1. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 1 PHYS 3446 – Lecture #16 Wednesday, Nov. 3, 2010 Dr. Andrew Brandt Particle Detection Time of Flight Cerenkov Counter Silicon Calorimeter Review Project assignments HW 7 due Wedsday

2. Project Assignments and tentative agenda Wednesday Dec. 1 Solar Neutrino Deficit Baral-Lord Long baseline neutrino experiments (neutrino mass) Butler-Mayfield G-2 experiments Ouyang-Wright HERA experiments: diffraction/large rapidity gaps Gray-Woo Friday Dec. 3 Quark-Gluon Plasma (RHIC) Byrd-Pryor Monday Dec. 6 Higgs Boson Theory Bridges-Corbin Standard Model+Beyond the Standard Model Higgs Boson Searches at Dzero Absher-Dean-Shumate Supersymmetry Theory Ibarra Blackhole/Extra Dimension Searches at ATLAS Contreras-LaRoque Wednesday, Nov. 3, 2010 2 PHYS 3446, Fall 2010 Andrew Brandt

3. Project Details 16 minute presentation+4 mins for questions (preferably powerpoint) will be done on Dec. 1, 3, 6 as outlined on previous slide. Let me know right away if some conflict. You should provide me with an outline and list of refs by Nov. 15 (10% of grade). By Nov. 22, you should provide me with a decent draft (10%), in order to get feedback in time to make modifications It is important to get an early start in case you have some questions about the project as it will be a significant part of your grade. At least 3 sources including original paper (and not including wikipedia); should answer most if not all of these questions as applicable. Suggested split: intro/detector results/data analysis 1)what is signature involved, are there other signatures not used, why? For experimental talk 1)was experiment designed to find the result for your talk 2)what detector was/will be used, describe detector’s and sub-detectors 3)what was/will be importance of discovery 4)who was involved names if small, institutions if large, ~how many people 5)what was major source of uncertainty, statistical or systematic 6)what were two most important systematic errors 7)what was largest background For theory talk 1) How well motivated is the theory—are there other alternative models that the LHC (or Tevatron) is sensitive to? Wednesday, Nov. 3, 2010 3 PHYS 3446, Fall 2010 Andrew Brandt

4. Project Grading Issues 1)What was the subject? 2) Did the presenters describe the detectors or theory adequately? 3) Did they describe the importance and/or method of the discovery/theory? 4) Did they describe the measurement or calculation, errors and backgrounds if applicable? 5) Was the talk interesting and comprehensible? Excessive jargon? 6) Was the time management good? 7) What overall grade would you give them if you were the prof? Why? Wednesday, Nov. 3, 2010 4 PHYS 3446, Fall 2010 Andrew Brandt

5. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 5 Scintillator + PMT can provide time resolution of 0.1 ns. –What position resolution does this corresponds to? 3cm Array of scintillation counters can be used to measure the time of flight (TOF) of particles and obtain their velocities –What can this be used for? To distinguish particles with the similar momentum but with different mass –How? Measure –the momentum (p) of a particle in the magnetic field –its time of flight (t) for reaching some scintillation counter at a distance L from the point of origin of the particle—this gives the velocity –from the momentum and velocity of the particle can determine its mass Time of Flight

6. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 6 What is Cerenkov radiation? –Emission of coherent radiation from the excitation of atoms and molecules When does this occur? –If a charged particle enters a dielectric medium with a speed faster than light in the medium –How is this possible? Since the speed of light is c/n in a medium with index of refraction n, if the particle’s  >1/n, its speed is larger than the local speed of light Cerenkov light has various frequencies but blue and ultraviolet band are most interesting –Blue can be directly detected w/ standard PMTs –Ultraviolet can be converted to electrons using photosensitive molecules mixed with some gas in an ionization chamber Cerenkov Detectors

7. n=1n>>1 Cerenkov Effect Use this property of prompt radiation to develop a fast timing counter particle Wednesday, Nov. 3, 2010 7 PHYS 3446, Fall 2010 Andrew Brandt

8. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 8 TOF is the distance traveled divided by the speed of the particle, t=L/v. Thus  t in flight time of the two particle with m1 m1 and m2 m2 is For known momentum, p, –Since In non-relativistic limit, Mass resolution of ~1% is achievable for low energies Time of Flight (TOF)

9. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 9 The angle of emission is given by The intensity of the produced radiation per unit length of the radiator is proportional to sin 2  c. For  n>1, light (Cerenkov Radiation) will be emitted while for  n<1, no light is observed. One can use multiple chambers of various indices of refraction to detect Cerenkov radiation from particles of different mass but with the same momentum Cerenkov Detectors

10. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 10 Threshold counters –Particles with the same momentum but with different mass will start emitting Cerenkov light when the index of refraction is above a certain threshold –These counters have one type of gas but could vary the pressure in the chamber to change the index of refraction to distinguish particles –Large proton decay experiments use Cerenkov detector to detect the final state particles, such as p  e+0e+0 Differential counters –Measure the angle of emission for the given index of refraction since the emission angle for lighter particles will be larger than heavier ones Cerenkov Detectors

11. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 11 Super-K Event Displays Stopping  33

12. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 12 Ring-imaging Cerenkov Counters (RICH) –Use UV emissions –An energetic charged particle can produce multiple UV photons distributed about the direction of the particle –These UV photons can then be put through a photo-sensitive medium creating a ring of electrons –These electrons then can be detected in an ionization chamber forming a ring –Babar experiment at SLAC used this type of detector Cerenkov Detectors

13. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 13 HW6 (due Mon 11/8) 7.2, 7.3, 7.4, 7.5 Look up Cerenkov Radiation and find (and write down) the full formula. What is the dependence on wavelength? How many photons would you expect from a 1 cm long quartz bar with n=1.5 for a wavelength range of 100 to 300 nm? 300-400? 400-700? 700- 1000??

14. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 14 Semiconductors can produce large signals (electron-hole pairs) for relatively small energy deposit (~3 eV) –Advantageous in measuring low energy at high resolution Silicon strip and pixel detectors are widely used for high precision position measurements (solid state MWPC) –Due to large electron-hole pair production, thin layers (200 – 300  m) of wafers sufficient for measurements –Output signal proportional to the ionization loss –Low bias voltages sufficient to operate (avoid recombination) –Can be deposited in thin stripes (20 – 50  m) on thin electrode –High position resolution achievable –Can be used to distinguish particles in multiple detector configurations So what is the catch? –Very expensive  On the order of $30k/m 2 Semiconductor Detectors

15. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 15 DØ Silicon Vertex Detector 2 3 4 9 8 11 1 6 7 5 1010 12 1 6 …... 1 2 3 4 One Si detector Barrel Disk

16. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 16 Magnetic measurement of momentum is not sufficient for physics, why? –The precision for angular measurements gets worse as particles’ momenta increases –Increasing magnetic field or increasing precision of the tracking device will help but will be expensive –Cannot measure neutral particle momenta How do we solve this problem? –Use a device that measures kinetic energies of particles Calorimeter –A device that absorbs full kinetic energy of a particle –Provides signal proportional to deposited energy Calorimeters

17. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 17 Large scale calorimeter were developed during 1960s –For energetic cosmic rays –For particles produced in accelerator experiments How do high energy EM (photons and electrons) and Hadronic particles deposit their energies? –Electrons: via bremsstrahlung –Photons: via electron-positron conversion, followed by bremsstrahlung of electrons and positrons –electron and photon interactions result in an electromagnetic shower that continues until all the initial energy is deposited Calorimeters

18. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 18 Electron Shower Process Photon, 

19. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 19 Hadrons are massive thus their energy deposit via brem is small They lose their energies through multiple nuclear collisions Incident hadron produces multiple pions and other secondary hadrons in the first collision The secondary hadrons then successively undergo nuclear collisions Mean free path for nuclear collisions is called nuclear interaction length and is substantially larger than that of EM particles Hadronic shower processes are therefore more extended and erratic than EM shower processes (also may produce neutrinos, so Hadronic energy resolution worse than EM) Calorimeters

20. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 20 High energy particles require large calorimeters to absorb all of their energies and measure them fully in the device (called total absorption calorimeters) Since the number of shower particles is proportional to the energy of the incident particles… One can deduce the total energy of the particle by measuring only a fraction of their energy, as long as the fraction is known  Called sampling calorimeters –Most the high energy experiments use sampling calorimeters Sampling Calorimeters

21. Wednesday, Nov. 3, 2010PHYS 3446, Fall 2010 Andrew Brandt 21 Principles of Calorimeters Total absorption calorimeter: See the entire shower energy Sampling calorimeter: See only some fraction of shower energy For EM Absorber plates For HAD