Directional Detectors and Digital Calorimeters

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

2. First a brief report on the performance of an actual directional detector. Ed Norbeck University of Iowa

3. 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. Ed Norbeck University of Iowa

4. Čerenkov light 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 θ Particle Ed Norbeck University of Iowa

5. HV Signal Muon angle (relative to vertical) allowed by QuarkNet scintillator paddles is ± 24º PMT1 Lucite cylinder 3” OD 4” long PMT2 Ed Norbeck University of Iowa

6. 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. Ed Norbeck University of Iowa

7. 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. Ed Norbeck University of Iowa

8. In these detectors the PMTs did not show the usual dark current pulses. Why? Is a bare PMT a directional Čerenkov detector? Ed Norbeck University of Iowa

9. A PMT by itself is a directional Čerenkov detector Side Up Facing the incoming muons Ed Norbeck University of Iowa

10. The down system is the same as the up but turned upside down. Ed Norbeck University of Iowa

11. What part of the PMT sees muons? Face only All counts Tail only No counts Ed Norbeck University of Iowa

12. 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) Ed Norbeck University of Iowa

13. 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! Ed Norbeck University of Iowa

14. Sampling Calorimeter Heavy metal absorber Detectors For good energy resolution need large sampling fraction Ed Norbeck University of Iowa

15. Common “thick” detectors • Čerenkov • Scintillator • Semiconductor Each has its own set of problems. All have low density, makes calorimeter longer Ed Norbeck University of Iowa

16. 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 Ed Norbeck University of Iowa

17. Signal from MIP in a thin detector Noise Threshold Number of counts Signal Amplitude If single MIP, energy lost in absorber known. Ed Norbeck University of Iowa

18. To measure energy in a jeteach particle must go into separate pixel. Requires excellent position resolution Many pixels Cubic meter detector 40 planes each with 10,000 1.0 cm2 pixels 400,000 single-bit channels Does not require A to D conversions! Ed Norbeck University of Iowa

19. Problems! • What if a MIP is recorded in two pixels? • May be below threshold in one plane • May collide and make several new MIPs Ed Norbeck University of Iowa

20. Extrapolate tracks back to find number of MIPs near junction Need elaborate computer programs “Particle flow algorithms” Ed Norbeck University of Iowa

21. 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 Ed Norbeck University of Iowa

22. A few events… μCalibration Runs 120 GeV protons with 1 m Fe beam block no μ momentum selection One of many perfect μevent μat an angle or multiple scattering μevent with double hits in x μevent with δ ray or πpunch through Ed Norbeck University of Iowa

23. A few events…e+ Run 1 - 16 GeV secondary beam Čerenkov signal required 8 GeV e+event 8 GeV e+event 8 GeV e+event with satellites 8 GeV e+event

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

25. A few events…Multiple particles 120 GeV protons without beam block 2-πevent (upstream shower?) 3-πevent (upstream shower?) Ed Norbeck University of Iowa

26. Concluding comments 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. Ed Norbeck University of Iowa