Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

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

Ezio Maina

TL;DR

The paper investigates the contribution of Multiple Parton Interactions to Z+n jets (n=2,3,4) at the LHC, comparing the correlated GS09 double parton distributions with factorized single PDFs (MSTW2008LO and CTEQ6LO). Using LO DPI formalism and reweighting techniques, it assesses how correlations and PDF choices affect MPI predictions across 7–14 TeV, focusing on Z+jets and gamma+jets channels. It finds that GS09 induces at most ~15% differences relative to MSTW, while PDF-driven uncertainties are large (30–90%), and MPI fractions grow with energy and jet separation, making early LHC measurements feasible with ~1 fb^-1 at 7 TeV. The study argues that multi-channel MPI measurements could enable extraction of double parton distributions from data, with gamma+3j offering complementary sensitivity depending on trigger strategies.

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 CTEQ6LO. 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 gamma+3-jets channel. The MPI cross section is dominated by relatively soft events with two jets balancing in transverse momentum.

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

TL;DR

The paper investigates the contribution of Multiple Parton Interactions to Z+n jets (n=2,3,4) at the LHC, comparing the correlated GS09 double parton distributions with factorized single PDFs (MSTW2008LO and CTEQ6LO). Using LO DPI formalism and reweighting techniques, it assesses how correlations and PDF choices affect MPI predictions across 7–14 TeV, focusing on Z+jets and gamma+jets channels. It finds that GS09 induces at most ~15% differences relative to MSTW, while PDF-driven uncertainties are large (30–90%), and MPI fractions grow with energy and jet separation, making early LHC measurements feasible with ~1 fb^-1 at 7 TeV. The study argues that multi-channel MPI measurements could enable extraction of double parton distributions from data, with gamma+3j offering complementary sensitivity depending on trigger strategies.

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 CTEQ6LO. 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 gamma+3-jets channel. The MPI cross section is dominated by relatively soft events with two jets balancing in transverse momentum.

Paper Structure

This paper contains 4 sections, 12 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Calculation
  3. Results
  4. Conclusions

Figures (2)

  • Figure 1: On the left: distribution of the angular separation in the transverse plane between the two highest $p_{T}$ jets in $Z+4j$ events. On the right: distribution of the total visible mass, $(\sum_{i=1}^n p_{i})^2$, in $Z+2j$ events. For both plots $\sqrt{s} = 7~{\rm TeV}$, $\Delta R_{jj}=0.7$.
  • Figure 2: Transverse momentum distribution of the hardest jet in $\gamma+3j$ events. $\sqrt{s} = 7~{\rm TeV}$, $\Delta R_{jj}=0.7$ and $p_{T_\gamma} \geq 80~{\rm GeV}$.