Introducing CLEO

1
Introducing CLEO

• Detectors for particle physics How they work
  and what they tell us

Ritchie Patterson July 18, 2005
2
Detectors for Particle Physics
CDF
install
ZEUS
BaBar
D0
Atlas
3
CESR
4
Collisions
First, e and e- annihilate to make a pair of
charm quarks
5
Collisions
First, e and e- annihilate to make a pair of
charm quarks
Then the charm quarks pull apart, pop some light
quarks, and form D mesons
6
Collisions
First, e and e- annihilate to make a pair of
charm quarks
Then the charm quarks pull apart, pop some light
quarks, and form D mesons
D mesons decay after 1ps into particles that CLEO
detects
7
More on Mesons

• Hydrogen Atom D Meson

charm quark
proton
up-quarkcloud
electroncloud
Electromagnetism bindselectron to proton
Strong Force bindsup-quark to charm-quark
8
Detecting Particles
9
What do we want from our detector?

• Imagine that a bomb explodes mid-air, and you
  want to study the fragments to find out
  everything you can about the bomb. What
  properties of the fragments would you want to
  measure?

10
What do we want from our detector?

• Imagine that a bomb explodes mid-air, and you
  want to study the fragments to find out
  everything you can about the bomb. What
  properties of the fragments would you want to
  measure?
• Direction of motion of each fragment just after
  explosion
• Speed (or momentum) of each fragment
• Mass of each fragment

11
CLEO-c Detector
12
Tracking Chambers
ZD6 layers
DR48 layers10,000 sense wires!
13
Tracking Chamber Operation
Particle
End View of Chamber X - wire at 0V (field
wire) ? - wire at 2000V (sense wire)

1. Particle ionizes the gas that fills the chamber.
2. Each released electron travels to nearest sense
   wire.
3. We measure arrival time of the electrons --
   precision of 1/10 mm

Trick of the trade Particles bend (why?), and
their curvature gives momentum
CollisionPoint
14
The Magnetic Field

• Superconducting coil surrounds the tracking
  chambers and produces a 1 Tesla magnetic field.
• As a result, charged particles follow curved
  paths.
• The direction of curvature reveals the sign of
  their electric charge.
• The amount of curvature varies inversely with
  momentum.

15
Our Event

• Notice
• the paths of the charged particles in the
  chambers
• their curvature

Which particle has the highest momentum? The
lowest?
16
What has CLEO measured so far?

• Direction of motion of charged particles -- Drift
  Chamber
• Momentum magnitude of charged particles -- Drift
  Chamber

17
Distinguishing pions from kaons
Ring Imaging Cerenkov Counter (RICH) The opening
angle of the Cerenkov radiation gives the
particle speed. Then momentum/speed reveals the
mass.
Cerenkov Radiation - Blue light produced when a
fast particle goes through material, analagous to
a sonic boom. The direction of the light
depends on particle speed. vlight c/n ?c
arccos (vlight/vparticle)
18
A particle in the RICH
Impact point ofparticle
Cerenkov photon
19
What has CLEO measured so far?

• Direction of motion of charged particles -- Drift
  Chamber
• Momentum magnitude of charged particles -- Drift
  Chamber
• Speed of charged particles -- RICH(together with
  momentum gives mass)

20
Next Electromagnetic Calorimeter
Electromagnetic Calorimeter Measures the energy
of light particles, ie photons and electrons
21
Electromagnetic Calorimeter
CsI crystalCLEO has 7800 like this one.
CsI nucleus
Light output is proportional to incident electron
or photon energy
Incident electron or photon
22
Electromagnetic Calorimeter
Simulation of an electron showering in the
calorimeter Pink - electron Blue - photon
23
What has CLEO measured so far?

• Direction of motion of charged particles -- Drift
  Chamber
• Momentum magnitude of charged particles -- Drift
  Chamber
• Speed of charged particles -- RICH(together with
  momentum gives mass)
• Energy of photons -- Electromagnetic calorimeter

24
Particle Detectors
25
Muon Detection
Muon steel Also serves as solenoid return yoke
26
What has CLEO measured so far?

• Direction of motion of charged particles -- Drift
  Chamber
• Momentum magnitude of charged particles -- Drift
  Chamber
• Speed of charged particles -- RICH(together with
  momentum gives mass)
• Energy of photons -- Electromagnetic calorimeter
• Muon ID -- Muon counters

Now, use energy and momentum conservation to
figure out what happened in the event.
27
Particle Decays vs Explosions

• Explosions
• Total mass unchanged
• Net momentum unchanged
• Kinetic energy may disappear into heat, sound

• Particle Decays
• Total mass may change
• Net momentum unchanged
• E (KE mass energy) unchanged

28
An Aside on Special Relativity

• Master equation E2 (Mc2)2 p2c2
• A generalization of the famous E mc2.
• Works for a single particle or a collection of
  particles
• Example
• Particle has momentum such that pc 500 MeV
  (Tracking Chamber)
• Particle is a kaon, so Mc2 500 MeV (each
  particle species has a specific mass.) (RICH
  told us we had a kaon)
• Plug these into the Master Equation to find that
  its energy is E 700 MeV.

29
Reconstructing decays

• Make a hypothesis, eg Particles A and B were
  produced in the decay of an unseen particle C,
  that is C?AB
• Compute mass of C, using (Mc2)2 E2 - p2c2EC
  EA EBvec(pC) vec(pA) vec(pB)
• If the computed mass of C matches the true mass
  of C, the hypotheses holds.
• If nottry another hypothesis
• Voila!

30
Example A search for D0 decays

• Here, Kaons and pions were combined to see
  whether they came from a D0 decay.
• When they did, they landed in the peak.
• When they didnt, they landed elsewhere.

Number of candidates (scaled)
31
At CLEO

• Look for new physics by looking for decays that
  are forbidden in the Standard Model
• Understand the Standard Model better so that we
  can recognize deviations that signal new physics
• Measure the fundamental parameters of the weak
  interaction
• Understand strong interactions

32
The Future

• Large Hadon Collider (LHC) will collide p and
  anti-p starting in 2007. ATLAS and CMS
  experiments at the LHC may see Higgs-like
  particles and new, weird phenomena.

33
The Future

• International Linear Collider (ILC) will collide
  e and anti-e starting in 2015. Will explore the
  phenomena seen at the LHC. Does the Higgs travel
  alone or with partners? Is one of the discovered
  particles dark matter? A sign of extra dimensions
  of space?

34
The Upshot

• You now know the tricks of the trade that have
  led to most of our knowledge about how
  fundamental particles interact with one another.
• As Ahren showed us, our understanding, embodied
  in the Standard Model, is detailed and elegant.
• But it seems clear that we are seeing only part
  of a larger picture. In the next few years, the
  techniques that Ive shown you, applied at new
  and very high energy accelerators (esp. LHC and
  later, ILC) are likely to reveal wide new vistas
  of nature, and our role in it.