## SciPost Submission Page

# Limits on the anomalous magnetic and electric dipole moments of the $\tau$-neutrino in $pp$ collisions at the LHC

### by A. Guti\'errez-Rodr{\'\i}guez, M. K\"oksal, A. A. Billur and M. A. Hern\'andez-Ru{\'\i}z.

#### This is not the current version.

### Submission summary

As Contributors: | MARIA HERNANDEZ |

Preprint link: | scipost_201810_00003v1 |

Date submitted: | 2018-10-27 |

Submitted by: | HERNANDEZ, MARIA |

Submitted to: | SciPost Physics Proceedings |

Proceedings issue: | The 15th International Workshop on Tau Lepton Physics (Amsterdam, 2018-09) |

Domain(s): | Theoretical |

Subject area: | High-Energy Physics - Phenomenology |

### Abstract

In this paper the production cross-section $pp\rightarrow (\gamma, Z) \to \nu_\tau \bar \nu_\tau \gamma+X$ in $pp$ collisions at $\sqrt{s}=13, 14, 33\hspace{0.8mm}TeV$ is presented. Furthermore, we estimate bounds at the $95\%$ C.L. on the dipole moments of the $\tau$-neutrino using integrated luminosity of ${\cal L}= 100, 500, 1000, 3000 \hspace{0.8mm}fb^{-1}$ collected with the ATLAS detector at the LHC and we consider systematic uncertainties of $\delta_{sys} = 0\%, \, 5\%, \,10\%$. We found that the current and future LHC bounds are weaker than other experiments reported in the literature. However, it is shown that the process under consideration is a good prospect for probing the dipole moments of the $\tau$-neutrino at the LHC.

###### Current status:

### Submission & Refereeing History

## Reports on this Submission

### Report 1 by Nicolo De Groot on 2018-11-26 Invited Report

### Strengths

1 - This paper is describing an potentially interesting measurement at the LHC

### Weaknesses

1 - The paper suggest it is presenting limits, it is not. It is a feasibility study

2- Some of the fit results are presented without proper explanation

3- The English can be improved

### Report

- I am puzzled by the presence of a photon-neutrino coupling in fig 1

- The fit results (5), (6), (7) are identical for F2 and F3, this seems odd. It is unclear what is fit to get these results, please explain this in the text.

- I don't see the added value for reporting both 13 and 14 TeV, since they are similar

- an annotated version of the paper is included to fix typos etc.

### Requested changes

1- Change the title to reflect the fact that this are prospects of a measurement, no actual limits

2- Check the photon-neutrino coupling in fig.1

3- Explain clearly what is fit, is it correct that F2 and F3 are completely identical ? Explain this in the text.

4- Only report 14 TeV and 33 TeV

5- Fix English

I have corrected my contribution

Sincerely,

Maria A. Hernandez-Ruiz

## Attachment:

SciPost_A_Gutierrez-Rodriguez-NEW.pdf

Dear author,

thank you for the improved version, I have 2 remaining issues which I would like to see answered.

1. figure 1: The Feynman diagrams contain neutrinos coupling to photons which is wrong. I think only the top two diagrams are physical and in those only when the neutrino couples to a Z.

2. Eqn 5 & 6. You expect to measure a total cross section $\sigma$ which will contain a term related to $F_2^2$, $F_3^2$ and also an interference term. How do you isolate the $F_2$ and $F_3$ in this case ? Do you understand why these equations are identical for $F_2$ and $F_3$ ?

Answer to question

1. figure 1: The Feynman diagrams contain neutrinos coupling to photons which is wrong. I think only

the top two diagrams are physical and in those only when the neutrino couples to a Z.

Answer:

The magnetic and electric dipole moments of the neutrino (MM) and (EDM) are one of the most sensitive probes of physics beyond the Standard Model (BSM). On this topic, in the original formulation of the Standard Model neutrinos are massless particles with

zero MM. However, in the minimally extended Standard Model containing gauge-singlet right-handed neutrinos, the MM induced by radiative corrections is unobservably small. Similarly, a EDM will also point to new physics and will be of relevance in astrophysics and cosmology, as well as terrestrial neutrino experiments.

Theoretically the electromagnetic properties of neutrinos best studied and well understood are the MM and the EDM. Despite that the neutrino is a neutral particle, neutrinos can interact with a photon through loop (radiative) diagrams. However, a convenient way of studying its electromagnetic properties on a model-independent way is through the effective neutrino-photon interaction vertex which is described by four independent form factors.

We study the anomalous MM and the EDM of the tau-neutrino, which are defined in terms of the F_2 and F_3 independent form factor.

We are following a focusing as that performed in our previous works [J. F. Nieves, Phys. Rev. D26, 3152 (1982)].

The most general expression for the vertex of interaction neutrino anti-neutrino photon is given by [J. F. Nieves, Phys. Rev. D26, 3152 (1982).] Eq. (1).

\begin{eqnarray}

\Gamma^{\alpha} & = & eF_{1}(q^{2})\gamma^{\alpha}+\frac{ie}{2m_{\nu_\tau}}F_{2}(q^{2})\sigma^{\alpha

\mu}q_{\mu}+ \frac{e}{2m_{\nu_\tau}}F_3(q^2)\gamma_5\sigma^{\alpha\mu}q_\mu \nonumber\\

&& + \, eF_4(q^2)\gamma_5(\gamma^\alpha-\frac{q\llap{/}q^\alpha}{q^2}),

\end{eqnarray}

2. Eqn 5 & 6. You expect to measure a total cross section which will contain a term related to ,

and also an interference term. How do you isolate the and in this case ? Do you understand why

these equations are identical for and ?

Answer:

The cross section of the process pp -> vvgamma + X depends on F_1 and F_2, however to estimate bounds on these parameters we consider F_1 (F_2) one at a time. For this reason, Eqs. (5) and (6) only depend on F_1 (F_2).

## Attachment:

SciPost_201810_00003.pdf

I correct:

2. Eqn 5 & 6. You expect to measure a total cross section which will contain a term related to ,

and also an interference term. How do you isolate the and in this case ? Do you understand why

these equations are identical for and ?

Answer to question

The cross section of the process pp -> vvgamma + X depends on F_2 and F_3, however to estimate bounds on these parameters we consider F_2 (F_3) one at a time. For this reason, Eqs. (5) and (6) only depend on F_2 (F_3).