LOGO

B. I. Stepanov Institute of Physics

National Academy of Sciences of Belarus

Status of the magnetic monopoles in ATLAS

Gomel, 2007

Yu. Kurochkin, Yu. Kulchitsky, I. Satsunkevich,

N. Rusakovich, Dz. Shoukavy

CONTENTS

Two photon vs. Drell-Yan

1 Introduction and limits on the monopole mass

2

Signature3

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4Conclusion and future plans

Introduction

WWHYHY does does quantisation of the electric quantisation of the electric chargecharge exist? 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 e g = n ħcħc/2/2 (P.A.M. Dirac, (P.A.M. Dirac, 1931)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.

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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.

The experimental limits on monopole mass

1 162 pbL

206.3 s GeV 300 s GeV

HERA e+ p – collisions

|n|=1,2,3,6

Tevatronp p – collisions

Experiment E-882

(Al) |n|=1, M > 285 GeV (Al) |n|=2, M > 355

GeV (Be) |n|=3, M > 325

GeV (Be) |n|=6, M > 420

GeV

(Al) M > 140 GeV

18172 pbL

M > 360 GeV

ГэВs 96,1

Drell - Yan

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CDF Run II

mechanism

45 > M < 102 GeV

LEP 2 e+ e- – collisions

18172 pbL

The experimental limits on monopole mass

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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).

Monopole production

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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 gβ Drell-YanTwo photon s=1/2

Cross section

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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 pp-collisions / Mod. Phys. Lett. A, 21, 2873,2006.

Signature

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.

If magnetic monopoles produced in ATLAS then monopole would be revealed by its unique

characteristics

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Behavior of a monopole in a magnetic field

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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.

Energy loss by ionization

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The energy loss dE/dx due to ionization for an electrically charged particle is given Bethe-Bloch formula

For magnetic monopoles with velocities we need make the replacement

210

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

- is the mean excitation energy of the scattering material

Energy loss by ionization

Z=10 (Неон)

For example, comparison energy loss pion and monopole in neon

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 ze=gβ (assuming n=1)

Z=10 (Neon)

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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 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

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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.

Conclusion and Plans

Gomel, 2007