backgrounds: • QCD jets • multi-particle t decays • under control with • cuts on Ntrackand isolation • Triggerable (t and ETmiss) • p(tracker) = E(calorimeter) • E/p bias: • 0.3% from QCD • 3.5% total, mainly from t decays • containing r+ (p+p0) • Need to reject the r+bcg • by a factor of 5 Ringberg Calibration Workshop - Irene Vichou

  12. E/p for isolated hadrons Make use of the fine EM calo granularity of the 1st sapling. A rejection of 11 is achieved at h=0.3 The residual bias in E/p due to the r+ (p+p0) bcg is 0.4% Nr of h-strips E(em1)/E(em) Ringberg Calibration Workshop - Irene Vichou

  13. E/p for hadrons • Statistics for 10 fb-1 • Global E/p bias is 0.6 % (OK if < 1%) • The E reaches • 120 GeV in TileCal (barrel + extended) • 240 GeV in the Endcap Lar • It is a good intercalibration method • Gives absolute scale for hadrons • Direct comparison with beam tests for h’s/mip in EM Ringberg Calibration Workshop - Irene Vichou

  14. Jet Energy Reconstruction • … before using the in situ… (in these studies) • fixed-cone algorithm • “Benchmark” E= a1xE1+a2xE2+a3xE3+a4xE4 • “a la H1” E=E1+a2(e2,j)xe2,j + a3(e3,j)xe3,j +a4xE4 • where 1…4 are PS,EM,HAD,cryostat correction terms • and j’s refer to cells • and E4 • a`sare function parametrisations wrt to parton energy • Preserves linearity (calo effects) and resolution Cones DR=0.4 and 0.7 Seed 2 GeV,Ecell>2s noise Etower (0.1x0.1) > 0.2 GeV Jet ? Jet E ? Ringberg Calibration Workshop - Irene Vichou

  15. Jet Energy Reconstruction Jet Energy Resolution terms And dependece on pseudorapidity DR=0.7 sampling constant 3% 50% Ringberg Calibration Workshop - Irene Vichou

  16. Taus calibration Will be covered in Ambreesh’s talk as it is part of test carried out in the new ATHENA framework Ringberg Calibration Workshop - Irene Vichou

  17. Extrapolation to high E And after calibrating….. What if wrong extrapolation to energies not reached before? Example: Use of a Monte-Carlo not reproducing well the e/h norm at 100 GeV norm at 500 GeV Ringberg Calibration Workshop - Irene Vichou

  18. In situ samples • Need: Absolute for verification • Wish: Statistics should be adequate above bcg • Trigger available • Wide Energy coverage • Choices: Mass reconstruction of the W • only light q jets • limited E and hreach • Balance of pT between Z and leading jet • wider E andhreach • b-jet content • good to transfer calibration across calorimeters? Ringberg Calibration Workshop - Irene Vichou

  19. In situ samples • Simulated using PYTHIA/JETSET • Fast simulation • smearing with calorimeter resolution • jet finding from deposited energy in towers • Full simulation • using GEANT 3.21 • G-Calor calorimeter response model • addition of pile-up events and electronics noise • digital filtering for cell energy reconstruction • In the following studies • Fixed cone algorithm used for jet reconstruction • Benchmark/Sampling method for jet E calculation • and also weighting method for the Z+jets Ringberg Calibration Workshop - Irene Vichou

  20. pTparton/pTjet In situ W  jj • W’s are abundant through the tt events sample • At low L 1500 lvjjbb final states/day ! • The jj final states of the W decay should satisfy: • Events easily triggered from isolated lepton and 2 b-jets. • No physics bcg’s. • Combinatorial bcg under the W peak ~ 30%. ~50 GeV out of cone losses >200 GeV jet overlap pbms (add cut of DR>0.8) Characteristics: Ringberg Calibration Workshop - Irene Vichou

  21. In situ W  jj After calibrating (full sim): >70 GeV 1% is achievable ~50 GeV 3% looks fair Further studies showed: overestimation of corrected jet energy towards the high end of E-spectrum was due to underestimation of the angle. Problem solved by taking into account E,h and f in the minimisation procedure and correct energies and angles. Result: E of parton and jet agree within ~ 1% over the range 50-250 GeV Ringberg Calibration Workshop - Irene Vichou

  22. In situ Wjet jet • Statistics: 100 K W’s for 10 fb-1 • The W jj decay in tt events should provide the wished 1% absolute scale precision from 50 to few hundred GeV for light quarks • Lower end of spectrum: • interplay between FSR and out of cone losses for specific reconstruction algorithms • Higher end • residual effects due to overlap are significant and special treatment has to be applied to overcome this without significant loss of statistics (e.g. by asking well-separated jets) Ringberg Calibration Workshop - Irene Vichou

  23. In situ Z+jet Direct Z production, events with Z+jets where Zee or Zmm Method: pT balance between Z (leptonic/precisely measured) and highest pT jet Large cross section, no statistics problem … but balance is not perfect  fractional imbalance between Z and jet: pT imbalance wrt to processes 20<pT<60 GeV jets 60<pT<120 GeV jets Ringberg Calibration Workshop - Irene Vichou

  24. In situ Z+jet • Selections to favour topologies with back-to-back Z and jet • azimuthal angle between Z and leading jet > 3.06 rad • loose jet veto: no other jet pT>40 GeV and |h|<3.2 (possible at high L) • tight jet veto: no other jet pT>15 GeV and |h|<4.9 pT imbalance wrt to selection cuts 20<pT<60 GeV 60<pT<120 GeV Fr I Ringberg Calibration Workshop - Irene Vichou

  25. In situ Z+jet Impact of cuts assessed also with full simulation Example is the jet veto capability with comparison between fast and full simulation Fraction on events with >1 jet is reconstructed wrt to the pT threshold applied Cone DR = 0.7 adjustment of pT threshold to take into account the EM scale calibration in full sim Good agreement between fast and full sim in jet veto efficiency! Ringberg Calibration Workshop - Irene Vichou

  26. In situ Z+jet Number of jets after cuts for 10 fb-1 integrated luminosity in calorimeter and pT regions Nr of b-jets 90% purity Rates after cuts are adequate for statistical sensitivity of 1% for pT<200 GeV. Nr of b-jets assuming 50% tagging efficiency hopefully sufficient to constrain b-jet scale to % level. g+jet sample offers 30 times more events but more tend to bias in selecting back-to-back events NB overall jet sample content: 28% gluon , 54% light quark, 12% c and 6% b-jets Ringberg Calibration Workshop - Irene Vichou

  27. In situ Z+jet Comparison between full and fast simulation all jets b-jets Fast: Full: Average Fractional Imbalance in three pT ranges pT>40 GeV and |h|<3.2 Ringberg Calibration Workshop - Irene Vichou

  28. In situ Z+jet Accuracy of the calibration in this sample Reconstructed jet pT rescaled to balance the Z pT wrt to the original parton pT GeV Fractional imbalance of the two pT’s Systematics and effect on fractional imbalance Uncertainties in modelling ISR: 1.5 factor inLQCD ±1.5%(0.3%) at low (high) pT Topology uncertainties on back-to-back: DF cut tightening by 0.06 rad  -0.7% to -0.1% Cone enlarging to DR=0.7  0.3% Ringberg Calibration Workshop - Irene Vichou

  29. Z+jet sample Reconstructed energy with a weighting method The ai’s are derived using the Z as a reference Parametrise the ai’s as functions of ETjet Non-lineraities wrt to the parton Ringberg Calibration Workshop - Irene Vichou

  30. x pT jet KTh h bisector KTx pT Z Z+jet resolutions Bisector method sxsensitive to ISR and detector resolution sh sensitive to ISR So, resolution due to jet rec Ringberg Calibration Workshop - Irene Vichou

  31. Z+jet resolutions Difference in resolution obtained with the bisector and the ‘classic’/true definition. Ringberg Calibration Workshop - Irene Vichou

  32. In situ jet calibration • The 1% jet calibration uncertainty is difficult but it seems not impossible with the current studies • The two types of in situ samples are somewhat complementary • W jj • will provide very accurately the E-scale at intermediate energies but • systematics rise at the low and high end of spectrum • Z to jet balance • can reach higher energies and |h| (even the forward) • systematics are very high at low energies, but above 60 GeV the 1% requirement seems possible • can offer separate calibration of b-jets • can transfer calibration across calorimeters • can check the linearity of calorimeter (TeV values at the endcap and forward regions) Ringberg Calibration Workshop - Irene Vichou

  33. Finally... • Test beam/ single particles and/or electronics calibration to set the cell at the EM scale • transfer to modules not tested where needed • Assign a detector Monte-Carlo that describes well the observed with particles • remember the high E end.. • Work on the machinery for jet/hadrons reconstruction/calibration (even if not final choices) and keep flexible • no best algorithm or best calibration scheme NOW • be ready to try any useful data • In situ calibration cross-check at LHC start (only feasibility studies and predictions now) • in situ intercalibration also Ringberg Calibration Workshop - Irene Vichou