Transcript Document

Searching for the Magnetic
Monopole and Other Highly
Ionizing Particles at
Accelerators Using NTDs
James L. Pinfold
University of Alberta
September 2008
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1
The Discovery of the North Pole
The 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!
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2
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
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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)
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Dirac’s Monopole (2)
Magnetic" Coulomb" field is B  grˆ / r 2
e-

 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:

e
 A.dr
p
 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:
e
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ie
c
 A.dr
i4 e
e c
1
A.dr  Ad
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& A  g
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Dirac’s Monopole (3)
 Hence Dirac’s quantization condition:
 c 
n
4eg
ge   n OR g 
e ( from
 2n n 1,2, 3..)
 2 
2
c
 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:
 c 
e   n
Charge is quantized!!
2g 
 If free quarks exist then the minimal electric charge
is e/3…the minimal
magnetic charge is then 3g

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Monopole Properties
Magnetic Charge
e=electron charge
gD= ћc/2e =68.5e
Colour Charge Monopole trajectory
Usually assumed is “parabolic” in the
to be 0
r-Z plane of a
Dyon electric
solenoidal field and
charge=1,2,3...
straight in the r-
plane
Electric charge =0.
Spin
Usually taken as Monopole mass
Magnetic Charge
0 or 1/2
FREE PARAMETER
e=quark charge =1/3
See next slide
gD  3gD
Energy gain in a
B-field: W= ngDBL
= n20.5 keV/G.cm
Energy loss
By ionization
(dE/dx)MM
= 4700 (dE/dx)MIP
See subsequent slides
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Production at
Accelerators
usually assumed
to be via Drell-Yan
or Photon Fusion
GUT monopoles
Coupling constant
can catalyse proton
decay via the
am= gD2/ћc
Rubakov-Callan
=34.25
Mechanism.
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Magnetic Monopole Energy Loss
 > 10-2
Ionization (à la Bethe-Bloch) (Zeeq)2= (gb)2
(a)
for b = 1 : (dE/dx)MM = 4700 (dE/dx)m.i.p.
10-4<<10-2 Excitation
Medium as Fermi gas
(b)
M + He  M + He*
+ Penning effect He*+ CH4  He + CH4 + e-
10-4<<10-3 Drell effect
(coupling of the atom magnetic moment with the MM magnetic charge)
 < 10-4
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Elastic collisions
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(c)
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Track Etch Monopole Detectors
Look for aligned etch pits
In 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.
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Types of NTDs Commonly Used
CR39
Rodyne/Makrofol
PLASTIC
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UG-5
GLASS
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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
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Making Etching Better
l
A better signal to noise ratio
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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
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A Typical Analysis Technique (2)
a)
 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 edges
 The 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
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b)
Ammonia vapor
NTD
Blueprint paper
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Calibration
Reduced etch rate
158 A GeV 207 Pb82+
Pbions +frag’s 5 < Z < 82
REL
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Seeking Monopoles at
Accelerators
 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.
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Accelerator Based Searches
31 searches
14 using
Plastic NTDs
3 using
emulsions
3 using
induction
11 using
counters
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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
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The 1st Accelerator Based Search
for Monopoles Using NTDs (1)
p-p Ecm ~50 GeV
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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
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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.
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Phy. Rev. D46, R881(1992)
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Direct Monopole Search at
LEP (OPAL)
monopole
Anti-monopole
Phys. Lett. B, 316, 407 (1993
 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
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Monopole Search Limits
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The MoEDAL Experiment - the
Monopole Search at the LHC
LHCb
MoEDAL
 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).
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The MoEDAL Detector
MoEDAL NTDs




~25 m2 area = 0 (layers) x 225 m2 =150 m2 of NTDs
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.
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The MoEDAL Detector Element
Aluminium face plate
25 x 25 cm

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
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
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The Next Step for NTDs at
Accelerators
MoEDAL
 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
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Extra Slides
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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
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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
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Z  Mmon > 510 GeV/c2
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The Definition of R
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