Transcript Observations of Ultra-high Energy Cosmic Rays TAUP 2005: Zaragoza

TAUP 2005: Zaragoza
Observations of Ultra-high
Energy Cosmic Rays
Alan Watson
University of Leeds
Spokesperson for Pierre Auger Observatory
[email protected]
Outline:
•
Present Status of Detectors
•
The Issues:
i Arrival Directions
-Galactic Centre?, BL Lac associations?
ii Hadronic Interactions changes are relevant
- effect on mass composition
iii Energy Spectrum
– is there a GZK-effect?
• Summary
Exposure and Event Numbers from various Instruments
km2 sr years > 3 EeV >10 EeV
AGASA: closed in January 2004:
HiRes I: monocular
1600
7000
827
~5000
1616
403
670
95
~3000
~500
(HiRes II: monocular
HiRes: stereo (PRELIMINARY)
~2500
HiRes apertures are strongly energy-dependent (later)
HiRes will cease operation in March 2006
Yakutsk:
~900
1303
171
Auger: data taking since Jan 2004
1750
3525
444
Telescope Array: plan is for 760 km2 with three fluorescence detectors
The Pierre Auger Observatory
design marries two
well-established techniques
The ‘HYBRID’ technique
Fluorescence →
Array of water
→
Cherenkov detectors
11
The Pierre Auger Observatory as planned
Surface Array
1600 detector stations
1.5 km spacing
3000 km2
Fluorescence Detectors
4 Telescope enclosures
6 Telescopes per
enclosure
24 Telescopes total
Status
905 surface detector
stations deployed
Three fluorescence
buildings complete each
with 6 telescopes
θ~ 48º, ~ 70 EeV
Typical flash ADC trace
Detector signal (VEM) vs
time (ns)
PMT 1
PMT 2
PMT 3
Flash
ADC
traces
Flash
ADC
traces
-0.5 0
0.5 1.0 1.5 2.0 2.5 3.0 µs
Lateral density
distribution
θ~ 60º, ~ 86 EeV
Flash ADC Trace for
detector late in the
shower
Lateral
density
distribution
PMT 1
PMT 2
PMT 3
-0.5 0
Flash ADC
traces
0.5 1.0 1.5 2.0 2.5 3.0 µs
Hybrid Event
θ~ 30º, ~ 8 EeV
Lateral density
distribution
Flash ADC
traces
Same Hybrid Event
θ~ 30º, ~ 8 EeV
Fitted Electromagnetic
Shower
Time μ sec
Tanks
Pixels
from Fly's Eye 1985
Angle Χ in the shower-detector plane
Angular Resolution
Entries 269
σ(ψ) ~ 1.24º
Laser
Beam
Hybrid Data
Angle in laser beam /FD detector plane
Hybrid Angular resolution
(68% CL)
0.6 degrees (mean)
Hybrid-SD only space angle difference
Surface array Angular resolution (68% CL)
<2.2º for 3 station events (E< 3EeV, θ < 60º )
< 1.7º for 4 station events (3<E<10 EeV)
< 1.4º for 5 or more station events (E>10 EeV)
Resolution of Core Position
Hybrid Data
Laser Data
+500
-500
501
Laser position – Hybrid and FD only (m)
Hybrid – SD only core position
Core position resolution:
Hybrid: < 60 m
Surface array: < 200 m
Energy Determination: Step 1
The energy scale is determined from the data and does
not depend on a knowledge of interaction models or of
the primary composition.
The detector signal at 1000
m from the shower core
–
called the ground
parameter or S(1000)
- is determined for each
surface detector event
using the lateral density
function.
S(1000) is proportional to
the primary energy.
Zenith angle ~ 48º
Energy ~ 70EeV
Energy Determination: step 2
The energy converter:
Use energy converter
for surface array
10EeV
log (E/EeV)
Compare ground
parameter S(1000)
with the fluorescence
detector energy
Hybrid Events with
strict event selection:
track length > 350g cm-2
Cherenkov contamination <10%
1 EeV
log S(1000)*
A Big Event - One that got away!
Shower/detector plane
Fluorescence Mirror
Energy
Estimate
>140 EeV
HiRes stereo events > 10 EeV plus AGASA events above 40 EeV
HiRes Collaboration: ICRC 2005: Westerhoff et al.
Methods of Inferring the Primary Mass
(i) Variation of Depth of Maximum with Energy
Elongation Rate (Linsley 1977, Linsley and Watson
1981)
dXmax/ dlog E < 2.3Xo g cm-2 /decade
from Heitler model
(ii)
Xmax =  ln (Eo/c )/ ln 2
Muon Content of Showers:-
N (>1 GeV) = AB(E/A)p (depends on
mass/nucleon)
N(>1 GeV) = 2.8A(E/A)0.86 ~ A0.14
So, more muons in Fe showers
New hadronic model: QGSJETII
Heck and Ostapchenko: ICRC 2005
Xmax vs. Energy for different models compared with data
Heck and Ostapchenko: ICRC 2005
Muon Number Ratio for different models and masses
SIBYLL
Heck and Ostapchenko: ICRC 2005
Muon measurements with the AGASA array
Claim: Consistent with proton dominant component
Log(Muon density@1000m[m–2])
Kenji Shinosaki: 129 events > 1019 eV
1
0
−1
−2
19
19.5
20
Log(Energy [eV])
20.5
Ratio of total energy to electromagnetic energy for fluorescence detector
Pierog et al. ICRC 2005
HiRes Spectrum Measurements
•Evidence for structure in Monocular Spectra
•Ankle at 1018.5 eV
•GZK cutoff
• reports by Bergman and Mannel at ICRC 2005
1018
1019
HR1 and HR2 Monocular
Weather and geometrical
uncertainty cuts applied
Stereo
Comparison of Various Spectra on JE3 vs E plots – NOT RECOMMENDED as
these are very misleading, as usually presented, and do the data a disservice.
HiRes I and II and Stereo
AGASA, Auger and HiRes I and II
Stereo and monocular
in poor agreement
NB: Provisional HiRes Stereo Spectrum is not so different from AGASA !!!!
HiRes I and HiRes II
Flux x 1029
• Fit to power
law.
• Single
index gives
poor Χ2
• Evidence
for
changing
index
HiRes Stereo Flux
1019
Springer et al. ICRC 2005
1020
log E
Sensitivity of HiRes II aperture to shower model
Ratio of
Apertures
computed with
SIBYLL
and QGSJET
Zech et al. HiRes Collaboration: ICRC 2005
AGASA aperture
Auger Aperture
Spectrum measured with Auger Observatory
The function is
F=(30.9±1.7)(E/EeV)-1.84±0.03
with Χ2 = 2.4 per degree of freedom
Issues of aperture, mass
and hadronic interactions
under control – systematic
uncertainties being assessed
Summary Spectrum above 2 EeV
aaw/Sept 2005
Summary
Arrival Directions:
No convincing evidence for anisotropy
Possibility of BL Lac association should be clarified in ~ 2 years
New Hadronic Interaction Model:
suggests that there could be a heavier mass > 10 EeV than has
been supposed by many in the past
Spectrum:
Auger: ~ 5 to 7 X AGASA by 2007
Spectrum that is largely mass and model independent
AGASA/HiRes could – possibly – be understood through combination
of improved understanding of HiRes aperture (composition/spectrum)
and AGASA choice of models and mass assumptions
ALL GROUPS HAVE REPORTED EVENTS ABOVE 100 EeV
QUESTION IS: WHAT IS THE DETAILED SHAPE OF THE SPECTRUM?