Kap 3 Jets jet definition jet reconstruction di

Kap. 3: Jets ● jet definition ● jet reconstruction ● di- and multi-jet events ● standard model processes with jets at LHC ● searches for new particles with jets Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 1

Jet-Definitions detector - level parton - level Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 2

Jets: General Request hadrons: experiment LHC: about 100 particles per jet, 2 – 5 jets per event Jets are sensitive to the fundamental hadronic process (direction/energy) Good agreement of theory and experiment needed: jet-algorithms parton (quark/gluon) : theory Inelastic scattering of hadrons: beam of colliding partons c. m. s. energy boost unknown: lorentz invariant jet variables needed! rapidity, transverse momentum, azimuthal angle Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 3

2 -Jet event at CDF (TEVATRON) Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 4

Cone - Algorithm Sum over all calorimeter activities within a certain cone of radius R around a high energetic cluster cut criteria for jet-cone: y(cut) typically 0. 5 … 1. 0 problem: overlaying jets Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 5

Jets in the Calorimeter of CDF 2 jet event cone algorithm, with R < 0. 7 3 jet event Martin zur Nedden, HU Berlin 5 jet event WS 2007/08: Physik am LHC 6

Jets in the Tracking system of CDF 2 jet events same events as before Clear separation partially difficult! 3 jet event 5 jet event Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 7

Jet-rates as Function of y(cut) LEP-data: Number of selected jets very sensitive on the value of the cut parameter y in the cone algorithm Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 8

Multi-Jet Events good test of QCD Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 9

Transversal Energy of Jets Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 10

Evidence for a Substructure at TEVATRON? σ(pp Di-Jet) as function of the masse of di-Jets, Comparision to theory MJJ - distribution Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 11

Cone-Algorithm vs. KT - Algorithm Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 12

KT - Algorithm Make a list of all hadrons (= calo clusters) Calculate for each cluster: Check for each cluster pair where is ? Yes: add clusters i and j to the same jet No: put cluster i on the list of new jets repeat up to the list is finished Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 13

Double differencial Jet Cross Sections God agreement with QCD predictions Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 14

Comparision to theoretical Models Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 15

Jet Algorithms for LHC (ATLAS) distance between both partons in the example of W jj in the (η, φ)-plain ET of jets in comparison to ET of partons (ratio) in the example of W jj, comparison of different algorithms Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 16

W-Mass Reconstruction of Di-Jet Events W j j H W W l υl j j W j j Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 17

Reconstruktion of Higgs and Z 0 pp hh bb bb pp WH bb l υ Martin zur Nedden, HU Berlin pp ττ j υτ l υl υτ WS 2007/08: Physik am LHC 18

Jet Physics at ATLAS Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 19

Jet Physics at ATLAS Martin zur Nedden, HU Berlin WS 2007/08: Physik am LHC 20