Search for magnetic monopoles with ANTARES By Nicolas PICOT CLEMENTE CNRS/Université de la Méditerranée/CPPM
Outlines Introduction Magnetic monopole signal in ANTARES Analysis Conclusion
Introduction of magnetic monopoles e- M.M. Initially introduced by Dirac in 1931: Make symmetric Maxwell’s equations. Imply the quantization of the electric charge. Magnetic charge is given by . The smallest magnetic charge is the Dirac charge gD, where k=1.
Introduction of magnetic monopoles ’t Hooft and Polyakov in 1974: Any unified gauge theory in which U(1)E.M. is embedded in a spontaneously broken semi-simple gauge group necessarily contains M.Ms. Transition example with the minimal GUT group: MM appearwith charge g=gDat the first transition. In this typical case the monopole mass is about ~ 1016GeVwith a radius of the order ~ 10-28 cm. Predicted magnetic monopole’s masses : 108 to 1017 GeV (depending on the unified gauge group).
Acceleration of magnetic monopoles in the Universe Energy gain in a magnetic coherent field: Magnetic monopoles with masses below 1014 GeV could be relativistic (with extragalactic sheets expecting to dominate the spectrum). Estimated energy loss when crossing the Earth is ~ 1011 GeV. M.M. with masses up to about 1014 GeV are expected to cross the Earth and be relativistic. M.M.
Magnetic monopole’s signal in ANTARES Direct Cherenkov emission > 0.74 : nseawater~1.35 Direct Cherenkov g from a MM with g=gD. x 8500 Number of photons emitted by a MM with the minimal charge gD ~ 68.5 e, compared to a muon of same velocity is about ~ 8500 more! Cherenkov g from a m.
Magnetic monopole’s signal in ANTARES Direct Cherenkov emission > 0.74 : nseawater~1.35 Direct Cherenkov g from a MM with g=gD. g from MM x 8500 Number of photons emitted by a MM with the minimal charge gD ~ 68.5 e, compared to a muon of same velocity is about ~ 8500 more! Cherenkov g from delta-rays. Cherenkov g from a m. g from d-rays g from m Indirect Cherenkov emission > 0.51 : The energy transferred to electrons allows to pull out electrons (d-rays), which can emit Cherenkov light.
Signal examples for upgoing magnetic monopoles Line number Hit Elevation Upgoing neutrino event Time Upgoingmagnetic monopole event b ~ 0.90
Atmospheric background light in sea water µ p p A search for upgoingmagnetic monopoles iseasierthan for downgoing. upgoing downgoing Only upgoing magnetic monopoles considered for instance.
Analysis plan Search for fast (b > 0.74) upgoing magnetic monopoles: Use of the muon reconstruction algorithm. Selection criteria to remove background events (atmospheric neutrinos and muons): Miscreconstructed Atm. muons Atm. neutrinos up. Atm. neutrinos do. Distribution of the reconstructedzenith angle for atmospheric background events and for upgoing monopoles. M.M. with b~0.75 M.M. with b~0.85 M.M. with b~0.99 Upgoing magnetic monopoles Selection of only upgoing reconstructed events (qzen < 90°).
Analysis plan Remove most of misreconstructed events with the fit quality factor L. Atm. muons Atm. neutrinos up. Atm. neutrinos do. M.M. with b~0.75 Distribution of the fit quality factor L for upgoingreconstructedatmospheric background events and monopoles. M.M. with b~0.85 M.M. with b~0.99
Analysis plan Large amount of light Selection applied on the number of cluster of hitted floors (T3). Cluster T3 or Atm. muons Atm. neutrinos up. 100 ns 200 ns Atm. neutrinos do. M.M. withb~0.75 M.M. withb~0.99 Distribution of the number of cluster of hittedfloorsT3 for upgoingreconstructedatmospheric background events and monopoles.
MRF Optimisation Model Rejection Factor: Based on a poissonian statistic method from Feldman-Cousins minimising the average upper limit with the expected number of background events known. Discriminative variables : T3, the number of cluster of hitted floors. L, the fit quality factor. Optimisation of the 90% C.L. sensitivity as a function of the T3, L cuts applied for 0.80 < bMM< 1. Example for Monopoles with and a L cutfixed. For this fit qualitycut, the best sensitivityisfound for T3 > 170.
Comparison MC/data Sample of 10days of 12-line data taken to compare data/MC distributions. Data sample Atm. muons Atm. neutrinos up. Atm. neutrinos do. Good agreement from L > -5.5. Best sensitivity found for T3 > 110.
Preliminary expected 90% C.L. sensitivity with the 12-line ANTARES detector Results from the requirement that galactic magnetic fields must be conserved PRELIMINARY ~1.1 expected background eventsafter one year of 12-line ANTARES data taking.
Conclusion Expected sensitivity based on a M.C. study. Need to process data. Study to be done for: Slower magnetic monopoles. Downgoing magnetic monopoles. Promising results for a potential discovery.