Complete LEP Data: Status of Higgs Boson Searches

The LEP experiments completed data-taking in November 2000. New preliminary combined results of the four LEP experiments ALEPH, DELPHI, L3 and OPAL are presented for various Higgs boson searches. Presented at the Third International Conference on Non-Accelerator New Physics, NANP–01, Moscow, Russia, June 2001 Complete LEP Data: Status of Higgs Boson Searches André Sopczak Lancaster University E-mail: [email protected] The LEP experiments completed data-taking in November 2000. New preliminary combined results of the four LEP experiments ALEPH, DELPHI, L3 and OPAL are presented for various Higgs boson searches. After 11 years of operation the LEP experiments have completed data-taking. In 2000 the center-of-mass energy was pushed to 209 GeV with most data taken around 206 GeV. In the last three years of operation a luminosity of about 687 pb was delivered to each experiment, which exceeded expectations. Despite hints for a Higgs boson discovery around 116 GeV data-taking was not continued in 2001. 1 Standard Model Higgs Boson In September 2000, ALEPH presented a data excess consistent with the reaction ee→HZ →bb̄qq̄ for a Higgs boson mass of about 115 GeV 1 which was not confirmed by the other LEP experiments. In November 2000, L3 provided support for a signal observation with a HZ→bb̄νν̄ candidate event at the same mass. For the summer conferences in 2001, all experiments updated their analyses and the probability of the data to be consistent with the Standard Model (SM) background is increased, as detailed in Table 1 . The confidence levels CLb for a signal observation and CLs for setting mass limits are shown in Fig. 1. The resulting SM Higgs boson mass limit is 114.1 GeV at 95% CL. The reconstructed mass distribution and a list of candidate events are shown in Fig. 2. In extensions of the SM the HZZ coupling might be weaker and thus the production cross section is reduced. Figure 3 shows limits on the reduction factor at 95% CL. Even if the SM cross section is reduced by a factor three, a Higgs boson mass up to 110 GeV is excluded. 10 -5 10 -4 10 -3 10 -2 10 -1 1 100 102 104 106 108 110 112 114 116 118 120 mH(GeV/c ) 1C L b