david milstead the university of liverpool• t’hooft/polyakov (1974) – breaking of `simple’...
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The Search for Magnetic Monopoles
Exotic04, Durham, April 2004
David Milstead The University of Liverpool
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Why magnetic monopoles
Solve open questions in physics
symmetrisation of electromagnetismelectric charge quantisationunification of forcesproton decayconfinement of quarks
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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
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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 ?
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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
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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
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Monopole Searches
• Ionisation• Induction• Trajectory• Nuclear decay
Signatures
Look in cosmic rays, materials, accelerators.
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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
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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
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Cabrera • Cosmic ray search 1981-1982 SLAC with SQUID• Famous observation of monopole, thermal noise,
spurned lover or student prank ?
Flux
time
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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…
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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
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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
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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
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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
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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.
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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.
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Southampton SQUID• DC SQUID (2G mod. 581) at Southampton
Oceanography Centre.• Sample sizes up to 1m long and 5cm radius.• 1/20th fluxon precision.
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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
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Calibration checkMonopole signal survives after strip traversal
stripi Solenoid ( = 1 gd)
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Beam pipe measurementsInduced current from strips
Dirac Monopole
Cur
rent
Strip numberNo candidates found
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‘Efficiency’ of beam pipe
Use γγ−> mm (comphep) model
Rising acceptance with charge
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Cross-section upper limits
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Comparison with other experiments
Best limit from moon-rock
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Upper limit for 6gd monopoles
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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
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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
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Next StepsMoedal Experiment at LHC Next to LHCB Detector
Plastic Track Detectors 7 TeV Mass SensitivityATLAS, CMS Searches Possible
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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
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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.
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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
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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
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More Calibration
Linear SQUID response
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Results: Cabrera revisited
position /m
1 DMi /arb
No repeatable signal !