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Particle ID Tony Weidbe rg 1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

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Page 1: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 1

Particle ID

• Electrons

• Muons

• Beauty/charm/tau

• Pi/K/p

Page 2: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 2

Electrons

• See calorimeter lectures– Different lateral and longitudinal shower profiles.

• E/p for electrons. – E measured by calorimeter.– P measured by momentum in tracker.– Should peak at 1 for genuine electrons and be > 1

for backgrounds. Why?

• Cerenkov & Transition radiation (see Guy Wilkinson’s lectures).

Page 3: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 3

Muons

• Use hadron absorber.– Muons only lose energy through ionization

penetrate absorber.– Electrons and hadrons shower absorbed.– Need > 5 interaction lengths, why ???– Absorber could be hadron calorimeter and/or

passive steel.

• Muon signature:– Track segment in muon chambers after absorber.– Matching track in tracker before calorimeter.

Page 4: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 4

Muon Backgrounds

• Hadron punch trhough.– How can we estimate this?

• Pi/K decays– Generates real muons?– How can we reduce this background?– How can we estimate residual

background?

Page 5: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 5

Beauty/Charm/Tau• Why is this important?• Detect “long” lifetime with micro-vertex

detector• life~ 1ps c ~ 300 m but remember time

dilation can help! • Collider geometry:

– Decay happens inside beam pipe.– Measure primary & secondary tracks.– Reconstruct primary & secondary vertices

or– Use impact parameter (2D or 3D) wrt

primary vertex.

Page 6: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 6

Micro-vertex

• Impact parameter resolution– Low pt dominated by multiple scattering.– High pt dominated by measurement error.– Need infinitely thin and infinitely accurate

tracking detector.

• Best compromise is silicon (pixels, micro-strips or CCDs).

Page 7: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 7

CDF SVX

• Silicon microstrips

• Wire bonded to hybrid with FE ASICs

• Barrel layers built up of many ladders.

Page 8: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 8

Page 9: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 9

Transverse flight Path

• J/ sample. Plot fight path projected onto transverse plane.

Page 10: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 10

ATLAS Vertexing

• Impact parameter resolution improves with pt why?

• Why does it saturate at high pt?

Page 11: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 11

ATLAS

• Significance = d/(d)

• Compare significance for b jets and u/d jets.

b jets

u jets

Page 12: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 12

Jet Weights

• Combine significance from all tracks in jet.

( ) / ( )

logi b i u i

ii

r f S f S

W r

B jets

u jets

Page 13: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 13

Efficiency b Vs Rejection Power

• Plot R (rejection power for u/g/c jets versus eb (b jet efficiency)

• Why is c more difficult to reject than u?

• Why is g more difficult to reject than u???

Page 14: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 14

Another way to tag b/c

• Use semi-leptonic deays:– b c l Detect charged l in jet at some pt

wrt jet axis.– l could be electrons or muons (which do

you think would be easier?).

Page 15: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 15

Pi/k/p

• Why do we need this?

• More difficult…

• dE/dx

• TOF

Page 16: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 16

Pi/K Separation

Page 17: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 17

TOF

})p/m1()p/m1{(Lt 2/1221

2/1222

1212 v

L

v

Lttt

2

22

21

p2

L)mm(t

L

t1t2

Page 18: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 18

TOF

• Scintillation Counter time resolution– Time spread from light paths through

scintillator.– Time spread from PMT.– Best resolution ~200 ps.

• Spark chambers– Can achieve ~60 ps

Page 19: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 19

Particle ID by Ionisation

• Measure ionisation dE/dx and momentum identify particle type.

• Requires very precise measurement of dE/dx difficult.

• Multiple measurements in a wire chamber truncated mean.

Page 20: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 20

Ionization: Bethe-Bloch Formula

=density correction: dielectric properties of medium shield growing range of Lorenz-compacted E-field that would reach more atoms laterally. Without this the stopping power would logarithmically diverge at large projectile velocities. Only relevant at very large

• BBF as a Function of is nearly independent of M of projectile except for max and very weak log dependence in if you know p and measure get M (particle ID via dE/dx): See slide

21• Nearly independent of medium. Dominant dependence is Z’/A

≈½ for most elements.

2 2 22 2 22max

2 2

21 4 1ln

2 2eA

e

m cN ZdT Zdx A m I

h

1ln ln and 28.816 (

2 2p

p Z AI

Page 21: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 21

12.2 Charged particles in matter(Ionisation and the Bethe-Bloch Formula, variation with )

+ can capture e-

Ec = critical energydefined via:dE/dxion.=dE/dxBrem.

BetheBloch

• Broad minimum @ ≈3.0(3.5) for Z=100(7) • At minimum, stopping power is nearly

independent of particle type and material

• Stopping Power at minimum varies from 1.1 to 1.8 MeV g-1 cm2)

• Particle is called minimum ionising (MIP) when at minimum

Page 22: Particle ID Tony Weidberg1 Particle ID Electrons Muons Beauty/charm/tau Pi/K/p

Particle ID Tony Weidberg 22

in drift chambergas

Ionisation variation with particle type

• P=mv=mc • variation in dE/dx is

useful for particle ID• variation is most

pronounced in low energy falling part of curve

• if you measured P and dE/dx you can determine the particle mass and thus its “name”

e