B' I' Stepanov Institute of Physics National Academy of Sciences of Belarus

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B. I. Stepanov Institute of PhysicsNational
Academy of Sciences of Belarus
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• Status of the magnetic monopoles in ATLAS

Yu. Kurochkin, Yu. Kulchitsky, I. Satsunkevich,
N. Rusakovich, Dz. Shoukavy
Gomel, 2007
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CONTENTS
1
Introduction and limits on the monopole mass
2
Two photon vs. Drell-Yan
Signature
3
4
Conclusion and future plans
Gomel, 2007
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Introduction
WHY does quantisation of the electric charge
exist?
In 1931 Dirac showed that the existence of
single magnetic monopole with magnetic charge g
explained the quantization of electric charge e
in terms of the Dirac quantization condition
e g n hc/2 (P.A.M. Dirac, 1931)
minimum magnetic charge
Besides explaining the quantization of electric
charge, the existence of magnetic charges
restores the symmetry of the Maxwells equations.
Thus, existence of both electric and magnetic
charge in the Universe requires charge
quantization. Since the quantization of electric
charge in nature is well established but still
mysterious, the discovery of just a single
monopole would provide a much wanted explanation.
Gomel, 2007
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Introduction
New situation was created in 1974 after
work's Polyakov and 'tHooft in which they
demonstrated monopole solutions in the SO(3)
Georgi-Glashow model. Later it was discovered
that any scheme of Grand Unification with an
electromagnetic U(1) subgroup embedded into a
semi-simple gauge group, which became
spontaneously broken by Higgs mechanism,
possessed monopole solutions inevitably.
The monopoles of the usual Grand Unification have
a mass of the order of the unification scale 1017
GeV and therefore cannot be discovered at the
current or future accelerators. They could only
be produced in the first instants of our Universe
and can be searched for in the penetrating cosmic
radiation. However, there are models of
the Grand Unification where the electroweak
symmetry breaking can give rise to monopoles of
mass 1 15 TeV . It was shown that the
unification scale could be significantly lowered
through appearance of extra dimensions.
Gomel, 2007
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The experimental limits on monopole mass
The most recent limits on the monopole mass

• HERA
• e p collisions
• n1,2,3,6

• Tevatron
• p p collisions
• Experiment E-882
• (Al) n1, M gt 285 GeV
• (Al) n2, M gt 355 GeV
• (Be) n3, M gt 325 GeV
• (Be) n6, M gt 420 GeV

LEP 2 e e- collisions
(Al) M gt 140 GeV
45 gt M lt 102 GeV
Drell - Yan
mechanism
M gt 360 GeV
CDF Run II
Gomel, 2007
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The experimental limits on monopole mass
The limits on the Dirac monopole mass which was
obtained at the Tevatron (D0 collaboration) from
the analysis of the process for ?? production via
virtual monopole loop are strongly criticized
and questioned1,2 (because the cross section
violate unitarity ).
1. L. Gamberg, G.Kalbfleisch, K. Milton, Found.
Phys. 30, 543 (2000)
2. K. Milton, G. Kalbfleisch, W. Luo, L. Gamberg,
Int. J. Mod.Phys. A 17, 732 (2002).
Gomel, 2007
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Monopole production
By a Dirac monopole we mean a particle
without electric charge or hadronic interactions
but with magnetic charge g satisfying the Dirac
quantization.
Going from lepton production we replace
e
gß
Two photon s1/2
Drell-Yan
Gomel, 2007
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Cross section
The comparison production cross section ? ?
fusion and Drell-Yan for monopole-antimonopole
pair in pp-collisions at ?s 14 TeV
The relative dominance vs. ? ? fusion changes for
monopoles
So, two photon production is the leading
mechanism for direct monopole searches at LHC
Yu. Kurochkin et. al. On production of magnetic
monopoles via ?? fusion at high energy
pp-collisions / Mod. Phys. Lett. A, 21, 2873,2006.
Gomel, 2007
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Signature
If magnetic monopoles produced in ATLAS then
monopole would be revealed by its unique
characteristics

• Behavior of a monopole in a magnetic field.
  Because monopoles will be accelerated along an
  external magnetic field the trajectories of
  monopoles and ordinary charged particles differ
  considerably.
• The large value of a magnetic charge means that
  ionization energy losses will be several orders
  of magnitude greater for monopoles than for
  electrically charged particle.
• The large transition radiation.

Gomel, 2007
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Behavior of a monopole in a magnetic field
While the trajectories of electrically charge
particles curve is rf plane, monopoles will curve
in the rz plane. Monopole trajectory is a
parabola, stretched by relativistic effect in the
rz plane
In the plane perpendicular to the magnetic field,
the motion is in a straight line, in sharp
contrast to electrically charged particles, which
curve in this plane.
Gomel, 2007
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Energy loss by ionization
The energy loss dE/dx due to ionization
for an electrically charged particle is given
Bethe-Bloch formula
- is the mean excitation energy of the scattering
material
For magnetic monopoles with velocities
we need make the replacement
The energy loss dE/dx due to ionization does not
depend on the mass of the incident particle but
just its kinematic properties
Gomel, 2007
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Energy loss by ionization
For example, comparison energy loss pion and
monopole in neon
Z10 (Neon)
Z10 (????)
Energy loss/cm MeV-charged particles and GeV-
monopoles

• Since magnetic charge cannot simulated in GEANT
  directly, then magnetic monopoles were simulated
  as heavy electrically charged fermions with an
  effective charge zegß (assuming n1)

Gomel, 2007
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Transition Radiation
As in ATLAS there is a detector of transition
radiation, then we have additional opportunity
for monopole search.
The energy radiated when particle with charge ze
crosses the boundary between vacuum and a medium
plasma frequency ?p is
The typical emission angle 1/?. For a particle
with ?103 the radiated photons are in the soft
x-ray range 2 to 20 keV.
The number of radiated photons
For monopole we make the replacement
Thus, for monopole will be some tens times more
radiated photons
Gomel, 2007
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Conclusion and Plans

• LHC will open a new era in search for magnetic
  monopoles of any nature.
• GEANT is a widely used tool for detector
  description and simulation, but it has not
  particles with magnetic charge.
• For reliable energy loss (and hence triggering
  possibility) need to take into account the
  energy gain inside Inner Detector by acceleration
  due to magnetic field.
• The main goal of the future
  works
• We need write additional GEANT code for magnetic
  monopole and understand trigger conditions.

Gomel, 2007