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Search for rare signals and CR flux measurements: background rejection and Montecarlo simulations

Search for rare signals and CR flux measurements: background rejection and Montecarlo simulations. Roberta Sparvoli Rome “Tor Vergata” University and INFN. Outline of the lectures. Lecture 1: Importance of rare signals in CR physics Detector strategies “Existed” and “existing” detectors

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Search for rare signals and CR flux measurements: background rejection and Montecarlo simulations

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  1. Search for rare signals and CR flux measurements:background rejection and Montecarlo simulations Roberta Sparvoli Rome “Tor Vergata” University and INFN

  2. Outline of the lectures • Lecture 1: • Importance of rare signals in CR physics • Detector strategies • “Existed” and “existing” detectors • Particle ID R. Sparvoli – MAPS 2009 - Perugia

  3. Outline of the lectures • Lecture 2: • Sources of background and their rejection • Efficiencies & Contaminations • Absolute fluxes • Conclusions Most of practical examples and results will be taken by the PAMELA experiment ! R. Sparvoli – MAPS 2009 - Perugia

  4. Lecture 1:Importance of rare signals incosmic ray physics R. Sparvoli – MAPS 2009 - Perugia

  5. Everything starts with … R. Sparvoli – MAPS 2009 - Perugia

  6. Evaporation of primordial black holes Anti-nucleosyntesis WIMP dark-matter annihilation in the galactic halo Background: CR interaction with ISM CR + ISM  p-bar + … and various ideas of theoretical interpretations R. Sparvoli – MAPS 2009 - Perugia

  7. Antimatter in early universe • The early Universe was a hot expanding plasma with equal number of baryons, antibaryons and photons. In thermal equilibrium the two-ways reaction was: • B + anti-B g + g • As the Universe expands, the density of particles and antiparticles falls, annihilation process ceases, effectively freezing the ratio: • - baryon/photon = antibaryon/photon ~ 10-18. • - Annihilation catastrophe. • Instead, in the present real Universe: • Baryon/photon ~ 6 * 10-10 (from direct observ. & microwave background); • Antibaryon/baryon < 10-4. R. Sparvoli – MAPS 2009 - Perugia

  8. Sakharov criteria • To account for the predominance of matter over antimatter, Sakharov (1967) pointed out the necessary conditions occurring in the Early Universe: • B violating interactions; • non-equilibrium situation; • CP and C violation. GUT theories ? Leptogenesys ? The processes really responsible are not presently understood! R. Sparvoli – MAPS 2009 - Perugia

  9. What about the observations? • Indirect -> • By measuring the spectrum of the Cosmic Diffuse Gamma emission • By searching for distortions of the Cosmic Microwave Background • Direct -> • By searching for Antinuclei • By measuring anti-p and e+ energy spectra BALLOONS / PAMELA / AMS R. Sparvoli – MAPS 2009 - Perugia

  10. Direct searches: current status • Antiprotons: DETECTED! secondary production • PCR+HISM • PCR+HeISM p + anti-psecondary antiprotons • aCR+HISM • aCR+HeISM • Positrons: DETECTED! secondary production • PCR+ ISM • NCR+ISMp+ -> m+ -> e+secondary positrons • Anti-nuclei: never detected ! • They would be the real signature of antistars because their production by “spallation” is negligible R. Sparvoli – MAPS 2009 - Perugia

  11. Antimatter Search: current limits R. Sparvoli – MAPS 2009 - Perugia

  12. CMB Large Scale Structure Rotation curves of galaxies SN Ia Galaxy clusters Lensing Bertone, Hooper & Silk, hep-ph/0404175, Bergstrom, hep-ph/0002126, Jungman et al, hep-ph/9506380 Dark Matter searches • Evidence for the existence of an unseen, “dark”, component in the energy density of the Universe comes from several independent observations at different length scales: R. Sparvoli – MAPS 2009 - Perugia

  13. tot = 1.0030.010 m ~ 0.22 [b=0.04]  ~ 0.74 Most of matter of non-baryonic nature and therefore “dark” ! The “Concordance Model” of cosmology The “concordance model” of big bang cosmology attempts to explain cosmic microwave background observations, as well as large scale structure observations and supernovae observations of the accelerating expansion of the universe. R. Sparvoli – MAPS 2009 - Perugia

  14. Different data: • WD supernovae • CMBR • Matter surveys • all agree • at one point R. Sparvoli – MAPS 2009 - Perugia

  15. Energy budget of the universe Dark Matter: 30% Dark Energy: 65% 22 % R. Sparvoli – MAPS 2009 - Perugia 74 %

  16. DM candidates: WIMP’s !SUSY particles ? R. Sparvoli – MAPS 2009 - Perugia

  17. R. Sparvoli – MAPS 2009 - Perugia

  18. SIGNALS from RELIC WIMPs • Direct searches:elastic scattering of a WIMP off detector nuclei • Measure of the recoil energy Indirect detection:in cosmic radiation • signals due to annihilation of accumulated cc in the centre of celestial bodies (Earth and Sun)  neutrino flux • signals due to cc annihilation in the galactic halo •  neutrinos •  gamma-rays •  antiprotons, positrons, antideuterons R. Sparvoli – MAPS 2009 - Perugia

  19. R. Sparvoli – MAPS 2009 - Perugia

  20. Contemporary measurements of primary and secondary CR elements • Many things about CRs are known, but many others still remain uncertain. • A satisfactory model of propagation of CR in the Galaxy is not yet fully established. Different mechanisms play a role in the acceleration, propagation, diffusion, but the correct balance among them is still under debate. R. Sparvoli – MAPS 2009 - Perugia

  21. For exotic physics searches • A really CRITICAL point ! • The effective possibility to disentangle exotic signal from pure secondary production depends strongly on the precise knowledge of the parameters which regulate the diffusion of cosmic rays in the Galaxy. • Still uncertainties in the data (and in the cross sections !!) put limits on the interpretations. R. Sparvoli – MAPS 2009 - Perugia

  22. Antiproton flux B/C Ratio AstrophysicB/C constraints Nuclear cross sections!! Secondaries/primaries to constrain propagation parameters D. Maurin, F. Donato R. Taillet and P.Salati ApJ, 555, 585, 2001 [astro-ph/0101231] F. Donato et.al, ApJ, 563, 172, 2001 [astro-ph/0103150] R. Sparvoli – MAPS 2009 - Perugia

  23. Lecture 1:Detector strategies R. Sparvoli – MAPS 2009 - Perugia

  24. Redundance • To search for rare particles in CR, an apparatus must have redundant information coming from its different subdetectors. • Only in this way it is possible to discriminate between the signal (very weak) and the background (very strong) •  Rare particle detectors are composite R. Sparvoli – MAPS 2009 - Perugia

  25. Antimatter • Current values in CR: • e+/(e+ + e-) ~ 10% • antip/p ~ 10-4 Background limits: e+/p < 10-4 (> 10 GeV) antip/e < 10-2 R. Sparvoli – MAPS 2009 - Perugia

  26. Definitions • Efficiency = n. good events recognized good n. good events • Contamination = n. bad events recognized good n. bad events • Rejection factor = Efficiency • Contamination High rejection factors needed ! R. Sparvoli – MAPS 2009 - Perugia

  27. Detector strategy: sign of the charge • Main task: determine the sign of the charge •  deflection in a magnetic field Charge of opposite sign would be deflected in opposite directions R. Sparvoli – MAPS 2009 - Perugia

  28. Magnetic spectrometers • Magnetic field: it can be produced by a permanent magnet or by a superconducting magnet. • For balloon missions: a superconducting magnet can be advantageous (intense field, no He evaporations problems) • For satellite/space stations missions: the problem of He evaporation can shorten the lifetime  permanent more practical. R. Sparvoli – MAPS 2009 - Perugia

  29. Magnetic spectrometers • Tracking system: it must lie inside the magnet, so to reconstruct – besides the charge - the curvature radius r. • In a magnetic field: • r B = mv/Ze = p/Ze = R • Quantity measured in a spectrometer: • R (rigidity) = momentum/charge R. Sparvoli – MAPS 2009 - Perugia

  30. Tracking systems • Must be very precise, since the curvature measurement error (DR) depends on the spatial resolution and on the number of measurements along the track. • Maximum Detectable Rigidity (MDR): • MDR = DR/R = 1 Among the most used are Drift Chambers and Silicon detectors (strip pitch can be tuned to the desired resolution  easily a few microns) R. Sparvoli – MAPS 2009 - Perugia

  31. mult. scatt. spat. resol. X MDR ~ 1 TV Momentum resolution and MDRex. PAMELA tracking system magnetic rigidity R = |pc/Z| magnetic deflection η = 1/R = |Z/pc| The higher the magnetic field strength, and the finer the granularity of the hodoscope’s tracking layers, the higher the rigidities that can be reached.

  32. Flight data: 0.171 GV positron Flight data: 0.169 GV electron R. Sparvoli – MAPS 2009 - Perugia

  33. Detector strategy: time-of-flight • A system of scintillators used to determine the time needed by a particle to cross it. • Possibility to: • Trigger the acquisition; • Reject albedo; • Measure the particle b; • Measure the particle charge (dE/dx in scintillators) R. Sparvoli – MAPS 2009 - Perugia

  34. Detector strategy: time-of-flight • In addition, b vs. R gives the particle mass, until a few GeV. R. Sparvoli – MAPS 2009 - Perugia

  35. Detector strategy: electron/hadron separation • An electromagnetic calorimeter, right after the spectrometer helps particles producing showers. In such a way, electron/hadron separation can be performed. hadron (19GV) electron (17GV) R. Sparvoli – MAPS 2009 - Perugia

  36. Detector strategy: calorimeters • The choice of the “passive” materials composing the calo must be done thining that: • X0 (radiation length)~ A/Z2 • l0(absorption length)~ A 2/3 • so one has to minimize X0 and maximazel0 . Generally: Lead/Tungsten interleaved with silicon strips/scintillating fibers R. Sparvoli – MAPS 2009 - Perugia

  37. e+ e+ p p Flight data PAMELA Rigidity: 20-30 GV Flight data PAMELA Rigidity: 42-65 GV Detector strategy: electron/hadron separation • To help discriminating electron from hadron, a neutron detector can be employed: •  Different yield in neutrons between the showers. R. Sparvoli – MAPS 2009 - Perugia

  38. Detector strategy: particle velocity (electron/hadron separation) • To help futher rejecting the bkg, one can add a detector measuring the velocity at high energy (above TOF). • Electromagnetic particles are relativistic, hadronic particles are slower: •  Very useful to adopt a “threshold-effect” detector, emitting light/signal only at relativistic speeds. R. Sparvoli – MAPS 2009 - Perugia

  39. Detector strategy: particle velocity • Two types of detector: • Cherenkov detectors: a particle emits light only if b > 1/n. • Transition Radiation Detectors: a highly relativist particles emits X-rays when crossing two different media. R. Sparvoli – MAPS 2009 - Perugia

  40. A single event in the RICH. The ring of Cherenkov light is clearly visible from a 1.3 GV electron at 8° incidence angle (CAPRICE94 data) R. Sparvoli – MAPS 2009 - Perugia

  41. Detector strategy: veto • Such a composite detector must be embedded in a veto system to minimize the background coming from outside. • The veto is generally made of scintillator in ON/OFF mode. • ATTENTION to veto in the main trigger ! R. Sparvoli – MAPS 2009 - Perugia

  42. AC-VETO CALO BG Event – rejected GOOD Event – VETO’ed GOOD EVENT VETO in 2nd level Trigger • Anticoincidence -VETO used only in 2nd level Trigger  high veto-rate by backscattering from CALO for good & rare events R. Sparvoli – MAPS 2009 - Perugia

  43. Lecture 1:“Existed” and “existing” detectors R. Sparvoli – MAPS 2009 - Perugia

  44. Stratospheric balloons R. Sparvoli – MAPS 2009 - Perugia

  45. CAPRICE97 CAPRICE98 The WiZard collaboration flights Collaboration New Mexico State University Tata Institute of Fundamental Research, Bombay Goddard Space Flight Center Royal Institute of Technology, Stockholm Centre de Recherches Nucleaires, Strasbourg Università di Perugia and INFN, Perugia INFN, Laboratori Nazionali di Frascati Università di Firenze and INFN, Firenze Università di Roma II and INFN, Roma Università di Trieste and INFN, Trieste Università di Bari and INFN, Bari R. Sparvoli – MAPS 2009 - Perugia

  46. Overview Aim of the activity is the detection of antimatter and dark matter signals in CR nei RC (antiprotons, positrons, antinuclei) for energies from hundreds of MeV to about 30 GeV, and measurements of primary CR from hundreds of MeV to about 300 GeV. 6 flights up to now: MASS89, MASS91, TRAMP-SI, CAPRICE 94, 97, 08. The flights started from New Mexico or Canada, with different geomagnetic cut-offs to optimize the investigation of different energy regions. The flights lasted about 20 hours. The instrument was built around a magnetic spectrometer (superconducting magnet, tracking system with multiwire or drift chambers). In additon, there was an imaging calorimeter below the magnet(streamer tubes in MASS 89 e 91, and tungsten/silicon in the following flights), a Time-Of-Flight system and, on top, a Gas-Cherenkov in the MASS flights, a TRD in TRAMP- SI and a Gas-RICH in the following flights. R. Sparvoli – MAPS 2009 - Perugia

  47. MASSMatter Antimatter Space Spectrometer

  48. CAPRICE R. Sparvoli – MAPS 2009 - Perugia

  49. HEAT-pbar HEAT-pbar (High Energy Antimatter Telescope) The HEAT-pbar Collaboration U of Chicago:A. Labrador, D. Müller, S.P. Swordy Northern Kentucky U.:S.L. Nutter Indiana U:A. Bhattacharyya, C. Bower, J.A. Musser U of Michigan:S.P. McKee, M. Schubnell, G. Tarlé, A.D. Tomasch Penn State U.:A.S. Beach, J.J. Beatty, S. Coutu, S. Minnick U. Minnesota:M. DuVernois R. Sparvoli – MAPS 2009 - Perugia

  50. Superconducting magnet spectrometer with Drift Tube Hodoscope (DTH) Multiple Ionization (dE/dx) Detector Time-of-Flight (TOF) system. HEAT-pbar flights R. Sparvoli – MAPS 2009 - Perugia

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