Study of double parton scattering in photon + 3 jets final state in proton-proton collisions at √s = 7 CMS.TeV

Abstract

Distributions sensitive to double parton scattering are investigated in the photon + 3 jets final state in proton-proton collisions at a center-of-mass energy of 7 CMS.TeV. The data were collected by the CMS experiment at the LHC with an integrated luminosity of 36 pb^-1 in 2010. The cross section σ for a final state with a photon and a jet of transverse momentum p_T > 75 CMS.GeV together with 2 jets of p_T > 20 CMS.GeV, where the photon and jets are within the fiducial volume of the CMS detector, is measured to be 124.9 ± 8.9 ( stat.) ± 22.6 ( syst.) pb. The differential cross sections are measured as a function of the difference in azimuthal angles and the transverse momentum balance between the photon-jet pair and the di-jet pair. Further it is investigated whether additional contributions from double parton scattering can improve the agreement between the measured data and the Monte Carlo predictions.

Public Figures in the Physics Analysis Summary

Figure	Caption
	Fig.1: Dominant Feynman diagrams for the direct photon subprocesses: qg->q(left) and qqbar->g(center) and for the photon + 3 jets production from double parton scattering (right).
	Fig.2: A possible orientation of the transverse momenta of the photon and the three jets in photon + 3 jets events (left). Illustration of the definition of the ∆S observable, applied to a photon + 3 jets SPS event (center) and a photon + 3 jets DPS event (right)
	Fig.3: Comparison of MC-based signal and background distributions for different DPS-discriminating observables: ∆φ23 (left), ∆relpT,23 (center), and ∆S (right). The signal distributions are all produced by PYTHIA 8 tune 4C. The comparison of background distributions are shown for three MC event generators: MADGRAPH interfaced with PYTHIA 8 tune 4C (top row), PYTHIA 8 tune 4C (center row), and SHERPA tune CT10 (bottom row). Three kinds of background contributions are included in these comparisons: direct photon + 3 jets SPS events, fragmentation photon (frag. photon) + 3 jets SPS events and misidentified photon (fake photon) + 3 jets events.
	Fig.4: Measured σηη distributions for photons with 75 < ET, < 95 CMS.GeV in the barrel region. The fit results (solid) and the background components (dashed) are also shown.
	Fig.5: Data and MC simulations with one photon and at least three jets as a function of the pT of the leading photon (upper left), the leading jet (upper right), the second leading jet (lower left) and the third leading jet (lower right). All distributions are normalized to unit area. The lower panel shows the ratio of the MC simulation to the data. The error bars on the ratio histogram represent the statistical uncertainty of the data and simulated samples added in quadrature.
	Fig.6: The detector level comparisons of DPS-discriminating observables, ∆φ23 (left), ∆rel pT,23 (center), and ∆S (right) between the data and several MC simulations. All distributions are normalized to unit area. The lower panel shows the ratio of the MC simulation to the data. The error bars on the ratio histogram represent the statistical uncertainty of the data and simulated samples added in quadrature.
	Fig.7: Normalized differential cross sections as a function of ∆φ23 (left), ∆rel pT,23 (center), and ∆S (right) compared to different MC predictions. The comparisons are shown for two MC classes: comparisons between the data and LO MC predictions, PYTHIA 6 and PYTHIA 8, (upper row), comparisons between the data and multijet-improved MC predictions, MADGRAPH interfaced with PYTHIA 6 or PYTHIA 8, and SHERPA , (lower row). The lower panels show the ratio of the MC prediction to the data. For the MC predictions, three kinds of contributions are included: direct photon + 3 jets events, fragmentation photon + 3 jets events and misidentified photon + 3 jets events. The band represents the total uncertainty of the data.

Tables of measured distributions after detector unfolding in PAS

Figure	Caption
	Tables: The measured value and uncertainties of each bin for the normalized differential cross section as a function of ∆φ23 (left), ∆rel pT,23 (center), and ∆S (right).

-- YouHaoChang - 2015-02-17