fisica e rivelazione dei gaggi gamma cosa si vuole...

Aldo Morselli INFN, Sezione di Roma 2 & Università di Roma Tor Vergata 1

Fisica e rivelazionedei gaggi gamma

Aldo MorselliINFN, Sezione di Roma 2 &

Università di Roma Tor Vergata

Roma, 7 Febb. 2006

Corso di Astroparticelle

Anno 2005-2006


Cosa si vuole studiare?

• Cielo nei raggi gamma

• Antimateria nell'Universo

• Brillamenti e tempeste solari

• …….

Come?


Gamma ray attenuation


Gamma ray

attenuation (2)

Relation between the temperature

of a black body and the frequency

at which most of the energy is

emitted

Transparency of the atmosphere for

radiation of different wavelengths.

The solid line show the height

above sea-level at which the

atmosphere becomes tranparent.


EGRET:the detector

Energy range: 20 MeV - 30 GeV

Weight: 1820 Kg

Power: 160 W

Field of view: 0. 5 sr

Dead Time: 100 ms

Effective Area (@1GeV) 1200 cm2

Angular resolution 5.8o

(@100MeV)

Sensitivity 0.1 GeV 5x10-8

for point 1 GeV 1x10-8

sources 10 GeV 2x10-8

(ph cm-2 s-1)*


EGRET – Principle of

gamma ray detectionA !-ray which enters the top of the EGRET

instrument will pass undetected through the large

anticoincidence scintillator surrounding the spark

chamber and has a probability 33% of converting

into an electron-positron pair in one of the thin

tantalum (Ta) sheets interleaved between the 28

closely spaced spark chambers in the upper portion

of the instrument.

Below the conversion stack are two 4 x 4 arrays of

plastic scintillation detector tiles spaced 60 cm apart

which register the passage of charged particles. If the

time-of-flight delay indicates a downward moving

particle which passed through a valid combination of

upper and lower scintillator tiles, and the

anticoincidence system has not been triggered by a

charged particle, the track information is recorded

digitally. In this manner, a three dimensional picture

of the path of the electron-positron pair is measured.

The energy deposition in the NaI(Tl) Total

absorption Shower Counter (TASC) located

directly below the lower array of plastic scintillators

is used to estimate the photon energy.


Elements of a pair-conversion telescope

• photons materialize

into matter-antimatter pairs:

E! --> me+c2 + me-c

2

• electron and positron

carry information about

the direction, energy and

polarization of the !-ray

(energy measurement)


Energy loss mechanisms:

Fractional energy loss for e+ and e- in leadPhoton total cross sections

Interaction of electrons and photons with matter

Pair


MultipleScattering

0.01

0.1

1

10

0.1 1 10

0.15Xo(deg)0.07Xo(deg)0.05Xo(deg)

pro

ject

ed a

ngula

r dis

trib

uti

on (

deg

rees

)

E(GeV)

0

1

2

3

4

5

6

0.1 1 10

0.15Xo(deg)0.07Xo(deg)0.05Xo(deg)

pro

ject

ed a

ngula

r dis

trib

uti

on (

deg

rees

)

E(GeV)


New Detector Technology

• Silicon strip detectorStrip-shaped

PN diode

50-500micron wide

300-500micron thick

VLSI amplifier

Stable particle tracker that allows micron-level tracking of gamma-rays

Well known technology in Particle Physics experiments.Used by our collaboration in balloon experiments (MASS, TS93, CAPRICE),on MIR Space Station ( SilEye) and on satellite (NINA)


Silicon Strip Detector Principle


the deep sky



EGRET All Sky Map (>100 MeV)Cygnus

Region

3C279

Geminga

Vela

Cosmic

Ray

Interactions

With ISM

LMC

PKS

0528+13

4PKS 0208-

512

Crab

PSR

B1706-

44


Third EGRET Catalog

271 Sources


Models for High Energy Emission: A cartoon


P

U

L

S

A

R

S

Multiwavelength light curves of the seven pulsars detected by GR O.

Multiwavelength observations of more will severely constrain theoretical model for pulsar emission.

High energy gamma-ray may dominate and can provide unique information on the map of

pulsar magnetosphere and emission mechanism.


Pulsars• Tutte le pulsars nei raggi

gamma hanno un cut-off ad

alta energia

• Il Polar Gap model

predice un ripido cut-off

• Outer gap model predice

un cut-off più graduale

• I dati di EGRET non

consentono di discriminare

fra i diversi modelli



What is the Universe made of ?We know that there isdark matter, which isneeded to explain thedynamics of stars inGalaxies and of galaxiesin clusters. This darkmatter does notinteract with light, andwe do not know wichparticles is made of.

• The peripheral stars of the galaxy M63 rotate around the center so fastthat they would fly away in space without the presence of additional massinside the galaxy. This is indirect evidence for the presence of dark matter


What is the Universe made of ?

"b = 0.04

"cdm= 0.23

"# = 0.73


Neutralino WIMPs

Assume $ present in the galactic halo

• $ is its own antiparticle => can annihilate in galactic halo

producing gamma-rays, antiprotons, positrons….

• Antimatter not produced in large quantities through standard processes

(secondary production through p + p --> p + X)

• So, any extra contribution from exotic sources ($ $ annihilation) is an

interesting signature

• ie: $ $ --> p + X

• Produced from (e. g.) $ $ --> q / g / gauge boson / Higgs boson and

subsequent decay and/ or hadronisation.


Search for the Nature of Dark Matter• The EGRET team (Mayer-Hasselwander et al, 1998) have seen a convincing signal for a strong excess of

emission from the galactic center, with I(E) x E2 peaking at ~ 2 GeV, and in an error circle of 0.2 degree

radius including the position l = 0o and b = 0o. In their paper it was speculated that among other possiblecauses, this excess could be due to the continuum !-ray spectrum from Wimp annihilation. With the

dramatically improved angular resolution and effective area of GLAST, this effect should become both more

localized and pronounced if it is a Galactic Center phenomenon.

EGRET Map of

Galactic Center

Region


EGRET data & Susy models

~2 degrees around the galactic center

EGRET data

A.Morselli, A.Lionetto, A.Cesarini, F.Fucito, P.Ullio, 2002

Annihilation channel b-bbar

M$ =50 GeV

background model(Galprop)

WIMP annihilation (DarkSusy)

Total Contribution

Nb=1.82 1021

N$=8. 51 104

Typical N$ values:

NFW: N$ = 104

Moore: N$ = 9 106

Isotermal: N$ = 3 101


~2 degrees around

the galactic center,

2 years data

(Galprop)

(one example from DarkSusy)

GLAST Expectation & Susy models

astro-ph/0305075


Differential yield

for each

annihilation channel

WIMP mass=200GeV

total yields

yields not due to %0decay


Differential yieldfor b bar

neutralino mass


GLAST


GLASTScheme

Gamma-Ray

Large Area Space

Telescope


Gamma-Ray Large Area Space Telescope

Anticoincidence

Shield

Imaging calorimeter tower ( 8.5 Rad.Length)

Silicon Tracker tower18 planes of X Y silicon detectors + converters

12 trays with 2.5% R.L. of Pb , 4 trays with 25% ,

2 trays without converters

1.68 m

84 cm

4*4 array of towers


GLAST Instrument Description

EGRET GLAST simulation

Geminga

Crab

Geminga

Crab

IC 443

!General Characteristics: imaging, wide field-

of-view, pair-conversion telescope, backed by EM

calorimetry using modern HEP technology:

"energy range: 10 MeV to 300 GeV

"energy resolution: 10%

"effective area: > 8,000 cm2 (above 1 GeV)

"field-of-view: ~2% sr

"point source sensitivity: 2 x 10-9 ph cm-2 s-1 (@ 100 MeV)

10-10 ph cm-2 s-1 ( > 1 GeV)

"source location determination: 30 arcsec - 5 arcmin

"cosmic ray/! rejection > 105 to 1


EGRET(Spark Chamber) VS. GLAST(Silicon Strip Detector)

EGRET on Compton GRO

(1991-2000) GLAST Large Area Telescope

(2006-2015)


Detector Technology: X-ray vs. Gamma-ray

X-ray (0.5 - 10keV)

Focusing possible

Large effective area

Excellent energy resolution

Very low background

Narrow view

Gamma-ray(0.1-500GeV)

No focusing possible

Wide field of view

Limited effective area

Moderate energy resolution

High background


GLAST Orbit


GLAST Large Area Telescope (LAT) Design

Instrument

Pair-conversion telescope

16 towers & modularity

height/width = 0.4 & large field-of-view

Tracker Modules

Si-strip detectors: fine pitch: 236 µm, high efficiency

12 front tracking planes (x,y): 0.45 Xo

reduce multiple scattering

4 back tracking planes (x,y): 1.0 Xo

increase sensitivity > 1 GeV

One of 18

Tracker trays(detectors top &

bottom)



Instrument


Calorimeter Modules



Mechanical Prototype of

Carbon Cell Design

8.5 rl

Compression Cell Design

Hodoscopic Imaging Array of CsI crystals:

~ 8.5 rl depth

PIN photodiode readout from both ends:

2 ch/xtal x 80 xtals/mod = 2,560 ch

segmentation allows pattern

recognition (“imaging”) and

leakage correction



Instrument


Anticoincidence Shield

Segmented, plastic scintillator tile array:

high efficiency, low-noise, hermetic;

segment ACD sufficiently and

only veto event if a track

points to hit tile



ACD tile readout

with Wavelength

Shifting Fiber


GLAST @ SLAC

12/16 Towers in the GRID on 7/10/05

Aldo Morselli INFN, Sezione di Roma 2 & Università di Roma Tor Vergata 4116/16 Towers in the GRID on 20/10/05

GLAST @ SLAC


The LAT Tracker numbers

11500 sensors11500 sensors

360 trays360 trays

18 towers18 towers

~ 1M channels~ 1M channels

83 m83 m22 SiSi surface surface

> 240K functional test> 240K functional test

recorded in DBrecorded in DB

~ 30M strip tested~ 30M strip tested

(30 test/strip on average)(30 test/strip on average)

> 60 physicist and engineers involved> 60 physicist and engineers involved

in the in the italianitalian teams from INFN teams from INFN

(Trieste, (Trieste, UdineUdine, , PadovaPadova, Pisa, , Pisa, PerugiaPerugia,,

Roma2, Roma2, BariBari) in partnership with ASI) in partnership with ASI


Celebrations for the end of Tracker construction

52 attendees from INFN, ASI, SLAC, NASA,

italian industrial partners


• August 2004Assembling of first tower completed

• Middle of October 2005Completion of the LAT – Environmental testing

• February 2006Delivery to NRL–

• August 2007Kennedy Space Flight Center

LAUNCH

GLAST Master Schedule

•November 2007

Science operation begins!

more info : http://people.roma2.infn.it/glast/


GLAST Performance


il file PDF in http://people.roma2.infn.it/~aldo/

fisica e rivelazione dei gaggi gamma cosa si vuole...

Documents