PHYSICAL REVIEW LETTERS 123, 021802 (2019) Magnetic Monopole Search with the Full MoEDAL Trapping Detector in 13 TeV pp Collisions Interpreted in Photon-Fusion and Drell-Yan Production B. Acharya,1,* J. Alexandre,1 S. Baines,1 P. Benes,2 B. Bergmann,2 J. Bernab´eu,3 A. Bevan,4 H. Branzas,5 M. Campbell,6 † ‡ S. Cecchini,7 Y. M. Cho,8, M. de Montigny,9 A. De Roeck,6 J. R. Ellis,1,10, M. El Sawy,6,§ M. Fairbairn,1 D. Felea,5 M. Frank,11 J. Hays,4 A. M. Hirt,12 J. Janecek,2 D.-W. Kim,13 A. Korzenev,14 D. H. Lacarr`ere,6 S. C. Lee,13 C. Leroy,15 G. Levi,16 A. Lionti,14 J. Mamuzic,3 A. Margiotta,16 N. Mauri,7 N. E. Mavromatos,1 P. Mermod,14 M. Mieskolainen,17 ∥ L. Millward,4 V. A. Mitsou,3, R. Orava,17 I. Ostrovskiy,18 J. Papavassiliou,3 B. Parker,19 L. Patrizii,7 G. E. Pav˘ ala˘ ş,5 J. L. Pinfold,9 V. Popa,5 M. Pozzato,7 S. Pospisil,2 A. Rajantie,20 R. Ruiz de Austri,3 Z. Sahnoun,7,¶ M. Sakellariadou,1 A. Santra,3 S. Sarkar,1 G. Semenoff,21 A. Shaa,9 G. Sirri,7 K. Sliwa,22 R. Soluk,9 M. Spurio,16 M. Staelens,9 M. Suk,2 M. Tenti,23 V. Togo,7 J. A. Tuszyński,9 V. Vento,3 O. Vives,3 Z. Vykydal,2 A. Wall,18 and I. S. Zgura5 (MoEDAL Collaboration) 1Theoretical Particle Physics and Cosmology Group, Physics Department, King’s College London, United Kingdom 2IEAP, Czech Technical University in Prague, Czech Republic 3IFIC, Universitat de Val`encia—CSIC, Valencia, Spain 4School of Physics and Astronomy, Queen Mary University of London, United Kingdom 5Institute of Space Science, Bucharest—Magurele,˘ Romania 6Experimental Physics Department, CERN, Geneva, Switzerland 7INFN, Section of Bologna, Bologna, Italy 8Physics Department, Konkuk University, Seoul, Korea 9Physics Department, University of Alberta, Edmonton, Alberta, Canada 10Theoretical Physics Department, CERN, Geneva, Switzerland 11Department of Physics, Concordia University, Montr´eal, Qu´ebec, Canada 12Department of Earth Sciences, Swiss Federal Institute of Technology, Zurich, Switzerland—Associate member 13Physics Department, Gangneung-Wonju National University, Gangneung, Republic of Korea 14D´epartement de Physique Nucl´eaire et Corpusculaire, Universit´e de Gen`eve, Geneva, Switzerland 15D´epartement de Physique, Universit´e de Montr´eal, Qu´ebec, Canada 16INFN, Section of Bologna and Department of Physics and Astronomy, University of Bologna, Italy 17Physics Department, University of Helsinki, Helsinki, Finland 18Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama, USA 19Institute for Research in Schools, Canterbury, United Kingdom 20Department of Physics, Imperial College London, United Kingdom 21Department of Physics, University of British Columbia, Vancouver, British Columbia, Canada 22Department of Physics and Astronomy, Tufts University, Medford, Massachusetts, USA 23INFN, CNAF, Bologna, Italy (Received 21 March 2019; published 9 July 2019) 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 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 Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3. 0031-9007=19=123(2)=021802(7) 021802-1 Published by the American Physical Society PHYSICAL REVIEW LETTERS 123, 021802 (2019) 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. DOI: 10.1103/PhysRevLett.123.021802 The existence of a magnetically charged particle would more detail in Ref. [23]. The first method adds measure- add symmetry to Maxwell’s equations and explain why ments performed at 1 mm intervals using a dipole sample of electric charge is quantized in nature, as shown by Dirac in known magnetic moment μ ¼ 2.98 × 10−6 Am2 to obtain 1931 [1]. Dirac predicted the fundamental magnetic charge the response of a single magnetic pole of strength ð 2α Þ ≃ 68 5 5 number (or Dirac charge) to be e= em . e where e P ¼ 9.03 × 10 g , based on the superposition principle. α D is the proton charge and em is the fine-structure constant. The second method measures directly the effect of a Consequently, in SI units, the magnetic charge can be magnetic pole of known strength using a long thin solenoid ¼ written in terms of the dimensionless quantity gD as qm providing P ¼ 32.4gD=μA for various currents ranging ngDec where n is an integer number and c is the speed of from 0.01 to 10 μA. The results of the calibration mea- light in vacuum. Because gD is large, a fast monopole can surements, with the calibration constant obtained from the induce ionization in matter thousands of times higher than a first method, are shown in Fig. 1. The two methods agree particle carrying the elementary electric charge. within 10%, which can be considered as the calibration It has subsequently been shown by ’t Hooft and uncertainty in the pole strength. The magnetometer Polyakov that the existence of the monopole as a topo- response is measured to be linear and charge symmetric logical soliton is a prediction of theories of the unifica- in a range corresponding to 0.3–300g . The plateau value 16 D tion of forces [2–5]. For a unification scale of 10 GeV of the calibration dipole sample was remeasured regularly such monopoles would have a mass M in the range during the campaign and was found to be stable to within 17 18 10 –10 GeV. In unification theories involving a number less than 1%. of symmetry-breaking scales [6–8], monopoles of much Samples were placed on a carbon-fiber movable con- lower mass can arise, although still beyond the reach of the veyer tray for transport through the sensing region of the Large Hadron Collider (LHC). However, an electroweak magnetometer, three at a time, separated by a distance of monopole has been proposed [9–12] that is a hybrid of the 46 cm. The transport speed was set to the minimum Dirac and ’t Hooft–Polyakov monopoles [2,3] with a mass available of 2.54 cm=s, as it was found in previous studies potentially accessible at the LHC and a minimum magnetic that the frequency and magnitude of possible spurious 2 charge gD, underlining the importance of searching for offsets increased with speed [21]. The magnetic charge large magnetic charges at the LHC. contained in a sample is measured as a persistent current in There have been extensive searches for monopole relics the superconducting coil surrounding the transport axis. from the early Universe in cosmic rays and in materials This is defined as the difference between the currents [13,14]. The LHC has a comprehensive monopole search measured after (I2) and before (I1) passage of a sample program using various techniques devised to probe TeV- scale monopole masses for the first time [15–17]. The results obtained by MoEDAL using 8 TeV pp collisions allowed the previous LHC constraints on monopole pair production [18] to be improved to provide limits on monopoles with jgj ≤ 3gD and M ≤ 3500 GeV [19], where ¼ g qmec. At 13 TeV LHC energies, MoEDAL extended the limits to jgj ≤ 5gD and masses up to 1790 GeV assuming Drell-Yan (DY) production [20,21]. In addition to the forward part used in previous analyses [20,21], the exposed Magnetic Monopole Trapper (MMT) volume analyzed here includes lateral components increas- ing the total aluminum mass to 794 kg; a schematic view is provided in the Supplemental Material [22]. All 2400 trapping detector samples were scanned in 2018 with a dc SQUID long-core magnetometer (2G Enterprises Model FIG. 1. Results of the calibration measurements with the 755) installed at the Laboratory for Natural Magnetism at superposition method using a magnetic dipole sample and ETH Zurich. The measured magnetometer response is the solenoid method with P ¼ 32.4gD=μA and various currents. translated into a magnetic pole P in units of Dirac charge The dashed lines represent the expected plateau values in units of by multiplying by a calibration constant C. Calibration was Dirac charge. The calibration constant is tuned using the performed using two independent methods, described in measurement from the superposition method. 021802-2 PHYSICAL REVIEW LETTERS 123, 021802 (2019) FIG. 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. FIG. 3. Results of multiple pole strength measurements (in units of Dirac charge) for the 87 candidate samples for which at through the sensing coil, after adjustment for the corre- least one of the two first measurement values was above the tray tray threshold jgj > 0.4g .