Introducing CLEO Detectors for particle physics: How they work and what they tell us Ritchie Patterson July 18, 2005

Detectors for Particle Physics CDF BaBarD0 ZEUS Atlas install

CESR

Collisions First, e + and e - annihilate to make a pair of charm quarks:

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:

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

More on Mesons Hydrogen AtomD Meson proton charm quark electron cloud up-quark cloud Electromagnetism binds electron to proton Strong Force binds up-quark to charm-quark

Detecting Particles

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?

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

CLEO-c Detector

Tracking Chambers ZD 6 layers DR 48 layers 10,000 sense wires!

Tracking Chamber Operation Particle Collision Point 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

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.

Our “Event” Notice the paths of the charged particles in the chambers their curvature Which particle has the highest momentum? The lowest?

What has CLEO measured so far? Direction of motion of charged particles -- Drift Chamber Momentum magnitude of charged particles -- Drift Chamber

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. v light = c/n  c = arccos (v light /v particle )

A particle in the RICH Impact point of particle Cerenkov photon

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)

Next: Electromagnetic Calorimeter Electromagnetic Calorimeter Measures the energy of light particles, ie photons and electrons

Electromagnetic Calorimeter CsI crystal CLEO has 7800 like this one. Incident electron or photon Light output is proportional to incident electron or photon energy e+e+ e+e+ e-e- e-e-  CsI nucleus

Electromagnetic Calorimeter Simulation of an electron showering in the calorimeter Pink - electron Blue - photon

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

Particle Detectors

Muon Detection Muon steel Also serves as solenoid return yoke

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.

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

An Aside on Special Relativity Master equation: E 2 = (Mc 2 ) 2 + p 2 c 2 A generalization of the famous E = mc 2. 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 Mc 2 = 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.

Reconstructing decays 1. Make a hypothesis, eg “Particles A and B were produced in the decay of an unseen particle C”, that is C  A+B 2. Compute mass of C, using (Mc 2 ) 2 = E 2 - p 2 c 2 E C = E A + E B vec(p C ) = vec(p A ) + vec(p B ) 3. If the computed mass of C matches the true mass of C, the hypotheses holds. 4. If not…try another hypothesis Voila!

Example: A search for D 0 decays Here, Kaons and pions were combined to see whether they came from a D 0 decay. When they did, they landed in the peak. When they didn’t, they landed elsewhere. Number of candidates (scaled)

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

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

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?

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 I’ve 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.