1. 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.

2. Higgs searches We are studying the possibility to observe
(SM) Higgs with MH in the
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

3. 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...

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

5. 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)

6. 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

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

8. 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.
C. Currat
studies,
year 2000
Victor
result R
any chance
to improve
M(JJ) resolution ? ? ?
nothing found so far...

9. 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)...

10. 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, ...