Probing the SM with Dijets at the LHC

TL;DR

The paper demonstrates that LHC dijet angular distributions, analyzed through the $F_\chi$ observable, provide precision constraints on the SM quark sector and a broad class of new physics scenarios. By computing SM plus dimension-six four-quark operator contributions to dijet production and fitting to ATLAS/CMS data, the authors derive 95% CL bounds on operator scales $\Lambda/\sqrt{|c_i|}$ in the ~1–3 TeV range, translating these into limits on quark/gluon compositeness, heavy gauge bosons, and oblique parameters. The analysis disfavors explanations of the top $A_{FB}$ anomaly that rely on large four-quark couplings and shows that dijet data already start to rival LEP in constraining the quark sector, with CMS 2011 data further strengthening the bounds. These results constrain TeV-scale BSM scenarios and highlight the dijet channel as a powerful probe of SM sectors and new heavy states at high energy.

Abstract

The LHC has started to explore the TeV energy regime, probing the SM beyond LEP and Tevatron. We show how the dijet measurements at the LHC are able to test certain sectors of the SM at an unprecedented level. We provide the best bounds on all possible four-quark interactions and translate them into limits on the compositeness scale of the quarks and gluons. We also provide constraints on extra gauge bosons, Z', W' and G', and on new interactions proposed to explain the present measurement of the forward-backward asymmetry of the top.

Figures (6)

• Figure 1: Dijet differential cross section as a function of $\chi$ for $m_{jj}>2$ TeV at the LHC with $\sqrt{s}=7$ TeV. The QCD contribution is shown in solid red line, while the green dashed line includes the contribution from the operator ${\cal O}^{(8)}_{qq}$ with $c^{(8)}_{qq}=-0.5$ and $\Lambda=1$ TeV.
• Figure 2: Excluded region in the $g_L-g_R$ plane by the $m_{jj}>2$ TeV dijet analysis.
• Figure 3: Excluded region in the $W$-$Y$ plane by the $m_{jj}>2$ TeV ATLAS dijet analysis.
• Figure 4: The red line shows the value of $c_A^{(8)}$ as a function of $\Lambda$ that fits the $A_{FB}$ of the top arXiv:1103.2297. The shaded regions delimited by the solid and dashed blue lines show the excluded region due to our dijet angular distribution analysis with cuts $m_{jj}^{cut} = 2 \,\mathrm{TeV}$ and $m_{jj}^{cut} = 1.2 \,\mathrm{TeV}$ respectively.
• Figure 5: Excluded region in the $g_L-g_R$ plane by the $m_{jj}>3$ TeV CMS dijet analysis.