Gauge-boson production with multiple jets near threshold

TL;DR

This work tackles the challenging high-$m_{eff}$ tail of gauge-boson plus multi-jet production, a key background for missing-energy searches at the LHC. It develops an SCET-based threshold-resummation framework using N-jettiness to factorize the cross section into hard, jet, and soft functions convoluted with PDFs, enabling controlled resummation of Sudakov logarithms near partonic threshold. For the specific process $pp\to\gamma+2$ jets, the authors obtain NLL predictions that show 50–100% enhancements over LO in the high-$m_{eff}$ region and display reduced scale uncertainties, demonstrating the practical significance of their approach for experimental background modeling. The framework lays groundwork for extending to $W/Z+n$ jets and Higgs production and for combining with fixed-order calculations to deliver precise predictions for LHC analyses.

Abstract

Signatures of new physics beyond the Standard Model are often characterized by large missing transverse energy ($\not E_T$) produced in association with multiple jets. The dominant Standard Model background to such processes comes from gauge-boson production in association with jets. A standard search strategy involves looking for an excess in the $m_{eff}$ distribution, where $m_{eff}= \not E_T +\sum_{J} p^T_J$ and $p^T_J$ denotes the transverse momentum of the $J$-th jet. The region of large $m_{eff}$ is dominated by jet production near threshold, giving rise to large Sudakov logarithms that can change the magnitude and shape of the $m_{eff}$ distribution. We present an effective theory framework for the resummation of such threshold logarithms. We perform an analysis for exclusive jet production using the N-jettiness global event shape, which allows theoretical control to also be maintained over large logarithms induced by vetoing additional jets. As a first step, we give explicit numerical results with next-to-leading-log (NLL) resummation for $pp \to γ+ 2$ jets in the large $m_{eff}$ region.

Figures (6)

• Figure 1: The left panel shows the average ratio of the second jet $p_T$ over the $p_T$ of the leading jet for the $ug$ partonic channel (magenta dotted line), the $uu$ partonic channel (blue dashed line), and for the total result (red solid line). The right panel shows the ratio of the cross section for one hard jet and one soft jet over the two hard-jet cross section, where the soft jet is defined by $100 \,\text{GeV} \leq p^T_2 \leq 0.2 \times m_{eff}/2$. The double-hard region is then defined as the difference of the cross section with both transverse momenta greater than 100 GeV, minus the cross section with either jet having a $p_T$ between 100 GeV and $0.2 \times m_{eff}/2$. These results use the LO approximation of the cross section.
• Figure 2: The four jettiness regions into which each event is divided, illustrated using the $q\bar{q} \to gg \gamma$ process. The dashed lines indicate the separation between the regions. Regions 1 and 3 correspond to the beam directions, while regions 2 and 4 correspond to the two jets.
• Figure 3: The solid and dashed lines correspond to the $m_{eff}$ distributions with NLL resummation and at LO, respectively. The $qg$ initial state is shown in red while the $q_1 q_2$ initial state, with $q_i$ representing any quark or anti-quark, is shown in blue.
• Figure 4: The dependence of the ratio $R_J$ on the choice of the jet scale $\mu_J$ for various kinematic points. From the right to the left, are the curves used to determine the jet scales for $m_{eff}$ = 1 TeV, 2 TeV and 4 TeV, respectively.
• Figure 5: A plot of the K-factor, defined as the ratio of the cross section with NLL resummation over the LO result, for the important partonic channels. The curves from top to bottom correspond to the $qg$ and $q_1 q_2$ initial states, where $q_i$ denotes any quark or anti-quark.