first results from pamela space experiment
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ISVHECRI 2008, Paris 1-6 September 2008
First results from PAMELA space experiment
Oscar AdrianiUniversity of Florence INFN – Florence, Italy
On behalf of the PAMELA collaboration
Oscar Adriani ISVHECRI 2008
Moscow St. Petersburg
Russia:
Sweden:KTH, Stockholm
Germany:Siegen
Italy:Bari Florence Frascati TriesteNaples Rome CNR, Florence
Tha PAMELA collaboration
Oscar Adriani ISVHECRI 2008
Pamela’s scientific objectives Study antiparticles in cosmic rays Search for antimatter Search for dark matter (e+ and pbar spectra) Study cosmic-ray propagation Study solar physics and solar modulation Study the electron spectrum (local sources?) Anti-
nucleosyntesis
WIMP dark-matter
annihilation in the galactic
haloBackground:CR interaction with ISMCR + ISM p-bar + …
Evaporation of primordial black holes
Oscar Adriani ISVHECRI 2008
PAMELA nominal capabilitiesEnergy range
• Antiprotons 80 MeV - 150 GeV
• Positrons 50 MeV – 270 GeV
• Electrons up to 400 GeV
• Protons up to 700 GeV
• Electrons+positrons up 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
Oscar Adriani ISVHECRI 2008
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 detectorplastic scintillators + PMT:- High-energy e/h discrimination
Main requirements high-sensitivity antiparticle identification and precise momentum measurement+ -
Oscar Adriani ISVHECRI 2008
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:• ~600 days of data taking (~73% live-time) • ~10 TByte of raw data downlinked• >109 triggers recorded and under analysis
Mirko Boezio, INFN Trieste - ICHEP08, 2008/08/01Mirko Boezio, INFN Trieste - ICHEP08, 2008/08/01
Oscar Adriani ISVHECRI 2008
32.3 GVpositron
Oscar Adriani ISVHECRI 2008
36 GeV/c interacting proton
Oscar Adriani ISVHECRI 2008
Galactic H and He spectraVery 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-
~ 2.76 for Z=1 ~ 2.71 for Z=2
Oscar Adriani ISVHECRI 2008
Geomagnetic cutoff
0.4 to 0.51.0 to 1.51.5 to 2.02 to 4
> 1410 to 147 to 104 to 7
Geomagnetic cutoff (GV/c)
Secondary reentrant-albedo protons
Magnetic equator
Magnetic poles( galactic protons)
•Up-ward going albedo excluded•SAA excluded
(statistical errors only)
Oscar Adriani ISVHECRI 2008
Interstellar spectrum
July 2006August 2007 February 2008
Decreasing
solar activity
Increasing G
CR flux
Solar modulation
sun-spot number
Ground neutron monitor PAMELA
(statistical errors only)
Oscar Adriani ISVHECRI 2008
Preliminary Results B/CPreliminary
Calorimeter based charge identification!
Oscar Adriani ISVHECRI 2008
Antiprotons
Oscar Adriani ISVHECRI 2008
High-energy antiproton analysisEvent selected from 590 days of data
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 2 (~95% efficiency)– consistency among TRK, TOF and CAL spatial
information • Galactic particle
• measured rigidity above geomagnetic cutoff• Down-ward going particle (no albedo)
S1
S2
CAL
S4
CARD
CAS
CAT
TOF
ND
TRK
.
S3
Oscar Adriani ISVHECRI 2008
ee--ee++
p, dp, dpp
‘Electrons’
‘Hadrons’
Calorimeter Selection
Tracker Identification
Protons (& spillover)
Antiprotons
Minimal track requirements
Strong track requirements:MDR > 850 GV
Ener
gy m
easu
red
in C
alo/
Defl
ecti
on in
Tra
cker
(M
IP/G
V)
Oscar Adriani ISVHECRI 2008
Antiproton/Proton ratioPreliminary
Oscar Adriani ISVHECRI 2008
Antiproton/Proton RatioPreliminary
Oscar Adriani ISVHECRI 2008
Positrons
Oscar Adriani ISVHECRI 2008
Positron identification
e- ( e+ )
pp-bar
The main difficulty for the positron measurement is the interacting-proton background:• fluctuations in hadronic shower development might mimic pure e.m. showers• proton spectrum harder than positron p/e+ increase for increasing energy
Energy-rigidity match
‘electrons’
‘hadrons’Ener
gy m
easu
red
in C
alo/
Defl
ecti
on in
Tra
cker
(M
IP/G
V)
Oscar Adriani ISVHECRI 2008
e+ background estimation from data
Fraction of charge released along the calorimeter track (left, hit, right)
+ • Energy-momentum match• Starting point of shower
Preliminarye-
‘presampler’ p
Rigidity: 6-8 GV
e+p
Oscar Adriani ISVHECRI 2008
Positrons to Electrons ratio
___ Moskalenko & Strong 1998
statistical errors only
Preliminary
¯
+
Charge sign dependent
solar modulation
Oscar Adriani ISVHECRI 2008
Conclusions• PAMELA is continously taking data since July 2006
• Presented preliminary results from ~600 days of data: Antiproton charge ratio (~1 GeV ÷100 GeV)
no evident deviations from secondary expectations more data to come at lower and higher energies (up to ~150 GeV)
Positron charge ratio (~400 MeV ÷10 GeV) indicates charge dependent modulation effects more data to come at lower and higher energies (up to ~200 GeV)
Galactic primary proton spectra primary spectra up to Z=8 to come
Galactic secondary-to-primary ratio (B/C) abundance of other secondary elements (Li,Be) and isotopes (d,3He) to come
High energy tail of proton SEP events spectra of other components (electrons, isotopes,…) to come
PAMELA is already providing significant experimental results, which will help in understanding CR origin and propagation
More exciting results will come in the next future!
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