Multiple Parton Interactions in Z+ jets production at the LHC. A comparison of factorized and non-factorized double parton distribution functions.

Abstract

Abstract:We examine the contribution of Multiple Parton Interactions to Z + n-jets production at the LHC, n = 2, 3, 4, where the Z boson is assumed to decay leptonically. We compare the results obtained with the correlated GS09 double parton distribution function with those obtained with two instances of fully factorized single parton distribution functions: MSTW2008LO and CTEQ6L1. It appears quite feasible to measure the MPI contribution to Z+2/3/4 jets already in the first phase of the LHC with a total luminosity of one inverse femtobarn at 7 TeV. If as expected the trigger threshold for single photons is around 80 GeV, Z + 2-jets production may well turn out to be more easily observable than the γ + 3-jets channel. The MPI cross section is dominated by relatively soft events with two jets balancing in transverse momentum.

Elements of a theory for multiparton interactions in QCD

“…The effects of such multiparton interactions are suppressed or average out in sufficiently inclusive observables, but they have important consequences for the details of the hadronic final state. The possible importance of multiparton interactions has been realized long ago [1,2] and phenomenological estimates have been given for many final states such as four jets (possibly including b quarks) [3][4][5][6][7][8][9], jets associated with photons or leptons [10], four leptons produced by the double Drell-Yan process [11][12][13] or from two charmonium states [14][15][16], as well as a number of channels with electroweak gauge bosons [17][18][19][20][21][22][23][24][25][26]. Experimental evidence for multiple hard scattering has been found in the production of multijets [27][28][29] and of a photon associated with three jets [30][31][32][33].…”

Fresh look at double parton scattering

“…The contribution to the cross section from the second term induced by the QCD evolution cannot be reduced to the form (5) with some new constant effective cross section as it was done in earlier estimations [35,40,41]. The QCD evolution effects for the cross section are anticipated to be larger than for the two-parton distribution functions, for those such effects were estimated in Refs.…”

Double parton scattering of weak gauge boson productions at the 13 TeV and 100 TeV proton-proton colliders

“…(1). We name it as "simply factorized" (SF) dPDF, which is widely used both in theoretical [39,[48][49][50][51][52][53][54][55][56][57] and experimental studies [4][5][6][7][8][9][10][11][12][13]24,36,37].…”

“…The comparison of the SF and GS09 dPDFs has been investigated in the Z ⊗ jets channel [48] and the W ⊗ W channel [39]. It was shown that both the SF and GS09 dPDFs give rise to consistent cross sections within ∼10% accuracy and, furthermore, the kinematics distributions of p T , η and invariance mass are insensitive to the choice of dPDFs.…”

“…A parton level analysis of the MPI contribution to the Z ⊗ jets final states has been carried out in Ref. [48] in which three colliding energies (8, 10 and 14 TeV) are studied. A dynamical approach to such final state within the Pythia event generator is studied in Ref.…”