Directional Detectors and Digital Calorimeters Ed Norbeck and Yasar Onel University of Iowa For the 25 th Winter Workshop on Nuclear Dynamics Big Sky, Montana 1-7 February 2009

25th WW 02/7/09Ed Norbeck University of Iowa2 First a brief report on the performance of an actual directional detector.

25th WW 02/7/09Ed Norbeck University of Iowa3 The QuarkNet group from Bettendorf HS have constructed and tested a directional particle detector that makes use of light produced by the Čerenkov effect. Much of the work was done by high school students Mitch Miller and Nathan Premo at the U of Iowa in 2008.

25th WW 02/7/09Ed Norbeck University of Iowa4 A charged particle moving at almost the speed of light through a transparent material makes light that goes off at a angle with respect to its direction. This angle is given by cos (θ) = 1/n where n is the index of refraction of the material. For n = 1.414, θ = 45º Particle θ Čerenkov light

25th WW 02/7/09Ed Norbeck University of Iowa5 Muon angle (relative to vertical) allowed by QuarkNet scintillator paddles is ± 24º HV Signal Lucite cylinder 3” OD 4” long PMT1 PMT2

25th WW 02/7/09Ed Norbeck University of Iowa6 Each point shows the size of the signal in PMT1 and PMT2. Blue points are with the same system turned upside down. With no exception the PMT looking up has the larger signal.

25th WW 02/7/09Ed Norbeck University of Iowa7 Here the 4 inch long lucite cylinder is replaced with a 2” long cylinder. The looking down PMT has the larger signal 3% of the time.

25th WW 02/7/09Ed Norbeck University of Iowa8 In these detectors the PMTs did not show the usual dark current pulses. Why? Is a bare PMT a directional Čerenkov detector?

25th WW 02/7/09Ed Norbeck University of Iowa9 A PMT by itself is a directional Čerenkov detector Up Facing the incoming muons Side

25th WW 02/7/09Ed Norbeck University of Iowa10 The down system is the same as the up but turned upside down.

25th WW 02/7/09Ed Norbeck University of Iowa11 What part of the PMT sees muons? Face only All counts Tail only No counts

25th WW 02/7/09Ed Norbeck University of Iowa12 Conclusions Directional Čerenkov detectors are simple and effective. A high-energy test beam may be available at your local high school. (There are over 300 high schools in the QuarkNet program)

25th WW 02/7/09Ed Norbeck University of Iowa13 Ed Norbeck, Burak Bilki, Yasar Onel and José Repond What is a digital calorimeter and why would anyone want one ? May get improved energy resolution by not measuring the energy!

25th WW 02/7/09Ed Norbeck University of Iowa14 Sampling Calorimeter Heavy metal absorberDetectors For good energy resolution need large sampling fraction

25th WW 02/7/09Ed Norbeck University of Iowa15 Common “thick” detectors Čerenkov Scintillator Semiconductor Each has its own set of problems. All have low density, makes calorimeter longer

25th WW 02/7/09Ed Norbeck University of Iowa16 Some excellent gas detectors RPC (Resistive Plate Chamber) GEM (Gas Electron Multiplier) MICROMEGAS (MICRO-Mesh-Gaseous Structure) All are “thin”, at most a few mm of gas. Sampling ratios of 10 -5

25th WW 02/7/09Ed Norbeck University of Iowa17 Amplitude Number of counts Threshold Noise Signal Signal from MIP in a thin detector If single MIP, energy lost in absorber known.

25th WW 02/7/09Ed Norbeck University of Iowa18 To measure energy in a jet each particle must go into separate pixel. Requires excellent position resolution Many pixels Cubic meter detector 40 planes each with 10, cm 2 pixels 400,000 single-bit channels Does not require A to D conversions!

25th WW 02/7/09Ed Norbeck University of Iowa19 Problems! What if a MIP is recorded in two pixels? May be below threshold in one plane May collide and make several new MIPs

25th WW 02/7/09Ed Norbeck University of Iowa20 Extrapolate tracks back to find number of MIPs near junction Need elaborate computer programs “Particle flow algorithms”

25th WW 02/7/09Ed Norbeck University of Iowa21 With analog calorimeter calibration is a major problem. With digital calorimeter drift in sensitivity can cause Missed point in a track or spurious point (noise) Both of these easily dealt with by Particle Flow Algorithm

25th WW 02/7/09Ed Norbeck University of Iowa22 A few events… μ Calibration Runs 120 GeV protons with 1 m Fe beam block no μ momentum selection One of many perfect μ event μ event with double hits in x μ at an angle or multiple scattering μ event with δ ray or π punch through

A few events…e + Run GeV secondary beam Čerenkov signal required 8 GeV e + event 8 GeV e + event with satellites8 GeV e + event

A few events… π + Run 1 – 16 GeV secondary beam Veto on Čerenkov signal 8 GeV π + event (typical) 8 GeV π + event (early shower)

25th WW 02/7/09Ed Norbeck University of Iowa25 A few events…Multiple particles 120 GeV protons without beam block 2- π event (upstream shower?) 3- π event (upstream shower?)

25th WW 02/7/09Ed Norbeck University of Iowa26 This technique allows detailed tracking for penetrating particles. (It is difficult to implement ten nuclear reaction lengths of silicon.) Digital calorimetry is a rapidly developing field. Cosmic ray studies used lead plates and emulsion 50 years ago. Spark chambers used camera readout. Concluding comments