Abstract
A search for γγ decays of a Higgs boson is performed in the data sample collected at LEP with the ALEPH detector between 1991 and 1999. This corresponds to an integrated luminosity of 672 pb −1 at centre-of-mass energies ranging from 88 to 202 GeV. The search is based on topologies arising from a Higgs boson produced in association with a fermion pair via the Higgs-strahlung process e + e −→Hf f ̄ , with f f ̄ =ν ν ̄ , e + e −,μ +μ −,τ +τ − or q q ̄ . Twenty-two events are selected in the data, while 28 events are expected from standard model processes. An upper limit is derived, as a function of the Higgs boson mass, on the product of the e + e −→Hf f ̄ cross section and the H→γγ branching fraction. In particular, a fermiophobic Higgs boson produced with the standard model cross section is excluded at 95% confidence level for all masses below 100.7 GeV/c 2 .
Highlights
Neutral Higgs bosons do not couple directly to massless photons
Twenty-two events are selected in the data compared with an expectation of 27.9 ± 1.6 events from all standard model background processes
The low mass background is dominated by events where both photons originated from the same jet, whereas the high mass background is dominated by events where the two photons originated from different jets
Summary
For instance the standard model Higgs boson couples to photons only through loops of charged particles, i.e., W’s, quarks and leptons, and the branching ratio into γγ is small (≈ 10−3 [1] for mH ∼ 90 GeV/c2). With some particular choices of parameters, the branching ratio into γγ may be enhanced in the MSSM, and can reach a value close to 100% in models with fermiophobia or with anomalous gauge couplings. The analysis is performed with the data collected with the ALEPH detector from 1991 to 1999 including the Z peak data collected during the LEP 2 period This sample corresponds to an integrated luminosity of 672 pb−1 at centre-of-mass energies ranging from 88 to 202 GeV.
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