La missione PAMELA:

primi risultati scientifici

Paolo Papini INFN – Firenze

a nome della collaborazione PAMELA

XCIV Congresso NazionaleSocietà Italiana di Fisica

Genova 22-27 Settembre, 2008

Moscow St. Petersburg

Russia:

Sweden:KTH, Stockholm

Germany:Siegen

Italy:Bari FlorenceFrascati TriesteNapl

esRome CNR, Florence

Tha PAMELA collaboration

PAMELA as a Space Observatory at 1 AU

PPayload forayload for AAntimatterntimatter MMatteratter EExploration and xploration and LLight Nuclei ight Nuclei AAstrophysicsstrophysics• Search for dark matter

annihilation• Search for antihelium (primordial

antimatter)• Search for new Matter in the

Universe (Strangelets?)• Study of cosmic-ray propagation • Study of solar physics and solar

modulation• Study of terrestrial

magnetosphere • Study of high energy electron

spectrum (local sources?)

PAMELA prehistory• Astromag/WiZard project (PAMELA precursor) on board of the Space

Station Freedom CANCELED• Balloon-borne experiments: MASS-89,91 TS-93 CAPRICE-94,97,98 • Space experiments*: NINA-1,2 SILEYE-1,2,3 ALTEA

(*study of low energy nuclei and space radiation environment)

1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 - - - - XASTROMAG

C 94 C 97 C 98TS 93 M 89 M 91NINA-1 NINA-2

SILEYE-1 SILEYE-2 SILEYE-3ALTEA

PAMELA history• 1996: PAMELA proposal• 22.12.1998: agreement between RSA (Russian Space Agency) and

INFN to build and launch PAMELA.Three models required by the RSA:

• Mass-Dimensional and Thermal Model (MDTM)• Technological Model (TM)• Flight Model (FM)

Starts PAMELA construction

• 2001: change of the satellite complete redefinition of mechanics

• 2006: flight!!!

1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

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

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 measure+ -

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:• more than 2 years of data taking (~73% live-

time) • ~10 TByte of raw data downlinked• >109 triggers recorded and under analysis

• Resurs-DK1: multi-spectral imaging of earth’s surface• PAMELA mounted inside a pressurized container• Lifetime >3 years (assisted) • Data transmitted to NTsOMZ, Moscow via high-speed radio downlink. ~16 GB per day

• Quasi-polar and elliptical orbit (70.0°, 350 km - 600 km)

• Traverses the South Atlantic Anomaly • Crosses the outer (electron) Van Allen belt at south pole

Resurs-DK1Mass: 6.7 tonnesHeight: 7.4 mSolar array area: 36 m2

350 km

610 km

70o

PAMELA

SAA

~90 mins

Resurs-DK1 satellite + orbit

Download @orbit 3754 – 15/02/2007 07:35:00 MWT

S1 S2 S3

orbit 3752 orbit 3753orbit 3751

Inner radiation belt

(SAA)

Outer radiation belt

NP SP

EQ EQ

95 min

S1

S2

S3

Low energy particles stops inside the apparatus Counting rates: S1>S2>S3

Analysis of a PAMELA orbit

SAA

RatemetersIndependent from trigger

Principle of operation

•Measured @ground with protons of known momentum

MDR~1TV•Cross-check in flight with protons (alignment) and electrons (energy from calorimeter)

Iterative 2 minimization as a function of track state-vector components

Magnetic deflection|η| = 1/R R = pc/Ze magnetic rigidity

R/R =

Maximum Detectable Rigidity (MDR)def: @ R=MDR R/R=1

MDR = 1/

Track reconstruction

Principle of operationZ measurement

Bethe Bloch ionization energy-loss of heavy (M>>me) charged particles

1st plane

pd

3He

4He

Li

Be

B,C

track average

e±

(saturation)

Principle of operation

• Particle identification @ low energy• Identify albedo (up-ward going particles < 0 ) NB! They mimic antimatter!

Velocity measurement

Principle of operation

• Interaction topologye/h separation

• Energy measurement of electrons and positrons (~full shower containment)

electron (17GV)hadron (19GV)

Electron/hadron separation

5%aE

ba

E

σE

+ NEUTRONS!!

Flight data: 0.169 GV electron

Flight data: 0.171 GV positron

32.3 GVpositron

36 GeV/c interacting proton

Flight data: 0.632 GeV/cantiproton annihilation

Flight data: 0.763 GeV/cantiproton annihilation

Nuclei

Galactic H 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• 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

escPP λQN LBM ->

NB! still large discrepancies among different primary flux measurements

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)

Preliminary Results B/CPrelim

inary

Calorimeter based charge identification!

Interstellar spectrum

July 2006August 2007 February 2008

Decre

asin

g

sola

r activ

ity

Incre

asin

g

GC

R fl

ux

Solar modulation

sun-spot number

Ground neutron monitor PAMELA

(statistical errors only)

φ [MV ]={ July 2006 627±2August 2007 557±2

February 2008 553±2 }

Antiprotoni

High-energy antiproton analysis

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

CA

RD

CA

S

CAT

TOF

ND

TRK

.

S3

Antiproton identification• dE/dx vs R (S1,S2,TRK) and vs R proton-concistency cuts

• electron-rejection cuts based on calorimeter-pattern topology

e- (+ p-bar)

p-bar

p

-1 Z +1

“spillover” p

p (+ e+)

electron (17GV)

Antiproton (19GV) 1 GV5 GV

Proton spillover background

MDR > 850 GV

Minimal track requirements

Strong track requirements:•strict constraints on 2 (~75% efficiency)•rejected tracks with low-resolution clusters along the trajectory

- faulty strips (high noise)- -rays (high signal and multiplicity)

High-energy antiproton selection

p-bar p

10 GV 50 GV

High-energy antiproton selection

R < MDR/10

p-bar p

10 GV 50 GV

Positroni

Positron selection with calorimeter

p (non-int)

ee--

ee++

p (non-int)

Fraction of charge released along the calorimeter track (left, hit, right)

p (int)

p (int)

Rigidity: 20-30 GV

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

Positron identification

e- ( e+ )

pp-bar

Energy-rigidity match

‘electrons’

‘hadrons’

En

erg

y m

easu

red

in

Calo

/D

efl

ecti

on

in

Tra

cker

(MIP

/GV

)

Positron selection with calorimeter

ee--

Fraction of charge released along the calorimeter track (left, hit, right)

ppee++

+ •Energy-momentum match•Starting point of shower

Rigidity: 20-30 GV

Preliminary

Positron selection with calorimeter

pp

ee--

ee++

pp

Flight data:rigidity: 20-30 GV

Fraction of charge released along the calorimeter track (left, hit, right)

Test beam dataMomentum: 50GeV/c

ee--ee--

ee++

•Energy-momentum match•Starting point of shower

Positron selection

ee--

pp

ee--

ee++

pp

Neutrons detected by ND

Rigidity: 20-30 GVFraction of charge released along the calorimeter track (left, hit, right)

ee++

•Energy-momentum match•Starting point of shower

Positron selection

Rigidity: 10-15 GV Rigidity: 15-20 GV

ee--ee--

ee++ee++pp

pp

pp

pp

Energy loss in silicon tracker detectors:• Top: positive (mostly p) and negative events (mostly e-)• Bottom: positive events identified as p and e+ by trasversal profile method

Rigidity: 6-8 GV

Proton background evaluation

Fraction of charge released along the

calorimeter track (left, hit, right)

+Constraints on:

Energy-momentum match

Shower starting-point

e+

p

e-

p

Positron to Electron Fraction

End 2007: ~20 000 positrons total

Charge sign dependent solar modulation

e- /e+

Rigidity (GV)

Electron to positron ratio

U.W. Langner, M.S. Potgieter, Advances in Space Research 34 (2004)

Preliminary

Fisica solare

Increase of low energy component

December 13th 2006 eventfrom 2006-12-1 to 2006-12-4

Increase of low energy component

December 13th 2006 eventfrom 2006-12-1 to 2006-12-4

from 2006-12-13 00:23:02 to 2006-12-13 02:57:46

Increase of low energy component

December 13th 2006 eventfrom 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

Increase of low energy component

December 13th 2006 eventfrom 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 03:49:09from 2006-12-13 03:49:09 to 2006-12-13 04:32:56

Increase of low energy component

Decrease of high energy component

Increase of low energy component

December 13th 2006 eventfrom 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 03:49:09from 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

Increase of low energy component

December 13th 2006 eventfrom 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 03:49:09from 2006-12-13 03:49:09 to 2006-12-13 04:32:56

from 2006-12-13 04:32:56 to 2006-12-13 04:59:16from 2006-12-13 08:17:54 to 2006-12-13 09:17:34

The 14th December 2006 Forbush Decrease

Modulation of galactic cosmic ray intensity

~5% Decrease at mid-latitude

Jungfraujoch Neutron Monitor (Rc~4.5 GV)

GLE

Erwin O. Flückiger

The 14th December 2006 Forbush Decrease

from 2006-12-1 to 2006-12-4

Preliminary

The 14th December 2006 Forbush Decrease

from 2006-12-1 to 2006-12-4

from 2006-12-14 08:58:42 to 2006-12-14 11:59:57

(red - black) / black

Preliminary

The 14th December 2006 Forbush Decrease

from 2006-12-1 to 2006-12-4

from 2006-12-14 12:00:01 to 2006-12-14 23:59:59

(red - black) / black

The 14th December 2006 Forbush Decrease

from 2006-12-1 to 2006-12-4

from 2006-12-15 00:00:01 a 2006-12-15 23:59:54

(red - black) / black

Preliminary

The 14th December 2006 Forbush Decrease

from 2006-12-1 to 2006-12-4

from 2006-12-16 00:00:04 a 2006-12-16 23:59:59

(red - black) / black

Preliminary

The 14th December 2006 Forbush Decrease

from 2006-12-1 to 2006-12-4

from 2006-12-17 00:00:04 a 2006-12-17 23:59:59

(red - black) / black

Preliminary

The 14th December 2006 Forbush Decrease

from 2006-12-1 to 2006-12-4

from 2006-12-17 00:00:04 a 2006-12-17 23:59:59

(red - black) / black

Preliminary

Fasce di radiazione

South-Atlantic Anomaly (SAA)

SAA

SAA morphology

Lati

tud

eA

ltit

ude Altitude

Longitude

Neutron rate(background)

B < 0.19 G0.19 G ≤ B < 0.20 G0.20 G ≤ B < 0.21 G

B > 0.30 G0.22 G ≤ B < 0.23 G0.21 G ≤ B < 0.22 G

Always: 10 GV < cutoff < 11

Fluxes in SAA

Preliminary

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

Radiation belts morphology spectrum

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!

CALO SELF TRIGGER EVENT: 167*103 MIP RELEASED279 MIP in S4 26 Neutrons in ND