Detecting the neutrino magnetic moment at hadron colliders

We consider the model based on the $SU(2{)}_R\times SU(2{)}_L\times U(1{)}_{B-L}$ gauge group with Majorana neutrinos. In this model the transit dipole magnetic moment $({\mu }^{\nu N}{)}_{if}$ which is associated with the $N_i\to {\nu }_f\gamma$ transition may be as large as a $\text{few}\times 10^{-8}{\mu }_B$. The possible manifestations of the $({\mu }^{\nu N}{)}_{if}$ at hadron colliders are investigated. In doing so, we assume that one of the three heavy right-handed neutrinos $N_{eR}$ is on the electroweak scale. The process of $N_{eR}$ production $p+p\to W_R^{-}\to e^{-}{N}_{eR}$, with the subsequent $N_{eR}$ decay through the channel $N_{eR}\to {\nu }_{eL}+\gamma$, is investigated. Problems caused by selecting the signal from background is examined. It is shown that the process in question is the most perspective one for detecting the $({\mu }^{\nu N}{)}_{if}$, provided the condition $m_{W_R}<6\mathrm{TeV}$ is realized. The cross section of $N_{\mu R}$ production under the collision of a high-energy light neutrino beam with the proton target ${\nu }_{\mu L}+p\to \gamma \to N_{\mu R}+p+X$ is investigated. The produced $N_{\mu R}$ neutrino is identified through the decay channel $N_{\mu R}\to {\mu }^{\pm }+2j$. Detection of both the positive and negative charged muons will point to the Majorana nature of the neutrino. On the other hand, detection of the right-handed polarized muons will be unambiguously indicative of a nonzero value of $({\mu }^{\nu N}{)}_{if}$.

Figure 1

The Feynman diagram for the subprocess $q_i{\overline{q}}_i\to \gamma \to N_{eR}{\nu }_{eL}$.

Figure 2

The Feynman diagram for the subprocess $q_i{\overline{q}}_j\to e^{-}{N}_{eR}\to e^{-}\gamma {\nu }_{eL}$.

Figure 3

The Feynman diagrams for the $W\gamma$ production.

Figure 4

The Feynman diagrams for the (ordinary) radiative $W$ decay.

Figure 5

The Feynman diagram for ${\nu }_{\mu L}{q}_i\to N_{\mu R}\to {\mu }^{\pm }jj{q}_i$.

Figure 6

The Feynman diagram for ${\nu }_{\mu L}{q}_i\to {\nu }_{\mu L}\to q_i{\mu }^{\pm }jj{q}_i$.