+
Overview of the main PAMELA physics results
Oscar AdrianiUniversity of Florence & INFN Firenze
17th Lomonosov ConferenceMoscow, August 26th, 2015
+PAMELA main physics tasks
1. Provide new high precision data about CR primary and secondary fluxes, to put constraints on the current acceleration and diffusion models of cosmic rays in the Galaxy.
2. Search for signatures of exotic processes connected to the Dark Matter problem;
3. Help solving the cosmological problem about the existence of the apparent asymmetry between matter and antimatter;
4. Investigate the heliosphere and Earth magnetosphere.
Main requirements: - high-sensitivity antiparticle identification - precise momentum measurement
PAMELA detectors
GF: 21.5 cm2 sr Mass: 470 kgSize: 130x70x70 cm3
Power Budget: 360W
Spectrometer microstrip silicon tracking system + permanent magnetIt provides:
- Magnetic rigidity R = pc/Ze- Charge sign- Charge value from dE/dx
Time-Of-Flightplastic scintillators + PMT:- Trigger- Albedo rejection;- Mass identification up to 1 GeV;- Charge identification from dE/dX.
Electromagnetic calorimeterW/Si sampling (16.3 X0, 0.6 λI) - Discrimination e+ / p, anti-p / e- (shower topology)- Direct E measurement for e-
Neutron detector36 He3 counters :- High-energy e/h discrimination
+ -
+PAMELAPayload for Matter/antimatter Exploration and Light-nuclei Astrophysics
Launch from Baykonur
• PAMELA on board of Russian satellite Resurs DK1• Orbital parameters:
- inclination ~70o ( low energy)- altitude ~ 360-600 km (elliptical) – now 500 km
(circular)
Launched on 15th June 2006PAMELA in continuous data-taking mode since
then!Recently celebrated 9 years!
+PAMELA published results Antiproton flux + antiproton/proton ratio (100 MeV-300 GeV)
Positron flux + positron/electron ratio (100 MeV-300 GeV)
Electron flux (1 – 500 GeV)
Proton and helium flux (1 GeV – 1.2 TeV)
B/C ratio (500 MeV – 100 GeV)
H and He isotope flux
AntiHe/He ratio
Proton flux vs. time – solar modulation (electron flux vs. time submitted)
Trapped proton and antiproton flux, albedo protons
SEP data (13 December 2006 and 17 May 2012 event)
Positrons anisotropy (just submitted)
Search for strangelets (just submitted)
e-
+Absolute fluxes of primary GCRsProtons, helium nuclei, electrons
+Proton and Helium Nuclei Spectra &
H/He ratio
Adriani et al., Science 332 (2011) 6025
First high-statistics and high-precision measurement
over three decades in energy Deviations from single power law (SPL):
• Spectra gradually soften in the range 30÷230GV• Spectral hardening @ R~235GV ~0.2÷0.3
SPL is rejected at 98% CL
• Origin of the hardening?• (e.g. see P. Blasi, arXiv:1312.1590)• - At the sources: multi-populations, etc.?• - Propagation effects?
Clear evidence of different H and He slopes above ~ 10 GV
+Global picture: PAMELA vs AMS-02 proton spectrum
Solar modulation
O. Adriani et al, Phys. Rep. (2014)
0.988
+Electron Spectrum
e+ + e-
e-
(ICRC 2013)
Solar modulation
+
Secondary cosmic raysSecondaries from homogeneously distributed interstellar matter (light nuclei)Antiparticles (antiprotons, positrons)
+ Boron and carbon fluxes and B/C
Adriani et al., ApJ 791 (2014), 93
Tuning of cosmic-ray propagation models with measurements of secondary/primary flux ratio
Modelization of cosmic-ray propagation in the Galaxy
Lithium and beryllium fluxes
●No MC corrections●Not unfolded●Only statistical errors
Li Be
Preliminary
●Shaded red area: particle slow-down effects(still to be corrected)
●Shaded grey area: relevant MDR effects for Be (due to saturated clusters)(still to be corrected)
N. Mori & E. Vannuccini et al.: “Measurement of Lithium and Beryllium cosmic-ray abundances by the PAMELA experiment” - CR 08: 01/08/2015
Li/Be Ratio
●No MC corrections●Not unfolded●Only statistical errors
Preliminary
●Shaded grey area: relevant MDR effects for Be (due to saturated clusters)(Still to be corrected)
N. Mori & E. Vannuccini et al.: “Measurement of Lithium and Beryllium cosmic-ray abundances by the PAMELA experiment” - CR 08: 01/08/2015
+
Isotopic separation with β (ToF) vs. Rigidity or multiple dE/dx (Calorimeter) vs. rigidity
Hydrogen and helium isotopes
W. Menn et al.: “Measurement of the isotopic composition of hydrogen and helium nuclei in cosmic rays with the PAMELA experiment” - Poster 1 CR: 30/7/2015
+Anti He/He and search for Strange Quark Matter
No antiHe detected in a sample of 6.330.000 events with |Z|>=2,from 0.6 to 600 GV.
Widest energy range ever reached
• No anomalous A/Z particle has been found (for Z <8 ) in the rigidity range
1 < R < 1.0 x 103 GV and mass range 4 < A < 1.2 x 105
• Upper limit as a function of Baryon Number (A) set
Accepted by PRL
+ PAMELA Antiparticle Results: Antiprotons
Secondary production calculations
O. Adriani et al,PRL 102 (2009) 051101; PRL 105 (2010) 121101;Phys. Rep. (2014).
+Positron fraction
M. Aguilar et al, PRL 110, 2013
Good agreement with FERMI and AMS data
+Positron flux
Adriani et al. , PRL 111 (2013) 081102
In the highest bin a lower limit has been estimated with 90% confidence level, due to a possible overestimation of the proton contamination.
Clear evidence
The positron fraction increase is due to an harder positron spectrum and not to a softer electron one.
Solar modulation
+Positron-excess interpretations
A primary positron source is certainly necessary!
Dark matter
- boost factor required
- lepton vs hadron yield must be consistent with p-bar observation
Astrophysical processes
• - known processes
• - large uncertainties on environmental parameters
e+ (and e-) produced as secondaries in the CR acceleration sites (e.g. SNR)
Contribution from diffuse mature & nearby young pulsars.
Contribution from DM annihilation.
+Search for anisotropy in the positron data
Significance maps for backtraced positrons in the 10 GV <R<200 GV, over the following angular scales: 10◦, 30◦, 60◦, 90◦.The significance has been computed using the protons measured as the isotropic reference sample
No evidence of positrons anisotropyin PAMELA data
Submitted to AP
+
Cosmic rays in the heliosphere
+
O. Adriani et al., ApJ 765 (2013), 91;M. S. Potgieter et al., Sol. Phys. (2014), 289
protons
electrons
increasingfluxes
Decreasing solar activity
PAMELA covers one solar cycle
Cycle23
PAMELACycle24
Neutron Monitor count (Data from http://cosmicrays.oulu.fi ) Effect of solar activity on CR fluxes
+Solar modulation: electron spectra
Adriani et al., submitted to ApJ
The ratios as a function of energy between the measured half-years (e−) fluxes from January 2007 till December 2009 and the measured fluxes for the period July-November 2006 overlaid with the corresponding computed spectra (solid lines).
The error bars are the quadratic sum of the statistical and systematic errors.
+SEP events (SEP from Dec. 13, 2006)
Ad
rian
i et a
l. - Ap
J 742 1
02,
2011
+Preliminary PAMELA SEP Spectra
100 MeV 1 GeV Proton Energy
Flux
E. Christian et al.: “Unseen GLEs (Ground Level Events)”- SH01: 30/07/2015
Completing the spectrum
PAMELA bridges the gap between low energy space-based and ground-‐based measurements to obtain a complete spectrum
+
Cosmic rays in the magnetosphere
+
Cosmic rays in the magnetosphereSorry, I
have no time!!!
!
All particlesPAMELA results
PAMELA overall resultsResults span 4 decades in energy and 13 in fluxes
Summary and conclusions (1)
PAMELA has been in orbit and studying cosmic rays for almost 9 years. Its operation time will continue until end 2015, possibly until end of current solar cycle.• Antiproton energy spectrum and ratio Measured up to ~300 GeV. No significant deviations from secondary production expectations. • High energy positron fraction (>10 GeV) Measured up to ~300 GeV. Increases significantly (and unexpectedly!) with energy. Primary source?• Positron flux -> Consistent with a new primary source. • Anisotropy studies: no evidence of anisotropy.• AntiHe/He ratio: broader energy range ever achieved.
Summary and conclusions (2)
• H and He absolute fluxes Measured up to ~1.2 TV. Complex spectral
structures observed (spectral hardening at ~200 GV).
• H and He isotope fluxes and ratio -> most complete measurements so far.
• Electron (e-) absolute flux Measured up to ~600 GeV. Possible deviations
from standard scenario, not inconsistent with an additional electron
component.
• B/C ratio and absolute fluxes up to 100 GeV/n.
• Solar physics: measurement of modulated fluxes and solar-flare particle
spectra
• Physics of the magnetosphere: first measurement of trapped antiproton flux
and detailed measurement of trapped proton flux.
Other studies and forthcoming results: Primary and secondary-nuclei
abundance (up to Oxygen), Solar modulation (long-term flux variation and
charge-dependent effects), Solar events: several new events under study.
+
Backup slides
+PAMELA & AMS (and Fermi) Electron (e-) Spectrum
Solar modulation
R. Munini et al.: “Solar modulation of galactic cosmic rays electrons and positrons over the 23rd solar minimum with the PAMELA experiment”- SH 07: 04/08/2015
+Electron energy measurements
spectrometer
calorimeter
Adriani et al. , PRL 106 (2011) 201101
Electron identification:• Negative curvature in the spectrometer• EM-like interaction pattern in the
calorimeter
Two independent ways to determine electron energy:
1.Spectrometer • Most precise• Non-negligible energy losses (bremsstrahlung) above the spectrometer unfolding
2.Calorimeter• Gaussian resolution• No energy-loss correction required
• Strong containment requirements
+
Solar neutrons can be produced by any solar event.PAMELA Neutron Detector (ND) is sensitive to neutrons fluxes coming from Sun.
Search of ND counts increasing after SEP event in comparison with counts during 1 orbit before the event.Two events under study: June 7th 2011December 13rd 2006
Search for solar neutrons
+New article about trapped protons
Differential fluxes are reported as a function of the first adiabatic invariant M, for sample values of K and L∗ invariants (equatorial region).
While spectral shapes are in a good qualitative agreement, measured flux intensities result to be up to about an order of magnitude lower with respect to model predictions, depending on the phase-space region. O. Adriani et al. ApJ
799, 1, L4 (2015)
+Light Nuclei and Isotopes
Tuning of cosmic-ray propagation models with measurements of secondary/primary flux ratio
2H/1H and 3He/4He are complementary to B/C measurements in constraining propagation models (Coste et al., A&A 539 (2012) A88)
+ Boron and carbon fluxes and B/C
Adriani et al., ApJ 791 (2014), 93
Tracking performance: σx = 14 μm, σy =
19 μm MDR = 250 GV
Modelization of cosmic-ray propagation in the Galaxy
+South-Atlantic Anomaly (SAA)
SAA
+South-Atlantic Anomaly (SAA)
SAA
SAA morphology
Lati
tud
eA
ltit
ud
e Altitude
Longitude
Neutron rate
+Geomagnetically trapped antiprotons
First measurement of p-bar trapped in the inner belt
29 p-bars discovered in
SAA and traced back to mirror
points
p-bar flux exceeds GRC flux by 3
orders of magnitude, as
expected by models
O. Adriani et al., ApJL 737 (2011), L29
+The PAMELA collaboration
BariFlorenceFrascatiItaly:
TriesteNaples Rome CNR, Florence
Moscow St.
Petersburg
Russia:
Germany:Siegen
Sweden:KTH, Stockholm
+Global picture: PAMELA vs AMS-02 helium nuclei spectrum
Solar modulation
1.036
+Lithium and Beryllium Isotopesβ (ToF) vs. Rigidity or Multiple dE/dx (Calorimeter) vs. rigidity
Ratio 7Li / 6Li
Lithium Beryllium
7Be / (9Be + 10Be)
W. Menn et al. : “Lithium and Beryllium Isotopes in the PAMELA experiment” - CR08:01/08/2015
+Primary positron sourcesDark Matter
e+ yield depend on the dominant decay channel ® LSPs (SUSY) seem disfavored due to
suppression of e+e- final states ® low yield (relative to p-bar)® soft spectrum from cascade decays
Other hypotheses possible and under study (i.e. Minimal DM Model, decaying DM, new gauge bosons, …)
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
LKP -- M= 300 GeV (Hooper & Profumo 2009)
More than 150 articles claim DM is discovered !
+Searching for a positron excess in the direction of the sun
No evidence of positron excess in the direction of the sun
Submitted to AP
+
2012 May 17th2012 March 7th
2012 January 27th2012 January 23rd
PAMELA bridges the gap below ACE, GOES and many others and above the Neutron Monitors to obtain a complete spectrum
Completing the spectrum
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