First results from PAMELA space experiment

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


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


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 measurement+ -


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


32.3 GVpositron


36 GeV/c interacting proton


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


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



Interstellar spectrum

July 2006August 2007 February 2008

Decreasing

solar activity

Increasing G

CR flux

Solar modulation

sun-spot number

Ground neutron monitor PAMELA



Preliminary Results B/CPreliminary

Calorimeter based charge identification!


Antiprotons


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


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)


Antiproton/Proton ratioPreliminary


Antiproton/Proton RatioPreliminary


Positrons


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)


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


Positrons to Electrons ratio

___ Moskalenko & Strong 1998

statistical errors only

Preliminary

¯

+

Charge sign dependent

solar modulation


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!

Date post:	14-Feb-2016
Category:	Documents
Upload:	lulu
View:	97 times
Download:	1 times

First results from PAMELA space experiment

Documents