Transcript Status of the Magnetic Monopoles in ATLAS

B. I. Stepanov Institute of Physics
National Academy of Sciences of Belarus
LOGO
Status of the magnetic monopoles
in ATLAS
Yu. Kurochkin, Yu. Kulchitsky, I. Satsunkevich,
N. Rusakovich, Dz. Shoukavy
Gomel, 2007
CONTENTS
1
Introduction and limits on the monopole mass
2
Two photon vs. Drell-Yan
3
Signature
4
Conclusion and future plans
Gomel, 2007
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 ħc/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
Maxwell’s
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
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
The experimental limits on monopole mass
HERA
Tevatron
LEP 2
e+ p – collisions
p p – collisions
e+ e- – collisions
s  300 GeV
Experiment E-882
s  206.3 GeV
L  62 1 pb1
|n|=1,2,3,6
(Al) M > 140 GeV
L  172 8 pb
1
(Al) |n|=1,
(Al) |n|=2,
(Be) |n|=3,
(Be) |n|=6,
M > 285 GeV
M > 355 GeV
M > 325 GeV
M > 420 GeV
Drell - Yan
mechanism
s 1,96 ГэВ
CDF Run II
M > 360 GeV
Gomel, 2007
L  172 8 pb1
45 > M < 102 GeV
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 γγ
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
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
Two photon s=1/2
e
gβ
Gomel, 2007
Drell-Yan
Cross section
The comparison production cross section γ γ fusion and Drell-Yan for
monopole-antimonopole pair in pp-collisions at s =14 TeV
The relative dominance vs. γ γ 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 γγ fusion at high energy ppcollisions / Mod. Phys. Lett. A, 21, 2873,2006.
Gomel, 2007
Signature
If magnetic monopoles produced in ATLAS then
monopole would be revealed by its unique
characteristics
1.
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.
2.
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.
3.
The large transition radiation.
Gomel, 2007
Behavior of a monopole in a magnetic field
While the trajectories of electrically charge particles curve is rφ
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
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   102 we need
make the replacement
ze  ng 
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
Energy loss by ionization
For example, comparison energy loss pion and monopole in neon
Z=10 (Neon)
Z=10 (Неон)
Energy loss/cm: MeV-charged particles and GeVmonopoles
•Since magnetic charge cannot simulated in GEANT directly, then
magnetic monopoles were simulated as heavy electrically charged
fermions with an effective charge ze=gβ (assuming n=1)
Gomel, 2007
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 ωp is
The typical emission angle ~ 1/γ. For a particle with γ=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
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