• mass resolution

We report on a number of simulation studies on how to improve the invariant mass resolution of a particle decaying into two large energy hadron jets. This is a preliminary step of an effort to observe associated WZ production. This process is extremely rare and competes with a large background, and any minor improvement in resolution deserves great attention.

These tools would be of interest in the study of many rare multi-jet processes. They are implemented here in a simulated measurement of $Z\rightarrow q\bar{q}$ decay (aiming eventually at a $H\rightarrow b\bar{b}$ decay), in associated WZ (WH) production in \proton \antiproton\ collisions at \ecm = 1.96 TeV recorded by the CDF II experiment at the Fermilab Tevatron Collider.

We generate WZ events with an identified charged lepton, a large imbalance in transverse momentum, and at least two large transverse energy jets. We determine the sample selection cuts by studying jet energy dependence of signal and background. The main backgrounds, noticeably W+jets production, are modeled based on experimental data whenever possible. We first try to optimize the sensitivity to a jet-jet invariant mass peak by complementing the information provided by the CDF calorimeter with that of the tracker. For mis-measured calorimeter jets, and for jets fragmenting with a large charged-to-neutral ratio, the jet axis could be better measured in the tracker. As a consequence the dijet invariant mass could be better measured. The study starts by checking the best ever achievable improvement by adopting the primary parton direction as jet axis. This study is performed on a $WZ\rightarrow l \nu q\bar{q}$ PHYTIA Monte Carlo in the simpler case of light decay quarks. Improvements in dijet mass resolution of the order of a few \% are obtained in a number of cases. Next we try to develop event-specific energy corrections for calorimeter jets. Again, improvements of the order of a few \% are obtained in a number of cases. The combination of these two methods indicates possible improvements in dijet mass resolution up to $\sim$5\%.,
\par

When the study is extended to using, rather than primary quark directions, tracker jet axes which are experimental observables, no real progress is predicted. However, the study is extended to event specific corrections to calorimeter jets based on information carried by observables in the event, including tracking. This study gives very interesting and promising indications: Resolution improves by $\sim4\%$. Criteria by which we select and merge jets due to final state radiation (FSR) are discussed, and the impact on dijet mass resolution of merging three jets to reconstruct W or Z in $q\bar{q}$ decay is studied.