Study of the highest energy cosmic rays

ICHEP `06, Moscow The Auger project – status and results

G. Matthiae

University and Sezione INFN of Roma “Tor Vergata”

Study of the highest energy cosmic rays • 17 Countries: Argentina, Bolivia, Australia, Brazil,

Rep.Ceca, France, Germany, Italy, Mexico, Netherlands, Poland, Portugal, Slovenia, Spain, UK, USA, Vietnam.

• About 300 physicists

1 particle/km2/century

p + γ 2.7 K → N+ π

Above Ethr ≈ 7*1019 eV, protons loose rapidly energy via pion photoproduction. Interaction length ≈ 6 Mpc Energy loss ≈ 20 % / interaction

Greisen-Zatsepin-Kuzmin

• AGASA sees a continuation of the spectrum beyond the GZK suppression

• Dashed curve represents the spectrum expected for extragalactic sources distributed unifomly in the Universe.

• Extremely poor statistics - only 11 events above 1020 eV

Auger hybrid detector Fluorescence Detector (FD)

• Longitudinal development of the shower

• Calorimetric measurement of the energy

Calibration of the energy scale

• Direction of the shower

12% duty cycle !

Surface Detector (SD)

• Front of shower at ground

• Direction of the shower

• “High” statistics

Southern Observatory (Argentina)

• Very low population density (< 0.1 / km2)

• Very good atmospheric conditions (clouds, aerosol…)

35o S latitude 69o W longitude

≈ 1400 m height ≈ 875 g/cm2

Very flat region“Pampa Amarilla”Malargüe (Argentina)

Future plan for Northern Observatory inColorado (USA)

50 km

Total area ~3000 km2

1600Surface detectors (“water tanks”)

1.5 km spacing

24 fluorescence telescopes 6 in each of 4 buildings

The Auger Observatory

About ¾ installed and operational

Completion in 2007

A surface detector (“water tank”) installed in the Pampa

Water Tank in the Pampa

Solar PanelElectronics enclosure40 MHz FADC, local triggers, 10 Watts

Communication antenna

GPS antenna

Batterybox

Plastic tank with 12 tons of water

three 9”PMTs

• -response ~ track• e/-response ~ energy

-signal of order em-signal

Inclined: em UP

SD calibration & monitoring

single muons

Noise

Base-Temperaturevs Time

Signal-Height vs Time

Signal-Height vs Base-Temp

Single tank response

Huge Statistics!Systematic error ~5%

± 3%

~100 p.e.

VEM

Vertical Equivalent Muon (VEM)

Doublets

Dia Noche

11m

Time resolution

Low energy events (~ 1015 eV) used to compare the time measurement of each tank

: physical dispersion due~13 ns) Time precision of individual tanks ~ 12 ns

Young & Old Shower‘‘young’ showeryoung’ shower

‘‘old’ showerold’ shower

density falls by factor ~150

… by factor ~4

(m)

~11020eV~1020eV

Lateral Distribution Function

~ 14 km

~ 8 km

One event of high energy:~1020 eV, ~60°34 tanks

~60°~60°

LDFS=A [r/rs (1+r/rs)] -β

rs = 700 mA, β from fit (β= 2-2.5)

S(1000) energy estimator

propagation time of 40 µs

Angular resolution from the surface detector depends on the number of tanks

Improved for hybrid events:

~ 0.6 degrees

The FD telescope (Schmidt optics)Field of view 30x30 degrees

Spherical mirror

PMT camera

Diaphragm

UV Filter

Shutter

The Schmidt optics

C

Spherical aberrationComa aberration

Diaphragm Coma

suppressed

C

C

C

spot

F

Spherical focal surface

Six Telescopes viewing 30°x30° each

Fluorescence Telescope

Spherical mirror (R=3.4 m)

Diaphragm and camera

Diaphragm, corrector ring and camera

Field of view: 300x300

Camera: 440 photomultipliersAperture of the pixels: 1.50

Atmospheric Fluorescence

Nitrogen emission spectrum 300 – 400 nm

Photon yield as a function of heightError about 15%

FD Absolute Calibration

Drum: uniform camera illumination

pulsed light sources, several wavelengths and intensity

light diffusing

Tyvek walls

light flux measured

by absolutely

calibrated PMT About 5 photons/ADC count

FD “TEST BEAM”Central Laser Facility

355 nmSteerable laser

optical fiber

SD tank

Laser Mirror DAQ

Backscattering

(Raman)

Elastic bcks. molecular/Rayleigh &

aerosol/Mie

LIDARAtmospheric absorption

LIDAR Station

Steerable system: “Shoot on shower” technique

Event FD on-line bin=100 ns

Background event

Longitudinal profile of showers from the FD telescopes

Fit with empirical formula of Gaisser-Hillas

Calorimetric measurement of the energy.

Another event well contained

Correction for energy loss (neutrinos, muons)

8 – 12 % at 1019 eV

New upper limit on photon fraction E0>10 EeV

• Xmax from showers longitudinal profile observed by the fluorescence detector

• ΔXmax ≈ 25 g cm-2

• 29 events

events

Distribution of the differences Δγ in standard deviations

between primary photon prediction and data

Δγ = 2 – 3.8

New Photon Limit (29 events)

HP: Haverah ParkA1,A2: AGASA

Constraint on top-down/non acceleration models

End 2009: about 2% limit at 10 EeV, 15% at 35 EeV

16% upper limit

Comparison to AGASA

Energy interval (1.0 – 2.5 EeV), angular scale 20°

2116 / 2159.5 ratio = 0.98 ± 0.02 ±0.01

(22% excess would give 2634 and a 10- excess)

Comparison to SUGAR

Energy interval (0.8 – 3.2 EeV), angular scale 5°

286 / 289.7 ratio = 0.98 ± 0.06 ± 0.01(85% excess would give 536 and a 14.5- excess)

Study of excess from the Galactic Center

Zenith angle dependence of the energy estimator S(1000)

Energy calibration – hybrid eventsEnergy obtained by the calorimetric measurement of the fluorescence detector sets the absolute energy scaleSimulation not needed.

log10 S(1000)

log10 E (EeV)

FD energy

Absolute calibration of the energy estimator S(1000) Corrected to 38 degrees

Statistics is now about ½ year of full Observatory (~7000 km2 sr yr) Efficiency =100% above 3 EeV

Systematic error onthe energy ±~ 25%

Auger