Improving Jet Resolution
A group of CDF physicists coordinated by Steve Kuhlmann have been working
on improving the resolution of the jet energy for the purpose of improving
the di-jet mass resolution, hence the mass limit that CDF can reach on
the Higgs boson search. People involved so far are; C. Bocci, D. Costanzo,
G. Latino, R. Paoletti, S. Lami. They have been able to improve the jet
resolution by about 30%. More work needs to be done to achieve a better
resolution. We plan to join this effort. Of course, any improvements in
the jet resolution can be applied to any other physics analysis that uses
jets. Top mass, SUSY, Technicolor, Topcolor, QCD analyses etc. can benefit
from better resolution and reduced systematic errors.
The jet resolution improvement obtained so far is shown in the following plot.
Improvement of jet resolution
This was obtained by studying Run 1 gamma+jets events.
Assuming this resolution, the expected limits on the Higgs Mass for RUN II
as a function of the integrated luminosity are shown in the following page.
Expected Higgs Mass limits
In Run I the jet energies were evaluated using only the calorimeter energy.
ET(jet) = ET(em) + ET(had). A cone algorithm was used to define a jet and
the energies in the elec. magnetic sector and the hadronic sector were added
using the calorimeter towers that the algorithm had chosen.
Corrections for non-linearities in the calorimeter were made, as well as
out-of-cone corrections. Now the idea is to use more information from other
detectors. The 30% improvement was obtained by using information from:
em calorimeter, had calorimeter, tracking and shower max detector(CES).
There is more to be gained from the information from these detector, in
addition other detectors can be used, namely:
R-phi view of shower max, Preshower counters, crack chambers,
phototube balance in had calor., same for em calor.
had. calorimeter in classification, silicon det. info?, muon hits?
Also b jet specific studies need to be done. Here is a list of studies.
1. b jets.
a. neutrino correction for b's into leptons
b. muon correction studies (what to subtract from the calorimeter).
c. can we use SVX information on L_xy?
d. are b jets different from light quark jets (different corrections?).
2. Improving resolution in general
a. optimize classification of type of towers
b. optimize energy assignment to each tower
c. check the preliminary results using Z+jets events
d. use di-jet events and b-bbar events
e. is what we have done adequate for jets above 40 GeV?
f. add the other detector information
3. Monte Carlo needs a lot of improvements to agree with the data.
4. Try using other algorithms, KT for example, to see if we obtain the
same resolution improvement.
5. Eventually make sure the energy scale is correct.
6. Evaluate the systematics.
LBNL has taken the responsibility for b jets studies. We will also do
some of the other studies. Not yet decided who will do what. We will be
doing 2c. shortly. The above program is expected to take at least one year