[Paper Review] Search in 8 TeV proton-proton collisions with the MoEDAL monopole-trapping test array

K. Bendtz, A. Katre+5 more|arXiv (Cornell University)|Nov 27, 2013

Particle physics theoretical and experimental studies21 references3 citations

TL;DR

This paper presents the first results from the MoEDAL magnetic monopole trapper (MMT) test array, deployed at the LHC in 2012 to search for magnetic monopoles in 8 TeV proton-proton collisions. Using a superconducting DC-SQUID magnetometer to detect persistent currents induced by trapped monopoles in aluminum rods, the study found no evidence for monopoles with magnetic charge above 0.4 times the Dirac charge, establishing a new exclusion limit for monopoles in the 1–4 Dirac charge range and masses up to 3.5 TeV.

ABSTRACT

The magnetic monopole appears in theories of spontaneous gauge symmetry breaking and its existence would explain the quantisation of electric charge. MoEDAL is the latest approved LHC experiment, designed to search directly for monopoles produced in high-energy collisions. It has now taken data for the first time. The MoEDAL detectors are based on two complementary techniques: nuclear-track detectors are sensitive to the high-ionisation signature expected from a monopole, and the magnetic monopole trapper (MMT) relies on the stopping and trapping of monopoles inside an aluminium array which is then analysed with a superconducting magnetometer. The first results obtained with the MoEDAL MMT test array deployed in 2012 are presented. This experiment probes monopoles carrying a multiple of the fundamental unit magnetic charge for the first time at the LHC.

Motivation & Objective

• To search for magnetic monopoles produced in 8 TeV proton-proton collisions at the LHC using a passive trapping technique.
• To test the feasibility of monopole trapping and detection using aluminum absorbers and superconducting magnetometers.
• To probe monopole magnetic charges and masses beyond the reach of general-purpose detectors.
• To establish a background-free method for direct measurement of monopole magnetic charge via electromagnetic induction.
• To provide the first experimental constraints on monopoles with multiple Dirac charges at the LHC.

Proposed method

• A test array of 11 aluminum boxes, each containing 18 rods, was installed near the LHCb interaction point to trap magnetic monopoles from proton-proton collisions.
• The array was exposed to 0.75 fb⁻¹ of 8 TeV proton-proton collisions and later retrieved for analysis.
• Each aluminum rod was cut into 20 cm (or mixed lengths for Box 11) samples and scanned with a DC-SQUID rock magnetometer at ETH Zurich.
• Persistent currents induced by trapped monopoles were measured and calibrated using dipole standards and thin solenoids to express results in units of Dirac magnetic charge.
• Measurements were repeated multiple times on each sample to distinguish real signals from spurious jumps due to instrumental instability.
• Data analysis included offset correction and resolution monitoring to ensure reliability and minimize false positives.

Experimental results

Research questions

• RQ1 Can magnetic monopoles with multiple Dirac charges be detected using a passive trapping and induction technique at the LHC?
• RQ2 What is the sensitivity of the MoEDAL MMT test array to monopoles with magnetic charge above the Dirac unit and masses up to 3.5 TeV?
• RQ3 Can the superconducting magnetometer detect persistent currents from trapped monopoles with high precision and low background?
• RQ4 How do instrumental instabilities affect measurement reliability, and can they be mitigated in future deployments?
• RQ5 What fraction of monopoles produced in proton-proton collisions would be stopped and trapped by the aluminum array, given realistic material and kinematic assumptions?

Key findings

• No magnetic monopoles were detected in any of the 606 aluminum samples from the 2012 MMT test array.
• The experiment excluded the presence of monopoles with magnetic charge greater than 0.4 times the Dirac charge (gD) in the aluminum array.
• The resolution of the magnetometer was sufficient to rule out monopoles with charge above 0.4gD with high confidence.
• Spurious signal jumps were observed but were traced to instrumental instabilities such as trapped flux, sample movement, and environmental disturbances.
• The array is estimated to have trapped more than 0.5% of monopoles with charge between n=1 and n=4 and mass up to 3.5 TeV, assuming a Drell-Yan production model.
• The results demonstrate the feasibility of a background-free, direct measurement of monopole magnetic charge using induction, paving the way for the full-scale MoEDAL MMT deployment.