Jets Working Group WG focused so far on the following 2 physics studies: - intermediate mass Higgs searches - single top The 2 topics require the reconstruction of jets, and their identification as b-jets. The WG will explore various jet algorithms. WG had 7 meetings so far.

Higgs searches We are studying the possibility to observe (SM) Higgs with MH in the 115-140 GeV/c2 range p beam jet 1 beam jet 2 q q' W H b lepton neutrino jet b To avoid the large QCD background, we select associated production: the two b quarks hadronize into jets

Higgs searches .2 HAssociated cross sections is ~ 0.38 pb (Pythia 6.3) for MH=115 GeV/c2 giving ~ 600 events per LHCb-year (2 fb-1) Simple selection: large Pt prompt lepton to tag W,Z the 2 jets contained in LHCb => gives ~100 events year But we have to fight against a very large background...

Higgs searches .3 Sources of background [pb] reducible background weapon to fight it: bbar 500 106 associated production ttbar 44 extra jet activity g*/Z+jets 104 b jet identification W + jets 105 b jet identification irreducible background ZW 6.3 di-jet mass resolution ZZ 2.5 di-jet mass resolution after all the cuts we might hope for a few events/year...

Jet reconstruction Fundamental is a good reconstruction of the jets, an efficient beauty identification, and the best di-jet mass resolution. We have concentrated on KT algorithm (~Durham adapted to pp collisions). In KT the distance between particles: KT also introduces distance to beam: with R an adjustable parameter. Find min of the two sets: if min{dij} > min{dib} merge i and j. Iterate until dij> dmax. Systematic studies of KT are in progress: Victor Coco (full simulation) Laurant Locatelli (generator)

KT Jets E correction With KT, Victor finds a dependence on Pt which can be corrected by an hyperbolic function: Eb/Ejet Hyperbolic fit (in GeV) Pt GeV

Jet mass from KT Preliminary results on di-jet mass: => resolution ~ 32% FWHM/Mass

Di-jet mass from KT Resolution due to neutrini, multi-jets, underlying evt,... FWHM/M Cone and Kt, visible particles Cone, Kt, all part. Kt no underlying, all part. 0 0.5 1 1.5 2 2.5 C. Currat studies, year 2000 Victor result R any chance to improve M(JJ) resolution ? ? ? nothing found so far...

Study of Jet algorithms Parameter space of KT being studied by Laurent at generator level. Exclusive mode (i.e. fixed number of jets) examined so far, in terms of di-jet mass resolution versus parameters. Now studying KT inclusive mode. Last will be the Cone, based on the assumption that the b direction is known by secondary vertexing. With Cone: study of different contributions to resolution. Maybe a chance to gain a few % in M(Jet,Jet)...

General scheme for Jet calibration In a more general context, we must revisit the question of jet calibration (see "Jet studies in LHCb", LHCb/99-016) For instance, the E parametrization could be of the kind E(jet) = a*E(tracks)+b*E(neutrals)+c*E(muons) with E(neutrals) = b1*E(ECAL) + b2*E(HCAL) or similar, plus corrections as a function of theta or Pt, etc. We should disentangle the different contributions to resolution: individual subdetector, 2) dispersion by B field, 3) charged/neutral identification, 4) neutrini, ...