[Paper Review] Studies on the anomalous magnetic and electric dipole moments of the tau-neutrino in $pp$ collisions at the LHC

A. Gutiérrez-Rodríguez, M. Köksal+2 more|arXiv (Cornell University)|Dec 6, 2017

Particle physics theoretical and experimental studies1 references3 citations

TL;DR

This study investigates the anomalous magnetic and electric dipole moments (MM and EDM) of the tau-neutrino via the process $pp \to \nu_\tau\bar{\nu}_\tau\gamma + X$ at the LHC, using ATLAS detector simulations across center-of-mass energies $\sqrt{s} = 8, 13, 14, 33$ TeV and integrated luminosities up to 3000 fb$^{-1}$. It reports the most stringent current limits at 95% C.L.: $\mu_{\nu_\tau} = 1.474 \times 10^{-6}\mu_B$ and $d_{\nu_\tau} = 2.424 \times 10^{-17}$ ecm, surpassing previous LEP and fixed-target results by a factor of ~2.23.

ABSTRACT

In this paper the production cross section $pp ightarrow (γ, Z) o ν_τ\bar ν_τγ+X$ in $pp$ collisions at $\sqrt{s}=8, 13, 14, 33TeV$ is presented. Furthermore, we estimate bounds at the $95\%C. L.$ on the dipole moments of the tau-neutrino using integrated luminosity of ${\cal L}=20, 50, 100, 200, 500, 1000, 3000 fb^{-1}$ collected with the ATLAS detector at the LHC and we consider systematic uncertainties of $δ_{sys}=0, 5, 10\%$. It is shown that the process under consideration is a good prospect for probing the dipole moments of the tau-neutrino at the LHC.

Motivation & Objective

• To probe the anomalous magnetic and electric dipole moments of the tau-neutrino in high-energy $pp$ collisions at the LHC.
• To evaluate the sensitivity of the ATLAS detector to these dipole moments across varying luminosities and center-of-mass energies.
• To improve upon existing experimental bounds from Borexino, DONUT, CERN-WA-066, and L3 experiments.
• To assess the impact of systematic uncertainties (0%, 5%, 10%) on the derived limits.

Proposed method

• The study computes the total cross section for $pp \to \nu_\tau\bar{\nu}_\tau\gamma + X$ using effective field theory with anomalous $\nu_\tau\bar{\nu}_\tau\gamma$ vertex couplings.
• It models the process as $pp \to (\gamma, Z) \to \nu_\tau\bar{\nu}_\tau\gamma + X$, including interference between SM and anomalous dipole contributions.
• Kinematic cuts on transverse energy ($E_T$), transverse momentum ($p_T$), and pseudorapidity ($\eta$) are applied to enhance signal sensitivity.
• Monte Carlo simulations are used to estimate signal and background contributions, with systematic uncertainties of 0%, 5%, and 10% considered.
• 95% confidence level (C.L.) limits on $\mu_{\nu_\tau}$ and $d_{\nu_\tau}$ are derived by scanning over anomalous coupling parameters.
• Two-parameter contours in the $(F_3 - F_2)$ plane are generated to visualize the sensitivity region across different luminosity and energy settings.

Experimental results

Research questions

• RQ1 Can the $pp \to \nu_\tau\bar{\nu}_\tau\gamma + X$ process at the LHC probe the anomalous magnetic moment of the tau-neutrino with higher sensitivity than previous experiments?
• RQ2 How do the luminosity and center-of-mass energy of the LHC affect the sensitivity to the tau-neutrino's dipole moments?
• RQ3 What are the projected 95% C.L. limits on $\mu_{\nu_\tau}$ and $d_{\nu_\tau}$ for future LHC runs with increasing integrated luminosity?
• RQ4 How do systematic uncertainties (0%, 5%, 10%) influence the derived bounds on the dipole moments?
• RQ5 Is the $\nu_\tau\bar{\nu}_\tau\gamma$ channel competitive with other existing and proposed experiments in probing neutrino electromagnetic properties?

Key findings

• The $pp \to \nu_\tau\bar{\nu}_\tau\gamma + X$ process provides a viable and sensitive channel for probing the anomalous magnetic moment of the tau-neutrino at hadron colliders.
• The most stringent 95% C.L. upper limit on the anomalous magnetic moment is $\mu_{\nu_\tau} = 1.474 \times 10^{-6}\mu_B$, achieved at $\sqrt{s} = 33$ TeV and $\mathcal{L} = 3000$ fb$^{-1}$.
• The most stringent 95% C.L. upper limit on the electric dipole moment is $d_{\nu_\tau} = 2.424 \times 10^{-17}$ ecm, also achieved under optimal luminosity and energy conditions.
• The limits are approximately 2.23 times more stringent than the previous best limit from the L3 experiment at LEP.
• The sensitivity to the magnetic dipole moment shows a slight asymmetry at $\sqrt{s} = 8$ TeV due to interference effects, but this diminishes at higher energies.
• Systematic uncertainties of up to 10% have a measurable but moderate impact on the final bounds, with the sensitivity remaining robust across all considered levels.