The Search for Magnetic Monopoles
Exotic04, Durham, April 2004
David Milstead The University of Liverpool
Why magnetic monopoles
Solve open questions in physics
symmetrisation of electromagnetismelectric charge quantisationunification of forcesproton decayconfinement of quarks
Dirac’s argument (1) • 1931• Angular momentum (L) in field of
monopole-electron system.
• One magnetic monopole ‘explains’ charge quantisation.
• n=1, g=µ0e/h = Dirac monopole.
ge
Lrθ
z
= µ0eg/4π z=nh/2
e=nh/gµ0
The Dirac Monopole
QED coupling of DM αg=g2/4π = 34c.f. electric charge coupling αe=e2/4π = 1/137Perturbative field theory impossible.Ionisation losses huge for DM.Is 1,3/2,3 DM fundamental magnetic charge?What about dyons ?What about colourful monopoles ?
Monopoles from Gauge Theories• T’hooft/Polyakov (1974) – Breaking of `simple’
symmetry group (eg SU(5), SO(10)) into U(1) sub-component leads to Dirac Monopole.
• Monopoles in SUSY gauge theories and string theory• Mass estimates vary between 104 – 1017 GeV
Mass – Mx/α
Consequences of GUT Monopoles
• Rubakov and Callan: GUT Monopoles catalyse proton decay.
• Baryon number violating fermioncondensate near to massive monopole.
uud
e+d u uMonopole
Monopoledduuuu + e+ + =
PionsProton
Monopole Searches
• Ionisation• Induction• Trajectory• Nuclear decay
Signatures
Look in cosmic rays, materials, accelerators.
Ionisation Loss• Adapted Bethe-Block formula for magnetic
charge. • dE/dx (DM) = (137/2)2 dE/dx (q)• No rise at low β
• Do we understand short range interactions?• How does a hadronic monopole interact ?
π+
Dirac Monopole
Induction Properties
Superconducting coil
i
i
i
distance
distance
)ˆ
ˆ(ˆ0 t
BjE m ∂∂
+−=×∇ µ
g
i=-(Φ + µ0g)/L
Flux ‘left by’ DM
dipole
Cabrera • Cosmic ray search 1981-1982 SLAC with SQUID• Famous observation of monopole, thermal noise,
spurned lover or student prank ?
Flux
time
Lunar SearchesMinimal atmosphere, 500 Myears of samplingAnalyse samples taken on Apollo 11,12 and 14 with a SQUID
Sample no.
pers
iste
nt c
urre
nt /
arb
Acknowledgements: We thank Neil A. Armstrong, Edwin E. Aldrin, Michael Collins…
Cosmic Ray Searches
Macro at Gran Sasso Lab. βFlux
upp
er li
mit
(cm
-2s-
1 sr-
1 )10
-16
10-1
5
Macro
Parker limit
Cabrera
Liquid scintillators, streamer tubes, plastic track detectors over 76 x 12 x 9 m3
Recent and Current Accelerator Searches
HERA ep
Tevatron Detector material charge > 1 DMmass < 800 GeVpp->γγmass < 1.5 TeVcharge > 1DM
Highly ionising tracks mass < 45 GeV0.2 < charge < 2DMe+e- -> γγγmass < 580 GeV0.2 < charge <2DM
LEP e+e-
Detector material,Highly ionising tracks 1 < charge < 6 DMmass < 150 GeV
First search in ep at =300 GeVSensitive to 150 GeV mass QED coupling for DiracMonopole gD
αg=gD2/4π =34
αem=1/137
Monopoles at HERA
p
s
m
m
e e’
αg
αem
αg
Processes predicted but not rate103 greater ionisation energy loss rate than mip
Magnetic Monopoles at H1
Monopoles with < 1 Dirac charge enter the detector.
Monopoles with > 1 Dirac charge trapped in the beam pipe.
Look for monopole with deep-inelastic probeSensitive to masses < 150 GeV
g
m m
Monopoles in the H1 Beam pipe Sensitive to 1 DM ≤ g ≤ 6 DM Bind to Al nucleus dipole moment and only released by melting (Milton et al.)Take 60cm section of H1 beam-pipe around interaction zone.Used 1994-1997 : lumi=60pb-1
Cut into 14 strips and 42 smaller samplesand pass through a SQUID.
SQUIDs as Monopole Detectors
1 DMvs
B (Φ/Α)
• Superconducting Quantum Interference Device
• Induce current on sc pick-up coils.• Measure B-field on sc loop with small breaks (SQUID) –
quantum mechanical tunnelling of e- pairs allows flux jumps (fluxons) (1 fluxon =1/2 µ0g).
• Measured current across SQUID modulates with period of a fluxon.
Southampton SQUID• DC SQUID (2G mod. 581) at Southampton
Oceanography Centre.• Sample sizes up to 1m long and 5cm radius.• 1/20th fluxon precision.
CalibrationUse solenoids with varying currents to study SQUID response
90 DM
10 DM
1.2 DM
i /ar
b
x 10
-1x
10-2
solenoidsc loop
i
B
position /cm
Calibration checkMonopole signal survives after strip traversal
stripi Solenoid ( = 1 gd)
Beam pipe measurementsInduced current from strips
Dirac Monopole
Cur
rent
Strip numberNo candidates found
‘Efficiency’ of beam pipe
Use γγ−> mm (comphep) model
Rising acceptance with charge
Cross-section upper limits
Comparison with other experiments
Best limit from moon-rock
Upper limit for 6gd monopoles
Hunt for massive stable charged particles
Upper limit on cross-section for heavy stable charged particles 0.19 nb
Sensitive to monopoles < 1 DM
H1
Look for parabolic trajectoriesElectric charge z= z0 + s tan θMagnetic charge z= z0 + s tan θ + s2 C
Tassoe+e- s1/2=35 GeV
zSensitive < 1g
s
Next StepsMoedal Experiment at LHC Next to LHCB Detector
Plastic Track Detectors 7 TeV Mass SensitivityATLAS, CMS Searches Possible
Summary and OutlookMagnetic monopoles play a fundamental role in modern physics theories.
No evidence from cosmic ray and high energy physics experiments.
Next energy window opened by the LHCDay 1 search possible
Magnetic Monopoles Already Exist !
F=q(E + v x B) + g(B – 1/c2 (v x E) )tEjB
tBE
B
E
∂∂
+=×∇
∂∂
−=×∇
=⋅∇
=⋅∇
ˆˆˆ
ˆˆ
0ˆ
ˆ
000
0
µεµ
ερ
-µ0jm
µ0ρm
Duality transformation gives magnetic monopoles.
By convention we set ρm=0
E’ = E cos α + c B sin αcB’ = cB cos α − E sin αcq’ = cq cos α + g sin αg’ = g cos α − cq sin α
Look for particles withdifferent electric/magneticcharge than observed.
Confinement of Quarks (I)Meissner effect expels magnetic field via electron-pair condensation
B
conductor
B
conductor
B
conductor
B
e-e-
e-e-e-e-
e-e-e-e-e-e-
e-e- e-e-m m
Monopoles in sc connected by flux tube
m
m
m
m
m
mm
m
mm
Confinement of Quarks (II)Chromo-magnetic monopoles form QCD ground state
quarks confined in flux lines through dualMeissner effect (‘t Hooft, 1985)
γq q
Search for monopoles in hadrons with electromagnetic probe
More Calibration
Linear SQUID response
Results: Cabrera revisited
position /m
1 DMi /arb
No repeatable signal !