Study of double parton scattering using four-jet scenarios in proton-proton collisions at √(s)=7 TeV with the CMS experiment at the Large Hadron Collider

Measurements of the differential cross sections for multijet scenarios in proton-proton collisions are presented as a function of the transverse momentum p_T and pseudorapidity, together with the correlations in azimuthal angle and the p_T balance among the jets. Two different scenarios are separately studied; in the first one an exclusive four-jet final state is selected in vertical stroke η vertical stroke <4.7, by requiring two hard jets with p_T>50 GeV each, together with two jets of p_T>20 GeV each. No other jets with p_T>20 GeV are allowed in the selected events. In the second one at least four jets with p_T>20 GeV are required: two of the four selected jets are asked to be originated by a b-quark in vertical stroke η vertical stroke <2.4, while no requests on the flavour of the other two jets, which are selected within vertical stroke η vertical stroke <4.7 are applied. The data sample was collected in 2010 at a center-of-mass energy of 7 TeV with the CMS detector at the LHC, with an integrated luminosity of 36 pb^-1. The total cross section is measured to be σ(pp→ 4j+X)=330±5 (stat.)±4(syst.) and σ(pp→2b+2j+X)=67.2±2.2(stat.)±22.5 (syst.) for, respectively, the two selected multijet scenarios. It is found that fixed-order matrix element calculations including parton showers describe the measured differential cross sections in some regions of phase space only, and that adding contributions from double parton scattering brings the Monte Carlo predictions closer to the data. A new method of extraction of double parton scattering contributions from an experimental measurement is introduced for the first time: it is applied to W+dijet measurements and to both multijet channels. Values of σ_eff are measured to be 19.0^+4.6_-3.0mb and 23.2^+3.3_-2.5mb for the two examined selections. These values are consistent between each other and compatible with measurements based on different physics channels at 7 TeV.