K.E. Johansson

An iterative discriminant analysis method to search for the Higgs particle at LEP2

Abstract The search for the Higgs boson in e + e − collisions at energies above the Z 0 mass requires an efficient method to reject the many background channels. We have investigated an iterated discriminant analysis to detect the signal of a Higgs boson produced in association with neutrinos. An efficiency for a 70 GeV/ c 2 Higgs particle of 50% and a background rejection factor of 290 000 have been achieved. The optimization and performance of the iterated discriminant analysis are described.

Using a neural network in the search for the Higgs boson

Abstract The search for the Standard Model Higgs boson in high energy e+e− collisions requires analysis techniques which efficiently discriminate against the very large background. A classifier based on a feed-forward neural network has been extensively used in a search in the channel where the Higgs boson is produced in association with neutrinos. The method has significantly improved the sensitivity of the search. With a simple preselection based on event topology followed by a neural network we have obtained a combined background rejection factor of more than 29 000 and a selection efficiency for Higgs particle events of 54%, assuming a mass of 55 GeV/c2 for the Higgs boson. We describe here the details of the analysis with emphasis on the neural network.

USE OF DISCRIMINANT ANALYSIS IN SEARCH OF A NEUTRAL HIGGS BOSON

When searching for the Higgs boson produced in e+e− collisions at energies close to the Z0 mass, a method to reject a very large background is needed. A method to pick up the signal of a Higgs boson produced in association with a pair of neutrinos has been investigated. After a preselection, which eliminates the majority of the background events, a discriminant analysis was used to achieve a background rejection factor of 168 while keeping an efficiency for Higgs boson events of 68% for a Higgs boson mass of 55 GeV/c2. For the combined preselection and discriminant analysis, the rejection factor is 50 000 and the efficiency is 48%.

HIGGS BOSON SEARCH WITH DISCRIMINANT ANALYSIS METHODS

Abstract We have investigated two different variations of discriminant analysis to detect the signal of a Higgs boson produced in association with neutrinos in e + e − collisions at 183xa0GeV. In one case eleven event variables were used together in two steps of an iterated discriminant analysis, while in the other case (structured discriminant analysis) groups of variables were treated independently. Background rejection factors of about 16xa0000 for the most important background were obtained with an efficiency of 32% for events with a Higgs boson mass of 85xa0GeV/ c 2 . The optimization and performance are described for the two variations, and the final results of the iterated discriminant analysis used in the DELPHI experiment are given.