1. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF1 Performance of Jets and missing ET in ATLAS Monika Wielers TRIUMF, Vancouver on behalf of the ATLAS Collaboration 10 th International Conference on Calorimetry in High Energy Physics Pasadena – March 2002

2. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF2 Contents Physics Goals for Jet/ETmiss Studies in ATLAS The ATLAS Calorimeter System Simulation of Detector Response and Pile-Up Jet Reconstruction in ATLAS Physics Examples for Jet Reconstruction E T miss Reconstruction Conclusions I won’t have time to discuss  physics

3. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF3 Physics Goals for Jet/E T miss Studies Jet Physics QCD Studies Measure jet cross section Reconstruction of resonances QCD: W  jet jet, Z  bb, t  b W Exotics: W’  jet jet SUSY: A  Measure jet multiplicity in SUSY decay Jet veto in central region to reject background Jet tagging in forward region Missing transverse energy measurement SUSY and other New Physics signatures, e.g. H  ZZ  ll Reconstruct inv. mass in decays with ’s, e.g. A , t  l b

4. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF4 The ATLAS Calorimeter System EM Calorimeter LArg technology Coverage: |  |<3.2 High granularity up to |  |=2.5 Hadronic Calorimeter Fe-Scintillating tiles in |  |<1.5 LArg EC (|  |<4.9) HEC, Cu/LAr : 1.5< |  |<3.2 FCAL: Cu/Tungsten/LAr 3.2<|  |<4.9

5. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF5 Simulation of Detector Response Geant 3 still “standard”simulation program Geant 4 to come  see various talks

6. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF6 Simulation of Pile-up Noise ~23 minimum bias events per bunch crossing at L =10 34 cm -2 s -1 LArg uses bipolar shaper for read-out “history” from around 27 bunch crossings Noise peaks around zero GeV Tile uses mono polar shapers “history” from 4 bunch crossings Response ~ Gaussian with FWHM of 50 ns

7. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF7 Simulation of Pile-up Noise ~700 minimum bias events need to be added to signal events at high luminosity (  30 BC’s) For given cell type weigh energy according to shaper response for given time Read minimum bias events via secondary stream On the fly via direct access file which is kept in memory Add an additional simulation step (together with pile-up in all other detectors) used to keep correlations between detectors Keep big number of min. bias events in memory Currently done in Fortran, work ongoing to get it running in C++

8. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF8 Factors influencing Jet Reconstruction Experimental factors Electronic (and pile-up) noise Different response to charged and neutral particles (  0 ) Non-linearities granularity Lateral shower size Dead material and cracks Longitudinal leakage Magnetic field effects Physics related factors Initial and final state radiation Fragmentation Underlying event Depending on luminosity: minimum bias events No unique strategy for jet reconstruction, depends on Jet reconstruction algorithm, luminosity, physics process

9. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF9 Energy Resolution Calorimeter resolution at |  |=0.3  /E = 52%/  E  3.0 GeV/E  1.7% for R=0.7 at L =10 33 cm -2 s -1  /E = 81%/  E  3.9 GeV/E  1.7% for R=0.4 at L =10 34 cm -2 s -1  High luminosity pile-up, + el noise  el. noise |  |=0.3 R=0.4R=0.7 El. Noise1.9 GeV3.3 GeV Pile-Up (L=10 34 cm –2 s -1 ) 4.7 GeV14 GeV

10. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF10 Physics Effects Particle level jet energy Parton energy Depends on physics process

11. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF11 Detector Level Generic (Sub) Detector Level cell signal reconstruction cell signal corrections Combined Detectors tower finding cluster finding Algorithmic flow of jet reconstruction in software (in C++) Get detector data Calibrate to EM scale Create towers and clusters (if input to jets) Prepare input (cell, cluster, tower, jet…) for jet finder Do jet finding Reconstruct and calibrate jets Do jet classification Redo any step if desired! Physics Jet Jet classification Analysis Jet Reconstruction ProtoJet building Jet finding Jet reconstruction

12. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF12 Forward Jet Tagging and Jet Veto Important for background reduction for heavy Higgs production via Vector-Boson-Fusion (  (VBF) ~ 1/5  (gg)) H produced centrally Accompanying jets in forward region Small hadronic activity in central region Veto low-p T jets  rejection of tt background  90 (80) % for |  |<4 at low (high) luminosity  (tt)~10%

13. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF13 Resonance Reconstruction Simple Resonance W  jj at L =10 34 cm -2 s -1 E T (W) ~ 150 GeV In resonance chain H  hh  bbbb no electronic, no pile-up noise Use m(h) as mass constraint to reduce combinatorial background apply recalibration using m(h)=m(bb) requires b-jet tagging Bias in jet direction if jets overlap

14. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF14 E T miss Reconstruction Important for new physics signatures (SUSY particle production and decay) Invariant mass reconstruction for channels involving A , t  l b, H  ZZ  ll E T miss reconstructed from cell energies within |  |<5 Accurate calibration of calorimeters vital L =10 33 cm -2 s -1 L =10 34 cm -2 s -1

15. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF15 E T miss Tails E T miss Reconstruction important for H  ZZ  ll with m(H)~500-700GeV Potential problem: background from Z+jet(s) events with badly measured jet p T (Z)>200GeV Assume jet is undetected Jet reconstructed Requirement of rejection factor of 1000 for E T miss > 200 GeV achieved!

16. Simulation Session @ Calor 2002, March. 27, 2002M. Wielers, TRIUMF16 Conclusions Lot’s of interesting physics to be done using jets and E T miss  Higgs, SUSY, the unknown,… ATLAS calorimeter well designed for jet/E T miss studies We are ready to face the challenge Let’s see what 2007 brings us, when first collisions are expected !