The PAMELA experiment: looking for antiparticles in Cosmic Rays

|
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
 17 views
of 59

Please download to get full document.

View again

Description
Firenze, 25 February 2009. The PAMELA experiment: looking for antiparticles in Cosmic Rays. Oscar Adriani University of Florence and INFN Florence. Outline. The PAMELA experiment: short review Results on cosmic-ray antimatter abundance: Antiprotons Positrons Other results:
Share
Transcript
Firenze, 25 February 2009 The PAMELA experiment:looking for antiparticles in Cosmic Rays Oscar Adriani University of Florence and INFN Florence Outline
  • The PAMELA experiment: short review
  • Results on cosmic-ray antimatter abundance:
  • Antiprotons
  • Positrons
  • Other results:
  • Cosmic-ray galactic light nuclei (primaries & secondaries)
  • Solar physics
  • Terrestrial physics
  • Conclusions
  •  Oscar Adriani  Florence, February 25th, 2009  Italy CNR, Florence Bari Florence Frascati Naples Rome Trieste Russia Moscow St. Petersburg Germany Sweden Siegen KTH, Stockholm Tha PAMELA collaboration  Oscar Adriani  Florence, February 25th, 2009  Why CR antimatter? Evaporation of primordial black holes Anti-nucleosyntesis First historical measurements of p-bar/p ratio WIMP dark-matter annihilation in the galactic halo Background: CR interaction with ISM CR + ISM  p-bar + …  Oscar Adriani  Florence, February 25th, 2009  Annihilation of relic Weakly Interacting Massive Particles (WIMPs) gravitationally confined in the galactic halo  Distortion of antiproton and positron spectra from purely secondary production A plausible dark matter candidate is neutralino (c), the lightest SUSY Particle (LSP). Most likely processes: cc  qq  hadrons anti-p, e+,… cc  W+W-,Z0Z0,…  e+,…  positron peak Ee+~Mc/2  positron continuum Ee+~Mc/20 Another possible candidate is the lightest Kaluza-Klein Particle (LKP): B(1) Fermionic final states no longer suppressed: B(1)B(1)  e+e- direct dicay  positron peak Ee+ ~ MB(1) Cosmic-ray Antimatter from Dark Matter annihilation Halo You are here Milky Way p-bar, e+ c c  Oscar Adriani  Florence, February 25th, 2009  Charge-dependent solar modulation (WIMPs) gravitationally Solar polarity reversal 1999/2000 Asaoka Y. Et al. 2002 Positron excess? ? ? ¯ +
  • CR + ISM  p-bar + …
  • Propagation dominated by nuclear interactions
  • Kinematical threshold: Eth~5.6 for the reaction
  • CR antimatter Experimental scenario before PAMELA Positrons Antiprotons ___ Moskalenko & Strong 1998
  • CR + ISM  p± + x m± + x  e± + x
  • CR + ISM  p0 + x gg e±
  • Propagation dominated by energy losses
  • (inverse Compton & synchrotron radiation)
  • Local origin (@100GeV 90% from <2kpc)
  •  Oscar Adriani  Florence, February 25th, 2009  PAMELA detectors (WIMPs) gravitationally 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
  •  Oscar Adriani  Florence, February 25th, 2009  Track reconstruction (WIMPs) gravitationally
  • 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 Principle of operation  Oscar Adriani  Florence, February 25th, 2009  track average (WIMPs) gravitationally Z measurement 4He B,C 3He Be Bethe Bloch ionization energy-loss of heavy (M>>me) charged particles d (saturation) p Li e± 1st plane Principle of operation  Oscar Adriani  Florence, February 25th, 2009  Velocity measurement (WIMPs) gravitationally
  • Particle identification @ low energy
  • Identify albedo (up-ward going particles b < 0 )
  •  NB! They mimic antimatter!
  • Principle of operation  Oscar Adriani  Florence, February 25th, 2009  Electron/hadron separation (WIMPs) gravitationally
  • Interaction topology
  • e/h separation
  • Energy measurement of electrons and positrons
  • (~full shower containment)
  • hadron (19GV) electron (17GV) Principle of operation + NEUTRONS!!  Oscar Adriani  Florence, February 25th, 2009  Multi-spectral remote sensing of earth’s surface (WIMPs) gravitationally near-real-time high-quality images Built by the Space factory TsSKB Progress in Samara (Russia) Operational orbit parameters: inclination ~70o altitude ~ 360-600 km (elliptical) Active life >3 years Data transmitted via Very high-speed Radio Link (VRL) The Resurs DK-1 spacecraft Mass: 6.7 tons Height: 7.4 m Solar array area: 36 m2
  • PAMELA mounted inside apressurized container
  • moved from parking to data-taking position few times/year
  •  Oscar Adriani  Florence, February 25th, 2009  PAMELA design performance (WIMPs) gravitationally Maximum detectable rigidity (MDR) energy rangeparticles in 3 years Antiprotons80 MeV ÷190 GeV O(104) Positrons50 MeV ÷ 270 GeV O(105) Electrons up to 400 GeV O(106) Protonsup to 700 GeV O(108) Electrons+positronsup to 2 TeV (from calorimeter) LightNuclei up to 200 GeV/n He/Be/C: O(107/4/5) Anti-Nuclei searchsensitivity of 3x10-8 in anti-He/He Magnetic curvature & trigger spillover shower containment
  • Unprecedented statistics and new energy range for cosmic ray physics (e.g. contemporary antiproton and positron maximum energy ~ 40 GeV)
  • Simultaneous measurements of many species
  •  Oscar Adriani  Florence, February 25th, 2009  Launch from Baikonur (WIMPs) gravitationallyJune 15th 2006, 0800 UTC. ‘First light’ June 21st 2006, 0300 UTC. • Detectors operated as expected after launch • Different trigger and hardware configurations evaluated PAMELA in continuous data-taking mode since commissioning phase ended on July 11th 2006 PAMELA milestones Main antenna in NTsOMZ Trigger rate* ~25Hz Fraction of live time* ~ 75% Event size (compressed mode) ~ 5kB 25 Hz x 5 kB/ev ~ 10 GB/day (*outside radiation belts) Till December 2008: ~800 days of data taking ~16 TByte of raw data downlinked ~16•108 triggers recorded and analysed (Data from May till now under analysis)  Oscar Adriani  Florence, February 25th, 2009  Antiprotons (WIMPs) gravitationally High-energy antiproton analysis (WIMPs) gravitationally
  • Analyzed data July 2006 – February 2008 (~500 days)
  • Collected triggers ~108
  • Identified ~ 10 106 protons and ~ 1 103 antiprotons between 1.5 and 100 GeV ( 100 p-bar above 20GeV )
  • Antiproton/proton identification:
  • rigidity (R)  SPE
  • |Z|=1 (dE/dx vs R)  SPE&ToF
  • b vs R consistent with MpToF
  • p-bar/p separation (charge sign)  SPE
  • p-bar/e- (and p/e+ ) separation CALO
  • Dominant background  spillover protons:
  • finite deflection resolution of the SPE  wrong assignment of charge-sign @ high energy
  • proton spectrum harder than positron  p/p-bar increase for increasing energy (103 @1GV 104 @100GV)
  •  Required strong SPE selection
  •  Oscar Adriani  Florence, February 25th, 2009  1 GV (WIMPs) gravitationally 5 GV Antiproton identification Preliminary!! -1  Z  +1 p (+ e+) p e-(+ p-bar) proton-consistency cuts (dE/dx vs R and b vs R) “spillover” p p-bar electron-rejection cuts based on calorimeter-pattern topology ( For |Z|=1, deflection=1/p )  Oscar Adriani  Florence, February 25th, 2009  Proton-spillover background (WIMPs) gravitationally MDR = 1/sh (evaluated event-by-event by the fitting routine) Minimal track requirements MDR > 850GV
  • 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)
  •  Oscar Adriani  Florence, February 25th, 2009  R < MDR/10 (WIMPs) gravitationally 10 GV 50 GV Proton-spillover background MDR = 1/sh (evaluated event-by-event by the fitting routine) p p-bar “spillover” p
  • MDR depends on:
  • number and distribution of fitted points along the trajectory
  • spatial resolution of the single position measurements
  • magnetic field intensity along the trajectory
  •  Oscar Adriani  Florence, February 25th, 2009  Antiproton-to-proton ratio (WIMPs) gravitationally *preliminary* PRL 102, 051101 (2009) (Petter Hofverberg’s PhD Thesis)  Oscar Adriani  Florence, February 25th, 2009  Positrons (WIMPs) gravitationally S1 (WIMPs) gravitationally CARD CAT S2 TOF SPE CAS S3 CALO S4 ND High-energy positron analysis
  • Analyzed data July 2006 – February 2008 (~500 days)
  • Collected triggers ~108
  • Identified ~ 150 103 electrons and ~ 9 103 positrons between 1.5 and 100 GeV (180 positrons above 20GeV)
  • Electron/positron identification:
  • rigidity (R)  SPE
  • |Z|=1 (dE/dx=MIP)  SPE&ToF
  • b=1 ToF
  • e-/e+ separation (charge sign)  SPE
  • e+/p (and e-/p-bar) separation CALO
  • Dominant background  interacting protons:
  • fluctuations in hadronic shower development  p0 ggmight mimic pure em showers
  • proton spectrum harder than positron  p/e+ increase for increasing energy (103 @1GV 104 @100GV)
  •  Required strong CALO selection
  •  Oscar Adriani  Florence, February 25th, 2009  Positron identification with CALO (WIMPs) gravitationally 51 GV positron
  • Identification based on:
  • Shower topology (lateral and longitudinal profile, shower starting point)
  • Total detected energy (energy-rigidity match)
  • Analysis key points:
  • Tuning/check of selection criteria with:
  • test-beam data
  • simulation
  • flight data  dE/dx from SPE & neutron yield from ND
  • Selection of pure proton sample from flight data (“pre-sampler” method):
  • Background-suppression method
  • Background-estimation method
  • 80 GV proton Final results make NON USE of test-beam and/or simulation calibrations. The measurement is based only on flight data with the background-estimation method  Oscar Adriani  Florence, February 25th, 2009  Z=-1 (WIMPs) gravitationally e- Rigidity: 20-30 GV p-bar (non-int) p-bar (int) NB! Z=+1 0.6 RM p (non-int) LEFT HIT RIGHT planes (e+) p (int) strips Positron identification Fraction of charge released along the calorimeter track  Oscar Adriani  Florence, February 25th, 2009  Positron identification (WIMPs) gravitationally Energy-momentum match Energy measured in Calo/ Deflection in Tracker (MIP/GV) e- ( e+ )  e  h p-bar p  Oscar Adriani  Florence, February 25th, 2009  Z=-1 (WIMPs) gravitationally Z=-1 e- e- Rigidity: 20-30 GV Rigidity: 20-30 GV + Constraints on: p-bar (non-int) p-bar (int) p-bar Energy-momentum match NB! Z=+1 Z=+1 p (non-int) e+ (e+) p (int) p Positron identification Fraction of charge released along the calorimeter track  Oscar Adriani  Florence, February 25th, 2009  Shower starting-point (WIMPs) gravitationally Longitudinal profile Positron identification 51 GV positron 80 GV proton  Oscar Adriani  Florence, February 25th, 2009  Z=-1 (WIMPs) gravitationally Z=-1 e- e- Rigidity: 20-30 GV Rigidity: 20-30 GV p-bar Shower starting-point Z=+1 Z=+1 Longitudinal profile Lateral profile e+ e+ p BK-suppression method p Positron identification Fraction of charge released along the calorimeter track + Constraints on: Energy-momentum match  Oscar Adriani  Florence, February 25th, 2009  The “pre-sampler” method (WIMPs) gravitationally Selection of a pure sample of protons from flight data CALORIMETER: 22 W planes: 16.3 X0 2 W planes: ≈1.5 X0 20 W planes: ≈15 X0  Oscar Adriani  Florence, February 25th, 2009  Proton background evaluation (WIMPs) gravitationally Rigidity: 20-28 GV e- Fraction of charge released along the calorimeter track (left, hit, right) + Constraints on: p (pre-sampler) Energy-momentum match Shower starting-point e+ p  Oscar Adriani  Florence, February 25th, 2009  Positron fraction (WIMPs) gravitationally astro-ph 0810.4995 Accepted by Nature  Oscar Adriani  Florence, February 25th, 2009  Do we have any antimatter excess in CRs? (WIMPs) gravitationally  Oscar Adriani  Florence, February 25th, 2009  Antiproton-to-proton ratio (WIMPs) gravitationallySecondary Production Models CR + ISM  p-bar + …
  • (Moskalenko et al. 2006) GALPROP code
  • Plain diffusion model
  • Solar modulation: drift model ( A<0, a=15o )
  • (Donato et al. 2001)
  • Diffusion model with convection and reacceleration
  • Solar modulation: spherical model (f=500MV )
  •  Uncertainty band related to propagation parameters (~10% @10GeV)
  •  Additional uncertainty of ~25% due to production cs should be considered !!
  • (Ptuskin et al. 2006) GALPROP code
  • Plain diffusion model
  • Solar modulation: spherical model ( f=550MV )
  • No evidence for any antiproton excess  Oscar Adriani  Florence, February 25th, 2009  Positron fraction (WIMPs) gravitationallySecondary Production Models CR + ISM  p± + … m± + …  e± + … CR + ISM  p0 + … gg e±
  • (Moskalenko & Strong 1998)
  • GALPROP code
  • Plain diffusion model
  • Interstellar spectra
  •  Oscar Adriani  Florence, February 25th, 2009  (Clem & Evenson 2007) (WIMPs) gravitationally ¯ ¯ Drift model + + A > 0 Positive particles A < 0 Charge dependent solar modulation  Oscar Adriani  Florence, February 25th, 2009  Positron fraction (WIMPs) gravitationallySecondary Production Models CR + ISM  p± + … m± + …  e± + … CR + ISM  p0 + … gg e± The positron fraction depends on the primary (+secondary) electron spectrum
  • (Moskalenko & Strong 1998)
  • GALPROP code
  • Plain diffusion model
  • Interstellar spectra
  • Soft electron spectrum (g = 3.54) Hard electron spectrum (g = 3.34)
  • (Delahaye et al. 2008)
  • Plain diffusion model
  • Solar modulation: spherical model (f=600MV)
  • Uncertainty band related to e- spectral index (ge= 3.44±0.1 MIN÷MAX)
  • Additional uncertainty due to propagation parameters should be considered (factor ~6 @1GeV ~4 @high-energy)
  •  Oscar Adriani  Florence, February 25th, 2009  Positron fraction (WIMPs) gravitationallySecondary Production Models Preferred by Pamela electron data! Quite robust evidence for a positron excess  Oscar Adriani  Florence, February 25th, 2009  Primary positron sources (WIMPs) gravitationally Dark Matter
  • e+ yield depend on the dominant decay channel
  • LSPs seem disfavored due to suppression of e+e- final states
  • low yield (relative to p-bar)
  • soft spectrum from cascade decays
  • LKPs seem favored because can annihilate directly in e+e-
  • high yield (relative to p-bar)
  • hard spectrum with pronounced cutoff @ MLKP (>300 GeV)
  • Boost factor required to have a sizable e+ signal
  • NB: constraints from p-bar data!!
  • LKP -- M= 300 GeV (Hooper & Profumo 2007)  Oscar Adriani  Florence, February 25th, 2009  Primary positron sources (WIMPs) gravitationally Astrophysical processes
  • Local pulsars are well-known sites of e+e- pair production:  they can individually and/or coherently contribute to the e+e- galactic flux and explain the PAMELA e+ excess (both spectral feature and intensity)
  • No fine tuning required
  • if one or few nearby pulsars dominate, anisotropy could be detected in the angular distribution
  • possibility to discriminate between pulsar and DM origin of e+ excess
  • All pulsars (rate = 3.3 / 100 years) (Hooper, Blasi, Seprico 2008) ~80 theoretical paper on Pamela data since our ArXiv publication!!!!!  Oscar Adriani  Florence, February 25th, 2009  PAMELA positron excess might be connected with ATIC electron+positron structures? (Chang et al 2008)  Oscar Adriani  Florence, February 25th, 2009  Primary positron sources electron+positron structures? PAMELA positron fraction alone insufficient to understand the origin of positron excess Additional experimental data will be provided by PAMELA:
  • e+ fraction @ higher energy (up to 300 GeV)
  • individual e- e+ spectra
  • anisotropy (…maybe)
  • high energy e++e- spectrum (up to 2 TV) Complementary information from:
  • gamma rays
  • neutrinos
  •  Oscar Adriani  Florence, February 25th, 2009  Galactic cosmic-ray origin & propagation electron+positron structures? H and He spectra electron+positron structures? (statistical errors only) Preliminary!!
  • 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
  • Very high statistics over a wide energy range  Precise measurement of spectral shape  Possibility to study time variations and transient phenomena  Oscar Adriani  Florence, February 25th, 2009  Secondary nuclei electron+positron structures? Preliminary!!
  • B nuclei of secondary origin:
  • CNO + ISM  B + …
  • Local secondary/primary ratio sensitive to average amount of traversed matter (lesc) from the source to the solar system
  • Local secondary abundance:
  • study of galactic CR propagation
  • (B/C used for tuning of propagation models)
  •  Oscar Adriani  Florence, February 25th, 2009  Solar physics electron+positron structures? Solar modulation Solar Energetic Particle events (SEPs) Interstellar spectrum electron+positron structures? PAMELA Ground neutron monitor sun-spot number Solar modulation Preliminary!! (statistical errors only) Increasing GCR flux July 2006 August 2007 February 2008 Decreasing solar activity  Oscar Adriani  Florence, February 25th, 2009  SOHO/LASCO electron+positron structures? SOHO/EIT December 2006 CME/SEP events Coronal Mass Ejection (CME) X-ray flares Solar Energetic Particles (SEPs) protons: 1÷100 MeV alphas: 150÷500 MeV  Oscar Adriani  Florence, February 25th, 2009  Increase of low energy component electron+positron structures? December 13th 2006 event from 2006-12-1 to 2006-12-4  Oscar Adriani  Florence, February 25th, 2009  Increase of low energy component electron+positron structures? 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  Oscar Adriani  Florence, February 25th, 2009  Increase of low energy component electron+positron structures? 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  Oscar Adriani  Florence, February 25th, 2009  Decrease of high energy component electron+positron structures? 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  Oscar Adriani  Florence, February 25th, 2009  Increase of low energy component electron+positron structures? 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  Oscar Adriani  Florence, February 25th, 2009  Increase of low energy component electron+positron structures? 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
    Related Search
    We Need Your Support
    Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

    Thanks to everyone for your continued support.

    No, Thanks