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 !