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La missione PAMELA: primi risultati scientifici

XCIV Congresso Nazionale Societ à Italiana di Fisica Genova 22-27 Settembre, 2008. La missione PAMELA: primi risultati scientifici. Paolo Papini INFN – Firenze a nome della collaborazione PAMELA. Italy :. CNR, Florence. Bari. Florence. Frascati. Naples. Rome. Trieste. Russia :.

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La missione PAMELA: primi risultati scientifici

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  1. XCIV Congresso Nazionale Società Italiana di Fisica Genova 22-27 Settembre, 2008 La missione PAMELA:primi risultati scientifici Paolo Papini INFN – Firenze a nome della collaborazione PAMELA

  2. Italy: CNR, Florence Bari Florence Frascati Naples Rome Trieste Russia: Moscow St. Petersburg Germany: Sweden: Siegen KTH, Stockholm Tha PAMELA collaboration

  3. PAMELA as a Space Observatory at 1 AUPayload forAntimatterMatterExploration and Light Nuclei Astrophysics • Search for dark matter annihilation • Search for antihelium (primordial antimatter)‏ • Search for new Matter in the Universe (Strangelets?) • Study of cosmic-ray propagation • Study of solar physics and solar modulation • Study of terrestrial magnetosphere • Study of high energy electron spectrum (local sources?)

  4. PAMELA prehistory Astromag/WiZard project (PAMELA precursor) on board of the Space Station FreedomCANCELED Balloon-borne experiments: MASS-89,91 TS-93 CAPRICE-94,97,98 Space experiments*: NINA-1,2 SILEYE-1,2,3 ALTEA (*study of low energy nuclei and space radiation environment) C 98 C 94 C 97 M 91 M 89 TS 93 NINA-2 NINA-1 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 - - - - X SILEYE-3 SILEYE-1 SILEYE-2 ASTROMAG ALTEA

  5. PAMELA history 1996: PAMELA proposal 22.12.1998: agreement between RSA (Russian Space Agency) and INFN to build and launch PAMELA. Three models required by the RSA: Mass-Dimensional and Thermal Model (MDTM) Technological Model (TM) Flight Model (FM)  Starts PAMELA construction 2001: change of the satellite complete redefinition of mechanics 2006: flight!!! 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

  6. PAMELA nominal capabilities Energy range Antiprotons 80 MeV - 150 GeV Positrons50 MeV – 270 GeV Electronsup to 400 GeV Protons up to 700 GeV Electrons+positronsup to 2 TeV (from calorimeter) Light Nuclei up to 200 GeV/n He/Be/C AntiNuclei search • Simultaneous measurement of many cosmic-ray species • New energy range • Unprecedented statistics

  7. PAMELA detectors Main requirements  high-sensitivity antiparticle identification and precise momentum measure + - Time-Of-Flight plastic scintillators + PMT: • Trigger • Albedo rejection; • Mass identification up to 1 GeV; - Charge identification from dE/dX. Electromagnetic calorimeter W/Si sampling (16.3 X0, 0.6 λI) • Discrimination e+ / p, anti-p / e- (shower topology) • Direct E measurement for e- Neutron detector plastic scintillators + PMT: • High-energy e/h discrimination GF: 21.5 cm2 sr Mass: 470 kg Size: 130x70x70 cm3 Power Budget: 360W Spectrometer microstrip silicon tracking system+ permanent magnet It provides: - Magnetic rigidity R = pc/Ze • Charge sign • Charge value from dE/dx

  8. PAMELA milestones • Launch from Baikonur: June 15th 2006, 0800 UTC. • Power On: June 21st 2006, 0300 UTC. • Detectors operated as expected after launch • PAMELA in continuous data-taking mode since commissioning phase ended on July 11th 2006 • As of ~ now: • more than 2 years of data taking (~73% live-time) • ~10 TByte of raw data downlinked • >109 triggers recorded and under analysis

  9. Resurs-DK1 satellite + orbit • Resurs-DK1: multi-spectral imaging of earth’s surface • PAMELA mounted inside a pressurized container • Lifetime >3 years (assisted) • Data transmitted to NTsOMZ, Moscow via high-speed radio downlink. ~16 GB per day • Quasi-polar and elliptical orbit (70.0°, 350 km - 600 km) • Traverses the South Atlantic Anomaly • Crosses the outer (electron) Van Allen belt at south pole PAMELA Resurs-DK1 Mass: 6.7 tonnes Height: 7.4 m Solar array area: 36 m2 350 km 70o SAA 610 km ~90 mins

  10. Analysis of a PAMELA orbit S1 S2 S3 SAA NP SP EQ EQ orbit 3752 orbit 3753 95 min orbit 3751 Low energy particles stops inside the apparatus  Counting rates: S1>S2>S3 Outer radiation belt Download @orbit 3754 – 15/02/2007 07:35:00 MWT S1 S2 S3 Inner radiation belt (SAA) Ratemeters Independent from trigger

  11. Principle of operation Track reconstruction • Measured @ground with protons of known momentum •  MDR~1TV • Cross-check in flight with protons (alignment) and electrons (energy from calorimeter) Iterative c2 minimization as a function of track state-vector components a Magnetic deflection |η| = 1/R R = pc/Ze magnetic rigidity sR/R = sh/h Maximum Detectable Rigidity (MDR) def: @ R=MDR sR/R=1 MDR = 1/sh

  12. Principle of operation track average 4He B,C 3He Be d (saturation) p Li e± 1st plane Z measurement Bethe Bloch ionization energy-loss of heavy (M>>me) charged particles

  13. Principle of operation Velocity measurement • Particle identification @ low energy • Identify albedo (up-ward going particles b < 0 ) •  NB! They mimic antimatter!

  14. Principle of operation Electron/hadron separation • Interaction topology • e/h separation • Energy measurement of electrons and positrons • (~full shower containment) hadron (19GV) electron (17GV) + NEUTRONS!!

  15. Flight data: 0.171 GV positron Flight data: 0.169 GV electron

  16. 32.3 GV positron

  17. 36 GeV/c interacting proton

  18. Flight data: 0.632 GeV/c antiproton annihilation

  19. Flight data: 0.763 GeV/c antiproton annihilation

  20. Nuclei

  21. NB! still large discrepancies among different primary flux measurements Galactic H spectra Preliminary!! Very high statistics over a wide energy range  Precise measurement of spectral shape  Possibility to study time variations and transient phenomena (statistical errors only) Power-law fit: ~ E-g g~ 2.76 for Z=1 • Proton of primary origin • Diffusive shock-wave acceleration in SNRs • Local spectrum: • injection spectrum  galactic propagation • Local primary spectral shape: • study of particle acceleration mechanism LBM ->

  22. Geomagnetic cutoff (GV/c) 0.4 to 0.5 1.0 to 1.5 1.5 to 2.0 2 to 4 4 to 7 7 to 10 10 to 14 > 14 Geomagnetic cutoff Preliminary!! (statistical errors only) Magnetic poles ( galactic protons) Secondary reentrant-albedo protons Magnetic equator • Up-ward going albedo excluded • SAA excluded

  23. Preliminary Results B/C Preliminary Calorimeter based charge identification!

  24. Solar modulation Interstellar spectrum PAMELA Ground neutron monitor sun-spot number Preliminary!! (statistical errors only) Increasing GCR flux July 2006 August 2007 February 2008 Decreasing solar activity

  25. Antiprotoni

  26. S1 CARD CAT S2 . TOF TRK CAS S3 CAL S4 ND High-energy antiproton analysis Basic requirements: • Clean pattern inside the apparatus • single track inside TRK • no multiple hits in S1+S2 • no activity in CARD+CAT • Minimal track requirements • energy-dependent cut on track c2 (~95% efficiency) • consistency among TRK, TOF and CAL spatial information • Galactic particle • measured rigidity above geomagnetic cutoff • down-ward going particle (no albedo)

  27. electron (17GV) Antiproton (19GV) 1 GV 5 GV Antiproton identification • dE/dx vs R (S1,S2,TRK) and b vs R proton-concistency cuts • electron-rejection cuts based on calorimeter-pattern topology -1  Z  +1 p (+ e+) p e-(+ p-bar) “spillover” p p-bar

  28. Proton spillover background Minimal track requirements MDR > 850 GV • Strong track requirements: • strict constraints on c2 (~75% efficiency) • rejected tracks with low-resolution clusters along the trajectory • - faulty strips (high noise) • - d-rays (high signal and multiplicity)

  29. 10 GV 50 GV High-energy antiproton selection p p-bar

  30. 10 GV 50 GV High-energy antiproton selection p p-bar R < MDR/10

  31. Positroni

  32. Positron selection with calorimeter p (non-int) p (int) • The main difficulty for the positron measurement is the interacting-proton background: • fluctuations in hadronic shower development p0 ggmight mimic pure e.m. showers • proton spectrum harder than positron  p/e+ increase for increasing energy e- p (non-int) e+ p (int) Fraction of charge released along the calorimeter track (left, hit, right) Rigidity: 20-30 GV

  33. Positron identification Energy-rigidity match e- ( e+ ) Energy measured in Calo/ Deflection in Tracker (MIP/GV)  ‘electrons’  ‘hadrons’ p-bar p

  34. Positron selection with calorimeter Rigidity: 20-30 GV e- e+ p Preliminary + Fraction of charge released along the calorimeter track (left, hit, right) • Energy-momentum match • Starting point of shower

  35. Positron selection with calorimeter Fraction of charge released along the calorimeter track (left, hit, right) Flight data: rigidity: 20-30 GV Test beam data Momentum: 50GeV/c e- e- e- p e+ e+ p • Energy-momentum match • Starting point of shower

  36. Positron selection Rigidity: 20-30 GV Fraction of charge released along the calorimeter track (left, hit, right) Neutrons detected by ND e- e- p e+ e+ p • Energy-momentum match • Starting point of shower

  37. Positron selection Energy loss in silicon tracker detectors: • Top: positive (mostly p) and negative events (mostly e-) • Bottom: positive events identified as p and e+ by trasversal profile method p e- p e- p e+ p e+ Rigidity: 10-15 GV Rigidity: 15-20 GV

  38. Proton background evaluation Preliminary!! Rigidity: 6-8 GV e- Fraction of charge released along the calorimeter track (left, hit, right) + Constraints on: e+ Energy-momentum match p Shower starting-point p

  39. Positron to Electron Fraction Charge sign dependent solar modulation End 2007: ~20 000 positrons total

  40. Electron to positron ratio Preliminary e-/e+ Rigidity (GV) U.W. Langner, M.S. Potgieter, Advances in Space Research 34 (2004)

  41. Fisica solare

  42. Increase of low energy component December 13th 2006 event from 2006-12-1 to 2006-12-4

  43. Increase of low energy component December 13th 2006 event from 2006-12-1 to 2006-12-4 from 2006-12-13 00:23:02 to 2006-12-13 02:57:46

  44. Increase of low energy component December 13th 2006 event from 2006-12-1 to 2006-12-4 from 2006-12-13 00:23:02 to 2006-12-13 02:57:46 from 2006-12-13 02:57:46 to 2006-12-13 03:49:09

  45. Decrease of high energy component Increase of low energy component Increase of low energy component December 13th 2006 event from 2006-12-1 to 2006-12-4 from 2006-12-13 00:23:02 to 2006-12-13 02:57:46 from 2006-12-13 02:57:46 to 2006-12-13 03:49:09 from 2006-12-13 03:49:09 to 2006-12-13 04:32:56

  46. Increase of low energy component December 13th 2006 event from 2006-12-1 to 2006-12-4 from 2006-12-13 00:23:02 to 2006-12-13 02:57:46 from 2006-12-13 02:57:46 to 2006-12-13 03:49:09 from 2006-12-13 03:49:09 to 2006-12-13 04:32:56 from 2006-12-13 04:32:56 to 2006-12-13 04:59:16

  47. Increase of low energy component December 13th 2006 event from 2006-12-1 to 2006-12-4 from 2006-12-13 00:23:02 to 2006-12-13 02:57:46 from 2006-12-13 02:57:46 to 2006-12-13 03:49:09 from 2006-12-13 03:49:09 to 2006-12-13 04:32:56 from 2006-12-13 04:32:56 to 2006-12-13 04:59:16 from 2006-12-13 08:17:54 to 2006-12-13 09:17:34

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