Detectors & Measurements II: Detectors & Measurements II: How we do physics without seeing…How we do physics without seeing…

Prof. Robin D. ErbacherUniversity of California, Davis

References: R. Fernow, Introduction to Experimental Particle Physics, Ch. 14, 15 D. Green, The Physics of Particle Detectors, Ch. 13 http://pdg.lbl.gov/2004/reviews/pardetrpp.pdf Lectures from CERN, Erbacher, Conway, …

Overview of Detectors and Fundamental Measurements:From Quarks to Lifetimes

Modern Collider Detectors

• the basic idea is to measure charged particles, photons, jets, missing energy accurately

• want as little material in the middle to avoid multiple scattering

• cylinder wins out over sphere for obvious reasons!

Call ‘em Spectrometers

• a “spectrometer” is a tool to measure the momentum spectrum of a particle in general

• one needs a magnet, and tracking detectors to determine momentum:

• helical trajectory deviates due to radiation E losses, spatial inhomogeneities in B field, multiple scattering, ionization

• Approximately:

€

dp

dt=

q

cv × B

€

p = 0.2998Bρ T - m

€

ρ = radius of curvature

Magnets for 4 DetectorsSolenoid Toroid

+ Large homogeneous field inside- Weak opposite field in return yoke - Size limited by cost- Relatively large material budget

+ Field always perpendicular to p+ Rel. large fields over large volume + Rel. low material budget- Non-uniform field- Complex structural design

Examples: •Delphi: SC, 1.2 T, 5.2 m, L 7.4 m•L3: NC, 0.5 T, 11.9 m, L 11.9 m•CMS: SC, 4 T, 5.9 m, L 12.5 m

Example: •ATLAS: Barrel air toroid, SC, ~1 T, 9.4 m, L 24.3 m

LHC Coils DifferentTwo ATLAS toroid coils

Superconducting CMS Solenoid Design

Charge and Momentum

CMS at CERN

S = Solenoid!

CMS Muon Chambers

CMS Spectrometer Details

• 12,500 tons (steel, mostly, for the magnetic return and hadron calorimeter)

• 4 T solenoid magnet

•10,000,000 channels of silicon tracking (no gas)

• lead-tungstate electromagnetic calorimeter

• 4π muon coverage

• 25-nsec bunch crossing time

•10 Mrad radiation dose to inner detectors

•...

CMS: All Silicon Tracker

All silicon: pixels and strips!

210 m2 silicon sensors6,136 thin detectors (1 sensor)9,096 thick detectors (2 sensors)9,648,128 electronics channels

Possible Future at the ILC: SiD

All silicon sensors:pixel/strip tracking

“imaging” calorimeterusing tungsten with Si wafers

Fixed Target Spectrometers

•Fixed target experiments study what happens when a beam of particles smashes into the atoms of a target.

•Most beam energy goes into target recoil, a fraction left to create new particles

•Particles produced, or scattered, generally fly forwards

•Detectors are typically cone-shaped, and placed downstream of the beamline.

Fixed Target Experiments

If we think of collider experiments as power tools for a broad range of discoveries, we can think

of fixed-target experiments as a set of scalpels to dissect particular particles and processes. The machine tool versus the surgeon's knife.

particle

Atom

impactparameter

b

Rutherford’s discovery of the nucleus pioneered fixed-target experiments.

Later such experiments found partons, and have continued to illuminate particle physics.

Probing the Structure of Matter

SLAC Endstation A:Electrons on nucleons

Probing the Structure of Matter

Kinematic reach is physical:Need to arrange spectrometerAccording to physics desired Polarized target material:

Frozen NH3 and ND3

Secondary Beam Particles

KTeV: Kaons at the TeVatron

The KTeV experiment was designed to search for direct CP violation in K -> 2 pion decays, and to study a wide variety of rare KL decays.

Studying Secondary Particles

Studying Secondary Particles

Intense beam of K0s created from TeV energy protons

Using Secondary Beams as Probes

NuTeV: Neutrinos at the Tevatron

•Ten sq ft on the face, 120 ft long

•690 tons of steel, 84 scintillator boxes in target cal

•Toroidal magnetic field

•Muon drift chambers

DIS

Structure of Nucleon, and sin2w

Neutrino Target & Product Detector

Using Secondary Beams as Probes

Charged CurrentCC Interaction

€

ν μ + q →ν μ + X

Neutral CurrentNC Interaction

€

ν μ + q → μ− + X

€

NC /CC ⇒ sin2 θw

Secondary Beams as Probes

Fundamental Measurements

Next time… Discussion of measurement of fundamental parameters in particle physics.

Fundamental Measurements

Charge: Charge of a particle can be determined two ways1) Direction of deflection in a magnetic field2) Charge-dependent quantity, such as ionization energy loss

Mass: