The long sought for Higgs particle could answer the question what mass really is. The Higgs particle is the missing component of the Standard Model. The Standard Modelincludes the matter particles, the quarks and leptons, and the mediators of the fundamental interactions and describes in great detail the fundamental processes like the strong, the weak and the electromagnetic interactions. One mystery remains – what is mass? The Higgs mechanism could be the answer, but to confirm it the Higgs particle responsible for the interaction has to be found. The discovery of the Higgs particle is the only way to establish the existence of the Higgs mechanism and therefore it is hunted at the high energy particle experiments, where the chances of success are greatest.

The Higgs particle search in DELPHI

As the Higgs particle is expected to be produced with rather low probability, the difficulty has always been to perform sufficiently efficient searches. In rare situations an ordinary particle collision can look a bit like the production of a Higgs particle. As the ordinary particle collisions are so numerous compared to a collision possibly giving rise to the production of a Higgs particle, this potential background can be fatal. We have therefore developed new analysis methods using either a neural network or discriminant analyses in order to make the search more efficient. When the LEP energy was increased a new Higgs particle mass range for exploration was opened. During the last five years of LEP operation the energy was constantly increased in order to increase the chance to observe the production of a Higgs particle. When the LEP accelerator was closed in November 2000, there were still no clear indications of the production of a Higgs particle. However, the ALEPH experiment registered some collisions that could be interpreted as the production of a Higgs particle with mass around 115 GeV. The situation is not clear, however, and the hunt for the Higgs particle has to continue at other accelerators like the Tevatron at Fermilab in US or the Large Hadron Collider at CERN.

Some technical publications

Using a neural network in the search for the Higgs particle.

Use of discriminant analysis in the search of a neutral Higgs boson

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

Some of the latest physics results:

Searches for neutral Higgs bosons in e⁺e^- collisions around Ös = 189 GEV

The DELPHI Higgs research team, Search for neutral Higgs bosons in e⁺e^- collisions from Ös = 192 GeV to 202 GeV.
Contribution to the Osaka ICHEP conference 2000.

Search for the Standard Model Higgs boson at LEP in year 2000,