Magnetic Monopole Search with the Full MoEDAL Trapping Detector in 13 TeV $pp$ Collisions Interpreted in Photon-Fusion and Drell-Yan Production

MoEDAL is designed to identify new physics in the form of stable or pseudostable highly ionizing particles produced in high-energy Large Hadron Collider (LHC) collisions. Here we update our previous search for magnetic monopoles in Run 2 using the full trapping detector with almost four times more material and almost twice more integrated luminosity. For the first time at the LHC, the data were interpreted in terms of photon-fusion monopole direct production in addition to the Drell-Yan-like mechanism. The MoEDAL trapping detector, consisting of 794 kg of aluminum samples installed in the forward and lateral regions, was exposed to $4.0{\mathrm{fb}}^{-1}$ of 13 TeV proton-proton collisions at the LHCb interaction point and analyzed by searching for induced persistent currents after passage through a superconducting magnetometer. Magnetic charges equal to or above the Dirac charge are excluded in all samples. Monopole spins 0, $½$, and 1 are considered and both velocity-independent and-dependent couplings are assumed. This search provides the best current laboratory constraints for monopoles with magnetic charges ranging from two to five times the Dirac charge.

Figure 1

Results of the calibration measurements with the superposition method using a magnetic dipole sample and the solenoid method with $P=32.4g_D/\mu \mathrm{A}$ and various currents. The dashed lines represent the expected plateau values in units of Dirac charge. The calibration constant is tuned using the measurement from the superposition method.

Figure 2

Magnetic pole strength (in units of Dirac charge) measured in the 2400 aluminum samples of the MoEDAL trapping detector exposed to 13 TeV collisions in 2015–2017, with every sample scanned twice.

Figure 3

Results of multiple pole strength measurements (in units of Dirac charge) for the 87 candidate samples for which at least one of the two first measurement values was above the threshold $|g|>0.4g_D$. More values are observed below threshold than above threshold for all of them, excluding the presence of a monopole with $|g|\ge g_D$.

Figure 4

Feynman-like diagrams for monopole pair direct production at leading order via the Drell-Yan (left) and photon-fusion (right) processes at the LHC. For scalar and vector monopoles, a four-vertex diagram is also added [30].

Figure 5

Production cross-section upper limits at 95% C.L. for the combined DY and $\gamma \gamma$ monopole pair production model with $\beta$-independent (left) and $\beta$-dependent (right) couplings in 13 TeV $pp$ collisions as a function of mass for spin-0 (top), spin-$½$ (middle), and spin-1 monopoles (bottom). The colors correspond to different monopole charges. The solid lines are cross-section calculations at leading order.