CMS logoCMS event Hgg
Compact Muon Solenoid
LHC, CERN

CMS-PAS-FSQ-13-001
Double Parton Scattering cross section limit from same-sign W bosons pair production in di-muon final state at LHC
Abstract: The double parton scattering (DPS) in proton-proton collisions at a center-of-mass energy of 8 TeV has been investigated using the same-sign W boson pair final state, with each W boson decaying into muon and associated neutrino. The data sample corresponds to an integrated luminosity of 19.7 fb$^{-1}$ collected by the CMS detector at the Large Hadron Collider. The observables sensitive to double parton scattering are defined and studied, followed by a multivariate analysis in order to enhance the process sensitivity. A limit on the DPS yield, along with the corresponding limit on the production cross section ($\sigma^{DPS}_{WW}$), has been evaluated.
Summary CMS Publications
Summary
A search for the same-sign W-pair DPS events in the di-muon final state is done using data from proton-proton collisions at center-of-mass energy of 8 TeV in a single signal region corresponding to an integrated luminosity of 19.7 fb$^{-1}$ collected by CMS detector. Different observables, expected to be sensitive to WW events from DPS production, have been used in a BDT approach to enhance the sensitivity respect to the single parton scattering production mechanism. Although no direct measurements of DPS yield are allowed with current statistics, we set an exclusion limit on DPS signal strength. BDT response shape gives the limit estimation, excluding at 95% CLs a signal strength $r >$ 1.897 (28 DPS events), with an expected exclusion of $r >$ 2.01 (30 DPS events), which means an upper limit on $\sigma ^{\text{DPS}}_{\mathrm{WW }} <$ 1.12 pb at 95% of confidence level. Considering the two scattering to be independent and no correlation between interacting partons, one can put in relation the limit on $\sigma ^{\text{DPS}}_{\mathrm{WW }}$ with the $\sigma_{\text{eff}}$. Considering the cross section for the production of a W boson that decays leptonically $\sigma_{\mathrm{ W\to \ell \nu}} =$ 37 509 pb and the corresponding branching ratio $ \mathrm{BR}( \mathrm{ W \to \ell \nu } ) =$ 0.326, the lower limit on the $\sigma_{\text{eff}}$ can be written as:

$\sigma_{\text{eff}} > \left( \sigma_{ \mathrm{ W \to \ell \nu } } \right)^2 \ / \ 2\, \left( \mathrm{BR}^2_{ \mathrm{ W\to \ell \nu} } \right) \, \sigma ^{\text{DPS}}_{\mathrm{WW}} =$ 5.91 mb.
Compact Muon Solenoid
LHC, CERN