Transcript First Results From PAMELA Space Experiment

ISVHECRI 2008, Paris 1-6 September 2008
First results from PAMELA
space experiment
Oscar Adriani
University of Florence
INFN – Florence, Italy
On behalf of the PAMELA collaboration
Tha PAMELA collaboration
Italy:
Bari
Florence Frascati
Naples
Rome
Trieste CNR, Florence
Russia:
Moscow
St. Petersburg
Germany:
Sweden:
Siegen
KTH, Stockholm
Oscar Adriani
ISVHECRI 2008
Pamela’s scientific objectives
 Study antiparticles in cosmic rays



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
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?)
Evaporation of
primordial black
holes
Antinucleosyntesis
WIMP dark-matter
annihilation in the
galactic halo
Background:
CR interaction with ISM
CR + ISM  p-bar + …
Oscar Adriani
ISVHECRI 2008
PAMELA nominal capabilities
• Antiprotons
Energy range
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
Main requirements  high-sensitivity antiparticle identification and precise momentum measurement
+
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-
GF: 21.5 cm2 sr
Mass: 470 kg
Size: 130x70x70 cm3
Power Budget: 360W
Neutron detector
plastic scintillators + PMT:
- High-energy e/h discrimination
Spectrometer
microstrip silicon tracking system + permanent magnet
It provides:
- Magnetic rigidity  R = pc/Ze
- Charge sign
- Charge value from dE/dx
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, 2008/08/01
Oscar Adriani
ISVHECRI 2008
32.3 GV
positron
Oscar Adriani
ISVHECRI 2008
36 GeV/c
interacting proton
Oscar Adriani
ISVHECRI 2008
Galactic H and He spectra
Very high statistics over a wide energy range
 Precise measurement of spectral shape
 Possibility to study time variations and transient
phenomena
Power-law fit: ~ E-g
g ~ 2.76 for Z=1
g ~ 2.71 for Z=2
(statistical errors only)
Oscar Adriani
ISVHECRI 2008
Geomagnetic cutoff
(statistical errors only)
Magnetic poles
( galactic protons)
Geomagnetic
cutoff (GV/c)
0.4 to 0.5
1.0 to 1.5
1.5 to 2.0
2 to 4
4 to 7
7 to 10
10 to 14
> 14
Secondary
reentrant-albedo
protons
•Up-ward going albedo excluded
•SAA excluded
Magnetic equator
Oscar Adriani
ISVHECRI 2008
Solar modulation
Interstellar spectrum
(statistical errors only)
Decreasing
solar activity
Increasing
GCR flux
July 2006
August 2007
February 2008
PAMELA
Ground neutron monitor
sun-spot number
Oscar Adriani
ISVHECRI 2008
Preliminary Results B/C
Calorimeter based charge identification!
Oscar Adriani
ISVHECRI 2008
Antiprotons
Oscar Adriani
ISVHECRI 2008
High-energy antiproton analysis
Event selected from 590 days of data
S1
Basic requirements:
• Clean pattern inside the apparatus
CAT
S2
– single track inside TRK
– no multiple hits in S1+S2
– no activity in CARD+CAT
TOF
TRK
CAS
.
• Minimal track requirements
– energy-dependent cut on track c2 (~95%
efficiency)
– consistency among TRK, TOF and CAL spatial
information
S3
CAL
S4
ND
• Galactic particle
• measured rigidity above geomagnetic cutoff
• Down-ward going particle (no albedo)
Oscar Adriani
ISVHECRI 2008
Energy measured in Calo/
Deflection in Tracker (MIP/GV)
Calorimeter Selection
e-
e+
‘Electrons’
p
p, d
‘Hadrons’
Tracker Identification
Strong track requirements:
MDR > 850 GV
Protons (& spillover)
Antiprotons
Minimal track requirements
Oscar Adriani
ISVHECRI 2008
Antiproton/Proton ratio
Oscar Adriani
ISVHECRI 2008
Antiproton/Proton Ratio
Oscar Adriani
ISVHECRI 2008
Positrons
Oscar Adriani
ISVHECRI 2008
Positron identification
The main difficulty for the positron measurement is the interactingproton background:
• fluctuations in hadronic shower development  p0 gg might mimic pure e.m. showers
Energy measured in Calo/
Deflection in Tracker (MIP/GV)
• proton spectrum harder than positron  p/e+ increase for increasing energy
Energy-rigidity match
e-
( e+ )
 ‘electrons’
p-bar
p
 ‘hadrons’
Oscar Adriani
ISVHECRI 2008
e+ background estimation from data
Rigidity: 6-8 GV
e-
p
e+
‘presampler’ p
Fraction of charge released along the
calorimeter track (left, hit, right)
match
+ •• Energy-momentum
Starting point of shower
Oscar Adriani
ISVHECRI 2008
Positrons to Electrons ratio
___ Moskalenko & Strong 1998
+
¯
Charge sign
dependent
solar
modulation
statistical errors only
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!
Oscar Adriani
ISVHECRI 2008