Like-Sign W Boson Production at the LHC as a Probe of Double Parton Scattering

Double parton scattering, i.e. two parton hard scattering processes in the same hadron-hadron collision, may constitute an important background for Higgs and other new particle searches at the LHC. We point out that like-sign W pair production provides a relatively clean way of searching for, and calibrating, double parton scattering at the LHC. Recently [1] the importance of double parton scattering at the Large Hadron Collider (LHC) has been readdressed. In particular it has been pointed out [1] that double parton scattering may constitute a significant background to Higgs boson production and decay via the bb̄ decay channel, which, for a Higgs mass below the WW threshold, is one of the most promising discovery channels. Of course, double scattering contributes to the background in many other processes, and similar analyses have been performed in the past for hadron collisions at lower energy [2]. However, the LHC and its discovery potential necessitates a very accurate estimation of backgrounds where double scattering may provide a significant contribution. Therefore it is essential to obtain a better quantitative understanding of double parton scattering and a more precise estimation of the effect. The double (multiple) scattering occurs when two (many) different pairs of partons scatter independently in the same hadronic collision. From the theoretical point of view, the presence of double scattering is required to preserve unitarity in the high energy limit, i.e. when the distribution of partons with small momentum fractions within a hadron is high. In principle, double scattering probes correlations between partons in the hadron in the transverse plane, and thus provides important additional information on hadron structure [6]. If a scattering event is characterized by high centre-of-mass energy and relatively modest partonic subprocess energy, which happens for example in the production of heavy gauge bosons or a Higgs boson at the LHC, then parton-parton correlations can be assumed to be negligible. Such an assumption leads to a simple factorised expression for the double scattering cross section (in the case of two distinguishable interactions, a and b) [6] σDS = σaσb σeff . (1) Here σa represents the single scattering cross section