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Particle ID. Electrons Muons Beauty/charm/tau Pi/K/p. Electrons. See calorimeter lectures Different lateral and longitudinal shower profiles. E/p for electrons. E measured by calorimeter. P measured by momentum in tracker.

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Particle id
ParticleID

  • Electrons

  • Muons

  • Beauty/charm/tau

  • Pi/K/p

Particle ID Tony Weidberg


Electrons
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).

Particle ID Tony Weidberg


Muons
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.

Particle ID Tony Weidberg


Muon backgrounds
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?

Particle ID Tony Weidberg


Beauty charm tau
Beauty/Charm/Tau

  • Why is this important?

  • Detect “long” lifetime with micro-vertex detector

  • life t~ 1ps  ct ~ 300 mm 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.

Particle ID Tony Weidberg


Micro vertex
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).

Particle ID Tony Weidberg


Cdf svx
CDF SVX

  • Silicon microstrips

  • Wire bonded to hybrid with FE ASICs

  • Barrel layers built up of many ladders.

Particle ID Tony Weidberg



Transverse flight path
Transverse flight Path

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

Particle ID Tony Weidberg


Atlas vertexing
ATLAS Vertexing

  • Impact parameter resolution improves with pt why?

  • Why does it saturate at high pt?

Particle ID Tony Weidberg


Atlas
ATLAS

  • Significance = d/s(d)

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

b jets

u jets

Particle ID Tony Weidberg


Jet weights
Jet Weights

u jets

  • Combine significance from all tracks in jet.

B jets

Particle ID Tony Weidberg


Efficiency b vs rejection power
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???

Particle ID Tony Weidberg


Another way to tag b c
Another way to tag b/c

  • Use semi-leptonic deays:

    • b c l n Detect charged l in jet at some pt wrt jet axis.

    • l could be electrons or muons (which do you think would be easier?).

Particle ID Tony Weidberg


Pi k p
Pi/k/p

  • Why do we need this?

  • More difficult…

  • dE/dx

  • TOF

Particle ID Tony Weidberg


Pi k separation
Pi/K Separation

Particle ID Tony Weidberg


TOF

L

t2

t1

Particle ID Tony Weidberg


TOF

  • Scintillation Counter time resolution

    • Time spread from light paths through scintillator.

    • Time spread from PMT.

    • Best resolution s~200 ps.

  • Spark chambers

    • Can achieve s~60 ps

Particle ID Tony Weidberg


Particle id by ionisation
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.

Particle ID Tony Weidberg


Ionization bethe bloch formula
Ionization: Bethe-Bloch Formula

  • d=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 bg

  • BBF as a Function of bg is nearly independent of M of projectile except for nmax and very weak log dependence in d

     if you know p and measure b  get M (particle ID via dE/dx): See slide 21

  • Nearly independent of medium. Dominant dependence is Z’/A ≈½ for most elements.

Particle ID Tony Weidberg


12 2 charged particles in matter ionisation and the bethe bloch formula variation with bg

m+ can

capture e-

Bethe

Bloch

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

  • Broad minimum @ bg≈3.0(3.5) for Z=100(7)

  • At minimum, stopping power is nearly independent of particle type and material

Emc = critical energy

defined via:

dE/dxion.=dE/dxBrem.

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

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

Particle ID Tony Weidberg


Ionisation variation with particle type

in drift

chamber

gas

Ionisation variation with particle type

  • P=mgv=mgbc

  • 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

Particle ID Tony Weidberg


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