Search for Higgs Boson (3)
 Figure 1 : Production cross sections of the Higgs particle at the Tevatron. (Red lines : Vector boson associated production, Blue line : Gluon fusion, Green line : Vector boson fusion). |
 Figure 2 : Decay modes of the Higgs particle. |
 Figure 3 : Ratio between an upper limit of the production cross section of the Higgs partile obtained from CDF+DØ and the prediction of the Standard Model. |
The latest results from our laboratory’s search for the Higgs particle in the CDF experiment have been announced. Due to the significance of these results, a press release was also made available to the media from Fermilab in the United States, where the CDF experiment facility is located. If you are interested in this press release, please see here. For a general introduction to the Higgs particle, please refer to the High Energy Physics Laboratory News dated September 4, 2007, and for our laboratory’s research on the Higgs particle search, see the High Energy Physics Laboratory News dated May 15, 2008. As stated in these laboratory news articles, the elementary processes through which the Higgs particle is produced in the CDF experiment include:
1. “Vector boson associated production” (Figure 1, red lines):
qq′ → WH, qq → ZH
2. “Gluon fusion” where gluons collide to form the Higgs particle (Figure 1, blue line):
gg → H
3. “Vector boson fusion” (Figure 1, green line):
qq′ → Hqq′
The decay modes of the Higgs particle are shown in Figure 2. For MH < 130 GeV/c2, the primary decay mode is bb, and for MH > 130 GeV/c2, the main decay mode is H → W+W−. This time, using data up to approximately 3.0 fb−1, we conducted a comprehensive analysis of the Higgs particle search in the mass region of 155 to 200 GeV/c2, thus focusing on the H → W+W− decay mode. The analysis of WH → WWW was conducted by Osaka City University, while the analysis of H → W+W− was performed by Duke University and the University of California, among others. Additionally, we combined the analyses from the DØ experiment, another experiment using the Tevatron accelerator, with those of our CDF experiment to produce the final results. The ratio of the upper limit to the theoretical calculation is shown in Figure 3. “Limit” means that anything beyond that is not considered probable. If the theoretical calculation is larger than this line, hence a ratio of less than 1, it can be concluded with a certain degree of confidence that a Higgs particle with such mass does not exist. As seen from the black solid line in the figure, the analysis excluded 170 GeV/c2 at a 95% confidence level. This indicates that experiments using the Tevatron accelerator are indeed getting closer to determining the existence of the Higgs particle, and new insights into the Higgs particle are beginning to emerge for the first time in about five years since the LEP experiment at CERN. Moving forward, as data collection and analysis at the Tevatron continue, it is expected that more light will be shed on the true nature of the Higgs particle.