James L. Pinfold University of Alberta

September 2008 24th ICNTS Bologna 1

Searching for the Magnetic Monopole and Other Highly

Ionizing Particles at Accelerators Using NTDs

Searching for the Magnetic Monopole and Other Highly

Ionizing Particles at Accelerators Using NTDs

James L. PinfoldUniversity of Alberta

James L. PinfoldUniversity of Alberta


The Discovery of the North PoleThe idea that a magnet has two poles was thought up by a French mercenary Petrus Peregrinus during the siege of Lucera in 1269:“… in this stone you should thoroughly comprehend there are two points of which one is called the North, the remaining one the South.” Epistola de Magnete Petrus Peregrinus (1269)

AhA!


Symmetrizing Maxwell Maxwell, in 1873, makes the connection between electricity & magnetism - the first Grand Unified Theory! Introducing a

magnetic monopole makes the Maxwell’s equations symmetric

The symmetrized Maxwell’s equations are invariant under rotations in the plane of the electric and magnetic field

This symmetry is called Duality it means that the distinction between electric and magnetic charge is merely one of definition


Dirac’s Monopole (1) Paul Dirac in 1931

hypothesized that the magnetic Monopole exists

In his conception the Monopole was the end of an infinitely long infinitely thin solenoid

This was called the “Dirac String”

A depiction of this Dirac string (solenoid) can be seen opposite (c)


Wouldn’t we see the Dirac string? A particle with charge, say an electron, traveling

around some path P in a region with zero magnetic field (B = 0 = x A) must acquire a phase φ; given in SI units by:

The only way we would NOT see the Dirac string is if the wave function of the electron only acquired a “trivial phase” i.e. = n2 (n =1,2,3..). That is, if:

Dirac’s Monopole (2)

e-

e

A.dr

p

e

ie

cA .dr

e i4e

c 1 A.dr Ad & A g

Magnetic "Coulomb" field is B g ˆ r / r 2


Dirac’s Monopole (3)

Hence Dirac’s quantization condition:

Where g is the “magnetic charge” and is the fine structure constant 1/137.

This means that g=68.5e (when n=1)! We can turn this around IF there is a magnetic monopole

then:

If free quarks exist then the minimal electric charge is e/3…the minimal magnetic charge is then 3g

e c

2g

n

ge c

2

n OR g

n

2e ( from

4eg

c2n n 1,2,3..)

Charge is quantized!!


Monopole PropertiesMagnetic Charge e=electron chargegD= ћc/2e =68.5e

Magnetic Charge Magnetic Charge e=quark e=quark charge =1/3charge =1/3 ggDD 3g 3gDD

Electric charge =0.Electric charge =0.

Dyon electric Dyon electric charge=1,2,3...charge=1,2,3...

Coupling constant Coupling constant

aamm= g= gDD22//ћћc c

=34.25=34.25

Energy gain in a Energy gain in a B-field: W= ngB-field: W= ngDDBL BL

= n20.5 keV/G.cm= n20.5 keV/G.cm

SpinSpinUsually taken asUsually taken as 0 or 1/20 or 1/2

Monopole mass Monopole mass FREE PARAMETERFREE PARAMETERSee next slideSee next slide

Colour Charge Colour Charge Usually assumedUsually assumed to be 0to be 0

Energy loss Energy loss By ionizationBy ionization (dE/dx)(dE/dx)MMMM

= 4700 (dE/dx)= 4700 (dE/dx)MIPMIP

See subsequent slidesSee subsequent slides

Monopole trajectory Monopole trajectory is “parabolic” in theis “parabolic” in the r-Z plane of a r-Z plane of a solenoidal field andsolenoidal field andstraight in the r-straight in the r-planeplane

Production at Production at Accelerators Accelerators usually assumed usually assumed to be via Drell-Yan to be via Drell-Yan or Photon Fusionor Photon Fusion

GUT monopoles GUT monopoles can catalyse proton can catalyse proton decay via the decay via the Rubakov-CallanRubakov-CallanMechanism.Mechanism.


Magnetic Monopole Energy Loss

10-4<<10-2 Excitation Medium as Fermi gas (b) 10-4<<10-3 Drell effect M + He M + He*

+ Penning effect He*+ CH4 He + CH4 + e-

(coupling of the atom magnetic moment with the MM magnetic charge)

< 10-4 Elastic collisions (c)

> 10-2 Ionization (à la Bethe-Bloch) (Zeeq)2= (gb)2 (a) for b = 1 : (dE/dx)MM = 4700 (dE/dx)m.i.p.


Track Etch Monopole Detectors

Look for aligned etch pitsIn multiple sheets

The passage of a highly ionizing particle through the plastic track-etch detector (eg CR39) is marked by an invisible damage zone along the trajectory.

The damage zone is revealed as a cone shaped etch-pit when the plastic detector is etched in a controlled manner using a hot sodium hydroxide solution.


Types of NTDs Commonly Used

CR39 Rodyne/Makrofol UG-5

PLASTIC GLASS


The Etching Procedure (to be used by MoEDAL - and used by SLIM)

Two etching conditions have been defined: Strong etching: 8N KOH + 1.25% Ethyl alcohol 77°C 30 h Soft etching: 6N NaOH+ 1% Ethyl alcohol 70°40 h

CR39 threshold: “soft”etching Z/β~ 7 - REL ~ 50 MeV cm2g-1

“strong”etching Z/β~ 14 - REL ~ 200 MeV cm2g-1


Making Etching Better

l

A better signal to noise ratio


A Typical Analysis Procedure (1)

A highly ionizing particle passes through the NTD leaving a microscopic trail

The latent track is manifested by etching VB is the bulk rate VT is the faster rate along the track The reduced etch rate is p = VT/VB

The reduced etch rate is simply related to the restricted energy loss REL = (dE/dX)E<Emax


A Typical Analysis Technique (2)

If the etching process is continued for a sufficient length of time a hole will be formed in the plastic (see (a))

These hole can be detected by the “ammonia technique” (see (b)):The plastic sheet is placed on top of

blueprint paper The two sheets are sealed along the

edgesThe package is exposed to ammonia

vapour Each hole in the plastic is revealed as

a blue spot on the blueprint paper This paper can then be used as a map

for more careful etching of the corresponding region of the other NTDs in the stack

a)a)

b)b)Ammonia vapor

NTDNTD

Blueprint paper


Calibration158 A GeV 207 Pb82+Pbions +frag’s 5 < Z < 82

Red

uced

etc

h ra

teR

educ

ed e

tch

rate

RELREL


Seeking Monopoles at Seeking Monopoles at AcceleratorsAccelerators

Seeking Monopoles at Seeking Monopoles at AcceleratorsAccelerators

DIRECT Experiments - Poles produced and detected immediately & directly, searches with: Scintillation counters & Wire chambers

Plastic NTDs

INDIRECT Experiments - in which monopoles are: Produced, stopped and trapped in

matter - (eg beam pipe)

Later they are extracted, accelerated & detected.

DIRECT Experiments - Poles produced and detected immediately & directly, searches with: Scintillation counters & Wire chambers

Plastic NTDs

INDIRECT Experiments - in which monopoles are: Produced, stopped and trapped in

matter - (eg beam pipe)

Later they are extracted, accelerated & detected.


Accelerator Based Searches

31 searches

14 using Plastic NTDs

3 using emulsions

3 using induction

11 using counters


Why Use NTDs in Accelerator Searches for Monopoles

NTDs are sensitive to magnetic monopoles with n ≥ 1 and a broad range of velocities

It should be completely insensitive to normally ionizing particles (to the level of 1 part in 1016)

It is capable of accurately tracking monopoles and measuring their properties (Z/)

It doesn’t need high voltage, gas, readout or a trigger The calibration of NTDs for highly ionizing particles is well

understood It is relatively radiation hard It easily covers the solid angle in a very cost effective way* For Ldt =1040 cm-2 + rapidity interval of y = 2, there will be ~1016 MIPs thru the detector


The 1st Accelerator Based Search for Monopoles Using NTDs (1)

p-p Ep-p Ecmcm ~50 GeV ~50 GeVp-p Ep-p Ecmcm ~50 GeV ~50 GeV


The 1st Accelerator Based Search for Monopoles Using NTDs (2)

12 stacks of plastic deployed Each stack consisted of 10 sheets:

3 and 5th were Makrofole-E The others were nitrocellulose


The MODAL Experiment The MODAL (at LEP) expt was run at √s =

91.1 GeV . The integrated luminosity 60+/-12 nb-1 The detector used CR-39 plastic foils covering a 0.86

x 4π sr angle surrounding the I5 IP at LEP. The polyhedral array was supported by a frame

which was mounted on a fixed stand. The vacuum pipe was 0.5 mm al.

The 12 detector faces were filled with CR-39 with thicknesses (A) 720 μm, (B) 1500 μm, (C) 730 μm.

Detector response of all three plastic detectors were calibrated using heavy ions at LBL.

Phy. Rev. D46, R881(1992)


Direct Monopole Search at LEP (OPAL)

The OPAL (LEP-1) monopole detector had a Dedicated plastic detector element (LEXAN) A dE/dX monopole trigger in the jet chamber

The OPAL search also employed the non-standard trajectory of the monopole in a solenoidal field

Search continued at LEP-2 using the jet chamber

monopole

Anti-monopole

Phys. Lett. B, 316, 407 (1993


Monopole Search Limits


The MoEDAL Experiment - the Monopole Search at the LHC

MOEDAL collaboration from: Canada (U of Alberta & U of Montreal); Italy (U of Bologna); CERN; Institute of Space Sciences, Romania. and, the USA (North Eastern University, Boston; U. of Cincinnati).

MoEDAL

LHCb


The MoEDAL Detector

MoEDAL is an experiment dedicated to the search highly ionizing exotic particles at the LHC, using plastic track-etch detectors

MoEDAL will run with p-p collisions at a luminosity of 1032 cm-2 s-1 and in heavy-ion running

We can detect up to a 7 TeV mass monopole with charge up to ~3g Due to make an initial deployment in 2009, with full deployment of

detectors in 2010.

LHCbLHCbVELOVELO

~25 m2 area = 0 (layers) x 225 m2 =150 m2 of NTDs

MoEDAL NTDsMoEDAL NTDsMoEDAL NTDsMoEDAL NTDs


The MoEDAL Detector Element

3 layers of Makrofol (each 500 mm thick) 3 layers CR39 (each 500 mm thick) 3 layers of Lexan (each 200 mm thick) Sheet size 25 x 25 cm

Aluminium face plate 25 x 25 cm


The Next Step for NTDs at Accelerators

The LHC will start up in September 2008 MoEDAL will submit its TDR for LHCC approval in the

Fall of 2008 Initial deployment of detectors in 2009 Full deployment in 2010 Plans for p-p and heavy-ion running

MoEDALMoEDAL


Extra Slides


Restricted Energy loss

Contribution to track formation is assumed to be only from the energy transferred by low energy delta rays with energies up to a threshold Eth

Threshold values range between 200 and 1000 eV


Multi-Gamma Events

Multi- events At the ISR pp multi-at √s = 53 GeV, < 2 x 10-37 cm2

At FNAL (D0 Collab.) search for high ET -pairs in p-pbar collisions, Mmon. > 870 GeV/c2 for spin-1/2 Dirac MMs (95% CL)

At LEP (L3 Collab.) search for Z Mmon > 510 GeV/c2


The Definition of R

James L. Pinfold University of Alberta

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