Azimuthal decorrelations and multiple parton interactions inγ+2jet andγ+3jet events inpp¯

Abstract

Samples of inclusive γ+2 jet and γ+3 jet events collected by the D0 experiment with an integrated luminosity of about 1 fb −1 in pp collisions at √ s = 1.96 TeV are used to measure cross sections as a function of the angle in the plane transverse to the beam direction between the transverse momentum (pT ) of the γ+leading jet system (jets are ordered in pT ) and pT of the other jet for γ + 2 jet, or pT sum of the two other jets for γ + 3 jet events. The results are compared to different models of multiple parton interactions (MPI) in the pythia and sherpa Monte Carlo (MC) generators. The data indicate a contribution from events with double parton (DP) interactions and are well described by predictions provided by the pythia MPI models with pT -ordered showers and by sherpa with the default MPI model. The γ + 2 jet data are also used to determine the fraction of events with DP interactions as a function of the azimuthal angle and as a function of the second jet pT .

Elements of a theory for multiparton interactions in QCD

“…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].…”

Measurement of isolated-photon pair production in pp collisions at $ \sqrt{s}=7\;TeV $ with the ATLAS detector

“…The contribution from the particle recently discovered by ATLAS and CMS in the search for the Standard Model Higgs boson is not included in the predictions: it is expected to be around 1% of the signal in the 120< m γγ <130 GeV interval, and negligible elsewhere. The contribution from multiple parton interactions is also neglected: measurements by DØ [32] and AT-LAS 5 show that events with two jets (in γ+jets or W+jets) have a contamination between 5% and 10% from double parton interactions. In our data sample, the fraction of selected di-photon candidates with at least two additional jets not overlapping with the photons and not from pile-up is around 8%, thus the overall contribution to the signal from multiple parton interactions is estimated to be lower than 1%.…”

Cancellation of Glauber gluon exchange in the double Drell-Yan process

“…A more solid theoretical understanding of double hard scattering with jets or heavy quarks would be of great practical value, because such processes have much higher rates than double Drell-Yan production and were already studied experimentally at the Tevatron [93][94][95][96][97][98] and in Run 1 of the LHC [99][100][101][102][103][104]. Further in-depth studies can surely be expected from Run 2.…”