1. TRD 2011 Bari1 COSMIC-RAY MEASUREMENTS WITH TRD’S ON BALLOONS AND IN SPACE ACCHIEVEMENTS AND PROMISES Dietrich Müller University of Chicago USA TRD WORKSHOP BARI SEPTEMBER 14-16, 2011

2. TRD 2011 Bari2 OUTLINE Introduction Threshold TRD’s: Electron and Positron Measurements (TREE, HEAT, AMS) TRD’s for Energy Measurements of Cosmic-Ray Nuclei (CRN, TRACER, CREAM) Outlook

3. TRD 2011 Bari3 THRESHOLD TRD’s REJECTION OF PROTON AND PION BACKGROUND IN MEASUREMENTS OF ELECTRONS AND POSITRONS Expected relative abundances: e - /p ≤ 10 -2 e + /p ~ 10 -4 Required discrimination at least 10 -3 to 10 -5

4. TRD 2011 Bari4 TRADITIONAL COMBINATION TRD/SHOWER COUNTER provides independent electron- proton identification TRD: e-p rejection 10 2 to 10 3 E. M. Calorimeter: e-p rejection 10 2 to 10 3 (longitudinal) 10 2 (horizontal profile)

5. TRD 2011 Bari5 POSITRONS IN COSMIC RAYS Electrons and Positrons discovered in 1960’s in c.r. Direct acceleration in cosmic-ray sources possible for negative electrons but unlikely for positrons Interstellar secondary production: p+p collisions, leading to pions which decay into positrons and electrons at about equal proportions

6. TRD 2011 Bari6 EARLY MEASUREMENTS OF POSITRON FRACTION e + /(e + +e - ) (Magnet spectrometers with spark chambers on balloons) Positron Fraction, 1970’s

7. TRD 2011 Bari7 “TREE” INSTRUMENT (Chicago 1970’s) measures e + + e - Transition Radiation Detector (TRD): Proton rejection 100 Shower Counter (longitudinal profile) Proton rejection 100

8. TRD 2011 Bari8 POSITRON- FRACTION Müller & Tang, 1987 With Earth’s Magnetic Field As Charge Analyzer SURPRISE!

9. TRD 2011 Bari9 POSITRONS FROM EXOTIC SOURCES? Pair-production in pulsar magnetospheres? WIMPs as dark matter candidates: Annihilation of neutralinos leading to electron-positron pairs (and characteristic gamma rays)? Hadronic production in giant molecular clouds?

10. TRD 2011 Bari10 HEAT e +/- Electron/Positron Spectrometer High Energy Antimatter Telescope (1990’s) Chicago Michigan Indiana Irvine Penn State (D. Müller, P.I.) TRD Magnet Shower Counter (longitudinal) Total rejection: better than 10 5

11. TRD 2011 Bari11 The Positron Fraction, e + /(e + +e - ) (Measurements in the 1990’s)

12. TRD 2011 Bari12 68 GeV e+ PAMELA Launched 2006 Positron identification from magnet spectrometer plus imaging calorimeter

13. TRD 2011 Bari13 Low E positron ratio from PAMELA corrected for solar modulation

14. TRD 2011 Bari14 e + /e - pair production in nearby pulsar (GEMINGA)

15. TRD 2011 Bari15 e+/e- from 200 GeV neutralino

16. TRD 2011 Bari16 Contributions from background protons at level 2x10 -4 Note: cosmic-ray protons have harder energy spectrum than electrons M. Schubnell (Michigan) (2009)

17. TRD 2011 Bari17 Analysis by M. Schubnell (2009) 200 GeV neutralino Geminga pulsar Proton contamination

18. TRD 2011 Bari18 AMS: Alpha Magnetic Spectrometer (S. Ting and many collaborators) Flight on Space Station LAUNCH 2011

19. TRD 2011 Bari19 AMS “UPGRADE” 2010 0.87 Tesla 0.125 Tesla

20. TRD 2011 Bari20 COSMIC-RAY ENERGY MEASUREMENTS WITH TRD’s

21. TRD 2011 Bari21 COSMIC-RAY ENERGY MEASUREMENTS WITH TRD’s REQUIREMENTS: (1)Energy-dependent signal over large range of Lorentz- factors γ = E/mc 2

22. TRD 2011 Bari22 Radiators made from plastic fibers Previously used on CRN detector Calibrated at accelerators with singly charged particles [L‘Heureux et al., 1990, NIM A 295, 246, 1990] TRD energy response measured in Xenon gas proportional counters

23. TRD 2011 Bari23 COSMIC-RAY ENERGY MEASUREMENTS WITH TRD’s REQUIREMENTS: (1)Energy-dependent signal over large range of Lorentz- factors γ = E/mc 2 (2)Threshold at γ ≤ 1,000

24. TRD 2011 Bari24 Energy range determined by radiator structure (Swordy et al. 1982)

25. TRD 2011 Bari25 COSMIC-RAY ENERGY MEASUREMENTS WITH TRD’s REQUIREMENTS: (1)Energy-dependent signal over large range of Lorentz- factors γ = E/mc 2 (2)Threshold at γ ≤ 1,000 (3)Rejection of Low-E background

26. TRD 2011 Bari26 ICRC 2007 Merida dE/dx TRD ENERGY RESPONSE IS DEGENERATE LORENTZ FACTOR γ SIGNAL (arb. units) TRACER 2003 FLIGHT

27. TRD 2011 Bari27 COSMIC-RAY ENERGY MEASUREMENTS WITH TRD’s REQUIREMENTS: (1)Energy-dependent signal over large range of Lorentz- factors γ = E/mc 2 (2)Threshold at γ ≤ 1,000 (3)Rejection of Low-E background (4)Sufficient signal resolution

28. TRD 2011 Bari28 Relative signal fluctuations scale with 1/Z  Good energy resolution for heavier nuclei Acceptable resolution for nuclei heavier than boron (Z 2 =25) (Müller 2004)

29. TRD 2011 Bari29 P. Meyer, D. Müller S. Swordy J. L’Heureux (U. Chicago) “CRN” Flown on Space Shuttle 1985

30. TRD 2011 Bari30 TRACER Detector System (U. of Chicago) “Transition Radiation Array for Cosmic Energetic Radiation” Scintillator 1 Cherenkov 1 dE/dx Array TRD 4 Modules Scintillator 2 Cherenkov 2 2 m 1.2 m 1600 proportional tubes, 2 cm dia, 200 cm long Radiator

31. TRD 2011 Bari31 TRACER IS BIG: 5 m 2 ster Currently the largest balloon-borne cosmic-ray detector AND HEAVY: 5,000 lbs, 250 Watt, 1 Mbit/sec data

32. TRD 2011 Bari32 SCIENCE: Jojo Boyle, Project Scientist Maximo Ave Florian Gahbauer Joerg Hörandel Christian Höppner Masakatsu Ichimura Andreas Obermeier Andrew Romero-Wolf Several Undergraduate Students TECHNICAL STAFF: G.Kelderhouse, Proj. Engineer Casey Smith, Project Engineer David Pernick Richard Northrop Paul Waltz A All at the University of Chicago Dietrich Müller, P.I. THE TRACER TEAM

33. TRD 2011 Bari33 LAUNCH 2006

34. TRD 2011 Bari34

35. TRD 2011 Bari35

36. TRD 2011 Bari36 AT FLOAT 40 km altitude (3 mbar)

37. TRD 2011 Bari37 BALLOON FLIGHTS OF TRACER 2003 ANTARCTICA 14 days 2006 SWEDEN  CANADA 4.5 days OXYGEN (Z=8) to IRON (Z=26) BORON (Z=5) to IRON (Z=26)

38. TRD 2011 Bari38 CHARGE IDENTIFICATION E Z 2003 Correlation Scintillator vs Cerenkov Signals (square root) 2006 Correlation Z (top) vs Z (bottom)

39. TRD 2011 Bari39 TRACER Detector System “Transition Radiation Array for Cosmic Energetic Radiation” Scintillator 1 Cherenkov 1 dE/dx Array TRD 4 Modules Scintillator 2 Cherenkov 2 2 m 1.2 m 1600 proportional tubes, 2 cm dia, 200 cm long Radiator

40. TRD 2011 Bari40 ICRC 2007 Merida Cherenkov dE/dx TRD ENERGY RESPONSE: Acrylic Cherenkov Counter (γ < 10) Specific Ionization in Gas (4 < γ < 1000) Transition Radiation Detector (γ > 400) LORENTZ FACTOR γ SIGNAL (arb. units) TRACER 2003 FLIGHT

41. TRD 2011 Bari41 PROPERTIES OF PROPORTIONAL TUBE ARRAY TRACER has 16 single tube layers, 8 for dE/dx measurement, and 8 for dE/dx+TR Signals are immune to δ-ray effects No gas deterioration at balloon altitude No problem with corona discharge Dynamic range of signal readout ~ 10 4

42. TRD 2011 Bari42 Path length Δx i of particle through each tube must be accurately known: Uncertainty in total ttrack length is ~ 3%

43. TRD 2011 Bari43 ENERGY RESOLUTION vs. CHARGE 2006 Flight

44. TRD 2011 Bari44 Example: Neon Nuclei (2003 Flight) ENERGY MEASUREMENT: correlation dE/dx vs TR

45. TRD 2011 Bari45

46. TRD 2011 Bari46 DIFFERENTIAL ENERGY SPECTRUM NEON NUCLEI

47. TRD 2011 Bari47 May 12, 2009Müller: Pamela Workshop Rome47 Previous Results from Space (HEAO-3 and CRN)

48. TRD 2011 Bari48 Individual Energy Spectra from TRACER 2003

49. TRD 2011 Bari49 “CNO GROUP” (TRACER: oxygen only) “IRON GROUP” (TRACER: iron only) COMPARISON WITH AIR SHOWER INTERPRETATIONS

50. TRD 2011 Bari50 MEASURED B/C RATIO TRACER 2006

51. TRD 2011 Bari51 “TRACER-PLUS” IMPROVE CHERENKOV READOUT ADD AEROGEL CHERENKOV WHAT’S NEXT ?

52. TRD 2011 Bari52 UNDER CONSTRUCTION: TRD FOR CREAM INSTRUMENT Balloon Flight 2012 (?)

53. TRD 2011 Bari53 CREAM TRD: HIGH THRESHOLD: LORENTZ FACTORS OF SECERAL 10 4 REJECTION OF LOW-ENERGY PARTICLES?

54. TRD 2011 Bari54 SUMMARY AND CONCLUSIONS Threshold TRD’s have been successful in several flights on balloon to detect cosmic-ray electrons and positrons. Anomalous increase of the positron fraction observed by HEAT and PAMELA should be confirmed by AMS-02. TRD’s in space and on balloons have determined the energy spectra of cosmic ray nuclei to 10 14 eV/nucleus and beyond. Current measurements are limited by statistics, not by saturation of TR response. New observations could approach the cosmic-ray “knee” above 10 15 eV.