Lhc Physics: Challenges for Qcd

One of the main goals of the LHC will be the search of the Higgs boson, the only piece of the otherwise thoroughly tested Standard Model (SM) of which we miss experimental evidence. Regardless of the existence of the Higgs boson, LHC will likely shed light on the physics Beyond-the-SM (BSM), which should be within reach, as LEP results and solar and atmospheric neutrino data suggest. In this context, the role played by QCD may appear an ancillary one. However, this seems to be quite at odd with the fact that LHC is a hadronic collider, and strong interactions will be responsible for a prominent part of the reactions taking place. On the other hand, one may claim that an accurate knowledge of QCD predictions will not be necessary for the discovery of – say – the Higgs in presence of a striking feature such as a narrow mass peak, which could give the possibility of normalizing the background directly with the data. However, if the discovery is based on a counting experiment, it relies by definition on precise predictions for SM backgrounds, dominated by QCD. These predictions will also prove essential for after-discovery studies, when the properties of the newly-found particles will have to be determined, or in the case of absence of BSM signals, in order to set limits on BSM scenarios. Having argued that QCD studies are one of the keys for a successful LHC physics program, one question remains: are there still motivations to keep