1. Roberta Sparvoli University of Rome ”Tor Vergata” and INFN
Constraints to Dark Matter and cosmic ray propagation by the PAMELA space experiment
Roberta Sparvoli
University of Rome ”Tor Vergata”
and INFN

2. Everything starts with …
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

3. and various ideas of theoretical interpretations
Anti-nucleosyntesis
WIMP dark-matter annihilation in the galactic halo
Background:
CR interaction with ISM
CR + ISM  p-bar + …
Evaporation of primordial black holes
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

4.  Roberta Sparvoli  October 8th, 2009  Como (Italy)

5.  Roberta Sparvoli  October 8th, 2009  Como (Italy)

6. Charge-dependent solar modulation
Solar polarity reversal 1999/2000
Asaoka Y. Et al. 2002 +
CR antimatter
Experimental scenario before PAMELA
WHAT DO WE NEED TO BETTER UNDERSTAND ?
Measurements at higher energies
Better knowledge of background
High statistics
Continuous monitoring of solar modulation
Long Duration Flights
Antiprotons
Positrons
Positron excess? ? ?
___ 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 90% from <2kpc)
CR + ISM  p-bar + …
Propagation dominated by nuclear interactions
Kinematical threshold: Eth~5.6 for the reaction
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

7.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
PAMELA pre-history
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

8. The PAMELA collaboration
Italy
Bari
Florence
Frascati
Trieste
Naples
Rome
CNR, Florence
Moscow
St. Petersburg
Russia
Germany
Siegen
Sweden
KTH, Stockholm
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

9. PAMELA Scientific goals
Halo
p-bar, e+
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

10. PAMELA design performance
Maximum detectable rigidity (MDR)
Magnetic curvature & trigger
spillover
shower
containment
energy range particles in 3 years
Antiprotons 80 MeV ÷190 GeV O(104)
Positrons 50 MeV ÷ 270 GeV O(105)
Electrons up to 400 GeV O(106)
Protons up to 700 GeV O(108)
Electrons+positrons up to 2 TeV (from calorimeter)
Light Nuclei up to 200 GeV/n He/Be/C: O(107/4/5)
Anti-Nuclei search sensitivity of 3x10-8 in anti-He/He
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

11.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
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
36 He3 counters
High-energy e/h discrimination
GF: 21.5 cm2 sr Mass: 470 kg
Size: 130x70x70 cm3
Power Budget: 360W
Overview of the apparatus
Spectrometer
microstrip silicon tracking system permanent magnet
It provides:
- Magnetic rigidity  R = pc/Ze
Charge sign
Charge value from dE/dx
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

12. The Resurs DK-1 spacecraft
Characteristic of the satellite
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

13.  Roberta Sparvoli  October 8th, 2009  Como (Italy)

14.  Roberta Sparvoli  October 8th, 2009  Como (Italy)

15.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
PAMELA milestones
Launch from Baikonur  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
Main antenna in NTsOMZ
Trigger rate* ~ 25 Hz
Fraction of live time* ~ 75%
Event size (compressed mode) ~ 5kB
25 Hz x 5 kB/ev  ~ 10 GB/day
(*outside radiation belts)
Today 1212 days in flight
>14 TBytes of raw data downlinked
>109 triggers recorded and under analysis
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

16. Antiproton/positron discrimination
energy measurement
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

17. Antiparticle selection
p, d p
‘Electron’
‘Hadron’
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

18.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
Antiprotons
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

19. High-energy antiproton analysis
Analyzed data July 2006 – February 2008 (~500 days)
Collected triggers ~108
Identified ~ protons and ~ antiprotons between 1.5 and 100 GeV ( 100 p-bar above 20 GeV )
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 high energy
proton spectrum harder than antiproton  p/p-bar increase for increasing energy
 Required strong SPE selection
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

20. Proton-spillover background
Electrons: efficiently removed by CALO
Pions (from interactions in dome) : about 3% in the pbar sample
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

21. PAMELA: Antiproton-to-proton ratio
PRL 102, (2009)
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

22. PAMELA: Antiproton-to-proton ratio
PRL 102, (2009)
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

23. PAMELA: Antiproton-to-proton ratio New (preliminary) data !
Full statistics
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

24. PAMELA: Antiproton flux preliminary
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

25.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
Positrons
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

26. High-energy positron analysis
Analyzed data July 2006 – February 2008 (~500 days)
Collected triggers ~108
Identified ~ electrons and ~ positrons between 1.5 and 100 GeV (180 positrons above 20 GeV )
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 gg might mimic pure em showers
proton spectrum harder than positron  p/e+ increase for increasing energy
 Required strong CALO selection S1 S2
CALO S4
CARD
CAS
CAT
TOF
SPE S3 ND
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

27. Positron identification with CALO
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
51 GV positron
80 GV proton
Final results make NO USE of test-beam and/or simulation calibrations.
The measurement is based only on flight data
with the background-estimation method
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

28.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
Particle selection after total energy cut and starting point of the shower
e - e+
(anti p) p - +
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

29. PAMELA: Positron fraction
NATURE 458, 697, 2009
(Moskalenko & Strong 1998)
GALPROP code
Plain diffusion model
Interstellar spectra
Solar modulation effects
Anomalous increasing ?
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

30. PAMELA: Positron fraction wrt other exp’s
NATURE 458, 697, 2009
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

31. Different statistical approaches for the bkg
Data: July 2006  December 2008
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

32. New data + systematic error
In publication
on APP !
Data: July 2006  December 2008
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

33. PAMELA antimatter data:
Do we have any antimatter excess in CRs?
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

34. Antiproton-to-proton ratio Secondary Production Models
CR + ISM  p-bar + …
~20%
 Uncertainty band related to propagation parameters GeV)
 Additional uncertainty of ~25% due to production cs should be considered !!
NB!
Solar modulation
Nuclear cross-section …
No evidence for any antiproton excess
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

35. Positron fraction Secondary Production Models
CR + ISM  p± + …  m± + …  e± + …
CR + ISM  p0 + …  gg  e±
Increasing positron fraction only if
ge- gp > 0.6
unlikely
(Serpico 2008)
Quite robust evidence for a positron excess
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

36. Primary positron sources
Dark 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
LKPs seem favored because can annihilate directly in e+e-
high yield (relative to p-bar)
hard spectrum with pronounced MLKP (>300 GeV)
Boost factor required to have a sizable e+ signal
NB: constraints from p-bar data!!
Other hypothesys possible and under study (i.e. Minimal DM Model, decaying DM, new gauge bosons, …)
LKP -- M= 300 GeV
(Hooper & Profumo 2007)
More than 150 articles
claim DM is discovered !
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

37.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
Example: dark matter
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

38. Primary positron sources
Astrophysical processes
Local pulsars are well-known sites of e+e- pair production (the spinning B of the pulsars strips e- that emit gammas then converting to pairs trapped in the cloud, accelerated and then escaping at the Poles) :
 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)
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

39.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
Example: pulsars
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

40.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
Explanation with supernovae remnants Shaviz and al. astro-ph.HE
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

41. Positrons from old SNR’s P. Blasi 0903.2794
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

42. Standard Positron Fraction
Theoretical Uncertainties
γ = 3.54
γ = 3.34
Need for high statistics CR measurements
T. Delahaye et al., arXiv: v3
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

43. Any positron source is an electron source too …
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

44. Recent claims of (e++e-) excess
g = 3.0
FERMI does not confirm the ATIC bump
but finds an excess wrt conventional diffusive models
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

45. PAMELA electron flux measurements
Key points wrt other experiments (ATIC, HESS, FERMI) :
Combination of CALO and SPECTROMETER allow energy self- calibration in flight  no dependence on ground calibrations or MC simulations
Very deep CALO (16 X0)  containment of the shower maximum beyond 1 TeV
Neutron detector help proton rejection, especially at high energy
No atmospheric contamination
Possibility to disentangle electrons from positrons
But ..
Smaller acceptance  lower statistics
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

46.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
PAMELA electron flux
preliminary
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

47. PAMELA electron flux wrt other exp’s
preliminary
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

48. Data ready by the end of the year
PAMELA electron flux
preliminary
Data ready by the end of the year
Primary source ???
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

49.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
Protons, nuclei, …
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

50. Galactic protons and Helium fluxes
preliminary p He
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

51. PAMELA proton and helium fluxes
preliminary
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

52. Proton flux compared to prev. exp’s
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

53. PAMELA secondary/primary nuclei ratios
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

54. PAMELA secondary/primary nuclei ratios
preliminary
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

55.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
Solar modulation
Interstellar spectrum
(statistical errors only)
Increasing
GCR flux
July 2006
August 2007
February 2008
solar activity
Decreasing
sun-spot number
Ground neutron monitor
PAMELA
 Roberta Sparvoli  October 8th, 2009  Como (Italy) 55

56.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
Solar modulation
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

57. Low energy e+: charge dependent solar modulation effects
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

58. Charge dependent solar modulation
Preliminary!! +
A > 0
Positive particles
A < 0
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

59.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
Summary
~40 14
 Roberta Sparvoli  October 8th, 2009  Como (Italy)

60.  Roberta Sparvoli  October 8th, 2009  Como (Italy)
Summary
PAMELA positron fraction alone insufficient to understand the origin of positron excess
Additional experimental data will be provided by PAMELA:
e+ higher energy (up to 300 GeV)
individual e- and e+ spectra
anisotropy (…maybe)
high energy e++e- spectrum (up to 2 TV)
Complementary information from:
gamma rays
neutrinos
PAMELA mission extended to end 2011 !
It will be possible to constrain further the nature of DM and models of cosmic ray propagation in the Galaxy.
 Roberta Sparvoli  October 8th, 2009  Como (Italy)