SEARCH FOR THE MAGNETIC MONOPOLE AT ATLAS Sergey Burdin The - - PowerPoint PPT Presentation

SEARCH FOR THE MAGNETIC MONOPOLE AT ATLAS

Sergey Burdin The University of Liverpool HEP Seminar @ University of Birmingham Oct 2, 2013

Outline

• Motivation
• Past searches
• Monopole interactions with matter
• Search at ATLAS
• Prospects

2 Oct 2013

2

• S. Burdin - Search for Magnetic Monopole

History

• One of the longest

searches in physics

• “Epistola de

Magnete” by Petrus Peregrinus

 Characterization of

magnets

 Magnets have two

poles

2 Oct 2013

3

• S. Burdin - Search for Magnetic Monopole

Maxwell’s Equations

2 Oct 2013

Duality:

4

• S. Burdin - Search for Magnetic Monopole

Charge quantization

• The existence of even one

magnetic monopole would explain charge quantization (Dirac 1931)

• A static system of an electric and a

magnetic monopoles separated by a distance r possesses angular momentum

• Quantization of angular

momentum charge quantization

2 Oct 2013

,... 2 , 1 ; 2   n n c ge 

If the free electric charge is e/3, gD is larger

5

• S. Burdin - Search for Magnetic Monopole

Magnetic Monopoles in theory

• In GUTs, monopoles are the solitons of

the GUT broken symmetries (‘t Hooft & Polyakov)

 Monopole mass  scale of GUT breaking

• Fermionic and bosonic monopoles

predicted in the breaking of supersymmetric theories (Argyres & Douglas, Seiberg & Witten)

 Monopole mass  scale of SUSY breaking

• Monopole condensation has been

proposed for EWSB (Csaki & Shirman & Terning)  origin of mass

 Monopoles are the solitons of a new magnetic

force

 Monopole mass  monopole condensation

scale electroweak scale

2 Oct 2013

Electro- weak Theory Grand Unified Theory Theory of Everything

gravity strong weak

electromagnetic

energy

102 GeV 1019 GeV 1016 GeV

6

• S. Burdin - Search for Magnetic Monopole

Past searches for magnetic monopoles

• Magnetic monopoles trapped in beampipes

 HERA, CDF/DØ beam-pipe

• Direct collider searches for monopole-

antimonopole pairs

 LEP: OPAL, MODAL  Tevatron: CDF (DØ)

• GUT magnetic monopoles

 MACRO, SLIM, RICE, AMANDA, Baikal, etc.

• Polar rocks - Bendtz et al. PRL 110 (2013) 121803

2 Oct 2013

7

• S. Burdin - Search for Magnetic Monopole

2 Oct 2013

8

• S. Burdin - Search for Magnetic Monopole

Summary of past astrophysical searches

2 Oct 2013

9

• S. Burdin - Search for Magnetic Monopole

Summary of past Collider searches

2 Oct 2013

10

• S. Burdin - Search for Magnetic Monopole

MoEDAL

• New experiment at

CERN starts taking data in 2015

• Passive detectors

around LHCb collision point

 Nuclear Track

Detectors

 Thin plastic foils  Track-etch technique  Trapping Detectors

• Also sensitive to

massive charged particles Z/β>~5

2 Oct 2013

11

• S. Burdin - Search for Magnetic Monopole

Classic dirac monopoles

• Point-like particle

 Assume spin ½

• Magnetic charge
• Magnetic coupling
• Magnetic charge is conserved like electric charge

 lowest mass magnetic monopole should be stable

2 Oct 2013

25 . 34 ~ 4 1 ) (

2 2

      c g

mm



12

• S. Burdin - Search for Magnetic Monopole

Monopole Production Mechanism

• Calculation of cross-section

derived from electron-electron scattering using naïve substitution eg (cf. Milton, Schwinger, Kurochkin et al. )

• Theoretical uncertainties are

large, with no prospect of significant improvement

2 Oct 2013

• Coupling constant mm34  no

perturbative expansion

• Often modelled by Drell-Yan pair

production

Tevatron LHC

13

• S. Burdin - Search for Magnetic Monopole

ATLAS Detector

2 Oct 2013

14

• S. Burdin - Search for Magnetic Monopole

Transition Radiation Tracker and LAr Calorimeter

2 Oct 2013

15

• S. Burdin - Search for Magnetic Monopole

Transition Radiation Tracker (TRT)

• Drift-tube straws filled with Xe

gas

• Surrounded by radiator foils

 Transition radiation photons

deposit additional energy

• Two readout thresholds

1.

Low threshold (LT) for tracking

2.

High threshold (HT) for electron identification

• Large energy deposits from

monopole and multiple δ-rays yield HT TRT hits

2 Oct 2013

16

• S. Burdin - Search for Magnetic Monopole

LAr Electromagnetic Calorimeter

• Second of three layers has best

spatial resolution

• Ionizing particles in liquid argon

create electron-ion pairs

• The electric field ED = 10 kV/cm

is applied to collect ionization electrons

 Scale charge appropriately to

determine energy deposited

2 Oct 2013

17

• S. Burdin - Search for Magnetic Monopole

Monopole Energy loss

• Ionization dominates:

(zeeq)2=(gβ)2

• For β=1 :

(dE/dx)mm= 4700 (dE/dx)m.i.p.

• Highly Ionizing Particle (HIP)

 Narrow high-energy deposits  Lots of δ-rays near trajectory

2 Oct 2013

S.P. Ahlen, Phys. Rev. D14, 2935 (1976); D17, 229 (1978); Rev. Mod. Phys. 52, 121 (1980).

M=1000 GeV/c2 in Ar

18

• S. Burdin - Search for Magnetic Monopole

Equations of Motion

• Monopoles accelerated by magnetic field 

bend in r-z plane but is straight in r-φ

2 Oct 2013

dp dt = gB

19

• S. Burdin - Search for Magnetic Monopole

Monopole Signature

• Straight r-φ track

in the tracker

• Monopoles are

highly ionizing

• Presence of many

-rays

 lots of TRT high

threshold hits

• Ionization

dominates dE/dx

No LAr

calorimeter shower

Narrow energy

deposit

2 Oct 2013

1200 GeV Magnetic Monopole

20

• S. Burdin - Search for Magnetic Monopole

Analysis Strategy

• Search for straight r-φ track in the tracker

 Many hits from -rays confuse standard tracking algorithm  Too many tracks are found  Use special reconstruction algorithm  Take only TRT hits for simplicity  Prove that hits from low energy -rays are understood

• Search for narrow cluster in the LAr calorimeter

 Calibrate the LAr calorimeter recombination correction for

highly ionizing particles using published heavy ion data

• Derive data-driven background estimate using ABCD

method

2 Oct 2013

21

• S. Burdin - Search for Magnetic Monopole

Analysis Strategy

• Want model-independent result as much as is

possible

 Use single-particle Monte Carlo (MC) samples to get

EK vs  efficiency maps

 Extract a cross-section limit for monopoles produced

in a given EKsinθ vs  range (fiducial region) where efficiency is high

• To set a mass limit and compare to CDF result

[PRL96, 201801(2006)]

• Assume Drell-Yan pair-production
• Efficiency determined by kinematics
• Cross-section prediction (with large uncertainties)

2 Oct 2013

22

• S. Burdin - Search for Magnetic Monopole

Monopole Monte Carlo Simulation

2 Oct 2013

• Implement full GEANT4 simulation of magnetic

monopoles

• Equations of motion
• Ionization
• -ray production
• LAr recombination correction for highly ionizing particles

23

• S. Burdin - Search for Magnetic Monopole

No Bending in r- Plane

2 Oct 2013

24

• S. Burdin - Search for Magnetic Monopole

Bending as Expected in r-z Plane

2 Oct 2013

25

• S. Burdin - Search for Magnetic Monopole

Recombination in LAr Calorimeter

 Some electron-ion pairs may recombine

• Electrons that have recombined will not be collected by

electrodes  ionization signal is reduced and energy deposition is underestimated

• Birks’ Law describes electron-ion recombination effects
• Default Birks’ constant measured with ICARUS LAr Time

Projection Chamber using cosmic ray muons and protons

→over-suppresses signal at high dE/dx

2 Oct 2013

dx dE E k E E

LAr D vis

/ ) /( 1 1   

• J. B. Birks, Proc. Phys. Soc A64 (1951) 874.

)/MeV cm (kV/cm)(g/ 0006 . 0486 .

2

  k

• S. Amoruso et al., NIM A523, 275 (2004).

26

• S. Burdin - Search for Magnetic Monopole

Extending Birks’ Law to HIPs

• Used GEANT4 to simulate heavy ion beams

traversing a box of LAr

• Compared simulation to published

experimental heavy ion results

2 Oct 2013

1.

• E. Shibamura et al., Nucl. Instrum. Meth. A260, 437 (1987).

2.

• T. Doke et al., Nucl. Instrum. Meth. A235, 136 (1985).

3. H.J. Crawford et al., Nucl. Instrum. Meth. A256, 47 (1987).

27

• S. Burdin - Search for Magnetic Monopole

Heavy ion Data-Simulation Comparison

• MC significantly

underestimates visible energy for high dE/dx

• Parameterize this

discrepancy for HIP visible energy correction

2 Oct 2013

[kV/cm]

D

Electric Field E 2 4 6 8 10 /E

vis

E

• r

¥

I/I 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 a) H ions

Data Simulation

dE/dx [MeV/cm] 10

2

10

3

10

4

10

¥

I/I 0.2 0.4 0.6 0.8 1 [kV/cm]

D

Electric Field E 2 4 6 8 10 /E

vis

• r E

¥

I/I 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 f) Au ions

Data Simulation HIP Correction

ED=7 kV/cm

ED=7 kV/cm H He Ne Fe La Au Birks’ Law

28

• S. Burdin - Search for Magnetic Monopole

HIP Correction to Birks’ LAW IN LAR

• Birks’ Law describes electron-ion recombination

effects in LAr  over-suppresses signal at high dE/dx

• Use published heavy ion data in LAr to derive HIP

correction

• Burdin, Horbatsch & Taylor, Nucl. Instrum. Meth. A664 (2012)

111.

2 Oct 2013

29

• S. Burdin - Search for Magnetic Monopole

e, γ: 0.07 High

Photons 1.1MeV Electrons 0.6MeV TRT PAI Electrons 0.6MeV G4

• Rays in the TRT
• Propagation and dE/dx
• f low energy -

electrons in TRT simulation have been validated by comparison of the simulation to teststand measurements done by A.Romaniouk in 1995

2 Oct 2013

δ

30

• S. Burdin - Search for Magnetic Monopole

Monte-Carlo Samples

• Signal samples

 Single particle samples for m=200-1500 GeV/c2  MadGraph Drell-Yan samples for m=200-1200 GeV/c2

• Background samples

 Dijet events of various transverse momentum ranges  Zee, We  +jets  t-tbar

2 Oct 2013

31

• S. Burdin - Search for Magnetic Monopole

Monopole Reconstruction

• Use electron trigger of 60 GeV threshold
• Look for narrow cluster in LAr calorimeter
• Count number of TRT hits in window around cluster



Select events where the number of TRT hits and the fraction of HT hits are above some threshold

2 Oct 2013

1200 GeV Magnetic Monopole

[mm]

TRT

X

• 1000
• 800
• 600
• 400
• 200

[mm]

TRT

Y 200 400 600 800 1000 ATLAS Simulation

32

• S. Burdin - Search for Magnetic Monopole

Final Selection Variables

• EM cluster size σR
• High-threshold TRT

hit fraction fHT=nHTTRT/nTRT

2 Oct 2013

R

s 0.01 0.02 0.03 0.04

HT

f 0.2 0.4 0.6 0.8 1

Data 2011 Monopole MC

A C D B ATLAS

• 1

L dt = 2.0 fb

= 7 TeV s

ò

33

• S. Burdin - Search for Magnetic Monopole

No events in the signal region

2 Oct 2013

R

s 0.01 0.02 0.03 0.04

HT

f 0.2 0.4 0.6 0.8 1

Data 2011 Monopole MC

A C D B ATLAS

• 1

L dt = 2.0 fb

= 7 TeV s

ò

• No events observed in 2 fb-1

→nA=0, nB=5, nC=16, nD=7001

• Expected background in the signal region A: μbkg=0.022±0.018

34

• S. Burdin - Search for Magnetic Monopole

Efficiencies (Includes ACCEPTANCE)

2 Oct 2013

Drell-Yan events

[GeV]

kin T

E 500 1000 1500 2000 2500 3000 Efficiency 0.2 0.4 0.6 0.8 1 1.2 ATLAS Simulation

Monopole mass 200 GeV Monopole mass 1500 GeV

Single-particle events

h

• 3
• 2
• 1

1 2 3 [GeV]

kin T

E 500 1000 1500 2000 2500 3000 Efficiency 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 ATLAS Simulation Monopole mass 800 GeV

|η|<1.37

35

• S. Burdin - Search for Magnetic Monopole

Results

• Given no data events
• bserved in the signal

region the CLs method yields 95% CL limits for different monopole masses distributed around 3 events

 Converted to cross-

sections using either number of expected signal events in case of the DY production mechanism or directly using efficiency (80%) and luminosity in the case of the model- independent production mechanism

2 Oct 2013

[GeV] m 200 400 600 800 1000 1200 1400 Monopole cross section [fb]

• 1

10 1 10

2

10

3

10 Observed limit (DY) ATLAS Data 2011

ò

= 7 TeV s

• 1

L dt = 2.0 fb Observed limit in fiducial region

• G. Aad et al., PRL 109, 261803 (2012).

36

• S. Burdin - Search for Magnetic Monopole

Drell-Yan mass limit

2 Oct 2013

M=862 GeV/c2

[GeV] m 200 400 600 800 1000 1200 1400 Monopole cross section [fb]

• 1

10 1 10

2

10

3

10 Observed limit (DY) ATLAS Data 2011

ò

= 7 TeV s

• 1

L dt = 2.0 fb Observed limit in fiducial region

M=862 GeV/c2 Theory DY (sketch)

37

• S. Burdin - Search for Magnetic Monopole

Future monopole searches at ATLAS

• A new trigger was introduced in September 2012

to select magnetic monopoles

 Uses a reconstruction algorithm similar to 2011 analysis  L1 EM threshold is reduced to 18 GeV better

efficiency for lower energy monopoles

• Extend search to higher magnetic charges, dyons,

spin-O

• A proposal for a TRT-based L1 hardware trigger is

being prepared

2 Oct 2013

38

• S. Burdin - Search for Magnetic Monopole

Collider cross-section limits

2 Oct 2013

39

• S. Burdin - Search for Magnetic Monopole

Prospects for LHC searches (after ~2 years @14TeV)

2 Oct 2013

This limit (added by speaker)

40

• S. Burdin - Search for Magnetic Monopole

Comparison to the first results from MoEDAL

• First results from MoEDAL Magnetic Monopole Trapper were presented

by Philippe Mermod (University of Geneva) at the EPS2013

2 Oct 2013

41

• S. Burdin - Search for Magnetic Monopole

Conclusion

• First LHC search for monopole has been

published (PRL 109 261803 (2012))

 We set the reference

• No magnetic monopole yet but
• “one would be surprised if Nature had made

no use of it.” (Dirac, 1931)

2 Oct 2013

42

• S. Burdin - Search for Magnetic Monopole