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Searching for the Magnetic Monopole and Other Highly Ionizing Particles at Accelerators Using NTDs James L. Pinfold University of Alberta September 2008 24th ICNTS Bologna 1 The Discovery of the North Pole The idea that a magnet has two poles was thought up by a French mercenary Petrus Peregrinus during the siege of Lucera in 1269: “… in this stone you should thoroughly comprehend there are two points of which one is called the North, the remaining one the South.” Epistola de Magnete Petrus Peregrinus (1269) AhA! September 2008 24th ICNTS Bologna 2 Symmetrizing Maxwell Maxwell, in 1873, makes the connection between electricity & magnetism - the first Grand Unified Theory! Introducing a magnetic monopole makes the Maxwell’s equations symmetric The symmetrized Maxwell’s equations are invariant under rotations in the plane of the electric and magnetic field This symmetry is called Duality it means that the distinction between electric and magnetic charge is merely one of definition September 2008 24th ICNTS Bologna 3 Dirac’s Monopole (1) Paul Dirac in 1931 hypothesized that the magnetic Monopole exists In his conception the Monopole was the end of an infinitely long infinitely thin solenoid This was called the “Dirac String” A depiction of this Dirac string (solenoid) can be seen opposite (c) September 2008 24th ICNTS Bologna 4 Dirac’s Monopole (2) Magnetic "Coulomb" field is B grˆ /r 2 e- Wouldn’t we see the Dirac string? A particle with charge, say an electron, traveling around some path P in a region with zero magnetic field (B = 0 = x A) must acquire a phase φ; given in SI units by: e A.dr p The only way we would NOT see the Dirac string is if the wave function of the electron only acquired a “trivial phase” i.e. = n2(n =1,2,3..). That is, if: e September 2008 ie c A.dr i4 e e c 1 A.dr Ad 24th ICNTS Bologna & A g 5 Dirac’s Monopole (3) Hence Dirac’s quantization condition: c n 4 eg ge n OR g e ( from 2n n 1,2, 3..) 2 2 c Where g is the “magnetic charge” and is the fine structure constant 1/137. This means that g=68.5e (when n=1)! We can turn this around IF there is a magnetic monopole then: c e n Charge is quantized!! 2g If free quarks exist then the minimal electric charge is e/3…the minimal magnetic charge is then 3g September 2008 24th ICNTS Bologna 6 Monopole Properties Magnetic Charge e=electron charge gD= ћc/2e =68.5e Colour Charge Monopole trajectory Usually assumed is “parabolic” in the to be 0 r-Z plane of a Dyon electric solenoidal field and charge=1,2,3... straight in the r- plane Electric charge =0. Spin Usually taken as Monopole mass Magnetic Charge 0 or 1/2 FREE PARAMETER e=quark charge =1/3 See next slide gD 3gD Energy gain in a B-field: W= ngDBL = n20.5 keV/G.cm Energy loss By ionization (dE/dx)MM = 4700 (dE/dx)MIP See subsequent slides September 2008 Production at Accelerators usually assumed to be via Drell-Yan or Photon Fusion GUT monopoles Coupling constant can catalyse proton decay via the am= gD2/ћc Rubakov-Callan =34.25 Mechanism. 24th ICNTS Bologna 7 Magnetic Monopole Energy Loss > 10-2 Ionization (à la Bethe-Bloch) (Zeeq)2= (gb)2 (a) for b = 1 : (dE/dx)MM = 4700 (dE/dx)m.i.p. 10-4<<10-2 Excitation Medium as Fermi gas (b) M + He M + He* + Penning effect He*+ CH4 He + CH4 + e- 10-4<<10-3 Drell effect (coupling of the atom magnetic moment with the MM magnetic charge) < 10-4 September 2008 Elastic collisions 24th ICNTS Bologna (c) 8 Track Etch Monopole Detectors Look for aligned etch pits In multiple sheets The passage of a highly ionizing particle through the plastic track-etch detector (eg CR39) is marked by an invisible damage zone along the trajectory. The damage zone is revealed as a cone shaped etch- pit when the plastic detector is etched in a controlled manner using a hot sodium hydroxide solution. September 2008 24th ICNTS Bologna 9 Types of NTDs Commonly Used CR39 Rodyne/Makrofol PLASTIC September 2008 24th ICNTS Bologna UG-5 GLASS 10 The Etching Procedure (to be used by MoEDAL - and used by SLIM) Two etching conditions have been defined: Strong etching: 8N KOH + 1.25% Ethyl alcohol 77°C 30 h Soft etching: 6N NaOH+ 1% Ethyl alcohol 70°40 h CR39 threshold: “soft”etching Z/β~ 7 - REL ~ 50 MeV cm2g-1 “strong”etching Z/β~ 14 - REL ~ 200 MeV cm2g-1 September 2008 24th ICNTS Bologna 11 Making Etching Better l A better signal to noise ratio September 2008 24th ICNTS Bologna 12 A Typical Analysis Procedure (1) A highly ionizing particle passes through the NTD leaving a microscopic trail The latent track is manifested by etching VB is the bulk rate VT is the faster rate along the track The reduced etch rate is p = VT/VB The reduced etch rate is simply related to the restricted energy loss REL = (dE/dX)E<Emax September 2008 24th ICNTS Bologna 13 A Typical Analysis Technique (2) a) If the etching process is continued for a sufficient length of time a hole will be formed in the plastic (see (a)) These hole can be detected by the “ammonia technique” (see (b)): The plastic sheet is placed on top of blueprint paper The two sheets are sealed along the edges The package is exposed to ammonia vapour Each hole in the plastic is revealed as a blue spot on the blueprint paper This paper can then be used as a map for more careful etching of the corresponding region of the other NTDs in the stack September 2008 24th ICNTS Bologna b) Ammonia vapor NTD Blueprint paper 14 Calibration Reduced etch rate 158 A GeV 207 Pb82+ Pbions +frag’s 5 < Z < 82 REL September 2008 24th ICNTS Bologna 15 Seeking Monopoles at Accelerators DIRECT Experiments - Poles produced and detected immediately & directly, searches with: Scintillation counters & Wire chambers Plastic NTDs INDIRECT Experiments - in which monopoles are: Produced, stopped and trapped in matter - (eg beam pipe) Later they are extracted, accelerated & detected. September 2008 24th ICNTS Bologna 16 Accelerator Based Searches 31 searches 14 using Plastic NTDs 3 using emulsions 3 using induction 11 using counters September 2008 24th ICNTS Bologna 17 Why Use NTDs in Accelerator Searches for Monopoles NTDs are sensitive to magnetic monopoles with n ≥ 1 and a broad range of velocities It should be completely insensitive to normally ionizing particles (to the level of 1 part in 1016) It is capable of accurately tracking monopoles and measuring their properties (Z/) It doesn’t need high voltage, gas, readout or a trigger The calibration of NTDs for highly ionizing particles is well understood It is relatively radiation hard It easily covers the solid angle in a very cost effective way * For Ldt =1040 cm-2 + rapidity interval of y = 2, there will be ~1016 MIPs thru the detector September 2008 24th ICNTS Bologna 18 The 1st Accelerator Based Search for Monopoles Using NTDs (1) p-p Ecm ~50 GeV September 2008 24th ICNTS Bologna 19 The 1st Accelerator Based Search for Monopoles Using NTDs (2) 12 stacks of plastic deployed Each stack consisted of 10 sheets: 3 and 5th were Makrofole-E The others were nitrocellulose September 2008 24th ICNTS Bologna 20 The MODAL Experiment The MODAL (at LEP) expt was run at √s = 91.1 GeV . The integrated luminosity 60+/-12 nb-1 The detector used CR-39 plastic foils covering a 0.86 x 4π sr angle surrounding the I5 IP at LEP. The polyhedral array was supported by a frame which was mounted on a fixed stand. The vacuum pipe was 0.5 mm al. The 12 detector faces were filled with CR-39 with thicknesses (A) 720 μm, (B) 1500 μm, (C) 730 μm. Detector response of all three plastic detectors were calibrated using heavy ions at LBL. September 2008 24th ICNTS Bologna Phy. Rev. D46, R881(1992) 21 Direct Monopole Search at LEP (OPAL) monopole Anti-monopole Phys. Lett. B, 316, 407 (1993 The OPAL (LEP-1) monopole detector had a Dedicated plastic detector element (LEXAN) A dE/dX monopole trigger in the jet chamber The OPAL search also employed the non-standard trajectory of the monopole in a solenoidal field Search continued at LEP-2 using the jet chamber September 2008 24th ICNTS Bologna 22 Monopole Search Limits September 2008 24th ICNTS Bologna 23 The MoEDAL Experiment - the Monopole Search at the LHC LHCb MoEDAL MOEDAL collaboration from: Canada (U of Alberta & U of Montreal); Italy (U of Bologna); CERN; Institute of Space Sciences, Romania. and, the USA (North Eastern University, Boston; U. of Cincinnati). September 2008 24th ICNTS Bologna 24 The MoEDAL Detector MoEDAL NTDs ~25 m2 area = 0 (layers) x 225 m2 =150 m2 of NTDs MoEDAL is an experiment dedicated to the search highly ionizing exotic particles at the LHC, using plastic track-etch detectors MoEDAL will run with p-p collisions at a luminosity of 1032 cm-2 s-1 and in heavy-ion running We can detect up to a 7 TeV mass monopole with charge up to ~3g Due to make an initial deployment in 2009, with full deployment of detectors in 2010. September 2008 24th ICNTS Bologna 25 The MoEDAL Detector Element Aluminium face plate 25 x 25 cm 3 layers of Makrofol (each 500 mm thick) 3 layers CR39 (each 500 mm thick) 3 layers of Lexan (each 200 mm thick) Sheet size 25 x 25 cm September 2008 24th ICNTS Bologna 26 The Next Step for NTDs at Accelerators MoEDAL The LHC will start up in September 2008 MoEDAL will submit its TDR for LHCC approval in the Fall of 2008 Initial deployment of detectors in 2009 Full deployment in 2010 Plans for p-p and heavy-ion running September 2008 24th ICNTS Bologna 27 Extra Slides September 2008 24th ICNTS Bologna 28 Restricted Energy loss Contribution to track formation is assumed to be only from the energy transferred by low energy delta rays with energies up to a threshold Eth Threshold values range between 200 and 1000 eV September 2008 24th ICNTS Bologna 29 Multi-Gamma Events Multi- events At the ISR pp multi- at √s = 53 GeV, < 2 x 10-37 cm2 At FNAL (D0 Collab.) search for high ET -pairs in p-pbar collisions, Mmon. > 870 GeV/c2 for spin-1/2 Dirac MMs (95% CL) At LEP (L3 Collab.) search for September 2008 24th ICNTS Bologna Z Mmon > 510 GeV/c2 30 September 2008 24th ICNTS Bologna 31 September 2008 24th ICNTS Bologna 32 The Definition of R September 2008 24th ICNTS Bologna 33