Cosmic Rays at 120,000 feet above Antarctica The Advanced Thin Ionization Calorimeter (ATIC) Experiment

Transcription

1 Cosmic Rays at 120,000 feet above Antarctica The Advanced Thin Ionization Calorimeter (ATIC) Experiment ATIC is a ~4,000 pound experiment, carried to the near-space environment (~23 miles) by a large volume (sufficient to fill a football stadium) helium filled balloon for days over the continent of Antarctica, to measure the charge composition and energy spectra of primary cosmic rays over the energy range from about to ev in order to investigate the relationship between high energy galactic matter and remnant supernova shock waves. Louisiana State University, Marshall Space Flight Center, University of Maryland, Southern University, Moscow State University, Max Plank Institute - Lindau LSU 11/15/05 ATIC Science - McMurdo 1

2 Cosmic Rays were discovered less than a hundred years ago In 1912 Victor Hess became the first cosmic ray balloonist Measured an increase in the background radiation as a function of altitude, but only up to about 17,000 feet Received the 1936 Nobel Prize in Physics for this work Data measured in 2003 by a simple 400 gm student-built sounding balloon payload. LSU 11/15/05 ATIC Science - McMurdo 2

3 Understanding the nature of cosmic rays Initial thoughts (1920 s) were that this mysterious radiation was some form of high energy photon Hence the name Cosmic RAYS In the 1930 s this viewpoint changed with the understanding that cosmic ray are mostly composed of high energy charged particles Effects due to Earth s magnetic field (east-west; latitude) Discovery of positron and muon Birth of elementary particle physics Until the advent of particle accelerators in the mid s, the cosmic ray beam was used to develop the theory of elementary particles. LSU 11/15/05 ATIC Science - McMurdo 3

4 The Space Age provided new tools In the 1960 s space probes began identifying individual cosmic ray components Sources from the Sun as well as outside our Solar System Electrons, protons and other elements were identified Began measuring the energy spectrum Measurements of the energy density gave first clue about the galactic cosmic ray (GCR) source GCR energy density is roughly equivalent to the energy released by a supernova every 50 to 100 years 70 s, 80 s and 90 s pushed the frontiers in both charge and energy Antiprotons, elements up to Uranium, energies to ~10 21 ev LSU 11/15/05 ATIC Science - McMurdo 4

5 Cosmic Rays extend over a large charge and energy range Tevatron, LHC Max Energy LSU 11/15/05 ATIC Science - McMurdo 5

6 Fundamental questions remain unanswered! Where does this galactic matter come from? How does it get accelerated to such high energies? LSU 11/15/05 ATIC Science - McMurdo 6

7 Recent Chandra X-ray observations of Tycho s Supernova Remnant Supernova remnant observed by Tycho Brahe in 1572 Outward moving shock wave indicated by high energy electrons (blue) Hot stellar debris (red & green) keeping pace with outer shock, contrary to standard theory Warren & Hughes et al. (2005) suggest that a large fraction of outward shock energy is accelerating atomic nuclei to speeds approaching the speed of light LSU 11/15/05 ATIC Science - McMurdo 7

8 Standard Model of Cosmic Ray Acceleration Supernova shock waves may accelerate cosmic rays via first order Fermi process Model predicts an upper energy limit of E ~ Z x ev ATIC Energy Range LSU 11/15/05 ATIC Science - McMurdo 8

9 ATIC Program Summary Investigate relationship between Supernova Remnant (SNR) Shocks and high energy galactic cosmic rays (GCR) Multiple flights needed to obtain necessary exposure ATIC-1 test flight during ATIC-2 during days exposure ATIC-3 scheduled for season Scientific Ballooning programs at Universities provides unique education experiences for the future aerospace workforce ATIC involved over 45 LSU & SU students Are SNR the cosmic accelerators for GCR Measure GCR Hydrogen to Nickel from 50 GeV to ~100 TeV total energy Determine spectral differences Study High Energy Electron Spectrum Flight test pixilated Silicon detector LSU 11/15/05 ATIC Science - McMurdo 9

10 ATIC Instrument Summary Measure charge, energy and number Ionization Calorimetry only practical method to measure high energy light elements Silicon Matrix (Si) has 4,480 pixels to measure GCR charge in presence of shower backscatter Graphite Target to interact the primary particle and generate fragments that, in turn, will start an electromagnetic cascade. Also provides some backscatter shielding Plastic scintillator hodoscopes (S1, S2, S3), embedded in Carbon target, provides event trigger plus charge & trajectory information Fully active calorimeter includes 400 Bismuth Germinate (BGO) crystals to foster and measure the nuclear - electromagnetic cascade showers Geometrical factor: 0.24 m 2 sr (S1 S3 BGO6) LSU 11/15/05 ATIC Science - McMurdo 10

11 Silicon Matrix Detector Si-Matrix: 4480 pixels each 2 cm x 1.5 cm mounted on offset ladders; 0.95 m x 1.05 m area; 16 bit ADC; CR-1 ASIC s; sparsified readout. LSU 11/15/05 ATIC Science - McMurdo 11

12 Plastic Scintillator Hodoscopes Scintillators: 3 x-y layers; 2 cm x 1 cm cross section; Bicron BC-408; Hamamatsu R5611 pmts both ends; two gain ranges; ACE ASIC. S1 336 channels; S2 280 channels; S3 192 channels; First level trigger: S1-S3 LSU 11/15/05 ATIC Science - McMurdo 12

13 BGO Calorimeter Calorimeter: 10 layers ; 2.5 cm x 2.5 cm x 25 cm BGO crystals, 40 per layer, each crystal viewed by R5611 pmt; three gain ranges; ACE ASIC; 1200 channels. LSU 11/15/05 ATIC Science - McMurdo 13

14 On-board Control & Data System Data System: All data recorded on-board; 150 Gbyte disk; LOS data rate 330 kbps; TDRSS data rate 6+ kbps; Underflight capability (not used). Housekeeping: Temperature, Pressure, Voltage, Current, Rates, Software Status, Disk status Command Capability: Power on / off; Trigger type; Thresholds; Pre-scaler; Housekeeping frequency; LOS data rate, Reboot nodes; High Volt settings; Data collection on / off LSU 11/15/05 ATIC Science - McMurdo 14

15 ATIC has been extensively simulated An example of a proton shower in the McMurdo flight configuration Trajectory resolution in S1 calculated from the BGO shower profile for 1 TeV protons. Energy dependence of the proton mean energy deposit and the energy resolution. Energy deposition in 20 cm depth BGO calorimeter for 10 2, 5x10 2, 10 3, 10 4, and 10 5 GeV protons. LSU 11/15/05 ATIC Science - McMurdo 15

16 Particle incident energy determined from shower profile in BGO calorimeter 8 TeV Total Energy Event Shower profiles for protons of indicated energy. Open symbols are simulations & filled symbols are flight data. LSU 11/15/05 ATIC Science - McMurdo 16

17 High altitude winds are circumpolar during summer LSU 11/15/05 ATIC Science - McMurdo 17

18 Assembly of ATIC at Willy Attach the upper support structure Assemble / test detector stack and mount in lower support structure Install Kelar pressure vessel shells Solar arrays provide power & the payload is rolled out the hanger door Attach the thermal protection ATIC is transported to the insulation launch pad LSU 11/15/05 ATIC Science - McMurdo 18

19 Finally everything was ready for launch LSU 11/15/05 ATIC Science - McMurdo 19

20 ATIC Test Flight from McMurdo 43.5 Gbytes Recorded Data 26,100,000 Cosmic Ray triggers 1,300,000 Calibration records 742,000 Housekeeping records 18,300 Rate records Low Energy Trigger > 10 GeV for protons >70% Live-time >90% of channels operating nominally Internal pressure (~8 psi) held constant Internal Temperature: C Altitude: 37 ± 1.5 km Launch: 12/28/00 04:25 UTC Begin Science: 12/29/00 03:54 UTC End Science: 01/12/01 20:33 UTC Termination: 01/13/01 03:56 UTC Recovery: 01/23/01; 01/25/01 LSU 11/15/05 ATIC Science - McMurdo 20

21 First ATIC Science Flight from McMurdo Launch: 12/29/02 04:59 UTC Begin Science: 12/30/02 05:40 UTC End Science: 01/18/03 01:32 UTC Termination: 01/18/03 02:01 UTC Recovery: 01/28/03; 01/30/03 65 Gbytes Recorded Data 16,900,000 Cosmic Ray triggers 1,600,000 Calibration records 184,000 Housekeeping records 26,000 Rate records High Energy Trigger > 75 GeV for protons >96% Live-time >90% of channels operating nominally Internal pressure (~8 psi) decreased slightly (~0.7 psi) for 1 st 10 days then held constant Internal Temperature: C Altitude: 36.5 ± 1.5 km LSU 11/15/05 ATIC Science - McMurdo 21

22 Flight and Recovery Flight path for ATIC-1 (2000) and ATIC-2 (2002) The good ATIC-1 landing on 1/13/01 (left) and the not so good landing of ATIC-2 on 1/18/03 (right) ATIC is designed to be disassembled in the field and recovered with Twin Otters. Two recovery flights are necessary to return all the ATIC components. Pictures show 1 st recovery flight of ATIC-1 LSU 11/15/05 ATIC Science - McMurdo 22

23 Steps in the data analysis Determine incident particle charge and energy Count the number of each species and bin in energies to produce an energy deposit spectrum Deconvolve the instrument response to produce an incident energy spectrum Unfold the transforming effects that occur as the GCR diffuse around the galaxy for millions of years. Use Leaky Box model of cosmic ray confinement Compare with expectations of SNR shock acceleration model LSU 11/15/05 ATIC Science - McMurdo 23

24 An example of event reconstruction Primary (He) Albedo x, cm z, cm y, cm y, cm z, cm x, cm LSU 11/15/05 ATIC Science - McMurdo 24

25 Charge resolution in the p-he group EBGO > 50 GeV EBGO > 500 GeV EBGO > 5 TeV LSU 11/15/05 ATIC Science - McMurdo 25

26 Charge resolution in the CNO-group EBGO > 50 GeV EBGO > 250 GeV EBGO > 1 TeV C O LSU 11/15/05 ATIC Science - McMurdo 26

27 Charge resolution in the Ne-Si group EBGO > 50 GeV EBGO > 250 GeV EBGO > 1 TeV Ne Mg Si S LSU 11/15/05 ATIC Science - McMurdo 27

28 Charge resolution in the Fe group EBGO > 50 GeV EBGO > 250 GeV EBGO > 1 TeV Fe S Ca LSU 11/15/05 ATIC Science - McMurdo 28

29 Deconvolution Primary Energy Spectra (E 0 ) Instrument + = Response Measured Energy Deposit Spectra (E d ) (must solve the inverse problem) A(E 0,E d ) = response matrix Obtained from FLUKA model of instrument See K.E. Batkov et al., 29 th ICRC, 2005 LSU 11/15/05 ATIC Science - McMurdo 29

30 Preliminary ATIC-2 Energy spectra for H and He Proton (top) and Helium (bottom) Energy Deposit spectra from the ATIC-2 flight used as the input to the first order de-convolution calculation. De-convolved Proton and Helium spectrum compared with other measurements and propagation calculations using the Leaky Box model (1, 3) and a diffusion model with weak reacceleration (2, 4). LSU 11/15/05 ATIC Science - McMurdo 30

31 Energy spectra of abundant nuclei C C O/10 Mg Mg O Si Si/10 Ne/100 Ne Fe Fe/100 HEAO-3-C2 ATIC-2 CRN LSU 11/15/05 ATIC Science - McMurdo 31

32 Electrons might provide additional information about the GCR source High energy electrons have a high energy loss rate Lifetime of ~10 5 years for >1 TeV electrons Transport of GCR through interstellar space is a diffusive process Implies that source of high energy electrons are < 1 kpc away Know that electrons are accelerated in SNR Only a handful of SNR meet the lifetime & distance criteria Kobayashi et al (2004) calculations show structure in electron spectrum at high energy LSU 11/15/05 ATIC Science - McMurdo 32

33 ATIC is able to identify GCR electrons Possible bump at GeV seen by both Kobayashi and ATIC may be a source signature? Long duration ATIC flight this season will be critical to resolving this issue e LSU 11/15/05 ATIC Science - McMurdo 33

34 Conclusions Deconvolution Algorithm is still preliminary Initial analysis of heavy ions indicate: Simple Leaky Box not good representation Diffusion model in which λ esc hardens with increasing energy gives better fit. For the diffusion model parameterization, the source energy spectral indices for H and He must be different Electrons show a bump in the GeV range Possibly THE most important result from ATIC ATIC has had two flights in Antarctica and is looking for its third Need at least two times around (~30 days) to confirm the electron results and collect the required heavy ion statistics. LSU 11/15/05 ATIC Science - McMurdo 34

35 Our enthusiastic crew is looking forward to another successful ATIC flight! LSU 11/15/05 ATIC Science - McMurdo 35