Although low mass Higgs boson searches at the Tevatron usually focus on the dominant bb decay channel, the diphoton final state is appealing because the photon ID efficiency and energy resolution are much better than that of b-jets. The better energy resolution leads to a narrow Mgg mass peak and reduced background. Furthermore, for this channel,the Higgs can be produced via the gluon-gluon fusion, which has a production cross section much larger than WH. We anticipate that this analysis will yield a 10% improvement on the combined CDF Higgs limit, and we are therefore pursuing it vigorously. Additionally, one can devise many possible beyond-the-standard-model scenarios in which the Higgs has suppressed couplings to fermions and the branching ration of the Higgs decaying into two photons is enhanced. Investigating these so-called “fermiophobic” models is an added benefit. Over the past two years, Dittmann and Bland have collaborated with R. Culbertson (Fermilab) and C. Group (U. Virginia) to optimize a search for H to diphoton. Kasmi joined the group in July 2010. Bland is the only graduate student at CDF working on this analysis. During the past year, Bland has presented her work at the 2010 APS April Meeting and the 2010 Pheno Symposium at the University of Wisconsin. In addition, she prepared a poster presentation for the 2010 Fermilab Users’ Meeting, and her poster won first prize in a contest sponsored by the Fermilab Graduate Student Association. With 5.4/fb of data, our H to diphoton analysis sets new limits for this channel at approximately 20 times higher than the SM prediction, as shown in the following Figure.

These limits are similar or better (as a function of Higgs mass) than current published results from H to tau tau, and comparable to limits from channels like ZH to 2 leptons and b bbar at around 140–150 GeV/c2. During 2010, Bland has worked to improve the analysis in three ways: (1) increasing the signal acceptance by including events in which one photon converts to an e+e− pair, (2) increasing the signal acceptance by including events in which one photon is in the plug region of the detector, and (3) using a multivariate approach to improve the efficiency for central photonidentification. Work on (1) has led to an extensive understanding of conversions in the CDF detector, and preliminary results indicate an improvement of about 10% in the overall limit on Higgs production for low mass. At CDF, we expect about 15–20% of central-central diphoton events to be lost due to conversions. At the LHC, the diphoton channel has been considered the most promising for a low mass Higgs search. It is therefore possible that techniques developed at the Tevatron may be useful for future CMS and ATLAS analyses where, for example, a much larger fraction of photons are expected to convert.