Two photons plus jet at LHC: the NNLO contribution from the gg initiated process

The production of the Standard Model Higgs boson of mass approximate to 100 -140 GeV at the LHC likely gives clear signals in the gamma gamma (1) and i n the gamma gamma jet (2) channels. The quantitative evaluation of the back ground to channel (1) is very hard since the next-to-leading order (NLO) an d next-to-next-to-leading order (NNLO) QCD corrections are large. In partic ular, the contributions of the NNLO QCD subprocess gs --> gamma gamma to in clusive yy production is comparable to the contribution of the leading orde r subprocess q (q) over bar --> gamma gamma. The quantitative description o f the background to channel (1), therefore, requires to calculate all corre ctions up to the NNNLO level. In this letter we present results on the cont ribution of the NNLO QCD subprocess gg --> g gamma gamma to the production rate of channel (2). We have found that in this case this NNLO contribution is less than 20% of the Born contribution. Since the NNLO contributions wi ll likely be dominated by this subprocess one can argue that in the case of channel (2) - contrary to the case of channel (1) - a quantitative descrip tion of the background can be achieved already at next-to-leading order acc uracy. (C) 1999 Elsevier Science B.V. All rights reserved.