qT Uncertainties for W and Z Production

Analysis of semi-inclusive DIS hadroproduction suggests broadening of transverse momentum distributions at small x below 10−3 ∼ 10−2, which can be modeled in the Collins-SoperSterman formalism by a modification of impact parameter dependent parton densities. We investigate these consequences for the production of electroweak bosons at the Tevatron and the LHC. If substantial small-x broadening is observed in forward Z0 boson production in the Tevatron Run-2, it will strongly affect the predicted qT distributions for W± and Z0 boson production at the LHC. INTRODUCTION: As we move from the Tevatron collider at 1.96 TeV to the Large Hadron Collider (LHC) at 14 TeV, we encounter an unexplored kinematic regime. In this regime we may discover phenomena with significant consequences for precision measurements and searches for new physics. In this paper,2 we analyze the consequences of anomalous transverse momentum (qT ) broadening driven by possible small-x effects in W and Z boson production at the Tevatron and LHC. At present, the form of the qT distributions of W , Z, and Higgs boson production at the LHC is largely unknown, in part because limited experimental data on qT distributions is available in Drell-Yan-like processes at small x. If we turn to the crossed deep inelastic scattering (DIS) process, qT broadening was observed at the HERA ep collider in the small x region: x = 10−4 ∼ 10−2 [2, 3, 4, 5]. We use these results to predict the effects in hadron-hadron processes. The resulting modifications in the transverse momentum distributions may affect the measurements of the W boson mass and width, as well as the W and Z boson background in the search for new gauge bosons. The qT broadening may also affect the detection of the Higgs boson at the LHC by altering its qT distribution and the relevant QCD background. PARAMETERIZING THE BROADENING: We now characterize the qT broadening which was observed in semi-inclusive DIS processes and consider implications for the 1 Contribution to the proceedings of the XIII International Workshop on Deep Inelastic Scattering (DIS 2005), April 27 May 1, 2005, Madison, WI, U.S.A. Presented by Fredrick Olness. 2 The results presented here are based on Ref. [1]; refer to this reference for a detailed description of the process and more extensive references. qT Uncertainties for W and Z Production 23rd August 2005 1 pp _ → Z X (√S = 1960 GeV)