Fission bombs versus Fusion Bombs Bikini Atoll Hbomb

Fission bombs versus Fusion Bombs Bikini Atoll H-bomb Test, 2013: $500/month plus free medical care from US Gov

Today’s Plan Particle Detectors Bubble Chamber example Cherenkov radiation Quiz

Elements of a multi-purpose particle spectrometer Special purpose experiments also have some of these components Vertexing (measure displaced vertices due to weak interaction decays). Silicon strip and pixel detectors. Tracking (measure charged tracks in a magnetic field; use the radius of curvature to deduce the momentum) Particle identification (Use Cerenkov emission or time of flight (TOF)) to distinguish pions from kaons etc… Calorimetry (measure energy deposited in electromagnetic or hadronic showers) Muons (measure muons that penetrate steel or other heavy absorber).

A bubble chamber photograph Donald Glaser, 1960 Nobel Prize in Physics for the bubble chamber 1968 Physics Nobel for Luis Alvarez: "for his decisive contributions to elementary particle physics, in particular the discovery of a large number of resonance states, made possible through his development of the technique of using hydrogen bubble chamber and data analysis" Fermilab bubble chamber

How to measure the radius of curvature and momentum from three points in a bubble chamber or tracking detector. From the radius curvature or sagitta one can obtain the momentum. R R Taylor expansion cos θ ≈ 1 – θ 2/2 So measure the “sagitta”, s, and determine p

The Geiger counter/The Proportional Counter Wire at positive HV; Why ? Question: What is the E field produced near a wire in a cylinder ? What is the potential difference across the tube ? Ans: E~1/r, integrate to obtain ΔV=ln(r 0/ra) Two versions: An avalanche discharge is produced near the wire (independent of the charge deposited). When operated in proportional mode at lower HV (the ionization is proportional to the charge deposited in the tube).

Multi-wire proportional chamber (MWPC) Can cover large areas with planes of MWPC’s. This enabled many discoveries and fundamental experiments in particle physics. 105 amplification factor near the wire. Georges Charpak, 1992 Nobel Prize in Physics

MWPCs were followed by Drift Chambers Similar to MWPC’s but provide two coordinates (one from the drift time of the ionization cloud to the wire. (spatial resolution is ~3 X times better than a MWPC). MWPC’s can handle higher rates than drift chambers. Solid state detectors based on silicon are even more robust.

A fixed target experiment Uses dipole magnets as momentum analyzers (“prisms”) and drift chambers and MWPC for tracking A single dipole with field B In the case of a non-uniform B field or multiple magnets

TPC (Time Projection Chambers) ATLAS Also used by Prof. Vahsen for directional dark matter detection. Alessandro Bettini (left) and Dave Nygren (right), inventor of the TPC Principle of the time projection chamber 3 -D tracking AND d. E/dx measurements.

Argonne Bubble Chamber event Measure the radii of curvature and scale. What is the vector momentum of each pion ?

Let’s now calculate the energy momentum 4 -vectors for each pion. How do we calculate the invariant mass of the pi-pi system ? However, the mass of the K 0 meson is 497. 7 Me. V

We identified the π+ π- parent, it is a K 0 meson ! Let’s try to identify the X particle. Question: how can we do this ? Introduce missing mass Let’s calculate Emiss first

Compare to known strange particles Aha, the missing X particle is a Σ.

Shielding by dipoles on left 1934 Nobel Prize in Physics, Pavel Cherenkov

Cherenkov radiation: another mechanism for relativistic charged particles If a particle travels faster than the phase velocity (“speed”) of light in a medium, Cherenkov radiation is produced. Recall n=c/v, where n is the index of refraction. How does C radiation depend on frequency ? OB=ct/n (Cherenkov wavefronts) OA=vt (particle moving to the right)

Cerenkov radiation by electrons Optical analogue of sonic boom Cerenkov radiation by electrons (few Me. V range) produces the “spooky blue glow” in the cooling pools of nuclear reactors Remember the frequency dependence. Radiation comes out in a cone in 3 d

The phototubes in the Super. Kamkiokande detector being serviced. The detector is located at the Kamioka mine in Gifu prefecture, Japan Cerenkov detectors can operate in the threshold mode or In the ring imaging mode Question: What is meant by threshold mode ?

Particle identification using Cerenkov radiation Question: What is this event display ? Bettini p 42 For water, n=1. 33, the Cerenkov threshold is E=0. 775 Me. V for electrons; E=213 Me. V for muons

Example: In the experiment of O. Chamberlain et al in which the anti-proton was discovered, the anti-proton momentum was approximately p=1. 2 Ge. V. What is the minimum refractive index needed to have the antiprotons above Cerenkov threshold ? Need γ and then β. How we do find γ ?

EM shower development in a calorimeter From Rossi, B. (1952); High-Energy Particles; Prentice-Hall