1. C ompensating H adron C alorimetry C ompensating H adron C alorimetry Why do we need it? How it may work? Does it really work? If not, can we survive? Aldo Penzo, INFN-Trieste FERMILAB - Research Techniques Seminar – Aug. 9, 2007

2. What kind of talk? Not a general “review”… Rather an account of – “episodes” in Calorimetry R&D – examples of “compensation” methods Therefore… – only partial coverage of the topic – (necessarily) subjective – (hopefully) not too biased Purpose: outline the changing scope of what is called “compensation”

3. Joule's apparatus for measuring the mechanical equivalent of heat in which the "work" of a falling weight is converted into the "heat" of agitation in the water. No need of high-tech for a good result...

4. ... just go for it! Take the best data you can... 1991 - Reconfigurable-stack calorimeter “Hanging File”: Scintillator-Absorber plates

5. Shower development and energy measurement

6. What’s going on in a developing shower? Everything that can be found in standard textbooks on Radiation Interactions in Matter (f.i. Landau-Lifschitz, Bruno Rossi, etc.) Photons/electrons undergo EM interactions and produce EM showers

7. Hadrons interact strongly and produce hadronic cascades copiously produced  o generate  pairs, originating EM showers inside hadronic cascades 2 scales for hadronic cascade development: –  abs for strongly interacting part – Xo for the EM part hadron  

8. 2 scales of shower development X0X0 I X 0, λ I [cm] Z

9. Development of hadron cascade Large fluctuations due to  o production

10. Dominance of low energy particles

11. Lateral cascade distribution Lead- scintillating fibre calorimeter The EM Component more concentrated on the central part of the shower: EM core

12. Hadronic vs EM response For instance in lead (Pb): Nuclear break-up (invisible) energy: 42% Ionization energy: 43% Slow neutrons (E ~ 1 MeV): 12% Low energy  ’s (E γ ~ 1 MeV): 3% Not all hadronic energy is “visible”:  Lost nuclear binding energy  neutrino energy  Slow neutrons, …

13. Hadronic shower reduced vs EM (and much broader) e/h = 1/

14. Interim outline High precision hadron calorimeters should have equal response to electromagnetic and strongly interacting particles (compensation condition e/h =1) in showers generated by incoming hadrons, in order to achieve: linear response in energy to hadrons, gaussian energy distribution for mono-energetic hadrons, electron-to-pion ratio close to unity, constant with energy, relative energy resolution (dE/E), improving as sqrt(1/E). This is of prime relevance for the measurement of jets, involving various particles of different energies, with a substantial fraction of neutral pions..

15. In practice… Significant episodes of the straggle for compensation in hadron calorimetry will be summarized and different methods will be compared. Recent progress aiming to differentiate and separately measure the shower products (interacting electromagnetically or strongly) will be discussed and technological solutions outlined

16. Compensation methods (mainly sampling calorimeters) Intrinsic compensation: Recover part of the “invisible energy” Decrease the electromagnetic contribution (often using composite passive materials) Off-line compensation: Weighting methods Multiple shower measurements (with 2 or more active media, selective to EM,etc)

17. High Z material as absorber Full compensation can be achieved with high Z material; large part of EM components will be deposited in absorber decreasing the EM energy deposition in active medium Tuning the thickness of the absorber and active layer High - absorber that can partially recover the invisible hadronic energy via nuclear and collisions processes.

18. 238U as passive, scintillator as active media. 238U: Absorber with high Z decreases EM response; Slow neutrons induce fission in the 238U, that compensates losses due to “invisible” energy Slow neutrons can be captured in the nucleus of 238U which emits a low energy γ’s and can further recover the “invisible” energy Scintillator: Slow neutrons loose their kinetic energy via elastic collisions with hydrogen in the scintillator (LAr - Fabjan, Willis, 1977)

19. Zeus U-scintillator Calorimeter Had EM

20. Response for e/h = 1 If e/h = 1 than: Hadron response linear Energy distribution “Poisson” Statistical fluctuations Constant term (calibration, non-linearity, etc Noise, etc

21. Tuning Pb thickness for e/  =1

22. So much about scintillator calorimeters: I will revisit later on… Now let’s turn to Si detectors in calorimetry: it so happened that such systems gave precise and interesting data on very detailed compensation effects…

23. 1983: Si-W EM prototype 24 Xo’s tungsten; 12 Si detectors (5x5cm) EM

24. SICAPO: Silicon Calorimeter Another hanging file reconfigurable calorimeter prototype

25. Large scale SICAPO test calorimeter The calorimeter vessel could accommodate: the Si mosaic detector planes and a number of absorbers between the detector planes The passive plates were W, Pb (High Z) as well as Fe, …,G10 (Low Z) (arranged in any desired configuration) The readout of this calorimeter consisted of 30 mosaic planes (of about 1600 cm 2 active area) each made of 400 silicon detectors. A detector had an area of about 4 cm 2, is 400  m thick, and operated at full depletion.

26. Support plate for Si detectors

27. Assembling the Si detectors

28. Tuning of absorbers for SICAPO The passive plates’ configuration could be arranged in order to achieve: local hardening effect (introducing thin low Z sheets near the detector’s planes) filtering effect (by using combinations of High and Low Z absorbers)

29. Hardening G10 plates inserted close to the detector planes….

30. Filtering PbFe–Si–PbFe configuration as a function of the thickness of Pb in the absorber (the overall absorber thickness, including the Fe plates is 23 mm).

31. Resolution for U-scint. Cal.

32. Evidence for Compensation in a Si Hadron Calorimeter E. Borchi, M. Bosetti, C. Leroy, S. Pensotti, A. Penzo, P.G. Rancoita, M. Rattagi, G. Terzi IEEE TRANS. ON NUCLEAR SCIENCE, 40 (1993)

33. Resolution vs sampling step

34. Linearity for Scintillator Cal.

35. Energy Resolution (for Scint. Cal.)

37. Offspring: PAMELA

38. Another example: in this case highly non-compensating In a quest for rad-hard materials as active parts for calorimetry, quartz fibers Only Cerenkov light, only (low energy) e+/-

39. The HF calorimeter Steel absorber with embedded fused-silica-core optical fibers where Cherenkov radiation forms the basis of signal generation. Thus, the detector is essentially sensitive only to the electromagnetic shower core and is highly non-compensating (e/h 5). Above Cherenkov threshold (E = 190 keV for electrons) they generate Cherenkov light, thereby rendering the calorimeter mostly sensitive to the electromagnetic component of showers.

40. CMS – HF: A full-scale technological benchmark Quartz Fiber Calorimeter ~ 1000 km quartz fibers 1 HF weights ~ 250 tons PMT readout (magn. field ~ 0 ) Co 60 source calibration ≤ 5%

41.  /e values for SPACAL and HF

42. Resolution of HF The electromagnetic energy resolution is dominated by photoelectron statistics and can be expressed in the customary form. The stochastic term a = 198% and the constant term b = 9%. The hadronic energy resolution is largely determined by the fluctuations in the neutral pion production in showers, and when it is expressed as in the electromagnetic case, a = 280% and b = 11%.

43. - Beam test results from a fine-sampling quartz fiber calorimeter for electron, photon and hadron detection - N. Akchurin et al.- Nucl.Instrum.Meth.A399:202-226,1997 - Test beam results of CMS quartz fibre calorimeter prototype and simulation of response to high-energy hadron jets - N. Akchurin et al. - Nucl.Instrum.Meth.A409:593- 597,1998 -On the differences between high-energy proton and pion showers and their signals in a non-compensating calorimeter - N. Akchurin et al. - Nucl.Instrum.Meth.A408:380-396,1998 CMS NOTE 2006/044 - Design, Performance, and Calibration of CMS Forward Calorimeter Wedges, G. Baiatian et al.

44. The challenge…. Mockett 1983 SLAC Summer Institute A technique is needed that is sensitive to the relative fraction of electromagnetic energy and hadronic energy deposited by the shower. This could be done hypothetically if the energy were sampled by two media: one which was sensitive to the beta equals one electrons and another which was sensitive to both the electrons and other charged particles. For example one sampler could be lucite which is sensitive only to the fast particles, while the other sampler could be scintillator. See also Erik Ramberg et al., Dave Winn et al., … ….and the DREAM…

45. Main theme: multiple measurements of every shower to suppress fluctuations Spatial changes in density of local energy deposit Fluctuations in EM fraction of total shower energy Binding energy losses from nuclear break-up fine spatial sampling with SciFi every 2mm clear fibers measuring only EM component of shower via Cherenkov light from electrons (E th = 0.25 MeV) measure MeV neutron component of shower. Like SPACAL Like HF Triple Readout DREAM = SPACAL + HF

46. 1)Muon detection with a dual-readout calorimeter. N. Akchurin, K. Carrell, J. Hauptman, H. Kim, H.P. Paar, A. Penzo, R. Thomas, R. Wigmans - Nucl.Instrum.Meth.A533:305-321,2004 2) Electron detection with a dual-readout calorimeter. N. Akchurin, K. Carrell, H. Kim, R. Thomas, R. Wigmans, J. Hauptman, H.P. Paar, A. Penzo - Nucl.Instrum.Meth.A536:29-51,2005 3) Hadron and jet detection with a dual-readout calorimeter. N. Akchurin, K. Carrell, J. Hauptman, H. Kim, H.P. Paar, A. Penzo, R. Thomas, R. Wigmans - Nucl.Instrum.Meth.A537:537-561,2005 4) Separation of scintillation and Cherenkov light in an optical calorimeter. N. Akchurin, O. Atramentov, K. Carrell, K.Z. Gumus, J. Hauptman, H. Kim, H.P. Paar, A. Penzo, R. Wigmans - Nucl.Instrum.Meth.A550:185-200,2005 5) Comparison of High-Energy Electromagnetic Shower Profiles Measured with Scintillation and Cherenkov Light. N. Akchurin, K. Carrell, J. Hauptman, H. Kim, A. Penzo, R. Thomas and R. Wigmans - Nucl.Instrum.Meth.A548:336-354,2005 DREAM Published Results (www.phys.ttu.edu/dream)

47. DREAM [Dual REAdout Module] prototype is 1.5 ton heavy Cell [basic element of detector] 2m long extruded copper rod, [4 mm x 4 mm]; 2.5mm hole contains 7 fibers:3 scintillator & 4 quartz(or acrylic plastic). In total, 5580 copper rods (1130Kg) and 90 km optical fibers. Composition (volume) Cu: S : Q : air = 69.3 : 9.4 :12.6 : 8.7 (%) Effective Rad. length (X 0 )=20.1mm;Moliere radius(r M )=20.35mm Nuclear Inter. length ( int )=200mm;10 int depth Cu. Filling fraction = 31.7%; Sampling fraction = 2.1% (S, Q fibers 0.8 mm  )

48. Fig. a : fiber bundles for read-out PMT; 38 bundles of fibers Fig b : front face of detector with rear end illuminated: shows 3 rings of honey-comb hexagonal structure..  Tower : readout unit Hexagonal shape with 270 cells (Fig. b); Readout 2 types of fibers to PMTs (PMT: Hamamatsu R580) (Fig. a)  Detector : 3 groups of towers (Fig. b) center(1), inner(6) & outer(12) rings; Signals of 19 towers routed to 38 PMT Effective radius 162 mm (0.8 int, 8 r M )

49. Test Beam Results c) d) a), b) energy distributions from scintillating and Cerenkov fibers for 100GeV single  - asymmetric, broad, smaller signal than e - typical features of non-comp. calorimeter. c) energy resolution (%) vs beam energy d) Scintillation signal response vs energy

50. After (Q+S)/E correction, the signal distributions are described well by gaussian distribution and energy resolution was dramatically improved. ( 12.3% resolution became 2.6% for 100GeV  beam). ( Fig. a & b) Energy resolution as a function of beam energy(Fig. c) are well described by E    a b E 1/2 ( b is related to sampling non-uniformity depending on impact point of the beam. ) c)

51. DREAM calibrated with 40 GeV e - into center of each tower, recover linear hadronic response up to 300 GeV for  - and “jets”

52. b. Method using the directionality of Cerenkov light Measure the light from both ends of fibers (F and B). B/F = ratio of light emitted in the backward and forward. Clear difference was found in B/F ratio between Cerenkov and scintillation light. Scintillation light is generated isotropically and only 20% difference in backward and forward signals. Cerenkov light in forward direction is ~6 times larger than in backward direction. B/F ratio for scintillator (a) and Cerenkov (b) signals generated by 80GeV electrons.

53. New issues and options (Light-Emitting) Active Media Study Xstals, Cerenkov radiators, neutron sensitive scintillators (Photon-Sensing) Detectors Develop SiPM (popular objective… … need good technology partners) (Time-Domain) Signal Processing Fast Pulse Shape digitizer

54. Compensating Calorimetry might be the art of compromise and balance… …and elegance instead of brute force, like…

55. Appareil à deux globes de verre inventorié dans les archives de l'Ecole polytechnique comme " appareil de Gay-Lussac " dans la catégorie des " appareils ayant trait à la chaleur "......it was never used for a real measurement....

56. Maybe go back to really old stuff? Provando e riprovando….