Search for Fermiophobic Higgs Boson in 3 γ + X Events The DØ Collaboration

We report the results of a search for an excess of 3γ+X events in 0.83±0.05 fb−1 of data collected by the DØ experiment at the Tevatron during the period 2002-2005. We estimate the backgrounds that are dominated by Direct Triphoton Production(DTP) and observe no excess of events above the Standard Model prediction. Thus, we set constraints on production rates of a fermiophobic Higgs boson in Two Higgs Doublet and Triplet Higgs Models. Preliminary Results for Winter 2007 Conferences 1 Theoretical Motivation The Standard Model describes our world at current experimentally accessible energies. However, the exact mechanism for EWSB remains a mystery. The spontaneous symmetry breaking mechanism requires a single doublet of complex scalar fields. But does Nature follow this minimalistic version or does it require a multi-Higgs sector or something completely different? In a more general framework where the parameter content of the theory is richer, we may expect deviations from the SM predictions in the form of significant changes in the Higgs boson discovery signatures. One such example is the so-called "fermiophobic" Higgs boson, which has suppressed couplings to all fermions. It may arise in a variety of models (e.g. [1]). A variation of this theme is the Higgs boson in certain top-color models, which may couple only to heavy quarks [2]. Some even more exotic possibilities have been suggested in the context of theories with large extra dimensions [3]. Finally, in the Minimal Supersymmetric Standard Model (MSSM), the width into bb̄ pairs can be suppressed due to 1-loop supersymmetry (SUSY) corrections, thus enhancing the branching ratios of a light Higgs boson into more exotic signatures [4, 5]. In all these cases, for masses mh < 100 GeV/c2 the Higgs boson decays to photon pairs [6]. Decays are mediated through a W or a heavy quark loop. Experimental searches for fermiophobic higgs (h f ) at LEP and the Tevatron have yielded negative results. Mass limits have been set in a benchmark model that assumes that coupling h fVV (V ≡W±,Z) has the same strength as in the Standard Model and that all fermion Branching Ratios (BR) are exactly zero. Combination of results obtained by the LEP collaborations OPAL [7], DELPHI [8], ALEPH [9], and L3 [10] yielded lower bound mh > 108.3 GeV/c2. This result was obtained utilizing channel e+e− → h f Z, h f → γγ. In Run 1 of the Tevatron, the limits on mh f from the DØ and CDF collaborations are respectively 78.5 GeV/c2 [11] and 82 GeV/c2 [12] at 95% C.L. , using the mechanism qq′ → V ∗h fV, h f → γγ, with the dominant contribution coming from V = W±. A preliminary search in the inclusive 2γ+X channel has been performed with 190 pb−1 of Run 2a data [15]. For an integrated luminosity of 2 fb−1, Run 2 will extend the coverage of mh f in the benchmark model slightly beyond that of LEP [13, 14]. In addition, Run 2 will be sensitive to the region 110 < mh f < 160 GeV/c 2 and BR(h f → γγ) > 4% which could not be probed at LEP. However, the h fVV coupling in a specific model could be suppressed relative to the hSMVV coupling by a mixing angle1, leading to a weakening of the above mass limits. If this suppression were quite severe (h fVV/hSMVV < 0.1), a very light h f (mh f 100 GeV/c2) would have eluded the searches at LEP and the Tevatron Run 1 in production mechanisms that rely upon the h fVV coupling. Therefore it is of interest to consider other production mechanisms for h f which may allow observable rates if the h fVV coupling is suppressed. Since the couplings h fVV and h fV H (where H is another Higgs boson in the model) are complementary, two LEP collaborations, i.e. OPAL [7] and DELPHI [8], also searched for fermiophobic Higgs bosons in the channel e+e− → A0h f , and ruled out the region mA +mh f < 160 GeV/c 2. However, a very light mh f < 50 GeV/c 2 is still possible if mA is sufficiently heavy. An alternative production mechanism that also depends on the complementary h fV H coupling is 1An angle that diagonalizes the CP-even Higgs matrix.