Hadronic Calorimetry and Jet/ t /E T miss Performance in ATLAS

1. Hadronic Calorimetry and Jet/t/ETmiss Performance in ATLAS LHC2003 Symposium FNAL May 2003 Bryan Caron University of Alberta caron@phys.ualberta.ca (on behalf of the ATLAS Collaboration)

2. Outline • ATLAS Calorimetry • Jets • Algorithms, energy scale and calibration • Forward jet tagging • -jets • Reconstruction efficiency • jet rejection • ETmiss • Resolution and tails • Summary Signatures for new physics at the LHC (SUSY, compositeness, …) B. Caron

3. Muon Detectors Electromagnetic Calorimeters Forward Calorimeters Solenoid EndCap Toroid Barrel Toroid Inner Detector Hadronic Calorimeters Shielding ATLAS Experiment B. Caron

4. ATLAS Calorimetry Electromagnetic Liquid Argon Calorimeters Tile Calorimeters η=1.475 η=1.8 η=3.2 Forward Liquid Argon Calorimeters Hadronic Liquid Argon EndCap Calorimeters B. Caron

5. Hadronic Tile Calorimeter • Fe absorber with scintillator tile readout with Δη x Δφ = 0.1 x 0.1, 3 longitudinal samplings, |h| < 1.7 B. Caron

6. Hadronic LAr Endcap Calorimeter • Cu absorbers in a parallel plate geometry, Δη x Δφ = 0.1 x 0.1 (1.5<|η|<2.5), Δη x Δφ = 0.2 x 0.2 (2.5<|η|<3.2), 4 samplings B. Caron

7. electromagnetic module FCal1 (Cu absorber), two hadronic modules FCal2 and FCal3 (W absorber) the modules are 28/91/89 radiation lengths and 2.7/3.7/3.6 hadronic interaction lengths deep (FCal1/2/3) Principle coverage is 3.1<|η|<4.9, with cells of Δη x Δφ ≈ 0.2 x 0.2 – but non-projective FCal fully integrated into rest of the calorimetry, minimizing cracks – Premium for physics Hadronic LAr Forward Calorimeter Cryostat walls (warm/cold) Hadronic EndCap (2 wheels) p from LHC to interaction vertex Electromagnetic EndCap FCal1 FCal3 Cu Shielding FCal2 B. Caron

8. Physics effects Fragmentation Initial and final state radiation Underlying event Minimum bias events Detector performance effects Non-linear response Magnetic field Dead material and cracks between calorimeters Longitudinal leakage Lateral shower size and granularity Finite cone size (out-of-cone loss) Electronic noise Design Goals Energy resolution (in |h|< 3) Non-linearity < 3% Jet tagging efficiency e > 90% Absolute E scale 1% (Jets) for ET > 100 GeV (in 3 < |h| < 5) Granularity: dh x df = 0.1 x 0.1 (in |h| < 3) adapted to hadron shower size Jet Reconstruction B. Caron

9. Jet Algorithms • Cone Algorithm • Highest ET tower for jet seed + cone • Iteration of cone direction, jet overlap, energy sharing, merging • KT Clustering Algorithm • Pairs closest calorimeter towers, merging all particles into jets • Cone size influence on reconstructed jet energy and resolution • DR=0.4 • DR=0.7 • DR=1.5 B. Caron

10. Dead Material and Crack Regions • Transition Regions • Barrel to endcap • Vertical crack at |h|=1 • End of coil and corners of cryostat walls at |h| ~1.45 • Hadronic Endcap and Forward calorimeter • |h| ~ 3.2 • ITC + scintillator in the crack region to recover the E loss • Calibration procedure includes weights for each calorimeter compartment with correction terms for energy loss in dead material B. Caron

11. Electronic Noise and Pile-up Jet Energy Resolution ● (○) no e-noise ■(□) e-noise ▲ (△) 2.5 cut DR=0.7 (0.4) Electronic Noise |h|=0.3 DR=0.4 ⋆ e-noise + pileup □ e-noise Pile-up + Electronic Noise |h|=0.3 B. Caron

12. Offline Jet Energy Calibration Back-to-back dijet events • Sampling Method • Weights applied to different calorimeter compartments • Enlarged cone size yields increased electronic noise • H1 Method • Weights applied directly to cell energies • Better resolution and residual nonlinearities |h|=0.3 B. Caron

13. ATLAS Test Beam Results • Combined Test:EM LAr and Hadronic Tile Calorimeter •  Energy Resolution • e/ ratio • Degree of non-compensation e/h e/h=1.35±0.04 (94) e/h=1.37±0.01 (96) e/h=1.31±0.01 (G-CALOR) B. Caron

14. ATLAS Test Beam Results • Hadronic Endcap Calorimeter p Energy Resolution e/p Ratio uncorrected corrected for E leakage B. Caron

15. ATLAS Test Beam Results • Hadronic Tile Calorimeter: Response to  (100 GeV) at h = 1.3 • Clean signal above electronic noise (~40 MeV) in outermost compartment • Important at high Luminosity where physics m’s may overlap other particles; minimum bias events deposit non-neglible amounts of E in innermost calorimeter layers Total Deposited E E in 3rd Compartment Em=100 GeV Em=100 GeV Electronic Noise B. Caron

16. Jet Energy Scale and Calibration • Goal of ~1% precision on the absolute jet energy scale • Difficult to improve due to measurement uncertainties resulting from parton fragmentation, hadronization • Systematics • ISR, FSR, out-of-cone energy loss, … • Initial (relative) energy scale calibration methods • E/p measurements for isolated high pT charged hadrons from t decays • Transfer energy scale calibration from test-beam • Inter-calibrate various calorimeters • Constrain absolute energy measurement scale for isolated ± • Track p measured in ID not obviously matched to the calorimeter E since it is not possible to completely reject ± overlapping with 0 B. Caron

17. in situ Jet Energy Calibration • W→jj decays from inclusive production • ±1% jet energy scale systematic uncertainty for pTjet > 70 GeV • Residual effects • FSR effects large for pT ~ 50 GeV due to out of cone energy losses (~10%) • Jet overlap effects for pT > 200 GeV requires 2 jets with DR>0.8 • Z+jet events • pT balance between highest pT jet and leptonic Z decay • Tight jet veto and Df>3.06 to reach ±1% sensitivity level B. Caron

18. Low pT Jet Reconstruction • Low pT jet veto • Z+jet(s) events for in situ calibration with pT balance between Z and jet(s) • background rejection via central jet veto • Good efficiency and background rejection for 15 (25) GeV jet veto threshold at low (high) L • Important in the search for Higgs from Vector Boson Fusion B. Caron

19. Higgs from Vector Boson Fusion Jets within 2 < |h| < 5 (end-cap and forward calorimeters) Efficient discrimination between pile-up and signal jets in FCAL Significance (signal/rms) in DR=0.2 cone around seed cell Constant fake rate of ~ 1(10)% for double (single) tag in 2 < |h| < 5 Forward Jet Tagging B. Caron

20. t-jet Reconstruction • Benchmark Processes • Charged Higgs • Light SM Higgs from VBF • SUSY at large tanβ • Backgrounds • Z → , , , and W+jet(s) MSSM B. Caron

21. t-jet Reconstruction • Identification • Well-collimated calorimeter cluster with (1,3) associated charged track(s) • Distinguishing variables • Rem = jet radius computed using only EM cells in the jet within DR=0.7 • ΔET12 = fraction of ET in EM/hadronic calorimeters within 0.1 < DR < 0.2 • Ntr= number of charged tracks pointing to cluster within DR = 0.3 t jets QCD jets 15 < pT < 30 ( ) 30 < pT < 70 ( ) 70 < pT < 140 ( ) 15 < pT < 30 ( ) 30 < pT < 70 ( ) 70 < pT < 140 ( ) B. Caron

22.  / jet separation  id: Jet with ET>30 GeV, |h|<2.5, Rem<0.07, DET12<0.1, Ntr(pT>2) =1(3) Good t/ jet separation over a broad pT range  efficiency versus jet rejection For t id efficiency of ~20% a rejection factor of 170-1200 against jets from W+jets and ; factor of 1700 against b-jets good sensitivity for identifying t’s in many physics channels, from light Higgs to heavy SUSY t-jet Reconstruction □ 70 < pT < 130 ● 50 < pT < 70 ○ 30 < pT < 50 ■ 15 < pT < 30 B. Caron

23. ETmiss Measurement • Why is good ETmiss measurement needed at the LHC? • ETmiss is an important signal for new physics (SUSY) • Aim • Minimize fake high-ETmiss tails produced by instrumental effects (poorly measured jets in a calorimeter crack, for example) • Accurately reconstruct narrow invariant mass distributions for new particles with neutrinos among their decay products qqH → qq tt →llnn • Critical calorimeter performance characteristics • Good energy resolution • Good response linearity • Hermetic coverage B. Caron

24. Calorimeter calibration Energy loss in dead material (cryostats) and calorimeter transitions (cracks) Non-linearity of calorimeter response to low-energy particles outside of clusters (~5% effect) Calorimeter coverage For mA=150 GeV, A→tt ETmiss resolution of 7 GeV Contributions: barrel (5 GeV), end-cap (4 GeV), forward (3 GeV) Electronic noise 1.5 s cell energy cutoff deteriorates resolution by < 10% (3 GeV) Influence of minimum bias events ETmiss Resolution mA=150 GeV Low L ▼ A →tt ▲ e-noise + pileup □ FCAL alone ET(tower) > 1 GeV B. Caron

25. ETmiss signature for SUSY searches Z+jet(s), Z →m+m- Well suited to study ETmiss tails for all possible final states Simple and well controlled channel Real sources of ETmiss: two highest ETmiss events contain n’s Highest pT jet for events with ETmiss > 50 GeV found in crack region between barrel and extended barrel calorimeters ETmiss Tails Leading jet lost Fullsim crack ETmiss > 50 GeV B. Caron

26. Combined Performance W → jj (low and high L) H → bb (low L) <mjj>=80.5 GeV <mjj>=80.5 GeV mH = 100 GeV t → b jj (inclusive tt) A → tt (high L) mtop = 175 GeV mA = 150 GeV All results from Full Simulation B. Caron

27. Summary • ATLAS Calorimetry • Strongest Features: Good energy resolution, hermeticity, and granularity • Jet Reconstruction • Good jet energy calibration from H1 method • In situ calibration for W→jj and Z+jet(s) to 1% level • Forward jet tagging for Higgs from VBF • Hadronic t decays • efficiently reconstructed and identified from calorimeter and inner detector tracking information • ETmiss performance • Calorimeter calibration and coverage dependent • Cell energy cutoff for electronic noise + pile-up • No large tails produced from high pT jets in less uniform calorimeter regions ATLAS is well suited to deliver upon a large physics potential B. Caron