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[論文レビュー] Probing torsion field with Einstein-Cartan gravity at the HL-LHC: an angular distribution case study

S. Elgammal|arXiv (Cornell University)|Jan 28, 2026
Particle physics theoretical and experimental studies被引用数 0
ひとこと要約

The paper uses HL-LHC 14 TeV simulated data to study the angular distribution of high-mass dimuon pairs in the Collins-Soper frame, testing a simplified Einstein-Cartan gravity model with a torsion field and dark gauge boson, and provides 95% CL limits and discovery reach.”

ABSTRACT

This analysis utilizes simulated data privately generated based on the High Luminosity Large Hadron Collider (HL-LHC) configuration to investigate the angular distribution of high-mass dimuon pairs produced during the foreseen proton-proton collisions at a center-of-mass energy of 14 TeV. The study focuses on the cos$θ_{CS}$ variable, which is defined in the Collins-Soper frame. In the Standard Model, the production of high-mass dimuon pairs is primarily governed by the Drell-Yan process, which demonstrates a significant forward-backward asymmetry. However, scenarios beyond the Standard Model suggest different shapes for the cos$θ_{CS}$ distribution. By observing excess events not predicted by the Standard Model, the angular distribution can help differentiate among these alternative models. Furthermore, we used a simplified Einstein-Cartan gravity model to analyze the simulated data. This analysis established upper limits at the 95\% confidence level regarding the masses of various particles within the model, including a spin-2 dark neutral gauge boson and the torsion field.

研究の動機と目的

  • Motivate searches for physics beyond the Standard Model through dilepton angular distributions at the HL-LHC.
  • Investigate a simplified Einstein-Cartan gravity model producing a dark neutral gauge boson A′ alongside dark matter.
  • Evaluate the cos theta_CS distribution to distinguish signal from Standard Model backgrounds.
  • Assess discovery potential and set exclusion limits for model parameters (M_TS, M_A′, M_χ) with HL-LHC-like data.

提案手法

  • Use a simplified EC gravity model with a torsion field S_μ and dark gauge boson A′ coupled to dark matter χ.
  • Generate signal and SM background samples at 14 TeV with MadGraph5_aMC@NLO, Pythia8, and DELPHES for HL-LHC realism.
  • Analyze dilepton (μ+μ−) events in the Collins-Soper frame and compute cosθ_CS from lab-frame observables.
  • Apply a pre-selection on muons (pT > 30 GeV, |η| < 2.5, isolation) and a dimuon mass > 60 GeV, followed by tight angular and kinematic cuts to suppress backgrounds.
  • Perform a shape-based analysis using the cosθ_CS distribution to discriminate signal (spin-2-like) from SM backgrounds.
  • Interpret results with a profile likelihood and CLs method to set 95% CL upper limits on cross section × BR(A′→μμ) as a function of M_TS.
Figure 1 : Feynman diagram for the simplified model based on Einstein-Cartan gravity; for the production of dark gauge boson (A ′ ) in association to dark matter ( $\chi$ ) pair [ 15 ] .
Figure 1 : Feynman diagram for the simplified model based on Einstein-Cartan gravity; for the production of dark gauge boson (A ′ ) in association to dark matter ( $\chi$ ) pair [ 15 ] .

実験結果

リサーチクエスチョン

  • RQ1Cos θ_CS の角度分布は、エインシュタイン–カルタン重力が予測するスピン-2のダーク媒介ニューモデルの信号を高質量の二重레プトンイベントで示すことができるか？
  • RQ2与えられた M_A′ および M_TS の値に対して、5σ発見を達成する HL-LHC 風のルミノシティ要件は何か？
  • RQ3M_χ = 500 GeV の下で、EC重力の下での A′ の質量範囲に対する torsion の質量 M_TS の 95% CL 除外は何か？
  • RQ4EC重力の信号予測は cosθ_CS 観測量において Drell–Yan や他の SM 背景とどのように比較されるか？

主な発見

  • EC 信号は cosθ_CS を原点周り対称に生成し、SM Drell–Yan の前方-後方パターンとは異なる。
  • より厳しい選択カットは DY, ZZ, tt̄, tW, WW, WZ 背景を著しく低減しつつ、高 pT で信号効率を維持する。
  • M_A′ = 200 GeV および M_TS = 4000 GeV の場合、約 500 fb−1 で 5σ 発見が到達可能；M_TS = 5000 GeV では 2000 fb−1 以上が必要。
  • M_A′ = 200, 300, 400, 500 GeV の下で EC フレームワークに対する M_TS の関数として cross section × BR(A′→μμ) の 95% CL 上限を導出。
  • M_χ = 500 GeV および結合 g_η = 0.125, g_D = 1.0 の条件下で、95% CL の除外領域は A′ = 200 GeV の場合約 1.4–5.5 TeV から、A′ = 500 GeV の場合約 1.7–6.9 TeV へ拡張される。
Figure 2 : Normalized distributions of cos $\theta_{CS}$ for one resonant model based on Einstein-Cartan gravity generated with a mass of $A^{\prime}$ equal to 200 GeV and Drell-Yan events at $\sqrt{s}=14$ TeV. All events must pass the pre-selection listed in table 3 and have a reconstructed invaria
Figure 2 : Normalized distributions of cos $\theta_{CS}$ for one resonant model based on Einstein-Cartan gravity generated with a mass of $A^{\prime}$ equal to 200 GeV and Drell-Yan events at $\sqrt{s}=14$ TeV. All events must pass the pre-selection listed in table 3 and have a reconstructed invaria

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