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Multiple Parton Interactions, top--antitop and W+4j production at the LHC

Ezio Maina

TL;DR

This paper quantifies the impact of Multiple Parton Interactions (MPI) at the LHC on two key channels: tt̄ production in the semileptonic decay and W+4j final states. It develops a DPI/TPI framework using σ_eff and perturbative-order separation to estimate backgrounds, demonstrating that MPI backgrounds to tt̄ are small (about 1%) in the relevant mass window, while the W+4j background from SPS is larger (about 7%). The authors show that MPI signals can be isolated in W+4j via jet-geometry and angular correlations, and they argue that Triple Parton Interactions might be accessible through specific jet-pair angular distributions. These results support the feasibility of MPI studies in early LHC data and highlight the value of cross-channel analyses to probe flavor, x-dependence, and multi-parton dynamics.

Abstract

The expected rate for Multiple Parton Interactions (MPI) at the LHC is large. This requires an estimate of their impact on all measurement foreseen at the LHC while opening unprecendented opportunities for a detailed study of these phenomena. In this paper we examine the MPI background to top-antitop production, in the semileptonic channel, in the early phase of data taking when the full power of $b$--tagging will not be available. The MPI background turns out to be small but non negligible, of the order of 20% of the background provided by W+4j production through a Single Parton Interaction. We then analyze the possibility of studying Multiple Parton Interactions in the W+4j channel, a far more complicated setting than the reactions examined at lower energies. The MPI contribution turns out to be dominated by final states with two energetic jets which balance in transverse momentum, and it appears possible, thanks to the good angular resolution of ATLAS and CMS, to separate the Multiple Parton Interactions contribution from Single Parton Interaction processes. The large cross section for two jet production suggests that also Triple Parton Interactions (TPI) could provide a non negligible contribution. Our preliminary analysis suggests that it might be indeed possible to investigate TPI at the LHC.

Multiple Parton Interactions, top--antitop and W+4j production at the LHC

TL;DR

This paper quantifies the impact of Multiple Parton Interactions (MPI) at the LHC on two key channels: tt̄ production in the semileptonic decay and W+4j final states. It develops a DPI/TPI framework using σ_eff and perturbative-order separation to estimate backgrounds, demonstrating that MPI backgrounds to tt̄ are small (about 1%) in the relevant mass window, while the W+4j background from SPS is larger (about 7%). The authors show that MPI signals can be isolated in W+4j via jet-geometry and angular correlations, and they argue that Triple Parton Interactions might be accessible through specific jet-pair angular distributions. These results support the feasibility of MPI studies in early LHC data and highlight the value of cross-channel analyses to probe flavor, x-dependence, and multi-parton dynamics.

Abstract

The expected rate for Multiple Parton Interactions (MPI) at the LHC is large. This requires an estimate of their impact on all measurement foreseen at the LHC while opening unprecendented opportunities for a detailed study of these phenomena. In this paper we examine the MPI background to top-antitop production, in the semileptonic channel, in the early phase of data taking when the full power of --tagging will not be available. The MPI background turns out to be small but non negligible, of the order of 20% of the background provided by W+4j production through a Single Parton Interaction. We then analyze the possibility of studying Multiple Parton Interactions in the W+4j channel, a far more complicated setting than the reactions examined at lower energies. The MPI contribution turns out to be dominated by final states with two energetic jets which balance in transverse momentum, and it appears possible, thanks to the good angular resolution of ATLAS and CMS, to separate the Multiple Parton Interactions contribution from Single Parton Interaction processes. The large cross section for two jet production suggests that also Triple Parton Interactions (TPI) could provide a non negligible contribution. Our preliminary analysis suggests that it might be indeed possible to investigate TPI at the LHC.

Paper Structure

This paper contains 5 sections, 12 equations, 7 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Calculation
  3. MPI background to top pair production
  4. Studying MPI in $W+4j$ processes
  5. Conclusions

Figures (7)

  • Figure 1:
  • Figure 2:
  • Figure 3: Visible mass distribution for the different contributions and for their sum. Cuts as in Eq.(\ref{['eq:cuts']}), Eq.(\ref{['eq:cuts_iso']}) and Eq.(\ref{['cuts:DeltaEta']}). The curves in the lower plot are normalized to one.
  • Figure 4: Largest $\Delta\phi$ separation between jet pairs for the different contributions and for their sum. Cuts as in Eq.(\ref{['eq:cuts']}), Eq.(\ref{['eq:cuts_iso']}) and Eq.(\ref{['cuts:DeltaEta']}). The curves in the lower plot are normalized to one.
  • Figure 5: $\Delta\phi$ separation between the two most energetic jets (on the left) and between the two least energetic among the four jets (on the right) for the different contributions and for their sum. Cuts as in Eq.(\ref{['eq:cuts']}), Eq.(\ref{['eq:cuts_iso']}) and Eq.(\ref{['cuts:DeltaEta']}). The curves in the lower plot are normalized to one.
  • ...and 2 more figures